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• Writing more efficient xquery code (avoiding redundant iteration)

  - by Coquelicot

  Here's a simplified version of a problem I'm working on: I have a bunch of xml data that encodes information about people. Each person is uniquely identified by an 'id' attribute, but they may go by many names. For example, in one document, I might find <person id=1>Paul Mcartney</person> <person id=2>Ringo Starr</person> And in another I might find: <person id=1>Sir Paul McCartney</person> <person id=2>Richard Starkey</person> I want to use xquery to produce a new document that lists every name associated with a given id. i.e.: <person id=1> <name>Paul McCartney</name> <name>Sir Paul McCartney</name> <name>James Paul McCartney</name> </person> <person id=2> ... </person> The way I'm doing this now in xquery is something like this (pseudocode-esque): let $ids := distinct-terms( [all the id attributes on people] ) for $id in $ids return <person id={$id}> { for $unique-name in distinct-values ( for $name in ( [all names] ) where $name/@id=$id return $name ) return <name>{$unique-name}</name> } </person> The problem is that this is really slow. I imagine the bottleneck is the innermost loop, which executes once for every id (of which there are about 1200). I'm dealing with a fair bit of data (300 MB, spread over about 800 xml files), so even a single execution of the query in the inner loop takes about 12 seconds, which means that repeating it 1200 times will take about 4 hours (which might be optimistic - the process has been running for 3 hours so far). Not only is it slow, it's using a whole lot of virtual memory. I'm using Saxon, and I had to set java's maximum heap size to 10 GB (!) to avoid getting out of memory errors, and it's currently using 6 GB of physical memory. So here's how I'd really like to do this (in Pythonic pseudocode): persons = {} for id in ids: person[id] = set() for person in all_the_people_in_my_xml_document: persons[person.id].add(person.name) There, I just did it in linear time, with only one sweep of the xml document. Now, is there some way to do something similar in xquery? Surely if I can imagine it, a reasonable programming language should be able to do it (he said quixotically). The problem, I suppose, is that unlike Python, xquery doesn't (as far as I know) have anything like an associative array. Is there some clever way around this? Failing that, is there something better than xquery that I might use to accomplish my goal? Because really, the computational resources I'm throwing at this relatively simple problem are kind of ridiculous.

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• Compress file to bytes for uploading to SQL Server

  - by Chris

  I am trying to zip files to an SQL Server database table. I can't ensure that the user of the tool has write priveledges on the source file folder so I want to load the file into memory, compress it to an array of bytes and insert it into my database. This below does not work. class ZipFileToSql { public event MessageHandler Message; protected virtual void OnMessage(string msg) { if (Message != null) { MessageHandlerEventArgs args = new MessageHandlerEventArgs(); args.Message = msg; Message(this, args); } } private int sourceFileId; private SqlConnection Conn; private string PathToFile; private bool isExecuting; public bool IsExecuting { get { return isExecuting; } } public int SourceFileId { get { return sourceFileId; } } public ZipFileToSql(string pathToFile, SqlConnection conn) { isExecuting = false; PathToFile = pathToFile; Conn = conn; } public void Execute() { isExecuting = true; byte[] data; byte[] cmpData; //create temp zip file OnMessage("Reading file to memory"); FileStream fs = File.OpenRead(PathToFile); data = new byte[fs.Length]; ReadWholeArray(fs, data); OnMessage("Zipping file to memory"); MemoryStream ms = new MemoryStream(); GZipStream zip = new GZipStream(ms, CompressionMode.Compress, true); zip.Write(data, 0, data.Length); cmpData = new byte[ms.Length]; ReadWholeArray(ms, cmpData); OnMessage("Saving file to database"); using (SqlCommand cmd = Conn.CreateCommand()) { cmd.CommandText = @"MergeFileUploads"; cmd.CommandType = CommandType.StoredProcedure; //cmd.Parameters.Add("@File", SqlDbType.VarBinary).Value = data; cmd.Parameters.Add("@File", SqlDbType.VarBinary).Value = cmpData; SqlParameter p = new SqlParameter(); p.ParameterName = "@SourceFileId"; p.Direction = ParameterDirection.Output; p.SqlDbType = SqlDbType.Int; cmd.Parameters.Add(p); cmd.ExecuteNonQuery(); sourceFileId = (int)p.Value; } OnMessage("File Saved"); isExecuting = false; } private void ReadWholeArray(Stream stream, byte[] data) { int offset = 0; int remaining = data.Length; float Step = data.Length / 100; float NextStep = data.Length - Step; while (remaining > 0) { int read = stream.Read(data, offset, remaining); if (read <= 0) throw new EndOfStreamException (String.Format("End of stream reached with {0} bytes left to read", remaining)); remaining -= read; offset += read; if (remaining < NextStep) { NextStep -= Step; } } } }

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• Large number of soft page faults when assigning a TJpegImage to a TBitmap

  - by Robert Oschler

  I have a Delphi 6 Pro application that processes incoming jpeg frames from a streaming video server. The code works but I recently noticed that it generates a huge number of soft page faults over time. After doing some investigation, the page faults appear to be coming from one particular graphics operation. Note, the uncompressed bitmaps in question are 320 x 240 or about 300 KB in size so it's not due to the handling of large images. The number of page faults being generated isn't tolerable. Over an hour it can easily top 1000000 page faults. I created a stripped down test case that executes the code I have included below on a timer, 10 times a second. The page faults appear to happen when I try to assign the TJpegImage to a TBitmap in the GetBitmap() method. I know this because I commented out that line and the page faults do not occur. The assign() triggers a decompression operation on the part of TJpegImage as it pushes the decompressed bits into a newly created bitmap that GetBitmap() returns. When I run Microsoft's pfmon utility (page fault monitor), I get a huge number of soft page fault error lines concerning RtlFillMemoryUlong, so it appears to happen during a memory buffer fill operation. One puzzling note. The summary part of pfmon's report where it shows which DLL caused what page fault does not show any DLL names in the far left column. I tried this on another system and it happens there too. Can anyone suggest a fix or a workaround? Here's the code. Note, IReceiveBufferForClientSocket is a simple class object that holds bytes in an accumulating buffer. function GetBitmap(theJpegImage: TJpegImage): Graphics.TBitmap; begin Result := TBitmap.Create; Result.Assign(theJpegImage); end; // --------------------------------------------------------------- procedure processJpegFrame(intfReceiveBuffer: IReceiveBufferForClientSocket); var theBitmap: TBitmap; theJpegStream, theBitmapStream: TMemoryStream; theJpegImage: TJpegImage; begin theBitmap := nil; theJpegImage := TJPEGImage.Create; theJpegStream:= TMemoryStream.Create; theBitmapStream := TMemoryStream.Create; try // 2 // ************************ BEGIN JPEG FRAME PROCESSING // Load the JPEG image from the receive buffer. theJpegStream.Size := intfReceiveBuffer.numBytesInBuffer; Move(intfReceiveBuffer.bufPtr^, theJpegStream.Memory^, intfReceiveBuffer.numBytesInBuffer); theJpegImage.LoadFromStream(theJpegStream); // Convert to bitmap. theBitmap := GetBitmap(theJpegImage); finally // Free memory objects. if Assigned(theBitmap) then theBitmap.Free; if Assigned(theJpegImage) then theJpegImage.Free; if Assigned(theBitmapStream) then theBitmapStream.Free; if Assigned(theJpegStream) then theJpegStream.Free; end; // try() end; // --------------------------------------------------------------- procedure TForm1.Timer1Timer(Sender: TObject); begin processJpegFrame(FIntfReceiveBufferForClientSocket); end; // --------------------------------------------------------------- procedure TForm1.FormCreate(Sender: TObject); var S: string; begin FIntfReceiveBufferForClientSocket := TReceiveBufferForClientSocket.Create(1000000); S := loadStringFromFile('c:\test.jpg'); FIntfReceiveBufferForClientSocket.assign(S); end; // --------------------------------------------------------------- Thanks, Robert

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• Java: how to do fast copy of a BufferedImage's pixels? (include unit test)

  - by WizardOfOdds

  I want to do a copy (of a rectangle area) of the ARGB values from a source BufferedImage into a destination BufferedImage. No compositing should be done: if I copy a pixel with an ARGB value of 0x8000BE50 (alpha value at 128), then the destination pixel must be exactly 0x8000BE50, totally overriding the destination pixel. I've got a very precise question and I made a unit test to show what I need. The unit test is fully functional and self-contained and is passing fine and is doing precisely what I want. However, I want a faster and more memory efficient method to replace copySrcIntoDstAt(...). That's the whole point of my question: I'm not after how to "fill" the image in a faster way (what I did is just an example to have a unit test). All I want is to know what would be a fast and memory efficient way to do it (ie fast and not creating needless objects). The proof-of-concept implementation I've made is obviously very memory efficient, but it is slow (doing one getRGB and one setRGB for every pixel). Schematically, I've got this: (where A indicates corresponding pixels from the destination image before the copy) AAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAA And I want to have this: AAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAABBBBAAA AAAAAAAAAAAAABBBBAAA AAAAAAAAAAAAAAAAAAAA where 'B' represents the pixels from the src image. I'm looking for an exact replacement of the method, not for an API link/quote. import org.junit.Test; import java.awt.image.BufferedImage; import static org.junit.Assert.*; public class TestCopy { private static final int COL1 = 0x8000BE50; // alpha at 128 private static final int COL2 = 0x1732FE87; // alpha at 23 @Test public void testPixelsCopy() { final BufferedImage src = new BufferedImage( 5, 5, BufferedImage.TYPE_INT_ARGB ); final BufferedImage dst = new BufferedImage( 20, 20, BufferedImage.TYPE_INT_ARGB ); convenienceFill( src, COL1 ); convenienceFill( dst, COL2 ); copySrcIntoDstAt( src, dst, 3, 4 ); for (int x = 0; x < dst.getWidth(); x++) { for (int y = 0; y < dst.getHeight(); y++) { if ( x >= 3 && x <= 7 && y >= 4 && y <= 8 ) { assertEquals( COL1, dst.getRGB(x,y) ); } else { assertEquals( COL2, dst.getRGB(x,y) ); } } } } // clipping is unnecessary private static void copySrcIntoDstAt( final BufferedImage src, final BufferedImage dst, final int dx, final int dy ) { // TODO: replace this by a much more efficient method for (int x = 0; x < src.getWidth(); x++) { for (int y = 0; y < src.getHeight(); y++) { dst.setRGB( dx + x, dy + y, src.getRGB(x,y) ); } } } // This method is just a convenience method, there's // no point in optimizing this method, this is not what // this question is about private static void convenienceFill( final BufferedImage bi, final int color ) { for (int x = 0; x < bi.getWidth(); x++) { for (int y = 0; y < bi.getHeight(); y++) { bi.setRGB( x, y, color ); } } } }

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• Debugging EXC_BAD_ACCESS that occurs only on release target for an iPhone app?

