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• Why does the the Java VM not recover after "Too many open files" errors?

  - by Michael

  In certain well-understood circumstances, our application will open too many sockets (database connections) and reach the maximum open files that the OS allows. We understand this; we are fixing the issue and also bumping up the limit. What we can't explain is why parts of our application don't recover even after the number of connections abates and we're well within the limit. In this case, it's an application running under Tomcat. When this happens, we first start seeing "Too many open files" errors: SEVERE: Socket accept failed java.net.SocketException: Too many open files at java.net.PlainSocketImpl.socketAccept(Native Method) at java.net.PlainSocketImpl.accept(PlainSocketImpl.java:390) at java.net.ServerSocket.implAccept(ServerSocket.java:453) at java.net.ServerSocket.accept(ServerSocket.java:421) at org.apache.tomcat.util.net.DefaultServerSocketFactory.acceptSocket(DefaultServerSocketFactory.java:61) at org.apache.tomcat.util.net.JIoEndpoint$Acceptor.run(JIoEndpoint.java:310) at java.lang.Thread.run(Thread.java:619) Eventually, we start seeing NoClassDefFoundErrors inside an application thread that's trying to open HTTP connections: java.lang.NoClassDefFoundError: org/apache/commons/httpclient/protocol/ControllerThreadSocketFactory at org.apache.commons.httpclient.protocol.DefaultProtocolSocketFactory.createSocket(DefaultProtocolSocketFactory.java:128) at org.apache.commons.httpclient.HttpConnection.open(HttpConnection.java:707) at org.apache.commons.httpclient.MultiThreadedHttpConnectionManager$HttpConnectionAdapter.open(MultiThreadedHttpConnectionManager.java:1349) [...] Caused by: java.lang.ClassNotFoundException: org.apache.commons.httpclient.protocol.ControllerThreadSocketFactory at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1387) at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1233) at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:320) ... 8 more When the errant connections go away, the server starts accepting connections again, and everything seems ok, but we're left with the latter error constantly being spewed to stderr. Although the application typically logs unloaded classes to stdout, I don't see any such logs just before, during or after the "Too many open files" errors. My initial theory was that the Hotspot JVM would unload seemingly unused classes when it encounters "Too many open files," but if so, it doesn't log the fact. I'd also expect it to recover if that were the case. Platform details: Java(TM) SE Runtime Environment (build 1.6.0_14-b08) Java HotSpot(TM) 64-Bit Server VM (build 14.0-b16, mixed mode) Apache Tomcat Version 6.0.18

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• Finding perfect numbers in C# (optimization)

  - by paradox

  I coded up a program in C# to find perfect numbers within a certain range as part of a programming challenge . However, I realized it is very slow when calculating perfect numbers upwards of 10000. Are there any methods of optimization that exist for finding perfect numbers? My code is as follows: using System; using System.Collections.Generic; using System.Linq; namespace ConsoleTest { class Program { public static List<int> FindDivisors(int inputNo) { List<int> Divisors = new List<int>(); for (int i = 1; i<inputNo; i++) { if (inputNo%i==0) Divisors.Add(i); } return Divisors; } public static void Main(string[] args) { const int limit = 100000; List<int> PerfectNumbers = new List<int>(); List<int> Divisors=new List<int>(); for (int i=1; i<limit; i++) { Divisors = FindDivisors(i); if (i==Divisors.Sum()) PerfectNumbers.Add(i); } Console.Write("Output ="); for (int i=0; i<PerfectNumbers.Count; i++) { Console.Write(" {0} ",PerfectNumbers[i]); } Console.Write("\n\n\nPress any key to continue . . . "); Console.ReadKey(true); } } }

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• java RMI newbie-- some basic questions about SSL and auth/.rate limiting an RMI service

  - by Arvind

  I am trying to work to secure a java based RMI service using SSL. I have some basic questions about the capabilities of using SSL. Specifically, from what I understand, the client and server connecting via SSL will need to have appropriate credential certificates in both client and server, for a client to be granted access to the server. Am I correct in my understanding? Also, what I want to know is, can a person who is already using my RMI service and has access to a client machine , make a copy of the certificate in the client machine to other client machines-- and then invoke my RMI service from those other machines as well? How do I prevent such a situation from occurring? I mean, in a REST API you can use OAuth authentication, can we have some kind of authentication in an RMI Service? Also, can I possibly limit usage of the RMI service? For eg, a specific client may be allowed to make only 5000 calls per day to my RMI service, and if he makes more calls the calls occurring after the 5000 calls limit are all denied? How do I do such rate limiting and/or authentication for my RMI Service?

