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• XSL Template - reducing replication

  - by Chris

  Hey Sorry about the extremely vague question title (any suggestions for improvements welcome) I have an XSL document that, currently, has lots of replication that I want to reduce. Here is the following XML snippet I am working with <Unit Status="alive"> I am currently using the following XSL to show images based on the status of the Unit <xsl:choose> <xsl:when test="@Status = 'alive'"> <img src="/web/resources/graphics/accept.png" /> </xsl:when> <xsl:when test="@Status = 'missingUnit'"> <img src="/web/resources/graphics/error.png" /> </xsl:when> <xsl:when test="@Status = 'missingNode'"> <img src="/web/resources/graphics/exclamation.png" /> </xsl:when> <xsl:when test="@Status = 'unexpectedUnit'"> <img src="/web/resources/graphics/exclamation_blue.png" /> </xsl:when> <xsl:otherwise> <!-- Should never get here --> <img src="/web/resources/graphics/delete.png" /> </xsl:otherwise> </xsl:choose> How do I put this code in a template or stylesheet that will allow me to stop copying / pasting this everywhere. Thanks

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• Which java technology should i use , if i want to build website with thousands of users

  - by Mirage

  Sorry for asking this question but i searched all java realted question but i got more confused. I am still not clear what should i start with 1)My main is build website in Java because someone told me that there are some machine learning or AI libraries available in java which i can use in java. so i decided to use that as it can reduce my work. Now i don't know java at all some people say following are used to build websites like 1)Servelts alone can build webiste 2)JSP alone can also build webiste 3)Struts 4)Spring with Hibernate 5)SEAM 6)JEE also for webistes Now guys i am confused where should i start from. Where does core JAVA fits in here. i was thinking of perhaps learning python as i know i have to learn Python only not its variations SO please guide me one thing which can solve my basic purpose of using ready made libraries of AI If i can do that with JSP then i will start with that. But i need to learn all of them then its better if can start learning python. I have 5 months to finish webiste. I really don't know why there are many braches of java for doing one thing Please help me.

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• iPhone static library Clang/LLVM error: non_lazy_symbol_pointers

  - by Bekenn

  After several hours of experimentation, I've managed to reduce the problem to the following example (C++): extern "C" void foo(); struct test { ~test() { } }; void doTest() { test t; // 1 foo(); // 2 } This is being compiled for iOS devices in XCode 4.2, using the provided Clang compiler (Apple LLVM compiler 3.0) and the iOS 5.0 SDK. The project is configured as a Cocoa Touch Static Library, and "Enable Linking With Shared Libraries" is set to No because I'm building an AIR native extension. The function foo is defined in another external library. (In my actual project, this would be any of the C API functions defined by Adobe for use in AIR native extensions.) When attempting to compile this code, I get back the error: FATAL:incompatible feature used: section type non_lazy_symbol_pointers (must specify "-dynamic" to be used) clang: error: assembler command failed with exit code 1 (use -v to see invocation) The error goes away if I comment out either of the lines marked 1 or 2 above, or if I change the build setting "Enable Linking With Shared Libraries" to Yes. (However, if I change the build setting, then I get multiple ld warning: unexpected srelocation type 9 warnings when linking the library into the final project, and the application crashes when running on the device.) The build error also goes away if I remove the destructor from test. So: Is this a bug in Clang? Am I missing some all-important and undocumented build setting? The interaction between an externally-provided function and a struct with a destructor is very peculiar, to say the least.

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• Codeigniter common templates

  - by Darthg8r

  Let's say that I have a website that has 100 different pages. Each page uses a common header and footer. Inside the header is some dynamic content that comes from a database. I'd like to avoid having to have code in every single controller and action that passes this common code into the view. function index() { // It sucks to have to include this on every controller action. data['title'] = "This is the index page"; data['currentUserName'] = "John Smith"; $this->load->view("main_view", data); } function comments() { // It sucks to have to include this on every controller action. data['title'] = "Comment list"; data['currentUserName'] = "John Smith"; $this->load->view("comment_view", data); } I realize that I could refactor the code so that the common parts are in a single function and the function is called by the action. Doing so would reduce SOME of the pain, but it still doesn't feel right since I'd still have to make a call to that function every time. What's the correct way to handle this?