  - by Bobby Moretti

  I'm developing an iPhone application. I have an EXC_BAD_ACCESS that occurs only in the release target; when I build the debug target the exception does not occur. However, when I set the NSZombieEnabled environment variable to YES, I still get the EXC_BAD_ACCESS with no further information. Is it even possible for NSZombieEnabled to work when executing the release target? I don't see why not, since gdb is running in both cases... Update: here is a printout of the top of the stack: #0 0x33369ebc in objc_msgSend () #1 0x3144f968 in -[EAInputStream _streamEventTrigger] () #2 0x3144fe78 in __streamEventTrigger () #3 0x338ae3a6 in CFRunLoopRunSpecific () #4 0x338adc1e in CFRunLoopRunInMode () #5 0x32ed6966 in -[NSRunLoop(NSRunLoop) runMode:beforeDate:] () #6 0x00005b06 in -[IOStreamDelegate removeMsg:] (self=0x142cc0, _cmd=<value temporarily unavailable, due to optimizations>, message=0x2fffe544) at /Users/robertmoretti/Documents/XXXXXXX/IOStreamDelegate.m:191 Here is a gdb session from inside the objc_msgSend call at the top: (gdb) p/x $r0 $6 = 0x3100000 (gdb) x/s $r1 0x32d7cff8: "release" (gdb) disassemble $pc Dump of assembler code for function objc_msgSend: 0x33369ea8 <objc_msgSend+0>: teq r0, #0 ; 0x0 0x33369eac <objc_msgSend+4>: moveq r1, #0 ; 0x0 0x33369eb0 <objc_msgSend+8>: bxeq lr 0x33369eb4 <objc_msgSend+12>: push {r3, r4, r5, r6} 0x33369eb8 <objc_msgSend+16>: ldr r4, [r0] 0x33369ebc <objc_msgSend+20>: ldr r5, [r4, #8] 0x33369ec0 <objc_msgSend+24>: ldr r6, [r5] 0x33369ec4 <objc_msgSend+28>: add r3, r5, #8 ; 0x8 0x33369ec8 <objc_msgSend+32>: and r5, r6, r1, lsr #2 0x33369ecc <objc_msgSend+36>: ldr r4, [r3, r5, lsl #2] 0x33369ed0 <objc_msgSend+40>: teq r4, #0 ; 0x0 0x33369ed4 <objc_msgSend+44>: add r5, r5, #1 ; 0x1 0x33369ed8 <objc_msgSend+48>: beq 0x33369efc <objc_msgSend+84> 0x33369edc <objc_msgSend+52>: ldr r12, [r4] 0x33369ee0 <objc_msgSend+56>: teq r1, r12 0x33369ee4 <objc_msgSend+60>: and r5, r5, r6 0x33369ee8 <objc_msgSend+64>: bne 0x33369ecc <objc_msgSend+36> 0x33369eec <objc_msgSend+68>: ldr r12, [r4, #8] 0x33369ef0 <objc_msgSend+72>: teq r4, r4 0x33369ef4 <objc_msgSend+76>: pop {r3, r4, r5, r6} 0x33369ef8 <objc_msgSend+80>: bx r12 0x33369efc <objc_msgSend+84>: pop {r3, r4, r5, r6} 0x33369f00 <objc_msgSend+88>: b 0x33369f04 <objc_msgSend_uncached> End of assembler dump. (gdb) p/x *$r0 $9 = 0x0 The exception occurs on the line 0x33369ebc <objc_msgSend+20>: ldr r5, [r4, #8]. r4 has just been given the value pointed to by r0, which happens to be 0. I am wondering what is supposed to be in the memory region of 0x3100000. Here's a memory dump of that area: (gdb) x/256w 0x3100000 0x3100000: 0x00000000 0x0000a293 0xaa650505 0x00000000 0x3100010: 0x0000a294 0xaa670505 0x00000000 0x0000a295 0x3100020: 0xaa690505 0x00000000 0x0000a296 0xaa6b0505 0x3100030: 0x00000000 0x0000a297 0xaa6d0505 0x00000000 0x3100040: 0x0000a298 0xaa6f0505 0x00000000 0x0000a299 0x3100050: 0xaa710505 0x00000000 0x0000a29a 0xaa730505 0x3100060: 0x00000000 0x0000a29b 0xaa750505 0x00000000 0x3100070: 0x0000a29c 0xaa770505 0x00000000 0x0000a29d 0x3100080: 0xaa790505 0x00000000 0x0000a29e 0xaa7b0505 0x3100090: 0x00000000 0x0000a29f 0xaa7d0505 0x00000000 0x31000a0: 0x0000a2a0 0xaa7f0505 0x00000000 0x0000a2a1 0x31000b0: 0xaa810505 0x00000000 0x0000a2a2 0xaa830505 0x31000c0: 0x00000000 0x0000a2a3 0xaa850505 0x00000000 0x31000d0: 0x0000a2a4 0xaa870505 0x00000000 0x0000a2a5 0x31000e0: 0xaa890505 0x00000000 0x0000a2a6 0xaa8b0505 0x31000f0: 0x00000000 0x0000a2a7 0xaa8d0505 0x00000000 0x3100100: 0x0000a2a8 0xaa8f0505 0x00000000 0x0000a2a9 0x3100110: 0xaa910505 0x00000000 0x0000a2aa 0xaa930505 0x3100120: 0x00000000 0x0000a2ab 0xaa950505 0x00000000 0x3100130: 0x0000a2ac 0xaa970505 0x00000000 0x0000a2ad 0x3100140: 0xaa990505 0x00000000 0x0000a2ae 0xaa9b0505 0x3100150: 0x00000000 0x0000a2af 0xaa9d0505 0x00000000 0x3100160: 0x0000a2b0 0xaa9f0505 0x00000000 0x0000a2b1 0x3100170: 0xaaa10505 0x00000000 0x0000a2b2 0xaaa30505 0x3100180: 0x00000000 0x0000a2b3 0xaaa50505 0x00000000 0x3100190: 0x0000a2b4 0xaaa70505 0x00000000 0x0000a2b5 0x31001a0: 0xaaa90505 0x00000000 0x0000a2b6 0xaaab0505 0x31001b0: 0x00000000 0x0000a2b7 0xaaad0505 0x00000000 0x31001c0: 0x0000a2b8 0xaaaf0505 0x00000000 0x0000a2b9 0x31001d0: 0xaab10505 0x00000000 0x0000a2ba 0xaab30505 0x31001e0: 0x00000000 0x0000a2bb 0xaab50505 0x00000000 0x31001f0: 0x0000a2bc 0xaab70505 0x00000000 0x0000a2bd 0x3100200: 0xaab90505 0x00000000 0x0000a2be 0xaabb0505 0x3100210: 0x00000000 0x0000a2bf 0xaabd0505 0x00000000 0x3100220: 0x0000a2c0 0xaabf0505 0x00000000 0x0000a2c1 0x3100230: 0xaac10505 0x00000000 0x0000a2c2 0xaac30505 0x3100240: 0x00000000 0x0000a2c3 0xaac50505 0x00000000 0x3100250: 0x0000a2c4 0xaac70505 0x00000000 0x0000a2c5 0x3100260: 0xaac90505 0x00000000 0x0000a2c6 0xaacb0505 0x3100270: 0x00000000 0x0000a2c7 0xaacd0505 0x00000000 0x3100280: 0x0000a2c8 0xaacf0505 0x00000000 0x0000a2c9 0x3100290: 0xaad10505 0x00000000 0x0000a2ca 0xaad30505 0x31002a0: 0x00000000 0x0000a2cb 0xaad50505 0x00000000 0x31002b0: 0x0000a2cc 0xaad70505 0x00000000 0x0000a2cd 0x31002c0: 0xaad90505 0x00000000 0x0000a2ce 0xaadb0505 0x31002d0: 0x00000000 0x0000a2cf 0xaadd0505 0x00000000 0x31002e0: 0x0000a2d0 0xaadf0505 0x00000000 0x0000a2d1 0x31002f0: 0xaae10505 0x00000000 0x0000a2d2 0xaae30505 0x3100300: 0x00000000 0x0000a2d3 0xaae50505 0x00000000 0x3100310: 0x0000a2d4 0xaae70505 0x00000000 0x0000a2d5 0x3100320: 0xaae90505 0x00000000 0x0000a2d6 0xaaeb0505 0x3100330: 0x00000000 0x0000a2d7 0xaaed0505 0x00000000 0x3100340: 0x0000a2d8 0xaaef0505 0x00000000 0x0000a2d9 0x3100350: 0xaaf10505 0x00000000 0x0000a2da 0xaaf30505 0x3100360: 0x00000000 0x0000a2db 0xaaf50505 0x00000000 0x3100370: 0x0000a2dc 0xaaf70505 0x00000000 0x0000a2dd 0x3100380: 0xaaf90505 0x00000000 0x0000a2de 0xaafb0505 0x3100390: 0x00000000 0x0000a2df 0xaafd0505 0x00000000 0x31003a0: 0x0000a2e0 0xab050505 0x00000000 0x0000a2e1 0x31003b0: 0xab070505 0x00000000 0x0000a2e2 0xab090505 0x31003c0: 0x00000000 0x0000a2e3 0xab0b0505 0x00000000 0x31003d0: 0x0000a2e4 0xab0d0505 0x00000000 0x0000a2e5 0x31003e0: 0xab0f0505 0x00000000 0x0000a2e6 0xab110505 0x31003f0: 0x00000000 0x0000a2e7 0xab130505 0x00000000 I don't really know what else to try; hopefully someone with more iphone experience will be able to recognize this memory as something meaningful.

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• Faster method for Matrix vector product for large matrix in C or C++ for use in GMRES

  - by user35959

  I have a large, dense matrix A, and I aim to find the solution to the linear system Ax=b using an iterative method (in MATLAB was the plan using its built in GMRES). For more than 10,000 rows, this is too much for my computer to store in memory, but I know that the entries in A are constructed by two known vectors x and y of length N and the entries satisfy: A(i,j) = .5*(x[i]-x[j])^2+([y[i]-y[j])^2 * log(x[i]-x[j])^2+([y[i]-y[j]^2). MATLAB's GMRES command accepts as input a function call that can compute the matrix vector product A*x, which allows me to handle larger matrices than I can store in memory. To write the matrix-vecotr product function, I first tried this in matlab by going row by row and using some vectorization, but I avoid spawning the entire array A (since it would be too large). This was fairly slow unfortnately in my application for GMRES. My plan was to write a mex file for MATLAB to, which is in C, and ideally should be significantly faster than the matlab code. I'm rather new to C, so this went rather poorly and my naive attempt at writing the code in C was slower than my partially vectorized attempt in Matlab. #include <math.h> #include "mex.h" void Aproduct(double *x, double *ctrs_x, double *ctrs_y, double *b, mwSize n) { mwSize i; mwSize j; double val; for (i=0; i<n; i++) { for (j=0; j<i; j++) { val = pow(ctrs_x[i]-ctrs_x[j],2)+pow(ctrs_y[i]-ctrs_y[j],2); b[i] = b[i] + .5* val * log(val) * x[j]; } for (j=i+1; j<n; j++) { val = pow(ctrs_x[i]-ctrs_x[j],2)+pow(ctrs_y[i]-ctrs_y[j],2); b[i] = b[i] + .5* val * log(val) * x[j]; } } } The above is the computational portion of the code for the matlab mex file (which is slightly modified C, if I understand correctly). Please note that I skip the case i=j, since in that case the variable val will be a 0*log(0), which should be interpreted as 0 for me, so I just skip it. Is there a more efficient or faster way to write this? When I call this C function via the mex file in matlab, it is quite slow, slower even than the matlab method I used. This surprises me since I suspected that C code should be much faster than matlab. The alternative matlab method which is partially vectorized that I am comparing it with is function Ax = Aprod(x,ctrs) n = length(x); Ax = zeros(n,1); for j=1:(n-3) v = .5*((ctrs(j,1)-ctrs(:,1)).^2+(ctrs(j,2)-ctrs(:,2)).^2).*log((ctrs(j,1)-ctrs(:,1)).^2+(ctrs(j,2)-ctrs(:,2)).^2); v(j)=0; Ax(j) = dot(v,x(1:n-3); end (the n-3 is because there is actually 3 extra components, but they are dealt with separately,so I excluded that code). This is partly vectorized and only needs one for loop, so it makes some sense that it is faster. However, I was hoping I could go even faster with C+mex file. Any suggestions or help would be greatly appreciated! Thanks! EDIT: I should be more clear. I am open to any faster method that can help me use GMRES to invert this matrix that I am interested in, which requires a faster way of doing the matrix vector product without explicitly loading the array into memory. Thanks!