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• jQuery getJSON request returning empty on a valid request

  - by mikemike

  I'm trying to grab some JSON from Apple's iTunes JSON service. The request is simple: http://ax.phobos.apple.com.edgesuite.net/WebObjects/MZStoreServices.woa/wa/wsSearch?term=jac&limit=25 If you visit the URL in your browser you will see some well-formed (backed up by jsonlint.com) JSON. When I use the following jQuery to make the request, however, the request finds nothing: $("#soundtrack").keypress(function(){ $.getJSON("http://ax.phobos.apple.com.edgesuite.net/WebObjects/MZStoreServices.woa/wa/wsSearch",{'term':$(this).val(), 'limit':'25'}, function(j){ var options = ''; for (var i = 0; i < j.results.length; i++) { options += '<option value="' + j.results[i].trackId + '">' + j.results[i].artistName + ' - ' + j.results[i].trackName + '</option>'; } $("#track_id").html(options); }); }); Firebug sees the request, but only receives an empty response. Any help would be appreciated here, as I'm at my whits end trying to solve it. You can view the script here: http://rnmtest.co.uk/gd/drives_admin/add_drive (soundtrack input box is at the bottom of the page). Thanks

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• complex sql which runs extremely slow when the query has order by clause

  - by basit.

  I have following complex query which I need to use. When I run it, it takes 30 to 40 seconds. But if I remove the order by clause, it takes 0.0317 sec to return the result, which is really fast compare to 30 sec or 40. select DISTINCT media.* , username from album as album , album_permission as permission , user as user, media as media where ((media.album_id = album.album_id and album.private = 'yes' and album.album_id = permission.album_id and (permission.email = '' or permission.user_id = '') ) or (media.album_id = album.album_id and album.private = 'no' ) or media.album_id = '0' ) and media.user_id = user.user_id and media.media_type = 'video' order by media.id DESC LIMIT 0,20 The id on order by is primary key which is indexed too. So I don't know what is the problem. I also have album and album permission table, just to check if media is public or private, if private then check if user has permission or not. I was thinking maybe that is causing the issue. What if I did this in sub query, would that work better? Also can someone help me write that sub query, if that is the solution? If you can't help write it, just at least tell me. I'm really going crazy with this issue.. SOLUTION MAYBE Yes, I think sub-query would be best solution for this, because the following query runs at 0.0022 seconds. But I'm not sure if validation of an album would be accurate or not, please check. select media.*, username from media as media , user as user where media.user_id = user.user_id and media.media_type = 'video' and media.id in (select media2.id from media as media2 , album as album , album_permission as permission where ((media2.album_id = album.album_id and album.private = 'yes' and album.album_id = permission.album_id and (permission.email = '' or permission.user_id = '')) or (media.album_id = album.album_id and album.private = 'no' ) or media.album_id = '0' ) and media.album_id = media2.album_id ) order by media.id DESC LIMIT 0,20

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• Project Euler Question 14 (Collatz Problem)

  - by paradox

  The following iterative sequence is defined for the set of positive integers: n -n/2 (n is even) n -3n + 1 (n is odd) Using the rule above and starting with 13, we generate the following sequence: 13 40 20 10 5 16 8 4 2 1 It can be seen that this sequence (starting at 13 and finishing at 1) contains 10 terms. Although it has not been proved yet (Collatz Problem), it is thought that all starting numbers finish at 1. Which starting number, under one million, produces the longest chain? NOTE: Once the chain starts the terms are allowed to go above one million. I tried coding a solution to this in C using the bruteforce method. However, it seems that my program stalls when trying to calculate 113383. Please advise :) #include <stdio.h> #define LIMIT 1000000 int iteration(int value) { if(value%2==0) return (value/2); else return (3*value+1); } int count_iterations(int value) { int count=1; //printf("%d\n", value); while(value!=1) { value=iteration(value); //printf("%d\n", value); count++; } return count; } int main() { int iteration_count=0, max=0; int i,count; for (i=1; i<LIMIT; i++) { printf("Current iteration : %d\n", i); iteration_count=count_iterations(i); if (iteration_count>max) { max=iteration_count; count=i; } } //iteration_count=count_iterations(113383); printf("Count = %d\ni = %d\n",max,count); }

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• Working around MySQL error "Deadlock found when trying to get lock; try restarting transaction"