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• ruby comma operator and step question

  - by ryan_m

  so, i'm trying to learn ruby by doing some project euler questions, and i've run into a couple things i can't explain, and the comma ?operator? is in the middle of both. i haven't been able to find good documentation for this, maybe i'm just not using the google as I should, but good ruby documentation seems a little sparse . . . 1: how do you describe how this is working? the first snippet is the ruby code i don't understand, the second is the code i wrote that does the same thing only after painstakingly tracing the first: #what is this doing? cur, nxt = nxt, cur + nxt #this, apparently, but how to describe the above? nxt = cur + nxt cur = nxt - cur 2: in the following example, how do you describe what the line with 'step' is doing? from what i can gather, the step command works like (range).step(step_size), but this seems to be doing (starting_point).step(ending_point, step_size). Am i right with this assumption? where do i find good doc of this? #/usr/share/doc/ruby1.9.1-examples/examples/sieve.rb # sieve of Eratosthenes max = Integer(ARGV.shift || 100) sieve = [] for i in 2 .. max sieve[i] = i end for i in 2 .. Math.sqrt(max) next unless sieve[i] (i*i).step(max, i) do |j| sieve[j] = nil end end puts sieve.compact.join(", ")

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• Asynchronous event loop design and issues.

  - by Artyom

  Hello, I'm designing event loop for asynchronous socket IO using epoll/devpoll/kqueue/poll/select (including windows-select). I have two options of performing, IO operation: Non-blocking mode, poll on EAGAIN Set socket to non-blocking mode. Read/Write to socket. If operation succeeds, post completion notification to event loop. If I get EAGAIN, add socket to "select list" and poll socket. Polling mode: poll and then execute Add socket to select list and poll it. Wait for notification that it is readable writable read/write Post completion notification to event loop of sucseeds To me it looks like first would require less system calls when using in normal mode, especially for writing to socket (buffers are quite big). Also it looks like that it would be possible to reduce the overhead over number of "select" executions, especially it is nice when you do not have something that scales well as epoll/devpoll/kqueue. Questions: Are there any advantages of the second approach? Are there any portability issues with non-blocking operations on sockets/file descriptors over numerous operating systems: Linux, FreeBSD, Solaris, MacOSX, Windows. Notes: Please do not suggest using existing event-loop/socket-api implementations

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• WPF: Editable ComboBox; how to make search/auto-fill functionality case sensitive?

  - by unforgiven3

  Say I have a ComboBox, like so: <ComboBox IsEditable="True" Height="30"> <ComboBoxItem>robot</ComboBoxItem> <ComboBoxItem>Robot</ComboBoxItem> </ComboBox> If a user comes along and starts by typing a lower-case 'r' into that ComboBox when it is empty, the ComboBox predictably auto-fills itself with the word 'robot'. Great. Now the same user comes along and starts typing an upper-case 'R' into that ComboBox when it is again empty. Unpredictable, the ComboBox auto-fills itself with the lower-case word 'robot'. Not great. I desperately want it to auto-fill itself with 'Robot', but WPF does not seem to want to smile down upon me. No matter what you do (CAPS lock, shift+key), the ComboBox will always auto-fill with the lower case 'robot', provided that the lower case 'robot' precedes the upper case 'Robot' in the ComboBox's items collection. Is there any way to prevent this? This behavior is maddening and makes for an absolutely abysmal user experience.

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• Why this base64 function stop working when increasing max length?

  - by flyout

  I am using this class to encode/decode text to base64. It works fine with MAX_LEN up to 512 but if I increase it to 1024 the decode function returns and empty var. This is the function: char* Base64::encode(char *src) { char* ptr = dst+0; unsigned triad; unsigned int d_len = MAX_LEN; memset(dst,'\0', MAX_LEN); unsigned s_len = strlen(src); for (triad = 0; triad < s_len; triad += 3) { unsigned long int sr = 0; unsigned byte; for (byte = 0; (byte<3)&&(triad+byte<s_len); ++byte) { sr <<= 8; sr |= (*(src+triad+byte) & 0xff); } sr <<= (6-((8*byte)%6))%6; // shift left to next 6bit alignment if (d_len < 4) return NULL; // error - dest too short *(ptr+0) = *(ptr+1) = *(ptr+2) = *(ptr+3) = '='; switch(byte) { case 3: *(ptr+3) = base64[sr&0x3f]; sr >>= 6; case 2: *(ptr+2) = base64[sr&0x3f]; sr >>= 6; case 1: *(ptr+1) = base64[sr&0x3f]; sr >>= 6; *(ptr+0) = base64[sr&0x3f]; } ptr += 4; d_len -= 4; } return dst; } Why could be causing this?

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• Opening a Unicode file with Perl

  - by Jaco Pretorius

  I'm using osql to run several sql scripts against a database and then I need to look at the results file to check if any errors occurred. The problem is that perl doesn't seem to like the fact that the results files are unicode. I wrote a little test script to test it and the output comes out all warbled. $file = shift; open OUTPUT, $file or die "Can't open $file: $!\n"; while (<OUTPUT>) { print $_; if (/Invalid|invalid|Cannot|cannot/) { push(@invalids, $file); print "invalid file - $inputfile - schedule for retry\n"; last; } } Any ideas? I've tried decoding using decode_utf8 but it makes no difference. I've also tried to set the encoding when opening the file. I think the problem might be that osql puts the result file in UTF-16 format, but I'm not sure. When I open the file in textpad it just tells me 'Unicode'. Edit: Using perl v5.8.8

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• Reducing moire when downsampling halftone comic images.