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• parallel computation for an Iterator of elements in Java

  - by Brian Harris

  I've had the same need a few times now and wanted to get other thoughts on the right way to structure a solution. The need is to perform some operation on many elements on many threads without needing to have all elements in memory at once, just the ones under computation. As in, Iterables.partition is insufficient because it brings all elements into memory up front. Expressing it in code, I want to write a BulkCalc2 that does the same thing as BulkCalc1, just in parallel. Below is sample code that illustrates my best attempt. I'm not satisfied because it's big and ugly, but it does seem to accomplish my goals of keeping threads highly utilized until the work is done, propagating any exceptions during computation, and not having more than numThreads instances of BigThing necessarily in memory at once. I'll accept the answer which meets the stated goals in the most concise way, whether it's a way to improve my BulkCalc2 or a completely different solution. interface BigThing { int getId(); String getString(); } class Calc { // somewhat expensive computation double calc(BigThing bigThing) { Random r = new Random(bigThing.getString().hashCode()); double d = 0; for (int i = 0; i < 100000; i++) { d += r.nextDouble(); } return d; } } class BulkCalc1 { final Calc calc; public BulkCalc1(Calc calc) { this.calc = calc; } public TreeMap<Integer, Double> calc(Iterator<BigThing> in) { TreeMap<Integer, Double> results = Maps.newTreeMap(); while (in.hasNext()) { BigThing o = in.next(); results.put(o.getId(), calc.calc(o)); } return results; } } class SafeIterator<T> { final Iterator<T> in; SafeIterator(Iterator<T> in) { this.in = in; } synchronized T nextOrNull() { if (in.hasNext()) { return in.next(); } return null; } } class BulkCalc2 { final Calc calc; final int numThreads; public BulkCalc2(Calc calc, int numThreads) { this.calc = calc; this.numThreads = numThreads; } public TreeMap<Integer, Double> calc(Iterator<BigThing> in) { ExecutorService e = Executors.newFixedThreadPool(numThreads); List<Future<?>> futures = Lists.newLinkedList(); final Map<Integer, Double> results = new MapMaker().concurrencyLevel(numThreads).makeMap(); final SafeIterator<BigThing> it = new SafeIterator<BigThing>(in); for (int i = 0; i < numThreads; i++) { futures.add(e.submit(new Runnable() { @Override public void run() { while (true) { BigThing o = it.nextOrNull(); if (o == null) { return; } results.put(o.getId(), calc.calc(o)); } } })); } e.shutdown(); for (Future<?> future : futures) { try { future.get(); } catch (InterruptedException ex) { // swallowing is OK } catch (ExecutionException ex) { throw Throwables.propagate(ex.getCause()); } } return new TreeMap<Integer, Double>(results); } }

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• Lock free multiple readers single writer

  - by dummzeuch

  I have got an in memory data structure that is read by multiple threads and written by only one thread. Currently I am using a critical section to make this access threadsafe. Unfortunately this has the effect of blocking readers even though only another reader is accessing it. There are two options to remedy this: use TMultiReadExclusiveWriteSynchronizer do away with any blocking by using a lock free approach For 2. I have got the following so far (any code that doesn't matter has been left out): type TDataManager = class private FAccessCount: integer; FData: TDataClass; public procedure Read(out _Some: integer; out _Data: double); procedure Write(_Some: integer; _Data: double); end; procedure TDataManager.Read(out _Some: integer; out _Data: double); var Data: TDAtaClass; begin InterlockedIncrement(FAccessCount); try // make sure we get both values from the same TDataClass instance Data := FData; // read the actual data _Some := Data.Some; _Data := Data.Data; finally InterlockedDecrement(FAccessCount); end; end; procedure TDataManager.Write(_Some: integer; _Data: double); var NewData: TDataClass; OldData: TDataClass; ReaderCount: integer; begin NewData := TDataClass.Create(_Some, _Data); InterlockedIncrement(FAccessCount); OldData := TDataClass(InterlockedExchange(integer(FData), integer(NewData)); // now FData points to the new instance but there might still be // readers that got the old one before we exchanged it. ReaderCount := InterlockedDecrement(FAccessCount); if ReaderCount = 0 then // no active readers, so we can safely free the old instance FreeAndNil(OldData) else begin /// here is the problem end; end; Unfortunately there is the small problem of getting rid of the OldData instance after it has been replaced. If no other thread is currently within the Read method (ReaderCount=0), it can safely be disposed and that's it. But what can I do if that's not the case? I could just store it until the next call and dispose it there, but Windows scheduling could in theory let a reader thread sleep while it is within the Read method and still has got a reference to OldData. If you see any other problem with the above code, please tell me about it. This is to be run on computers with multiple cores and the above methods are to be called very frequently. In case this matters: I am using Delphi 2007 with the builtin memory manager. I am aware that the memory manager probably enforces some lock anyway when creating a new class but I want to ignore that for the moment. Edit: It may not have been clear from the above: For the full lifetime of the TDataManager object there is only one thread that writes to the data, not several that might compete for write access. So this is a special case of MREW.

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• Severe Tomcat crash has me stumped

  - by Eric Banderhide

  I'm pretty used to crashing my tomcat server. But I don't think I made any changes at all and seem to have broken it completely. Was working one min then not the next. I really hope someone can help here is the Catalina.out: Dec 20, 2012 1:35:56 AM org.apache.catalina.startup.Embedded initDirs SEVERE: Cannot find specified temporary folder at Dec 20, 2012 1:35:57 AM org.apache.catalina.core.AprLifecycleListener init INFO: Loaded APR based Apache Tomcat Native library 1.1.23. Dec 20, 2012 1:35:57 AM org.apache.catalina.core.AprLifecycleListener init INFO: APR capabilities: IPv6 [true], sendfile [true], accept filters [false], random [true]. Dec 20, 2012 1:35:57 AM org.apache.coyote.http11.Http11AprProtocol init INFO: Initializing Coyote HTTP/1.1 on http-8040 Dec 20, 2012 1:35:57 AM org.apache.coyote.ajp.AjpAprProtocol init INFO: Initializing Coyote AJP/1.3 on ajp-8042 Dec 20, 2012 1:35:57 AM org.apache.catalina.startup.Catalina load INFO: Initialization processed in 587 ms Dec 20, 2012 1:35:57 AM org.apache.catalina.core.StandardService start INFO: Starting service Catalina Dec 20, 2012 1:35:57 AM org.apache.catalina.core.StandardEngine start INFO: Starting Servlet Engine: Apache Tomcat/6.0.33 Dec 20, 2012 1:35:57 AM org.apache.catalina.startup.HostConfig deployDirectory INFO: Deploying web application directory docs Dec 20, 2012 1:35:57 AM org.apache.catalina.startup.HostConfig deployDirectory INFO: Deploying web application directory ROOT Dec 20, 2012 1:35:57 AM org.apache.catalina.startup.HostConfig deployDirectory INFO: Deploying web application directory myApp Dec 20, 2012 1:35:57 AM org.apache.catalina.loader.WebappClassLoader validateJarFile INFO: validateJarFile(/lhome/me/tomcat6/webapps/myApp/WEB-INF/lib/javax.servlet.jar) - jar not loaded. See Servlet Spec 2.3, section 9.7.2. Offending class: javax/servlet/Servlet.class Dec 20, 2012 1:35:58 AM org.apache.coyote.http11.Http11AprProtocol start INFO: Starting Coyote HTTP/1.1 on http-8040 Dec 20, 2012 1:35:58 AM org.apache.coyote.ajp.AjpAprProtocol start INFO: Starting Coyote AJP/1.3 on ajp-8042 Dec 20, 2012 1:35:58 AM org.apache.catalina.startup.Catalina start INFO: Server startup in 880 ms Error Reading TLE line 1: java.lang.Exception: TLE line 1 not valid first line Error Creating SGP4 Satellite Dec 20, 2012 1:36:26 AM org.apache.coyote.http11.Http11AprProtocol pause INFO: Pausing Coyote HTTP/1.1 on http-8040 Dec 20, 2012 1:36:26 AM org.apache.coyote.ajp.AjpAprProtocol pause INFO: Pausing Coyote AJP/1.3 on ajp-8042 Dec 20, 2012 1:36:27 AM org.apache.catalina.core.StandardService stop INFO: Stopping service Catalina Dec 20, 2012 1:36:30 AM org.apache.catalina.loader.WebappClassLoader clearReferencesJdbc SEVERE: The web application [/myApp] registered the JDBC driver [com.mysql.jdbc.Driver] but failed to unregister it when the web application was stopped. To prevent a memory leak, the JDBC Driver has been forcibly unregistered. Dec 20, 2012 1:36:30 AM org.apache.catalina.loader.WebappClassLoader clearReferencesThreads SEVERE: The web application [/myApp] is still processing a request that has yet to finish. This is very likely to create a memory leak. You can control the time allowed for requests to finish by using the unloadDelay attribute of the standard Context implementation. Dec 20, 2012 1:36:30 AM org.apache.catalina.loader.WebappClassLoader clearReferencesThreads SEVERE: The web application [/myApp] appears to have started a thread named [Timer-0] but has failed to stop it. This is very likely to create a memory leak. Dec 20, 2012 1:36:30 AM org.apache.coyote.http11.Http11AprProtocol destroy INFO: Stopping Coyote HTTP/1.1 on http-8040 Dec 20, 2012 1:36:30 AM org.apache.coyote.ajp.AjpAprProtocol destroy INFO: Stopping Coyote AJP/1.3 on ajp-8042 Dec 20, 2012 1:37:12 AM org.apache.catalina.startup.Catalina stopServer SEVERE: Catalina.stop: java.net.ConnectException: Connection refused at java.net.PlainSocketImpl.socketConnect(Native Method) at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:339) at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:200) at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:182) at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:391) at java.net.Socket.connect(Socket.java:579) at java.net.Socket.connect(Socket.java:528) at java.net.Socket.<init>(Socket.java:425) at java.net.Socket.<init>(Socket.java:208) at org.apache.catalina.startup.Catalina.stopServer(Catalina.java:422) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:601) at org.apache.catalina.startup.Bootstrap.stopServer(Bootstrap.java:338) at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:416) And I have a new log that has been created, I've never seen it before but it seems to think its something severe. A long one but here it is: Massive Error Log I've never seen before

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• Problem using delete[] (Heap corruption) when implementing operator+= (C++)

  - by Darel

  I've been trying to figure this out for hours now, and I'm at my wit's end. I would surely appreciate it if someone could tell me when I'm doing wrong. I have written a simple class to emulate basic functionality of strings. The class's members include a character pointer data (which points to a dynamically created char array) and an integer strSize (which holds the length of the string, sans terminator.) Since I'm using new and delete, I've implemented the copy constructor and destructor. My problem occurs when I try to implement the operator+=. The LHS object builds the new string correctly - I can even print it using cout - but the problem comes when I try to deallocate the data pointer in the destructor: I get a "Heap Corruption Detected after normal block" at the memory address pointed to by the data array the destructor is trying to deallocate. Here's my complete class and test program: #include <iostream> using namespace std; // Class to emulate string class Str { public: // Default constructor Str(): data(0), strSize(0) { } // Constructor from string literal Str(const char* cp) { data = new char[strlen(cp) + 1]; char *p = data; const char* q = cp; while (*q) *p++ = *q++; *p = '\0'; strSize = strlen(cp); } Str& operator+=(const Str& rhs) { // create new dynamic memory to hold concatenated string char* str = new char[strSize + rhs.strSize + 1]; char* p = str; // new data char* i = data; // old data const char* q = rhs.data; // data to append // append old string to new string in new dynamic memory while (*p++ = *i++) ; p--; while (*p++ = *q++) ; *p = '\0'; // assign new values to data and strSize delete[] data; data = str; strSize += rhs.strSize; return *this; } // Copy constructor Str(const Str& s) { data = new char[s.strSize + 1]; char *p = data; char *q = s.data; while (*q) *p++ = *q++; *p = '\0'; strSize = s.strSize; } // destructor ~Str() { delete[] data; } const char& operator[](int i) const { return data[i]; } int size() const { return strSize; } private: char *data; int strSize; }; ostream& operator<<(ostream& os, const Str& s) { for (int i = 0; i != s.size(); ++i) os << s[i]; return os; } // Test constructor, copy constructor, and += operator int main() { Str s = "hello"; // destructor for s works ok Str x = s; // destructor for x works ok s += "world!"; // destructor for s gives error cout << s << endl; cout << x << endl; return 0; }

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• How to implement this .NET client and PHP server synchronization scenario?

  - by pbean

  I have a PHP webserver and a .NET mobile application. The .NET application needs data from a database, which is provided (for now) by the php webserver. I'm fairly new to this kind of scenario so I'm not sure what the best practices are. I ran into a couple of problems and I am not certain how to overcome them. For now, I have the following setup. I run a PHP SOAP server which has a couple of operations which simply retrieve data from the database. For this web service I have created a WSDL file. In Visual Studio I added a web reference to my project using the WSDL file and it generated some classes for it. I simply call something like "MyWebService.GetItems();" and I get an array of items in my .NET application, which come straight from the database. Next I also serialize all these retrieved objects to local (permanent) storage. I face a couple of challenges which I don't know how to resolve properly. The idea is for the mobile client to synchronize the data once (at the start of the day), before working, and then use the local storage throughout the day, and synchronize it back at the end of the day. At the moment all data is downloaded through SOAP, and not a subset (only what is needed). How would I know which new information should be sent to the client? Only the server knows what is new, but only the client knows for sure which data it already has. I seem to be doing double work now. The data which is transferred with SOAP basically already are serialized objects. But at the moment I first retrieve all objects through SOAP and the .NET framework automatically deserializes it. Then I serialize all data again myself. It would be more efficient to simply download it to storage, and then deserialize it. The mobile device does not have a lot of memory. In my test data this is not really a problem, but with potentially tenths of thousands of records I can imagine this will become a problem. Currently when I call the SOAP method, it loads all data into memory (as an array) but as described above perhaps it would be better to have it stored into storage directly, and only retrieve from storage the objects that are needed. But how would I store this? An array would serialize to one big XML (or binary) file from which I cannot choose which objects to load. Would I make (possible tenths of thousands) separate files? Also at the end of the day when I want to send the changes back to the server, how would I know which objects to send... since they're not in memory? I hope my troubles are clear and I hope you are able to help me figure out how to implement this the best way. :) Some things are already fixed (like using .NET on the mobile device, using PHP and having a MySQL database server) but other things can most certainly be changed (like using SOAP).