  - by Anon Guy

  Hi all: I have a MySQL table with about 5,000,000 rows that are being constantly updated in small ways by parallel Perl processes connecting via DBI. The table has about 10 columns and several indexes. One fairly common operation gives rise to the following error sometimes: DBD::mysql::st execute failed: Deadlock found when trying to get lock; try restarting transaction at Db.pm line 276. The SQL statement that triggers the error is something like this: UPDATE file_table SET a_lock = 'process-1234' WHERE param1 = 'X' AND param2 = 'Y' AND param3 = 'Z' LIMIT 47 The error is triggered only sometimes. I'd estimate in 1% of calls or less. However, it never happened with a small table and has become more common as the database has grown. Note that I am using the a_lock field in file_table to ensure that the four near-identical processes I am running do not try and work on the same row. The limit is designed to break their work into small chunks. I haven't done much tuning on MySQL or DBD::mysql. MySQL is a standard Solaris deployment, and the database connection is set up as follows: my $dsn = "DBI:mysql:database=" . $DbConfig::database . ";host=${DbConfig::hostname};port=${DbConfig::port}"; my $dbh = DBI->connect($dsn, $DbConfig::username, $DbConfig::password, { RaiseError => 1, AutoCommit => 1 }) or die $DBI::errstr; I have seen online that several other people have reported similar errors and that this may be a genuine deadlock situation. I have two questions: What exactly about my situation is causing the error above? Is there a simple way to work around it or lessen its frequency? For example, how exactly do I go about "restarting transaction at Db.pm line 276"? Thanks in advance.

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• OpenStreetMap Proximity search using mySQL

  - by Chris

  Hi, I'm just playing around with a dataset of my region generated by JOSM. I moved it into a mySQL DB with the 0.6 API scheme using Osmosis and now I'm desperately trying the following: I want to get all streets of a city. AFAIK there is no tag/relation in the OSM data to determine this so I tried it using a proximity search to get all nodes in a radius around a node representing the city center. Most of the time I looked at the approaches here: http://stackoverflow.com/questions/574691/mysql-great-circle-distance-haversine-formula What I got is the following SQL code that should get me the closest 100 nodes around the node with id 36187002 and within a radius of 10km. set @nodeid = 36187002; set @dist = 10; select longitude, latitude into @mylon, @mylat from nodes where id=@nodeid limit 1; SELECT id, ( 6371 * acos( cos( radians(@mylon) ) * cos( radians( latitude ) ) * cos( radians( longitude ) - radians(@mylat) ) + sin( radians(@mylon) ) * sin( radians( latitude ) ) ) ) AS distance FROM nodes HAVING distance < @dist ORDER BY distance LIMIT 0 , 100; Well.. it doesn't work. :( I guess the main problem is that OSM lats/lons are multiplied by 10.000.000 and I don't know how I can correct this function to make it work. Any ideas about this? All solutions/alternatives are very welcome! Have a nice weekend! Chris

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• FileSystem.GetFiles() + UnauthorizedAccessException error?

  - by OverTheRainbow

  Hello, It seems like FileSystem.GetFiles() is unable to recover from the UnauthorizedAccessException exception that .Net triggers when trying to access an off-limit directory. In this case, does it mean this class/method isn't useful when scanning a whole drive and I should use some other solution (in which case: Which one?)? Here's some code to show the issue: Private Sub bgrLongProcess_DoWork(ByVal sender As System.Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles bgrLongProcess.DoWork Dim drive As DriveInfo Dim filelist As Collections.ObjectModel.ReadOnlyCollection(Of String) Dim filepath As String 'Scan all fixed-drives for MyFiles.* For Each drive In DriveInfo.GetDrives() If drive.DriveType = DriveType.Fixed Then Try 'How to handle "Access to the path 'C:\System Volume Information' is denied." error? filelist = My.Computer.FileSystem.GetFiles(drive.ToString, FileIO.SearchOption.SearchAllSubDirectories, "MyFiles.*") For Each filepath In filelist DataGridView1.Rows.Add(filepath.ToString, "temp") 'Trigger ProgressChanged() event bgrLongProcess.ReportProgress(0, filepath) Next filepath Catch Ex As UnauthorizedAccessException 'How to ignore this directory and move on? End Try End If Next drive End Sub Thank you. Edit: What about using a Try/Catch just to have GetFiles() fill the array, ignore the exception and just resume? Private Sub bgrLongProcess_DoWork(ByVal sender As System.Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles bgrLongProcess.DoWork 'Do lengthy stuff here Dim filelist As Collections.ObjectModel.ReadOnlyCollection(Of String) Dim filepath As String filelist = Nothing Try filelist = My.Computer.FileSystem.GetFiles("C:\", FileIO.SearchOption.SearchAllSubDirectories, "MyFiles.*") Catch ex As UnauthorizedAccessException 'How to just ignore this off-limit directory and resume searching? End Try 'Object reference not set to an instance of an object For Each filepath In filelist bgrLongProcess.ReportProgress(0, filepath) Next filepath End Sub

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• Apache RewriteRule: it is possible to 'detect' the first and second parameter?