  - by drawnonward

  How can I reduce moire effects when downsampling halftone comic book images during live zoom on an iPhone or iPad? I am writing a comic book viewer. It would be nice to provide higher resolution images and allow the user to zoom in while reading the comic book. However, my client is averse to moire effects and will not allow this feature if there are noticeable moire artifacts while zooming, which of course there are. Modifying the images to be less susceptible to moire would only work if the modifications were not perceptible. Blur was specifically prohibited, as is anything that removes the beloved halftone dots. The images are black and white halftone and line art. The originals are 600 dpi but what we ship with the application will be half that at best, so probably 2500 pixels or less tall. So what are my options? If I write a custom downsampling algorithm would it be fast enough for real time on these devices? Are there other tricks I can do? Would it work to just avoid the size ratios that have the most visual moire effects? As you zoom in an out, there are definitely peaks where the moire effects are worst. Is there a way to calculate what those points are and just zoom to a nearby scale that is not as bad? Any suggestions are welcome. I have very little experience with image and signal processing, but am enjoying the opportunity to learn. I know nothing of wavelets and acutance and other jargon, so please be verbose.

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• Reducing Time Complexity in Java

  - by Koeneuze

  Right, this is from an older exam which i'm using to prepare my own exam in january. We are given the following method: public static void Oorspronkelijk() { String bs = "Dit is een boodschap aan de wereld"; int max = -1; char let = '*'; for (int i=0;i<bs.length();i++) { int tel = 1; for (int j=i+1;j<bs.length();j++) { if (bs.charAt(j) == bs.charAt(i)) tel++; } if (tel > max) { max = tel; let = bs.charAt(i); } } System.out.println(max + " keer " + let); } The questions are: what is the output? - Since the code is just an algorithm to determine the most occuring character, the output is "6 keer " (6 times space) What is the time complexity of this code? Fairly sure it's O(n²), unless someone thinks otherwise? Can you reduce the time complexity, and if so, how? Well, you can. I've received some help already and managed to get the following code: public static void Nieuw() { String bs = "Dit is een boodschap aan de wereld"; HashMap<Character, Integer> letters = new HashMap<Character, Integer>(); char max = bs.charAt(0); for (int i=0;i<bs.length();i++) { char let = bs.charAt(i); if(!letters.containsKey(let)) { letters.put(let,0); } int tel = letters.get(let)+1; letters.put(let,tel); if(letters.get(max)<tel) { max = let; } } System.out.println(letters.get(max) + " keer " + max); } However, I'm uncertain of the time complexity of this new code: Is it O(n) because you only use one for-loop, or does the fact we require the use of the HashMap's get methods make it O(n log n) ? And if someone knows an even better way of reducing the time complexity, please do tell! :)

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• What java web application framework to use?

  - by frohiky

  One of the main products of my company is an Oracle Forms (and Reports) based application, that "needs" to be re-written in another technology. Why? Users want a more rich interface experience, and we want, preferably, to reduce costs with an open source application server. For this (HUGE) project, we intend to use a java web application framework, keep these points in mind: We have: hundreds of tables on our database (the ORM must be as flexible as possible); some logic which is (and will still be) based on PL/SQL procedures/functions/packages; a lot of CRUDs (the application itself is of an considerable size); a demand to work with/generate documents and workflows; an intranet based user environment; We want: to offer a RIA interface experience; use (if possible) an open source app server; a rapid (as possible) development framework; a somewhat mature framework with a "wise" roadmap (and a considerable community support); a MVC approach combined with JS or GWT widgets (e.g. Vaadin or SmartGWT); Well, in the past weeks I've read a lot of posts, Q&As on stackoverflow, and much more: Wicket, JSF, Tapestry, Grails, GWT, Struts2, Play, Spring, Seam, Echo, .... the list goes on! I've even researched about Alfresco..! The obvious question: Which one to use? At this time, any insight, recommendation, shared experience, advice will be more then welcome!