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• How to call virtual function of an object in C++

  - by SoonDead

  I'm struggling with calling a virtual function in C++. I'm not experienced in C++, I mainly use C# and Java so I might have some delusions, but bear with me. I have to write a program where I have to avoid dynamic memory allocation if possible. I have made a class called List: template <class T> class List { public: T items[maxListLength]; int length; List() { length = 0; } T get(int i) const { if (i >= 0 && i < length) { return items[i]; } else { throw "Out of range!"; } }; // set the value of an already existing element void set(int i, T p) { if (i >= 0 && i < length) { items[i] = p; } else { throw "Out of range!"; } } // returns the index of the element int add(T p) { if (length >= maxListLength) { throw "Too many points!"; } items[length] = p; return length++; } // removes and returns the last element; T pop() { if (length > 0) { return items[--length]; } else { throw "There is no element to remove!"; } } }; It just makes an array of the given type, and manages the length of it. There is no need for dynamic memory allocation, I can just write: List<Object> objects; MyObject obj; objects.add(obj); MyObject inherits form Object. Object has a virtual function which is supposed to be overridden in MyObject: struct Object { virtual float method(const Input& input) { return 0.0f; } }; struct MyObject: public Object { virtual float method(const Input& input) { return 1.0f; } }; I get the elements as: objects.get(0).method(asdf); The problem is that even though the first element is a MyObject, the Object's method function is called. I'm guessing there is something wrong with storing the object in an array of Objects without dynamically allocating memory for the MyObject, but I'm not sure. Is there a way to call MyObject's method function? How? It's supposed to be a heterogeneous collection btw, so that's why the inheritance is there in the first place. If there is no way to call the MyObject's method function, then how should I make my list in the first place?

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• Sending typedef struct containing void* by creating MPI drived datatype.

  - by hankol

  what I understand studying MPI specification is that an MPI send primitive refer to a memory location (or a send buffer) pointed by the data to be sent and take the data in that location which then passed as a message to the another Process. Though it is true that virtual address of a give process will be meaningless in another process memory address; It is ok to send data pointed by pointer such as void pointer as MPI will any way pass the data itself as a message For example the following works correctly: // Sender Side. int x = 100; void* snd; MPI_Send(snd,4,MPI_BYTE,1,0,MPI_COMM_WORLD); // Receiver Side. void* rcv; MPI_Recv(rcv, 4,MPI_BYTE,0,0,MPI_COMM_WORLD); but when I add void* snd in a struct and try to send the struct this will no succeed. I don't understand why the previous example work correctly but not the following. Here, I have defined a typedef struct and then create an MPI_DataType from it. With the same explanation of the above the following should also have succeed, unfortunately it is not working. here is the code: #include "mpi.h" #include<stdio.h> int main(int args, char *argv[]) { int rank, source =0, tag=1, dest=1; int bloackCount[2]; MPI_Init(&args, &argv); typedef struct { void* data; int tag; } data; data myData; MPI_Datatype structType, oldType[2]; MPI_Status stat; /* MPI_Aint type used to idetify byte displacement of each block (array)*/ MPI_Aint offsets[2], extent; MPI_Comm_rank(MPI_COMM_WORLD, &rank); offsets[0] = 0; oldType[0] = MPI_BYTE; bloackCount[0] = 1; MPI_Type_extent(MPI_INT, &extent); offsets[1] = 4 * extent; /*let say the MPI_BYTE will contain ineteger : size of int * extent */ oldType[1] = MPI_INT; bloackCount[1] = 1; MPI_Type_create_struct(2, bloackCount,offsets,oldType, &structType); MPI_Type_commit(&structType); if(rank == 0){ int x = 100; myData.data = &x; myData.tag = 99; MPI_Send(&myData,1,structType, dest, tag, MPI_COMM_WORLD); } if(rank == 1 ){ MPI_Recv(&myData, 1, structType, source, tag, MPI_COMM_WORLD, &stat); // with out this the following printf() will properly print the value 99 for // myData.tag int x = *(int *) myData.data; printf(" \n Process %d, Received : %d , %d \n\n", rank , myData.tag, x); } MPI_Type_free(&structType); MPI_Finalize(); } Error message running the code: [Looks like I am trying to access an invalid memory address space in the second process] [ubuntu:04123] *** Process received signal *** [ubuntu:04123] Signal: Segmentation fault (11) [ubuntu:04123] Signal code: Address not mapped (1) [ubuntu:04123] Failing at address: 0xbfe008bc [ubuntu:04123] [ 0] [0xb778240c] [ubuntu:04123] [ 1] GenericstructType(main+0x161) [0x8048935] [ubuntu:04123] [ 2] /lib/i386-linux-gnu/libc.so.6(__libc_start_main+0xf3) [0xb750f4d3] [ubuntu:04123] [ 3] GenericstructType() [0x8048741] [ubuntu:04123] *** End of error message *** Can some please explain to me why it is not working. any advice will also be appreciated thanks,

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• Updating resources in SharpDX - why can I not map a dynamic texture?

  - by sebf

  I am trying to map a Texture2D resource in DirectX11 via SharpDX. The resource is declared as a ShaderResource, with Default usage and the 'Write' CPU flag specified. My call however fails with a generic exception from SharpDX: _Parent.Context.MapSubresource(_Resource, 0, SharpDX.Direct3D11.MapMode.Write, SharpDX.Direct3D11.MapFlags.None, out stream); I see from this question that it is supported. The MSDN docs and this other question hint that instead of using Context.MapSubresource() I should be using Texture2D.Map(), however, the DirectX11 Texture2D class does not define Map() (though it does for the DX10 equivalent). If I call the above with MapMode.WriteDiscard, the call succeeds but in this case the previous content of the texture is lost, which is no good when I only want to update a section of it. Has the Map() method been removed in DirectX11 or am I looking in the wrong place? Is the MapSubresource() method unsuitable or am I using it wrong?

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• SQL SERVER – Puzzle – Challenge – Error While Converting Money to Decimal

  - by pinaldave

  Earlier I wrote SQL SERVER – Challenge – Puzzle – Usage of FAST Hint and I did receive some good comments. Here is another question to tease your mind. Run following script and you will see that it will thrown an error. DECLARE @mymoney MONEY; SET @mymoney = 12345.67; SELECT CAST(@mymoney AS DECIMAL(5,2)) MoneyInt; GO The datatype of money is also visually look similar to the decimal, why it would throw following error: Msg 8115, Level 16, State 8, Line 3 Arithmetic overflow error converting money to data type numeric. Please leave a comment with explanation and I will post a your answer on this blog with due credit. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Pinal Dave, SQL, SQL Authority, SQL Error Messages, SQL Puzzle, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, SQLServer, T SQL, Technology

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• Fitting it together, database, reporting, applications in C#

  - by alvonellos

  Introduction Preamble I was hesitant to post this, since it's an application whose intricate details are defined elsewhere, and answers may not be helpful to others. Within the past few weeks (I was actually going to write a blog post about this after I finished) I've discovered that the barrier I'm encountering is one that's actually quite common for newer developers. This question is not so much about a specific thing as it is about piecing those things together. I've searched the internet far and wide, and found many tutorials on how to create applications that are kind of similar to what I'm looking for. I've also looked at hiring another, more experienced, developer to help me along, but all I've gotten are unqualified candidates that don't have the experience necessary and won't take care of the client or project like I will. I'd rather have the project never transpire than to release a solution that is half-baked. I've asked professors at my school, but they've not turned up answers to my question. I'm an experienced developer, and I've written many applications that are -- very abstractly -- close to what I'm doing, but my experiences from those applications aren't giving me enough leverage to solve this particular problem. I just hope that posting this article isn't a mistake for me to write. Project Description I have a project I'm working on for a client that is a rewrite of an application, originally written in Foxpro 2.6 by someone before me, that performs some analysis (which, sadly, I'm not allowed to disclose as per of my employment contract) on financial data. One day, after a long talk between the client and I -- where he intimately described his frustrations with all the bugs I've been hacking out of this code for 6 months now -- he told me to just rewrite it and gave me a month to write a good 1/8 of this 65k LOC Foxpro monstrosity. this 65k line of code foxpro monstrosity. It'll take me a good 3 - 6 months to rewrite this software (I know things the original programmer did not, like inheritance) going as I am right now, but I'm quickly discovering that I'm going to need to use databases. Prior to this contract I didn't even know about foxpro, and so I've had to learn foxpro on the fly, write procedures and make modifications to the database. I've actually come to like it, and this project would be rewritten in Foxpro if it were still a supported language, because over the past few months, I've come to like the features of Foxpro that make it so easy to develop data-driven applications. I once perfomed an experiment, comparing C# to Foxpro. What took me 45 minutes in C# took me two in Foxpro, and I knew C# prior to Foxpro. I was hoping to leverage the power of C#, but it intimidates me that in foxpro, you can have one line of code and be using a database. Prior to this, I have never written any serious database development from scratch. All the applications that I've written are in a different league. They are either completely data-naive or data-naive enough that I can get away with not using a database through serialization or by designing algorithms that work with the data in a manner that is stateless, so there is no need to worry about databases. I've come to realize, very quickly, that serialization and my efficacy with data structures has been my crutch all these years that's prevented me from adventuring into databases, and has consequently hindered my success in real-world programming. Sure, I've written some database stuff in Perl and Python, and I've done forms and worked with relational databases and tables, I'm a wizard in Access and Excel (seriously) and can do just about anything, but it just feels unnatural writing SQL code in another language... I don't mind writing SQL, and I don't It's that bridge between the database and the program code that drives me absolutely bonkers. I hope I'm not the only one to think this, but it bothers me that I have to create statements like the following string sSql = "SELECT * from tablename" When there's really no reason for that kind of unchecked language binding between two languages and two API's. Don't get my wrong, SQL is great, but I don't like the idea that, when executing commands on a SQL database, that one must intermix database and application software, and there's no database independence, which means that different versions of different databases can break code. This isn't very nice. The nicest thing about Foxpro is the cohesiveness between programming language and database. It's so easy, and Foxpro makes it easy, because the tool just fits the task. I can see why so many developers have created a career with this language, because it lowered the barrier of entry to data-driven applications that so many businesses need. It was wonderful. For my purposes today, with the demands and need for community support, extensibility, and language features, Foxpro isn't a solution that I feel would be the right tool for the job. I'm also worried about working too heavy with the database, because I've seen data-driven .NET applications have issues with database caches, running out of memory, and objects in the database not being collected. (Memory leaks) And OH the queries. Which one, how, and why? There are a plethora of different ways that a database can be setup, I think I counted 5 or 6 different kinds of database applications alone that I can chose from. That is a great mountain for me to climb when I don't even know where to begin when it comes to writing data-driven applications. The problem isn't that I don't know SQL or that I don't know C#. I know both and have worked with both extensively. It's making them work together that's the problem, and it's something I've never done in C# before. Reports The client likes paper. The data needs to be printed out in a format that is extensible, layered, and easy to use. I have never done reporting before, and so this is a bit of a problem. From the data source comes crystal reports, and so there's a dependency on the database, from what I understand. Code reuse A large part of the design decision that I've gone through so far is to break the task of writing a piece of this software into routines and modular DLL's and so forth such that much of the code can be reused. For example, when I setup this database, I want to be able to reuse the same database code over and over again. I also want to make sure that when the day comes that another developer is here, that he/she will be able to pick up just where I left off. The quicker I develop these applications, the better off I am. Tasks & Goals In my project, I need to write routines that apply algorithms and look for predefined patterns in financial data. Additionally, I need to simulate trading based on predefined algorithms and data. Then I need to prepare reports on that data. Additionally, I need to have a way to change the code base for this application quickly and effectively, without hacking together some band-aid solution for a problem that really needs a trauma ward. Special Considerations The solution must be fast, run quickly on existing hardware, and not be too much of a pain to maintain and write. I understand that anything I write I'm married to -- I'm responsible for the things that I write because my reputation and livelihood is dependent on it. Do I really need a database? What about performance? Performance was such a big issue that I hand wrote a data structure that is capable of performing 2 billion operations, using a total of 4 gigs of memory in under 1/4 of a second using the standard core two duo processor. I could not find a similar, pre-written data structure in C# to perform this task. What setup do I use in terms of database? What about reporting? I'd prefer to have PDF's generated, but I'd like to be able to visually sketch those reports and then just have a ReportFactory of some sort, that when I pass some variables in, it just does that data. About Me I'm a lone developer for a small business in this area. This is the first time I've done this and I've never had the breadth and depth of my knowledge tested. I'm incredibly frustrated with this project because I feel incredibly overwhelmed with the task at hand. I'm looking for that entry level point where I can draw a line and say "this is what I need to do" Conclusion I may have not been clear enough on my post. I'm still new to this whole thing, and I've been doing my best to contribute back to the community that I've leached so much knowledge from. I'd be glad to edit my post and add more information if possible. I'm looking for a big-picture solution or design process that helps me get off the ground in this world of data-driven applications, because I have a feeling that it's going to be concentric to my entire career as a programmer for some time. Specifically, if you didn't get it from the rest of the post (I may not have been clear enough) I really need some guidance as to where to go in terms of the design decisions for this project. Some things that'll be useful will be a pro/con list for the different kinds of database projects available in VS2010. I've tried, but generating that list has been as hard as solving the problem itself... If you could walk a developer writing a data-driven application for the first time in C#, how would you do that? Where would you point them to?

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• SQL SERVER – Challenge – Puzzle – Why does RIGHT JOIN Exists

  - by pinaldave

  I had interesting conversation with the attendees of the my SQL Server Performance Tuning course. I was asked if LEFT JOIN can do the same task as RIGHT JOIN by reserving the order of the tables in join, why does RIGHT JOIN exists? The definitions are as following: Left Join – select all the records from the LEFT table and then pick up any matching records from the RIGHT table   Right Join – select all the records from the RIGHT table and then pick up any matching records from the LEFT table Most of us read from LEFT to RIGHT so we are using LEFT join. Do you have any explaination why RIGHT JOIN exists or can you come up with example, where RIGHT JOIN is absolutely required and the task can not be achieved with LEFT JOIN. Other Puzzles: SQL SERVER – Puzzle – Challenge – Error While Converting Money to Decimal SQL SERVER – Challenge – Puzzle – Usage of FAST Hint Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Pinal Dave, SQL, SQL Authority, SQL Puzzle, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• Microsoft Press Weekend Deal 26/May/2012 - Microsoft® Manual of Style, 4th Edition

  - by TATWORTH

  At http://shop.oreilly.com/product/0790145305770.do?code=MSDEAL, Microsoft Press are offering the Microsoft® Manual of Style, 4th Edition as a PDF for 50% off using the MSDEAL code."Maximize the impact and precision of your message! Now in its fourth edition, the Microsoft Manual of Style provides essential guidance to content creators, journalists, technical writers, editors, and everyone else who writes about computer technology. Direct from the Editorial Style Board at Microsoft—you get a comprehensive glossary of both general technology terms and those specific to Microsoft; clear, concise usage and style guidelines with helpful examples and alternatives; guidance on grammar, tone, and voice; and best practices for writing content for the web, optimizing for accessibility, and communicating to a worldwide audience. Fully updated and optimized for ease of use, the Microsoft Manual of Style is designed to help you communicate clearly, consistently, and accurately about technical topics—across a range of audiences and media." There is a sample chapter for free download at the above link

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• Freshy Ubuntu 12.10 install (Newbie)

  - by Alexander Marcev

  Hi i just installed ubuntu 12.10 on my ssd(picture below) and i set up my home directory to the 1 TB disc(picture below). I want in general use the ssd as my root folder as u can see, and install only the apps which are necessary. Games and other stuff goes to the 1 TB disc, but this disc shows me in gparted a usage of 14 GB on a freshly install, whats wrong? What about the ssd, do i have to manually optimize things? thx Alex PS: What if i want to install a Game to my home folder, i heard sth. of a symbol link, how to do that?

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• The broken Promise of the Mobile Web