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• Prevent "hg status" from showing everything under untracked directories

  - by Wei Hu

  I find the output of hg status too verbose for untracked directories. Suppose I have an empty repository that's managed by both git and hg. So there would be two directories, .git and .hg. The output of git status is: # Untracked files: # (use "git add <file>..." to include in what will be committed) # # .hg/ The output of hg status is: ? .git/HEAD ? .git/config ? .git/description ? .git/hooks/applypatch-msg.sample ? .git/hooks/commit-msg.sample ? .git/hooks/post-commit.sample ? .git/hooks/post-receive.sample ? .git/hooks/post-update.sample ? .git/hooks/pre-applypatch.sample ? .git/hooks/pre-commit.sample ? .git/hooks/pre-rebase.sample ? .git/hooks/prepare-commit-msg.sample ? .git/hooks/update.sample ? .git/info/exclude Is there a way to reduce its output to something like the following line? ? .git/

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• Is it legal to have different SOAP namespaces/versions between the request and response?

  - by Lord Torgamus

  THIRD EDIT: I now believe that this problem is due to a SOAP version mismatch (1.1 request, 1.2 response) masquerading as a namespace problem. Is it illegal to mix versions, or just bad style? Am I completely out of luck if I can't change my SOAP version or the service's? SECOND EDIT: Clarified error message, and tried to reduce "tl;dr"-ness. EDIT: [Link deleted, not related] Using soapUI, I'm sending a request that starts with: <soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" ... and getting a response that starts with: <soap:Envelope xmlns:soap="http://www.w3.org/2003/05/soap-envelope" ... I know the service is getting the info, because processes down the line are working. However, my soapUI teststep fails. It has two active assertions: "SOAP Response" and "Not SOAP Fault." The failure marker is next to "SOAP Response," with the following message: line -1: Element Envelope@http://www.w3.org/2003/05/soap-envelope is not a valid Envelope@http://schemas.xmlsoap.org/soap/envelope/ document or a valid substitution. I have tried mixing and matching the namespace prefixes and schema URLs. Changing prefixes seems to have no effect; changing URLs causes a VersionMismatch error. I have also tried to use a substitution group, but that doesn't seem to be legal.

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• Does Perl auto-vivify variables used as references in subroutine calls?

  - by FM

  I've declared 2010 to be the year of higher-order programming, so I'm learning Haskell. The introduction has a slick quick-sort demo, and I thought, "Hey, that's easy to do in Perl". It turned to be easier than I expected. Note that I don't have to worry about whether my partitions ($less and $more) are defined. Normally you can't use an undefined value as an array reference. use strict; use warnings; use List::MoreUtils qw(part); my @data = (5,6,7,4,2,9,10,9,5,1); my @sorted = qsort(@data); print "@sorted\n"; sub qsort { return unless @_; my $pivot = shift @_; my ($less, $more) = part { $_ < $pivot ? 0 : 1 } @_; # Works, even though $less and $more are sometimes undefined. return qsort(@$less), $pivot, qsort(@$more); } As best I can tell, Perl will auto-vivify a variable that you try to use as a reference -- but only if you are passing it to a subroutine. For example, my call to foo() works, but not the attempted print. use Data::Dumper qw(Dumper); sub foo { print "Running foo(@_)\n" } my ($x); print Dumper($x); # Fatal: Can't use an undefined value as an ARRAY reference. # print @$x, "\n"; # But this works. foo(@$x); # Auto-vivification: $x is now []. print Dumper($x); My questions: Am I understanding this behavior correctly? What is the explanation or reasoning behind why Perl does this? Is this behavior explained anywhere in the docs?

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• Wizard style navigation, dismissing a view and showing another one

  - by Robin Jamieson

  I'm making a set of screens similar to a wizard and I'd like to know how to make a view dismiss itself and its parent view and immediately show a 'DoneScreen' without worrying about resource leaks. My views look like the following: Base -> Level1 -> DoneScreen -> Level2 -> DoneScreen The Level1 controller is a navigation controller created with a view.xib and shown with [self presentModalViewController ...] by the Base controller. The Level1 controller is also responsible for creating the 'DoneScreen' which may be shown instead of the Level2 Screen based on a certain criteria. When the user taps a button on the screen, the Level1 controller instantiates the the Level2 controller and it displays it via [self.navigationController pushViewController ..] and Level2 controller's view has a 'Next' button. When the use hits the 'Next' button in the Level2 screen, I need to dismiss the current Level2's view as well as the Level1's view and display the 'DoneScreen', which would have been created and passed in to the Level2 controller from Level1. (partly to reduce code duplication, and partly to separate responsibilities among the controllers) In the Level2 controller, if I show the 'DoneScreen' first and dismiss itself with [self.navigationController popViewControllerAnimated:YES]; then the Level1 controller's modal view is still present above the 'Base' but under the Done screen. What's a good way to clear out all of these views except the Base and then show the 'DoneScreen'? Any good suggestions on how to get this done in a simple but elegant manner?