  - by Rick Strahl

  High end mobile devices have been with us now for almost 7 years and they have utterly transformed the way we access information. Mobile phones and smartphones that have access to the Internet and host smart applications are in the hands of a large percentage of the population of the world. In many places even very remote, cell phones and even smart phones are a common sight. I’ll never forget when I was in India in 2011 I was up in the Southern Indian mountains riding an elephant out of a tiny local village, with an elephant herder in front riding atop of the elephant in front of us. He was dressed in traditional garb with the loin wrap and head cloth/turban as did quite a few of the locals in this small out of the way and not so touristy village. So we’re slowly trundling along in the forest and he’s lazily using his stick to guide the elephant and… 10 minutes in he pulls out his cell phone from his sash and starts texting. In the middle of texting a huge pig jumps out from the side of the trail and he takes a picture running across our path in the jungle! So yeah, mobile technology is very pervasive and it’s reached into even very buried and unexpected parts of this world. Apps are still King Apps currently rule the roost when it comes to mobile devices and the applications that run on them. If there’s something that you need on your mobile device your first step usually is to look for an app, not use your browser. But native app development remains a pain in the butt, with the requirement to have to support 2 or 3 completely separate platforms. There are solutions that try to bridge that gap. Xamarin is on a tear at the moment, providing their cross-device toolkit to build applications using C#. While Xamarin tools are impressive – and also *very* expensive – they only address part of the development madness that is app development. There are still specific device integration isssues, dealing with the different developer programs, security and certificate setups and all that other noise that surrounds app development. There’s also PhoneGap/Cordova which provides a hybrid solution that involves creating local HTML/CSS/JavaScript based applications, and then packaging them to run in a specialized App container that can run on most mobile device platforms using a WebView interface. This allows for using of HTML technology, but it also still requires all the set up, configuration of APIs, security keys and certification and submission and deployment process just like native applications – you actually lose many of the benefits that  Web based apps bring. The big selling point of Cordova is that you get to use HTML have the ability to build your UI once for all platforms and run across all of them – but the rest of the app process remains in place. Apps can be a big pain to create and manage especially when we are talking about specialized or vertical business applications that aren’t geared at the mainstream market and that don’t fit the ‘store’ model. If you’re building a small intra department application you don’t want to deal with multiple device platforms and certification etc. for various public or corporate app stores. That model is simply not a good fit both from the development and deployment perspective. Even for commercial, big ticket apps, HTML as a UI platform offers many advantages over native, from write-once run-anywhere, to remote maintenance, single point of management and failure to having full control over the application as opposed to have the app store overloads censor you. In a lot of ways Web based HTML/CSS/JavaScript applications have so much potential for building better solutions based on existing Web technologies for the very same reasons a lot of content years ago moved off the desktop to the Web. To me the Web as a mobile platform makes perfect sense, but the reality of today’s Mobile Web unfortunately looks a little different… Where’s the Love for the Mobile Web? Yet here we are in the middle of 2014, nearly 7 years after the first iPhone was released and brought the promise of rich interactive information at your fingertips, and yet we still don’t really have a solid mobile Web platform. I know what you’re thinking: “But we have lots of HTML/JavaScript/CSS features that allows us to build nice mobile interfaces”. I agree to a point – it’s actually quite possible to build nice looking, rich and capable Web UI today. We have media queries to deal with varied display sizes, CSS transforms for smooth animations and transitions, tons of CSS improvements in CSS 3 that facilitate rich layout, a host of APIs geared towards mobile device features and lately even a number of JavaScript framework choices that facilitate development of multi-screen apps in a consistent manner. Personally I’ve been working a lot with AngularJs and heavily modified Bootstrap themes to build mobile first UIs and that’s been working very well to provide highly usable and attractive UI for typical mobile business applications. From the pure UI perspective things actually look very good. Not just about the UI But it’s not just about the UI - it’s also about integration with the mobile device. When it comes to putting all those pieces together into what amounts to a consolidated platform to build mobile Web applications, I think we still have a ways to go… there are a lot of missing pieces to make it all work together and integrate with the device more smoothly, and more importantly to make it work uniformly across the majority of devices. I think there are a number of reasons for this. Slow Standards Adoption HTML standards implementations and ratification has been dreadfully slow, and browser vendors all seem to pick and choose different pieces of the technology they implement. The end result is that we have a capable UI platform that’s missing some of the infrastructure pieces to make it whole on mobile devices. There’s lots of potential but what is lacking that final 10% to build truly compelling mobile applications that can compete favorably with native applications. Some of it is the fragmentation of browsers and the slow evolution of the mobile specific HTML APIs. A host of mobile standards exist but many of the standards are in the early review stage and they have been there stuck for long periods of time and seem to move at a glacial pace. Browser vendors seem even slower to implement them, and for good reason – non-ratified standards mean that implementations may change and vendor implementations tend to be experimental and  likely have to be changed later. Neither Vendors or developers are not keen on changing standards. This is the typical chicken and egg scenario, but without some forward momentum from some party we end up stuck in the mud. It seems that either the standards bodies or the vendors need to carry the torch forward and that doesn’t seem to be happening quickly enough. Mobile Device Integration just isn’t good enough Current standards are not far reaching enough to address a number of the use case scenarios necessary for many mobile applications. While not every application needs to have access to all mobile device features, almost every mobile application could benefit from some integration with other parts of the mobile device platform. Integration with GPS, phone, media, messaging, notifications, linking and contacts system are benefits that are unique to mobile applications and could be widely used, but are mostly (with the exception of GPS) inaccessible for Web based applications today. Unfortunately trying to do most of this today only with a mobile Web browser is a losing battle. Aside from PhoneGap/Cordova’s app centric model with its own custom API accessing mobile device features and the token exception of the GeoLocation API, most device integration features are not widely supported by the current crop of mobile browsers. For example there’s no usable messaging API that allows access to SMS or contacts from HTML. Even obvious components like the Media Capture API are only implemented partially by mobile devices. There are alternatives and workarounds for some of these interfaces by using browser specific code, but that’s might ugly and something that I thought we were trying to leave behind with newer browser standards. But it’s not quite working out that way. It’s utterly perplexing to me that mobile standards like Media Capture and Streams, Media Gallery Access, Responsive Images, Messaging API, Contacts Manager API have only minimal or no traction at all today. Keep in mind we’ve had mobile browsers for nearly 7 years now, and yet we still have to think about how to get access to an image from the image gallery or the camera on some devices? Heck Windows Phone IE Mobile just gained the ability to upload images recently in the Windows 8.1 Update – that’s feature that HTML has had for 20 years! These are simple concepts and common problems that should have been solved a long time ago. It’s extremely frustrating to see build 90% of a mobile Web app with relative ease and then hit a brick wall for the remaining 10%, which often can be show stoppers. The remaining 10% have to do with platform integration, browser differences and working around the limitations that browsers and ‘pinned’ applications impose on HTML applications. The maddening part is that these limitations seem arbitrary as they could easily work on all mobile platforms. For example, SMS has a URL Moniker interface that sort of works on Android, works badly with iOS (only works if the address is already in the contact list) and not at all on Windows Phone. There’s no reason this shouldn’t work universally using the same interface – after all all phones have supported SMS since before the year 2000! But, it doesn’t have to be this way Change can happen very quickly. Take the GeoLocation API for example. Geolocation has taken off at the very beginning of the mobile device era and today it works well, provides the necessary security (a big concern for many mobile APIs), and is supported by just about all major mobile and even desktop browsers today. It handles security concerns via prompts to avoid unwanted access which is a model that would work for most other device APIs in a similar fashion. One time approval and occasional re-approval if code changes or caches expire. Simple and only slightly intrusive. It all works well, even though GeoLocation actually has some physical limitations, such as representing the current location when no GPS device is present. Yet this is a solved problem, where other APIs that are conceptually much simpler to implement have failed to gain any traction at all. Technically none of these APIs should be a problem to implement, but it appears that the momentum is just not there. Inadequate Web Application Linking and Activation Another important piece of the puzzle missing is the integration of HTML based Web applications. Today HTML based applications are not first class citizens on mobile operating systems. When talking about HTML based content there’s a big difference between content and applications. Content is great for search engine discovery and plain browser usage. Content is usually accessed intermittently and permanent linking is not so critical for this type of content.  But applications have different needs. Applications need to be started up quickly and must be easily switchable to support a multi-tasking user workflow. Therefore, it’s pretty crucial that mobile Web apps are integrated into the underlying mobile OS and work with the standard task management features. Unfortunately this integration is not as smooth as it should be. It starts with actually trying to find mobile Web applications, to ‘installing’ them onto a phone in an easily accessible manner in a prominent position. The experience of discovering a Mobile Web ‘App’ and making it sticky is by no means as easy or satisfying. Today the way you’d go about this is: Open the browser Search for a Web Site in the browser with your search engine of choice Hope that you find the right site Hope that you actually find a site that works for your mobile device Click on the link and run the app in a fully chrome’d browser instance (read tiny surface area) Pin the app to the home screen (with all the limitations outline above) Hope you pointed at the right URL when you pinned Even for you and me as developers, there are a few steps in there that are painful and annoying, but think about the average user. First figuring out how to search for a specific site or URL? And then pinning the app and hopefully from the right location? You’ve probably lost more than half of your audience at that point. This experience sucks. For developers too this process is painful since app developers can’t control the shortcut creation directly. This problem often gets solved by crazy coding schemes, with annoying pop-ups that try to get people to create shortcuts via fancy animations that are both annoying and add overhead to each and every application that implements this sort of thing differently. And that’s not the end of it - getting the link onto the home screen with an application icon varies quite a bit between browsers. Apple’s non-standard meta tags are prominent and they work with iOS and Android (only more recent versions), but not on Windows Phone. Windows Phone instead requires you to create an actual screen or rather a partial screen be captured for a shortcut in the tile manager. Who had that brilliant idea I wonder? Surprisingly Chrome on recent Android versions seems to actually get it right – icons use pngs, pinning is easy and pinned applications properly behave like standalone apps and retain the browser’s active page state and content. Each of the platforms has a different way to specify icons (WP doesn’t allow you to use an icon image at all), and the most widely used interface in use today is a bunch of Apple specific meta tags that other browsers choose to support. The question is: Why is there no standard implementation for installing shortcuts across mobile platforms using an official format rather than a proprietary one? Then there’s iOS and the crazy way it treats home screen linked URLs using a crazy hybrid format that is neither as capable as a Web app running in Safari nor a WebView hosted application. Moving off the Web ‘app’ link when switching to another app actually causes the browser and preview it to ‘blank out’ the Web application in the Task View (see screenshot on the right). Then, when the ‘app’ is reactivated it ends up completely restarting the browser with the original link. This is crazy behavior that you can’t easily work around. In some situations you might be able to store the application state and restore it using LocalStorage, but for many scenarios that involve complex data sources (like say Google Maps) that’s not a possibility. The only reason for this screwed up behavior I can think of is that it is deliberate to make Web apps a pain in the butt to use and forcing users trough the App Store/PhoneGap/Cordova route. App linking and management is a very basic problem – something that we essentially have solved in every desktop browser – yet on mobile devices where it arguably matters a lot more to have easy access to web content we have to jump through hoops to have even a remotely decent linking/activation experience across browsers. Where’s the Money? It’s not surprising that device home screen integration and Mobile Web support in general is in such dismal shape – the mobile OS vendors benefit financially from App store sales and have little to gain from Web based applications that bypass the App store and the cash cow that it presents. On top of that, platform specific vendor lock-in of both end users and developers who have invested in hardware, apps and consumables is something that mobile platform vendors actually aspire to. Web based interfaces that are cross-platform are the anti-thesis of that and so again it’s no surprise that the mobile Web is on a struggling path. But – that may be changing. More and more we’re seeing operations shifting to services that are subscription based or otherwise collect money for usage, and that may drive more progress into the Web direction in the end . Nothing like the almighty dollar to drive innovation forward. Do we need a Mobile Web App Store? As much as I dislike moderated experiences in today’s massive App Stores, they do at least provide one single place to look for apps for your device. I think we could really use some sort of registry, that could provide something akin to an app store for mobile Web apps, to make it easier to actually find mobile applications. This could take the form of a specialized search engine, or maybe a more formal store/registry like structure. Something like apt-get/chocolatey for Web apps. It could be curated and provide at least some feedback and reviews that might help with the integrity of applications. Coupled to that could be a native application on each platform that would allow searching and browsing of the registry and then also handle installation in the form of providing the home screen linking, plus maybe an initial security configuration that determines what features are allowed access to for the app. I’m not holding my breath. In order for this sort of thing to take off and gain widespread appeal, a lot of coordination would be required. And in order to get enough traction it would have to come from a well known entity – a mobile Web app store from a no name source is unlikely to gain high enough usage numbers to make a difference. In a way this would eliminate some of the freedom of the Web, but of course this would also be an optional search path in addition to the standard open Web search mechanisms to find and access content today. Security Security is a big deal, and one of the perceived reasons why so many IT professionals appear to be willing to go back to the walled garden of deployed apps is that Apps are perceived as safe due to the official review and curation of the App stores. Curated stores are supposed to protect you from malware, illegal and misleading content. It doesn’t always work out that way and all the major vendors have had issues with security and the review process at some time or another. Security is critical, but I also think that Web applications in general pose less of a security threat than native applications, by nature of the sandboxed browser and JavaScript environments. Web applications run externally completely and in the HTML and JavaScript sandboxes, with only a very few controlled APIs allowing access to device specific features. And as discussed earlier – security for any device interaction can be granted the same for mobile applications through a Web browser, as they can for native applications either via explicit policies loaded from the Web, or via prompting as GeoLocation does today. Security is important, but it’s certainly solvable problem for Web applications even those that need to access device hardware. Security shouldn’t be a reason for Web apps to be an equal player in mobile applications. Apps are winning, but haven’t we been here before? So now we’re finding ourselves back in an era of installed app, rather than Web based and managed apps. Only it’s even worse today than with Desktop applications, in that the apps are going through a gatekeeper that charges a toll and censors what you can and can’t do in your apps. Frankly it’s a mystery to me why anybody would buy into this model and why it’s lasted this long when we’ve already been through this process. It’s crazy… It’s really a shame that this regression is happening. We have the technology to make mobile Web apps much more prominent, but yet we’re basically held back by what seems little more than bureaucracy, partisan bickering and self interest of the major parties involved. Back in the day of the desktop it was Internet Explorer’s 98+%  market shareholding back the Web from improvements for many years – now it’s the combined mobile OS market in control of the mobile browsers. If mobile Web apps were allowed to be treated the same as native apps with simple ways to install and run them consistently and persistently, that would go a long way to making mobile applications much more usable and seriously viable alternatives to native apps. But as it is mobile apps have a severe disadvantage in placement and operation. There are a few bright spots in all of this. Mozilla’s FireFoxOs is embracing the Web for it’s mobile OS by essentially building every app out of HTML and JavaScript based content. It supports both packaged and certified package modes (that can be put into the app store), and Open Web apps that are loaded and run completely off the Web and can also cache locally for offline operation using a manifest. Open Web apps are treated as full class citizens in FireFoxOS and run using the same mechanism as installed apps. Unfortunately FireFoxOs is getting a slow start with minimal device support and specifically targeting the low end market. We can hope that this approach will change and catch on with other vendors, but that’s also an uphill battle given the conflict of interest with platform lock in that it represents. Recent versions of Android also seem to be working reasonably well with mobile application integration onto the desktop and activation out of the box. Although it still uses the Apple meta tags to find icons and behavior settings, everything at least works as you would expect – icons to the desktop on pinning, WebView based full screen activation, and reliable application persistence as the browser/app is treated like a real application. Hopefully iOS will at some point provide this same level of rudimentary Web app support. What’s also interesting to me is that Microsoft hasn’t picked up on the obvious need for a solid Web App platform. Being a distant third in the mobile OS war, Microsoft certainly has nothing to lose and everything to gain by using fresh ideas and expanding into areas that the other major vendors are neglecting. But instead Microsoft is trying to beat the market leaders at their own game, fighting on their adversary’s terms instead of taking a new tack. Providing a kick ass mobile Web platform that takes the lead on some of the proposed mobile APIs would be something positive that Microsoft could do to improve its miserable position in the mobile device market. Where are we at with Mobile Web? It sure sounds like I’m really down on the Mobile Web, right? I’ve built a number of mobile apps in the last year and while overall result and response has been very positive to what we were able to accomplish in terms of UI, getting that final 10% that required device integration dialed was an absolute nightmare on every single one of them. Big compromises had to be made and some features were left out or had to be modified for some devices. In two cases we opted to go the Cordova route in order to get the integration we needed, along with the extra pain involved in that process. Unless you’re not integrating with device features and you don’t care deeply about a smooth integration with the mobile desktop, mobile Web development is fraught with frustration. So, yes I’m frustrated! But it’s not for lack of wanting the mobile Web to succeed. I am still a firm believer that we will eventually arrive a much more functional mobile Web platform that allows access to the most common device features in a sensible way. It wouldn't be difficult for device platform vendors to make Web based applications first class citizens on mobile devices. But unfortunately it looks like it will still be some time before this happens. So, what’s your experience building mobile Web apps? Are you finding similar issues? Just giving up on raw Web applications and building PhoneGap apps instead? Completely skipping the Web and going native? Leave a comment for discussion. Resources Rick Strahl on DotNet Rocks talking about Mobile Web© Rick Strahl, West Wind Technologies, 2005-2014Posted in HTML5  Mobile   Tweet !function(d,s,id){var js,fjs=d.getElementsByTagName(s)[0];if(!d.getElementById(id)){js=d.createElement(s);js.id=id;js.src="//platform.twitter.com/widgets.js";fjs.parentNode.insertBefore(js,fjs);}}(document,"script","twitter-wjs"); (function() { var po = document.createElement('script'); po.type = 'text/javascript'; po.async = true; po.src = 'https://apis.google.com/js/plusone.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(po, s); })();

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• SQL SERVER – Solution to Puzzle – Simulate LEAD() and LAG() without Using SQL Server 2012 Analytic Function

  - by pinaldave

  Earlier I wrote a series on SQL Server Analytic Functions of SQL Server 2012. During the series to keep the learning maximum and having fun, we had few puzzles. One of the puzzle was simulating LEAD() and LAG() without using SQL Server 2012 Analytic Function. Please read the puzzle here first before reading the solution : Write T-SQL Self Join Without Using LEAD and LAG. When I was originally wrote the puzzle I had done small blunder and the question was a bit confusing which I corrected later on but wrote a follow up blog post on over here where I describe the give-away. Quick Recap: Generate following results without using SQL Server 2012 analytic functions. I had received so many valid answers. Some answers were similar to other and some were very innovative. Some answers were very adaptive and some did not work when I changed where condition. After selecting all the valid answer, I put them in table and ran RANDOM function on the same and selected winners. Here are the valid answers. No Joins and No Analytic Functions Excellent Solution by Geri Reshef – Winner of SQL Server Interview Questions and Answers (India | USA) WITH T1 AS (SELECT Row_Number() OVER(ORDER BY SalesOrderDetailID) N, s.SalesOrderID, s.SalesOrderDetailID, s.OrderQty FROM Sales.SalesOrderDetail s WHERE SalesOrderID IN (43670, 43669, 43667, 43663)) SELECT SalesOrderID,SalesOrderDetailID,OrderQty, CASE WHEN N%2=1 THEN MAX(CASE WHEN N%2=0 THEN SalesOrderDetailID END) OVER (Partition BY (N+1)/2) ELSE MAX(CASE WHEN N%2=1 THEN SalesOrderDetailID END) OVER (Partition BY N/2) END LeadVal, CASE WHEN N%2=1 THEN MAX(CASE WHEN N%2=0 THEN SalesOrderDetailID END) OVER (Partition BY N/2) ELSE MAX(CASE WHEN N%2=1 THEN SalesOrderDetailID END) OVER (Partition BY (N+1)/2) END LagVal FROM T1 ORDER BY SalesOrderID, SalesOrderDetailID, OrderQty; GO No Analytic Function and Early Bird Excellent Solution by DHall – Winner of Pluralsight 30 days Subscription -- a query to emulate LEAD() and LAG() ;WITH s AS ( SELECT 1 AS ldOffset, -- equiv to 2nd param of LEAD 1 AS lgOffset, -- equiv to 2nd param of LAG NULL AS ldDefVal, -- equiv to 3rd param of LEAD NULL AS lgDefVal, -- equiv to 3rd param of LAG ROW_NUMBER() OVER (ORDER BY SalesOrderDetailID) AS row, SalesOrderID, SalesOrderDetailID, OrderQty FROM Sales.SalesOrderDetail WHERE SalesOrderID IN (43670, 43669, 43667, 43663) ) SELECT s.SalesOrderID, s.SalesOrderDetailID, s.OrderQty, ISNULL( sLd.SalesOrderDetailID, s.ldDefVal) AS LeadValue, ISNULL( sLg.SalesOrderDetailID, s.lgDefVal) AS LagValue FROM s LEFT OUTER JOIN s AS sLd ON s.row = sLd.row - s.ldOffset LEFT OUTER JOIN s AS sLg ON s.row = sLg.row + s.lgOffset ORDER BY s.SalesOrderID, s.SalesOrderDetailID, s.OrderQty No Analytic Function and Partition By Excellent Solution by DHall – Winner of Pluralsight 30 days Subscription /* a query to emulate LEAD() and LAG() */ ;WITH s AS ( SELECT 1 AS LeadOffset, /* equiv to 2nd param of LEAD */ 1 AS LagOffset, /* equiv to 2nd param of LAG */ NULL AS LeadDefVal, /* equiv to 3rd param of LEAD */ NULL AS LagDefVal, /* equiv to 3rd param of LAG */ /* Try changing the values of the 4 integer values above to see their effect on the results */ /* The values given above of 0, 0, null and null behave the same as the default 2nd and 3rd parameters to LEAD() and LAG() */ ROW_NUMBER() OVER (ORDER BY SalesOrderDetailID) AS row, SalesOrderID, SalesOrderDetailID, OrderQty FROM Sales.SalesOrderDetail WHERE SalesOrderID IN (43670, 43669, 43667, 43663) ) SELECT s.SalesOrderID, s.SalesOrderDetailID, s.OrderQty, ISNULL( sLead.SalesOrderDetailID, s.LeadDefVal) AS LeadValue, ISNULL( sLag.SalesOrderDetailID, s.LagDefVal) AS LagValue FROM s LEFT OUTER JOIN s AS sLead ON s.row = sLead.row - s.LeadOffset /* Try commenting out this next line when LeadOffset != 0 */ AND s.SalesOrderID = sLead.SalesOrderID /* The additional join criteria on SalesOrderID above is equivalent to PARTITION BY SalesOrderID in the OVER clause of the LEAD() function */ LEFT OUTER JOIN s AS sLag ON s.row = sLag.row + s.LagOffset /* Try commenting out this next line when LagOffset != 0 */ AND s.SalesOrderID = sLag.SalesOrderID /* The additional join criteria on SalesOrderID above is equivalent to PARTITION BY SalesOrderID in the OVER clause of the LAG() function */ ORDER BY s.SalesOrderID, s.SalesOrderDetailID, s.OrderQty No Analytic Function and CTE Usage Excellent Solution by Pravin Patel - Winner of SQL Server Interview Questions and Answers (India | USA) --CTE based solution ; WITH cteMain AS ( SELECT SalesOrderID, SalesOrderDetailID, OrderQty, ROW_NUMBER() OVER (ORDER BY SalesOrderDetailID) AS sn FROM Sales.SalesOrderDetail WHERE SalesOrderID IN (43670, 43669, 43667, 43663) ) SELECT m.SalesOrderID, m.SalesOrderDetailID, m.OrderQty, sLead.SalesOrderDetailID AS leadvalue, sLeg.SalesOrderDetailID AS leagvalue FROM cteMain AS m LEFT OUTER JOIN cteMain AS sLead ON sLead.sn = m.sn+1 LEFT OUTER JOIN cteMain AS sLeg ON sLeg.sn = m.sn-1 ORDER BY m.SalesOrderID, m.SalesOrderDetailID, m.OrderQty No Analytic Function and Co-Related Subquery Usage Excellent Solution by Pravin Patel – Winner of SQL Server Interview Questions and Answers (India | USA) -- Co-Related subquery SELECT m.SalesOrderID, m.SalesOrderDetailID, m.OrderQty, ( SELECT MIN(SalesOrderDetailID) FROM Sales.SalesOrderDetail AS l WHERE l.SalesOrderID IN (43670, 43669, 43667, 43663) AND l.SalesOrderID >= m.SalesOrderID AND l.SalesOrderDetailID > m.SalesOrderDetailID ) AS lead, ( SELECT MAX(SalesOrderDetailID) FROM Sales.SalesOrderDetail AS l WHERE l.SalesOrderID IN (43670, 43669, 43667, 43663) AND l.SalesOrderID <= m.SalesOrderID AND l.SalesOrderDetailID < m.SalesOrderDetailID ) AS leag FROM Sales.SalesOrderDetail AS m WHERE m.SalesOrderID IN (43670, 43669, 43667, 43663) ORDER BY m.SalesOrderID, m.SalesOrderDetailID, m.OrderQty This was one of the most interesting Puzzle on this blog. Giveaway Winners will get following giveaways. Geri Reshef and Pravin Patel SQL Server Interview Questions and Answers (India | USA) DHall Pluralsight 30 days Subscription Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, Readers Contribution, Readers Question, SQL, SQL Authority, SQL Function, SQL Puzzle, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• /sbin/getty process causing 100% CPU utilization

  - by scrrr

  I have an instance of Ubuntu 12.04 LTS (GNU/Linux 3.2.0-25-virtual i686) running as a KVM-VM on a host-machine that runs one more VM beside it. I deploy a Ruby on Rails application using the Capistrano deployment-gem. However, if I deploy twice in a row in a short time, the CPU usage jumps to 100% because of the /sbin/getty process. How can this be? I believe getty is a rather simple program that passes a login-name from a terminal to a login-process. Also: In my Capfile (Capistrano configuration file) I am running certain commands after the Rails application is deployed including a call to sudo /sbin/restart <APPNAME> which is an upstart task. Could this be related somehow? I can always kill the getty process and the problem is gone until the next deployment, but I would rather understand and fix the problem. Any help is appreciated. Attached is a screenshot of my problem.

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• C# Neural Networks with Encog

  - by JoshReuben

  Neural Networks ·       I recently read a book Introduction to Neural Networks for C# , by Jeff Heaton. http://www.amazon.com/Introduction-Neural-Networks-C-2nd/dp/1604390093/ref=sr_1_2?ie=UTF8&s=books&qid=1296821004&sr=8-2-spell. Not the 1st ANN book I've perused, but a nice revision.   ·       Artificial Neural Networks (ANNs) are a mechanism of machine learning – see http://en.wikipedia.org/wiki/Artificial_neural_network , http://en.wikipedia.org/wiki/Category:Machine_learning ·       Problems Not Suited to a Neural Network Solution- Programs that are easily written out as flowcharts consisting of well-defined steps, program logic that is unlikely to change, problems in which you must know exactly how the solution was derived. ·       Problems Suited to a Neural Network – pattern recognition, classification, series prediction, and data mining. Pattern recognition - network attempts to determine if the input data matches a pattern that it has been trained to recognize. Classification - take input samples and classify them into fuzzy groups. ·       As far as machine learning approaches go, I thing SVMs are superior (see http://en.wikipedia.org/wiki/Support_vector_machine ) - a neural network has certain disadvantages in comparison: an ANN can be overtrained, different training sets can produce non-deterministic weights and it is not possible to discern the underlying decision function of an ANN from its weight matrix – they are black box. ·       In this post, I'm not going to go into internals (believe me I know them). An autoassociative network (e.g. a Hopfield network) will echo back a pattern if it is recognized. ·       Under the hood, there is very little maths. In a nutshell - Some simple matrix operations occur during training: the input array is processed (normalized into bipolar values of 1, -1) - transposed from input column vector into a row vector, these are subject to matrix multiplication and then subtraction of the identity matrix to get a contribution matrix. The dot product is taken against the weight matrix to yield a boolean match result. For backpropogation training, a derivative function is required. In learning, hill climbing mechanisms such as Genetic Algorithms and Simulated Annealing are used to escape local minima. For unsupervised training, such as found in Self Organizing Maps used for OCR, Hebbs rule is applied. ·       The purpose of this post is not to mire you in technical and conceptual details, but to show you how to leverage neural networks via an abstraction API - Encog   Encog ·       Encog is a neural network API ·       Links to Encog: http://www.encog.org , http://www.heatonresearch.com/encog, http://www.heatonresearch.com/forum ·       Encog requires .Net 3.5 or higher – there is also a Silverlight version. Third-Party Libraries – log4net and nunit. ·       Encog supports feedforward, recurrent, self-organizing maps, radial basis function and Hopfield neural networks. ·       Encog neural networks, and related data, can be stored in .EG XML files. ·       Encog Workbench allows you to edit, train and visualize neural networks. The Encog Workbench can generate code. Synapses and layers ·       the primary building blocks - Almost every neural network will have, at a minimum, an input and output layer. In some cases, the same layer will function as both input and output layer. ·       To adapt a problem to a neural network, you must determine how to feed the problem into the input layer of a neural network, and receive the solution through the output layer of a neural network. ·       The Input Layer - For each input neuron, one double value is stored. An array is passed as input to a layer. Encog uses the interface INeuralData to hold these arrays. The class BasicNeuralData implements the INeuralData interface. Once the neural network processes the input, an INeuralData based class will be returned from the neural network's output layer. ·       convert a double array into an INeuralData object : INeuralData data = new BasicNeuralData(= new double[10]); ·       the Output Layer- The neural network outputs an array of doubles, wraped in a class based on the INeuralData interface. ·        The real power of a neural network comes from its pattern recognition capabilities. The neural network should be able to produce the desired output even if the input has been slightly distorted. ·       Hidden Layers– optional. between the input and output layers. very much a “black box”. If the structure of the hidden layer is too simple it may not learn the problem. If the structure is too complex, it will learn the problem but will be very slow to train and execute. Some neural networks have no hidden layers. The input layer may be directly connected to the output layer. Further, some neural networks have only a single layer. A single layer neural network has the single layer self-connected. ·       connections, called synapses, contain individual weight matrixes. These values are changed as the neural network learns. Constructing a Neural Network ·       the XOR operator is a frequent “first example” -the “Hello World” application for neural networks. ·       The XOR Operator- only returns true when both inputs differ. 0 XOR 0 = 0 1 XOR 0 = 1 0 XOR 1 = 1 1 XOR 1 = 0 ·       Structuring a Neural Network for XOR  - two inputs to the XOR operator and one output. ·       input: 0.0,0.0 1.0,0.0 0.0,1.0 1.0,1.0 ·       Expected output: 0.0 1.0 1.0 0.0 ·       A Perceptron - a simple feedforward neural network to learn the XOR operator. ·       Because the XOR operator has two inputs and one output, the neural network will follow suit. Additionally, the neural network will have a single hidden layer, with two neurons to help process the data. The choice for 2 neurons in the hidden layer is arbitrary, and often comes down to trial and error. ·       Neuron Diagram for the XOR Network ·       ·       The Encog workbench displays neural networks on a layer-by-layer basis. ·       Encog Layer Diagram for the XOR Network:   ·       Create a BasicNetwork - Three layers are added to this network. the FinalizeStructure method must be called to inform the network that no more layers are to be added. The call to Reset randomizes the weights in the connections between these layers. var network = new BasicNetwork(); network.AddLayer(new BasicLayer(2)); network.AddLayer(new BasicLayer(2)); network.AddLayer(new BasicLayer(1)); network.Structure.FinalizeStructure(); network.Reset(); ·       Neural networks frequently start with a random weight matrix. This provides a starting point for the training methods. These random values will be tested and refined into an acceptable solution. However, sometimes the initial random values are too far off. Sometimes it may be necessary to reset the weights again, if training is ineffective. These weights make up the long-term memory of the neural network. Additionally, some layers have threshold values that also contribute to the long-term memory of the neural network. Some neural networks also contain context layers, which give the neural network a short-term memory as well. The neural network learns by modifying these weight and threshold values. ·       Now that the neural network has been created, it must be trained. Training a Neural Network ·       construct a INeuralDataSet object - contains the input array and the expected output array (of corresponding range). Even though there is only one output value, we must still use a two-dimensional array to represent the output. public static double[][] XOR_INPUT ={ new double[2] { 0.0, 0.0 }, new double[2] { 1.0, 0.0 }, new double[2] { 0.0, 1.0 }, new double[2] { 1.0, 1.0 } };   public static double[][] XOR_IDEAL = { new double[1] { 0.0 }, new double[1] { 1.0 }, new double[1] { 1.0 }, new double[1] { 0.0 } };   INeuralDataSet trainingSet = new BasicNeuralDataSet(XOR_INPUT, XOR_IDEAL); ·       Training is the process where the neural network's weights are adjusted to better produce the expected output. Training will continue for many iterations, until the error rate of the network is below an acceptable level. Encog supports many different types of training. Resilient Propagation (RPROP) - general-purpose training algorithm. All training classes implement the ITrain interface. The RPROP algorithm is implemented by the ResilientPropagation class. Training the neural network involves calling the Iteration method on the ITrain class until the error is below a specific value. The code loops through as many iterations, or epochs, as it takes to get the error rate for the neural network to be below 1%. Once the neural network has been trained, it is ready for use. ITrain train = new ResilientPropagation(network, trainingSet);   for (int epoch=0; epoch < 10000; epoch++) { train.Iteration(); Debug.Print("Epoch #" + epoch + " Error:" + train.Error); if (train.Error > 0.01) break; } Executing a Neural Network ·       Call the Compute method on the BasicNetwork class. Console.WriteLine("Neural Network Results:"); foreach (INeuralDataPair pair in trainingSet) { INeuralData output = network.Compute(pair.Input); Console.WriteLine(pair.Input[0] + "," + pair.Input[1] + ", actual=" + output[0] + ",ideal=" + pair.Ideal[0]); } ·       The Compute method accepts an INeuralData class and also returns a INeuralData object. Neural Network Results: 0.0,0.0, actual=0.002782538818034049,ideal=0.0 1.0,0.0, actual=0.9903741937121177,ideal=1.0 0.0,1.0, actual=0.9836807956566187,ideal=1.0 1.0,1.0, actual=0.0011646072586172778,ideal=0.0 ·       the network has not been trained to give the exact results. This is normal. Because the network was trained to 1% error, each of the results will also be within generally 1% of the expected value.