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• Reversible pseudo-random sequence generator

  - by user350651

  I would like some sort of method to create a fairly long sequence of random numbers that I can flip through backwards and forwards. Like a machine with "next" and "previous" buttons, that will give you random numbers. Something like 10-bit resolution (i.e. positive integers in a range from 0 to 1023) is enough, and a sequence of 100k numbers. It's for a simple game-type app, I don't need encryption-strength randomness or anything, but I want it to feel fairly random. I have a limited amount of memory available though, so I can't just generate a chunk of random data and go through it. I need to get the numbers in "interactive time" - I can easily spend a few ms thinking about the next number, but not comfortably much more than that. Eventually it will run on some sort of microcontroller, probably just an Arduino. I could do it with a simple linear congruential generator (LCG). Going forwards is simple, to go backwards I'd have to cache the most recent numbers and store some points at intervals so I can recreate the sequence from there. But maybe there IS some pseudo-random generator that allows you to go both forwards and forwards? It should be possible to hook up two linear feedback shift registers (LFSRs) to roll in different directions, no? Or maybe I can just get by with garbling the index number using a hash function of some sort? I'm going to try that first. Any other ideas?

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• Is there a way to trace through only project source in Delphi?

  - by Justin

  I'm using Delphi 2010 and I'm wondering if there's a way to trace through code which is in the project without tracing through calls to included VCLs. For example - you put in a breakpoint and then use Shift+F7 to trace through line-by-line. Now you run into a call to some lengthy procedure in a VCL - in my case it's often a Measurement Studio or other component that draws the doodads for a bunch of I/O, OPC, or other bits. At any rate, what happens is that the debugger hops out of the active source file, opens the component source, and traces through that line by line. Often this is hundreds or thousands of lines of code I don't care about - I just want to have it execute and return to the next source line in MY project. Obviously you can do this by setting breakpoints around every instance of an external call, but often there are too many to make this practical - I'd be spending an hour setting a hundred breakpoints every time I wanted to step through a section of code. Is there a setting or a tool somewhere that can do this? Allow one to trace through code within the project while silently executing code which is external to the project? Thanks in advance, Stack Overflow!

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• Python - wxPython custom button -> unbound method __init__()? what?

  - by Wallter

  After looking at questions like this it doesn't make sense that my __init__(self, parrent, id) would be throwing a unbound error? help? main.py import wx from customButton import customButton from wxPython.wx import * class MyFrame(wx.Frame): def __init__(self, parent, ID, title): wxFrame.__init__(self, parent, ID, title, wxDefaultPosition, wxSize(400, 400)) # Non-important code here... # This is the first declaration of the Button1 # This is also where the ERROR is thrown. # Omitting this line causes the window to execute # flawlessly. self.Button1 = customButton.__init__(self, parent, -1) # ... finishes in a basic wx.program style... customButton.py # I've included all of the code in the file # because have no idea where the bug/error happens import wx from wxPython.wx import * class Custom_Button(wx.PyControl): # The BMP's Over_bmp = None #wxEmptyBitmap(1,1,1) # When the mouse is over Norm_bmp = None #wxEmptyBitmap(1,1,1) # The normal BMP Push_bmp = None #wxEmptyBitmap(1,1,1) # The down BMP def __init__(self, parent, id, **kwargs): wx.PyControl.__init__(self,parent, id, **kwargs) # Set the BMP's to the ones given in the constructor #self.Over_bmp = wx.Bitmap(wx.Image(MOUSE_OVER_BMP, wx.BITMAP_TYPE_ANY).ConvertToBitmap()) #self.Norm_bmp = wx.Bitmap(wx.Image(NORM_BMP, wx.BITMAP_TYPE_ANY).ConvertToBitmap()) #self.Push_bmp = wx.Bitmap(wx.Image(PUSH_BMP, wx.BITMAP_TYPE_ANY).ConvertToBitmap()) #self.Pos_bmp = self.pos self.Bind(wx.EVT_LEFT_DOWN, self._onMouseDown) self.Bind(wx.EVT_LEFT_UP, self._onMouseUp) self.Bind(wx.EVT_LEAVE_WINDOW, self._onMouseLeave) self.Bind(wx.EVT_ENTER_WINDOW, self._onMouseEnter) self.Bind(wx.EVT_ERASE_BACKGROUND,self._onEraseBackground) self.Bind(wx.EVT_PAINT,self._onPaint) self._mouseIn = self._mouseDown = False def _onMouseEnter(self, event): self._mouseIn = True def _onMouseLeave(self, event): self._mouseIn = False def _onMouseDown(self, event): self._mouseDown = True def _onMouseUp(self, event): self._mouseDown = False self.sendButtonEvent() def sendButtonEvent(self): event = wx.CommandEvent(wx.wxEVT_COMMAND_BUTTON_CLICKED, self.GetId()) event.SetInt(0) event.SetEventObject(self) self.GetEventHandler().ProcessEvent(event) def _onEraseBackground(self,event): # reduce flicker pass def _onPaint(self, event): dc = wx.BufferedPaintDC(self) dc.SetFont(self.GetFont()) dc.SetBackground(wx.Brush(self.GetBackgroundColour())) dc.Clear() dc.DrawBitmap(self.Norm_bmp) # draw whatever you want to draw # draw glossy bitmaps e.g. dc.DrawBitmap if self._mouseIn: # If the Mouse is over the button dc.DrawBitmap(self, self.Mouse_over_bmp, self.Pos_bmp, useMask=False) if self._mouseDown: # If the Mouse clicks the button dc.DrawBitmap(self, self.Push_bmp, self.Pos_bmp, useMask=False)