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• CodePlex Daily Summary for Saturday, June 05, 2010

  CodePlex Daily Summary for Saturday, June 05, 2010New Projects555 Calculator: A simple calculator to help choosing resistor and capacitor values to get the frequency you're looking for on a 555 timer.BleQua .NET: PL: Program sieciowy BleQua .NET jest multi-komunikatorem. EN: Network program BleQua .NET is multicomunicator.ChatDiplomaWork: ChatSample is the sample project.CSUFVGDC Summer Jam: Repository for VGDC summer game jam.Database Export Wizard: ExportWizard is a Step Wizard for Database Export using ASP.net and SQL Server. It allows easy export in any of the standard formats: CSV, TXT, HTM...Dozer Enterprise Library for .NET: a light .net framework for enterprise applications developmentEmployee Management System: This is an Employee Management System. the goal here is to offer a software that caters to small to mid sized businesses for free. This program a...Fanray: My project on Codeplex.Infragistics Analytics Framework: This project includes wrappers for the Infragistics controls that integrate with the recently launched Microsoft Silverlight Analytics Framework. ...KIME Simio Extensions: This is the official project of KIME Solutions. Here you find any current developments of KIME that are publicly available. KIME develops extension...MindTouch Community Extensions: MindTouch Community Extentions is a Native C# extention library for MindTouch Core that will have Dekiscript functions for full coverage of the API...NginxTray: NginxTray allows you manage easily Nginx Web Server by a Tray icon.NStore: NStore is a virtual store example done with ASP.NET MVC 2.0 tecnologyProjet Campus Numerique + Appli Mobile: Projet de création d'un campus numérique pour l'ISEN et d'un application mobile d'accès.SharePoint 2010 Feature Upgrade Kit: A set of tools for managing upgradable Features in SharePoint 2010. (Upgrading Features is a means of deploying code/artifact updates to existing S...SiteMap Utility for DNN Blog Module: This is a mini-project which allows you to easily add or generate an XML site map to your DotNetNuke® website for the search engines to use to inde...Space Explorer: A small app to help users examine folders to see which files and subfolders are taking up space. Still in development, no releases available curren...SQL Compact Toolbox: SQL Compact Toolbox is a Visual Studio 2010 add-in, that adds scripting, import, export, migrate, rename, run script and other upcoming SQL Server ...Twilverlight: Twliverlight is TweetDeck mixed with Silverlight. Much as I like using TweetDeck, it hogs my memory out, so this is an attempt to write a memory-ef...Visual Studio 2010 FxCop Extension: Visual Studio 2010 FxCop Extension allows to integrate stand-alone FxCop into Visual Studio 2010. You'll be able to analysis your source code with ...VisualStudio 2010 JavaScript Outlining: Visual Studio 2010 editor extension for JavaScript code blocks and custom regions outlining Wiki Shelf: Wiki Shelf is a Wikipedia browser app. The goal is to bring the library experience of browsing books, studying, and researching to the Wikipedia u...X-Arena - Magic: Projeto de PDS2 no Curso de Tecnologia em Desenvolvimento de Software no CEFETRN. O desenvolvimento do jogo Quiz Arena possui como pr...New Releases555 Calculator: 555Calc release v1.0: The initial 1 point uh-oh release of 555Calc.BleQua .NET: BleQua .NET 1.0.0.0: First releaseChatterbot JBot: JBot 1.0.1.155: Change presentation technology from Window Forms to Widndown Presentation Fundation.Community Forums NNTP bridge: Community Forums NNTP Bridge V26: Release of the Community Forums NNTP Bridge to access the social and anwsers MS forums with a single, open source NNTP bridge. This release has ad...Community Forums NNTP bridge: Community Forums NNTP Bridge V27: Release of the Community Forums NNTP Bridge to access the social and anwsers MS forums with a single, open source NNTP bridge. This release has ad...Community Forums NNTP bridge: Community Forums NNTP Bridge V28: Release of the Community Forums NNTP Bridge to access the social and anwsers MS forums with a single, open source NNTP bridge. This release has ad...CSS 360 Planetary Calendar: Final Release: =============================================================================== Final Release Version: 2.0 Tools Used: - Collaboration, Releas...Database Export Wizard: Version 3: As described in CodeProject article: Database Export Wizard for ASP.net and SQL Server. http://www.codeproject.com/KB/aspnet/DatabaseExportWizard.aspxEdu Math: Edu Math 2.0.10.122: Change version .NET Framework.Employee Management System: V1 (beta): This version is still in beta testing. Any issues, comments or suggestions are greatly appreciated. The export to excel function in this release o...ESB.NET: ESBDeploy_7.0.27.0 (x64 and x86) [ESB.NET 7.0 RC1]: Release Details Changes Since Last Release (since 6.3.47.1) - Targets .NET Framework 4, Visual Studio.NET 2010, Workflow 4 - Flowchart workflow ada...Free Silverlight & WPF Chart Control - Visifire: Visifire SL and WPF Charts v3.1.1 beta 2 Released: Hi, This release contains the following enhancements: *ShowIndicator() and HideIndicator() function has been implemented in Chart. So now user wi...Free Silverlight & WPF Chart Control - Visifire: Visifire SL and WPF Charts v3.5.4 beta 2 Released: Hi, This release contains the following enhancements: *ShowIndicator() and HideIndicator() function has been implemented in Chart. So now user wi...FsCheck: A random testing framework: FsCheck 0.7: What to download? If you use F# April 2010 CTP with Visual Studio 2008 or Visual Studio 2010, either Source or Binaries will do. To open source in...Git Source Control Provider: V 0.5: For VS 2010 users, it is recommanded to install it within Visual Studio by selecting Tools | Extension Manager. Run Visual Studio. Go to Tools ...GPdotNET - Genetic Programming Tool: GPdotNETv0.95: 1. Localization support 2. Export functionality for GP Model with training and testing data. 3. Export GPModel with Testing and Training data. 4....JoshDOS: JoshDOS 1.1: 1.1 adds a toutorial of how to create new commands and of course, you need the COMSOS user kit or dev kit. Ver 1.1 also includes a demo called Gue...KIME Simio Extensions: KIME.SimioDebugStep: This simple Simio step allows you to debug any number of expressions from within the simulation run. The debug information is displayed using a mes...NginxTray: NginxTray 0.3 Beta 2: NginxTray 0.3 Beta 2NginxTray: NginxTray 0.5 Beta 3: NginxTray 0.5 Beta 3NginxTray: NginxTray 0.6 RC1: NginxTray 0.6 RC1Open Source PLM Activities: Prodeos_OC beta 1.0: The “Innovator – MS Office Connector” is a product developed by Prodeos (www.prodeos.com). It is a light connector made to facilitate the use of Mi...Paint.NET PSD Plugin: 1.5.1: Changes in this release: Bitmap-mode images can now be loaded. Thanks to dhnc for filing the bug. Plugin no longer crashes on files with user m...SharePoint 2010 Feature Upgrade Kit: 1.0.0.0: This release contains:- - Custom application page to manage the upgrade of Site and Web-scoped Features. To come in the next release: - Companio...SiteMap Utility for DNN Blog Module: Blog SiteMap Utility v01.00.01: This is the first public release of the SiteMap Utility for the core DotNetNuke® Blog Module. Please see the documentation on this site on how to...SqlDiffFramework-A Visual Differencing Engine for Dissimilar Data Sources: SqlDiffFramework 1.0.2.0: Maintenance Release Defect Fixes: Issue # 3: 3 Issue # 4: 4 Enhancements: About Box now displays regional and language settings in effect. SDF...SuperSocket: First release of SuperSocket: !First release of SuperSocketThe Fastcopy Helper: FastcopyHelper: Fastcopy Helper 2.0 This is a final one. You can use it on the way. In order to use it , you should have the .NET3.5 ! 此软件必须下载 .NET3.5平台，方可使用！TV Show Renamer: TV Show Renamer Beta 3: I found the bug the prevented it from closing correctly so I fixed it and had to release it right away. If anyone else finds any problems. contact me.UrzaGatherer: UrzaGatherer v2.0: UrzaGatherer is the first stable version. This release include UrzaBackgroundPictures.VisualStudio 2010 JavaScript Outlining: VisualStudion 2010 Javascript Outlining 1.0: Features Outlines JavaScript codeblock regions for the code placed between { }. Both places on a new line. Outlines custom regions defined by: //...Wouter's SharePoint Demo Land: Navigation Service with Proxy: A SharePoint 2010 Service Application that uses service proxies to relay commands to the actual service. The demo proxy makes use of in-memory comm...盘古分词-开源中文分词组件: V2.0.0.0: 进一步优化性能，分词速度达到将近 500K ，1.2.0.1 版本只有 320K 修改 PanGu.Lucene.Analyzer, 支持 Lucene.net 2.9 版本。 增加对字典中以数字开头的专业非中文词汇的识别 增加英文分词开关，权重由英文小写权重和英文词根权重两个参数来决定...Most Popular ProjectsCommunity Forums NNTP bridgeOutSyncASP.NET MVC Time PlannerNeatUploadMoonyDesk (windows desktop widgets)AgUnit - Silverlight unit testing with ReSharperViperWorks IgnitionASP.NET MVC ExtensionsAviva Solutions C# Coding GuidelinesMute4Most Active ProjectsCommunity Forums NNTP bridgeRawrpatterns & practices – Enterprise LibraryIonics Isapi Rewrite FilterGMap.NET - Great Maps for Windows Forms & PresentationN2 CMSStyleCopFarseer Physics Enginesmark C# LibraryMirror Testing System

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• Visual History for Chrome Maps Out Your Browser History in an Interactive Graph

  - by Jason Fitzpatrick

  Curious how your adventures on the web interweave? Visual History for Chrome maps out related web sites in your browsing history into an interactive chart–visualize your browsing over the last hours, days, or months. One of the interesting elements of Visual History is that it doesn’t simply link sites together via activated hyperlinks but by consecutive use within 20 minute increments–thus if you frequently hit up Gmail, Facebook, and Reddit first thing in the morning, they’ll all appear together in a usage cluster. Site can be organized by URL, sub-domain, or domain. Visual History is free, Chrome only. Visual History for Chrome [Chrome Web Store] HTG Explains: What The Windows Event Viewer Is and How You Can Use It HTG Explains: How Windows Uses The Task Scheduler for System Tasks HTG Explains: Why Do Hard Drives Show the Wrong Capacity in Windows?

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