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• How to disable selective keys on the keyboard?

  - by Vilx-

  I'd like to write an application which disables certain keys on the keyboard while it's working. More specifically I'm interested in keys that might make the application loose focus (like ALT+TAB, WinKey, Ctrl+Shift+Esc, etc.) The need for this is has to do with babies/animals bashing wildly at the keyboard. :) My first idea was to use SetWindowsHookEx, however I ran into a problem. Since I need a global hook, the procedure would have to reside in a .DLL which would get injected in all active applications. But a .DLL can be either 64-bit or 32-bit, not both. And on a 64-bit system there are both types of applications. I guess then that I must write two copies of the hook .DLL - one for 32-bit and the other for 64-bit. And then I'd also have to launch two copies of the application as well, because the application first has to load the DLL itself before it can pass it on to SetWindowsHookEx(). Sounds pretty clumsy and awkward. Is there perhaps a better way? Or maybe I've misunderstood something?

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• Optimization headers for UITableView?

  - by Pask

  I have an optimization problem for the headers of a table with plain style. If I use the standard view for the table (the classic gray with titles set by titleForHeaderInSection:) everything is ok and the scrolling is smooth and immediate. When, instead, use this code to set my personal view: - (UIView *)tableView:(UITableView *)tableView viewForHeaderInSection:(NSInteger)section { return [self headerPerTitolo:[titoliSezioni objectAtIndex:section]]; } - (UIImageView *)headerPerTitolo:(NSString *)titolo { UIImageView *headerView = [[[UIImageView alloc] initWithFrame:CGRectMake(10.0, 0.0, 320.0, 44.0)] autorelease]; headerView.image = [UIImage imageNamed:kNomeImmagineHeader]; headerView.alpha = kAlphaSezioniTablePlain; UILabel * headerLabel = [[[UILabel alloc] initWithFrame:CGRectZero] autorelease]; headerLabel.backgroundColor = [UIColor clearColor]; headerLabel.opaque = NO; headerLabel.textColor = [UIColor whiteColor]; headerLabel.font = [UIFont boldSystemFontOfSize:16]; headerLabel.frame = CGRectMake(10.0,-11.0, 320.0, 44.0); headerLabel.textAlignment = UITextAlignmentLeft; headerLabel.text = titolo; [headerView addSubview:headerLabel]; return headerView; } scrolling is jerky and not immediate (sliding the finger on the screen does not match an immediate shift of the table). I do not know what caused this problem, maybe the fact that every time the method viewForHeaderInSection: is called, the code runs to create a new UIImageView. I tried many ways to solve the problem, such as creating an array of all the necessary view: apart from more time spent loading at startup, there is a continuing problem of low reactivity of the table. 've Attempted by reducing the size of UIImageView positioned from about 66 KB to 4 KB: not only has a deterioration in quality of colors (which distorts a bit 'original graphics), but ... the problem persists! Perhaps you have suggestions about it, or know me obscure techniques that enable me to optimize this aspect of my application ... I apologize for my English, I used Google for translation.

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• File Storage for Web Applications: Filesystem vs DB vs NoSQL engines

  - by El Yobo

  I have a web application that stores a lot of user generated files. Currently these are all stored on the server filesystem, which has several downsides for me. When we move "folders" (as defined by our application) we also have to move the files on disk (although this is more due to strange design decisions on the part of the original developers than a requirement of storing things on the filesystem). It's hard to write tests for file system actions; I have a mock filesystem class that logs actions like move, delete etc, without performing them, which more or less does the job, but I don't have 100% confidence in the tests. I will be adding some other jobs which need to access the files from other service to perform additional tasks (e.g. indexing in Solr, generating thumbnails, movie format conversion), so I need to get at the files remotely. Doing this over network shares seems dodgy... Dealing with permissions on the filesystem as sometimes given us problems in the past, although now that we've moved to a pure Linux environment this should be less of an issue. What are the downsides of storing files as BLOBs in MySQL? I guess that it would massively increase the database size and reduce the effectiveness of caches, but are there other problems? Do the same problems exist with NoSQL systems like Cassandra? Does anyone have any other suggestions that might be appropriate?

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• HDFS some datanodes of cluster are suddenly disconnected while reducers are running

  - by user1429825

  I have 8 slave computers and 1 master computer for running Hadoop (ver 0.21) some datanodes of cluster are suddenly disconnected while I was running MapReduce code on 10GB data After all mappers finished and around 80% of reducers was processed, randomly one or more datanode disconned from network. and then the other datanodes start to disappear from network even if I killed the MapReduce job when I found some datanode was disconnected. I've tried to change dfs.datanode.max.xcievers to 4096, turned off fire-walls of all computing node, disabled selinux and increased the number of file open limit to 20000 but they didn't work at all... anyone have a idea to solve this problem? followings are error log from mapreduce 12/06/01 12:31:29 INFO mapreduce.Job: Task Id : attempt_201206011227_0001_r_000006_0, Status : FAILED java.io.IOException: Bad connect ack with firstBadLink as ***.***.***.148:20010 at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.createBlockOutputStream(DFSOutputStream.java:889) at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.nextBlockOutputStream(DFSOutputStream.java:820) at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.run(DFSOutputStream.java:427) and followings are logs from datanode 2012-06-01 13:01:01,118 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: Receiving block blk_-5549263231281364844_3453 src: /*.*.*.147:56205 dest: /*.*.*.142:20010 2012-06-01 13:01:01,136 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: DatanodeRegistration(*.*.*.142:20010, storageID=DS-1534489105-*.*.*.142-20010-1337757934836, infoPort=20075, ipcPort=20020) Starting thread to transfer block blk_-3849519151985279385_5906 to *.*.*.147:20010 2012-06-01 13:01:19,135 WARN org.apache.hadoop.hdfs.server.datanode.DataNode: DatanodeRegistration(*.*.*.142:20010, storageID=DS-1534489105-*.*.*.142-20010-1337757934836, infoPort=20075, ipcPort=20020):Failed to transfer blk_-5797481564121417802_3453 to *.*.*.146:20010 got java.net.ConnectException: > Connection timed out at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method) at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:701) at org.apache.hadoop.net.SocketIOWithTimeout.connect(SocketIOWithTimeout.java:206) at org.apache.hadoop.net.NetUtils.connect(NetUtils.java:373) at org.apache.hadoop.hdfs.server.datanode.DataNode$DataTransfer.run(DataNode.java:1257) at java.lang.Thread.run(Thread.java:722) 2012-06-01 13:06:20,342 INFO org.apache.hadoop.hdfs.server.datanode.DataBlockScanner: Verification succeeded for blk_6674438989226364081_3453 2012-06-01 13:09:01,781 WARN org.apache.hadoop.hdfs.server.datanode.DataNode: DatanodeRegistration(*.*.*.142:20010, storageID=DS-1534489105-*.*.*.142-20010-1337757934836, infoPort=20075, ipcPort=20020):Failed to transfer blk_-3849519151985279385_5906 to *.*.*.147:20010 got java.net.SocketTimeoutException: 480000 millis timeout while waiting for channel to be ready for write. ch : java.nio.channels.SocketChannel[connected local=/*.*.*.142:60057 remote=/*.*.*.147:20010] at org.apache.hadoop.net.SocketIOWithTimeout.waitForIO(SocketIOWithTimeout.java:246) at org.apache.hadoop.net.SocketOutputStream.waitForWritable(SocketOutputStream.java:164) at org.apache.hadoop.net.SocketOutputStream.transferToFully(SocketOutputStream.java:203) at org.apache.hadoop.hdfs.server.datanode.BlockSender.sendChunks(BlockSender.java:388) at org.apache.hadoop.hdfs.server.datanode.BlockSender.sendBlock(BlockSender.java:476) at org.apache.hadoop.hdfs.server.datanode.DataNode$DataTransfer.run(DataNode.java:1284) at java.lang.Thread.run(Thread.java:722) hdfs-site.xml <configuration> <property> <name>dfs.name.dir</name> <value>/home/hadoop/data/name</value> </property> <property> <name>dfs.data.dir</name> <value>/home/hadoop/data/hdfs1,/home/hadoop/data/hdfs2,/home/hadoop/data/hdfs3,/home/hadoop/data/hdfs4,/home/hadoop/data/hdfs5</value> </property> <property> <name>dfs.replication</name> <value>3</value> </property> <property> <name>dfs.datanode.max.xcievers</name> <value>4096</value> </property> <property> <name>dfs.http.address</name> <value>0.0.0.0:20070</value> <description>50070 The address and the base port where the dfs namenode web ui will listen on. If the port is 0 then the server will start on a free port. </description> </property> <property> <name>dfs.datanode.http.address</name> <value>0.0.0.0:20075</value> <description>50075 The datanode http server address and port. If the port is 0 then the server will start on a free port. </description> </property> <property> <name>dfs.secondary.http.address</name> <value>0.0.0.0:20090</value> <description>50090 The secondary namenode http server address and port. If the port is 0 then the server will start on a free port. </description> </property> <property> <name>dfs.datanode.address</name> <value>0.0.0.0:20010</value> <description>50010 The address where the datanode server will listen to. If the port is 0 then the server will start on a free port. </description> <property> <name>dfs.datanode.ipc.address</name> <value>0.0.0.0:20020</value> <description>50020 The datanode ipc server address and port. If the port is 0 then the server will start on a free port. </description> </property> <property> <name>dfs.datanode.https.address</name> <value>0.0.0.0:20475</value> </property> <property> <name>dfs.https.address</name> <value>0.0.0.0:20470</value> </property> </configuration> mapred-site.xml <configuration> <property> <name>mapred.job.tracker</name> <value>masternode:29001</value> </property> <property> <name>mapred.system.dir</name> <value>/home/hadoop/data/mapreduce/system</value> </property> <property> <name>mapred.local.dir</name> <value>/home/hadoop/data/mapreduce/local</value> </property> <property> <name>mapred.map.tasks</name> <value>32</value> <description> default number of map tasks per job.</description> </property> <property> <name>mapred.tasktracker.map.tasks.maximum</name> <value>4</value> </property> <property> <name>mapred.reduce.tasks</name> <value>8</value> <description> default number of reduce tasks per job.</description> </property> <property> <name>mapred.map.child.java.opts</name> <value>-Xmx2048M</value> </property> <property> <name>io.sort.mb</name> <value>500</value> </property> <property> <name>mapred.task.timeout</name> <value>1800000</value> <!-- 30 minutes --> </property> <property> <name>mapred.job.tracker.http.address</name> <value>0.0.0.0:20030</value> <description> 50030 The job tracker http server address and port the server will listen on. If the port is 0 then the server will start on a free port. </description> </property> <property> <name>mapred.task.tracker.http.address</name> <value>0.0.0.0:20060</value> <description> 50060 </property> </configuration>

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• Caching Authentication Data

  - by PartlyCloudy

  Hi, I'm currently implementing a REST web service using CouchDB and RESTlet. The RESTlet layer is mainly for authentication and some minor filtering of the JSON data served by CouchDB: Clients <= HTTP = [ RESTlet <= HTTP = CouchDB ] I'm using CouchDB also to store user login data, because I don't want to add an additional database server for that purpose. Thus, each request to my service causes two CouchDB requests conducted by RESTlet (auth data + "real" request). In order to keep the service as efficent as possible, I want to reduce the number of requests, in this case redundant requests for login data. My idea now is to provide a cache (i.e.LRU-Cache via LinkedHashMap) within my RESTlet application that caches login data, because HTTP caching will probabily not be enough. But how do I invalidate the cache data, once a user changes the password, for instance. Thanks to REST, the application might run on several servers in parallel, and I don't want to create a central instance just to cache login data. Currently, I save requested auth data in the cache and try to auth new requests by using them. If a authentication fails or there is now entry available, I'll dispatch a GET request to my CouchDB storage in order to obtain the actual auth data. So in a worst case, users that have changed their data will perhaps still be able to login with their old credentials. How can I deal with that? Or what is a good strategy to keep the cache(s) up-to-date in general? Thanks in advance.

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• Is it wise to use temporary tables?

  - by Industrial

  Hi guys, We have a mySQL database table for products. We are utilizing a cache layer to reduce database load, but we think that it's a good idea to minimize the actual data needed to be stored in the cache layer to speed up the application further. All the products in the database, that is visible to visitors have a price attached to them: The prices are stored in a different table, called prices . There are multiple price categories depending on which discount level each visitor (customer) applies to. From time to time, there are campaigns which means that a special price for each product is available. The special prices are stored in a table called specials. Is it a bad to make a temp table that binds the tables together? It would only have the neccessary information and would ofcourse be cached. -------------|-------------|------------ | productId | hasPrice | hasSpecial -------------|-------------|------------ 1 | 1 | 0 2 | 1 | 1 By doing such, it would be super easy to know if the specific product really has a price, without having to iterate through the complete prices or specials table each time a product should be listed or presented. Are temp tables a common thing for web applications or is it just bad design?

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