  - by DaNieL

  Im really really a newbie in regexp and i cant figure out how to do that. My goal is to have the RewriteRule to 'slice' the request url in 3 parts: example.com/foo #should return: index.php?a=foo&b=&c= example.com/foo/bar #should return: index.php?a=foo&b=bar&c= example.com/foo/bar/baz #should return: index.php?a=foo&b=bar&c=baz example.com/foo/bar/baz/bee #should return: index.php?a=foo&b=bar&c=baz/bee example.com/foo/bar/baz/bee/apple #should return: index.php?a=foo&b=bar&c=baz/bee/apple example.com/foo/bar/baz/bee/apple/and/whatever/else/no/limit/in/those/extra/parameters #should return: index.php?a=foo&b=bar&c=baz/bee/apple/and/whatever/else/no/limit/in/those/extra/parameters In short, the first parameter in the url (foo) should be given to a, the second (bar) to b, and the rest of the string in c I wroted this one <IfModule mod_rewrite.c> RewriteEngine on RewriteCond %{REQUEST_FILENAME} !-f RewriteCond %{REQUEST_FILENAME} !-d RewriteCond %{REQUEST_URI} !=/favicon.ico RewriteRule ^(([a-z0-9/]))?(([a-z0-9/]+))?(([a-z0-9]+))(.*)$ index.php?a=$1&b=$2&c=$3 [L,QSA] </IfModule> but obviously doesnt work, and i dont even know if what i want is possible. Any suggestion?

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• Programming R/Sweave for proper \Sexpr output

  - by deoksu

  Hi I'm having a bit of a problem programming R for Sweave, and the #rstats twitter group often points here, so I thought I'd put this question to the SO crowd. I'm an analyst- not a programmer- so go easy on me my first post. Here's the problem: I am drafting a survey report in Sweave with R and would like to report the marginal returns in line using \Sexpr{}. For example, rather than saying: Only 14% of respondents said 'X'. I want to write the report like this: Only \Sexpr{p.mean(variable)}$\%$ of respondents said 'X'. The problem is that Sweave() converts the results of the expression in \Sexpr{} to a character string, which means that the output from expression in R and the output that appears in my document are different. For example, above I use the function 'p.mean': p.mean<- function (x) {options(digits=1) mmm<-weighted.mean(x, weight=weight, na.rm=T) print(100*mmm) } In R, the output looks like this: p.mean(variable) >14 but when I use \Sexpr{p.mean(variable)}, I get an unrounded character string (in this case: 13.5857142857143) in my document. I have tried to limit the output of my function to 'digits=1' in the global environment, in the function itself, and and in various commands. It only seems to contain what R prints, not the character transformation that is the result of the expression and which eventually prints in the LaTeX file. as.character(p.mean(variable)) >[1] 14 >[1] "13.5857142857143" Does anyone know what I can do to limit the digits printed in the LaTeX file, either by reprogramming the R function or with a setting in Sweave or \Sexpr{}? I'd greatly appreciate any help you can give. Thanks, David

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• advanced xml? multi level .. php parsing

  - by dave1019

  hi my knowledge of xml and php is somewhat basic but have been able to parse a simple xml document (one level) ~ <numbers> <number>1</number> <number>2</number> </numbers> i'm attempting to parse an xml document from a website providing the latest market prices for gold bullion. I think i'm going to need a paid professional but want to give it a shot the xml file looks like this: <envelope> <message type="MARKET_DEPTH_A" version="0.1"> <market> <pitches> <pitch securityClassNarrative="GOLD" securityId="AUXLN" considerationCurrency="GBP" > <buyPrices> <price actionIndicator="B" quantity="0.153" limit="23477" /> </buyPrices> <sellPrices> <price actionIndicator="S" quantity="0.058" limit="23589" /> </sellPrices> </pitch> </pitches> </market> </message> </envelope> and simply i have no idea how to access the values within the "headings". (whatever the term is) sounds like i'm asking for someone to do it for me, which I don't want, but I don't know what to search for ~ it doesn't look like a regular xml structure to me. thanks!

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• SQL CE: Limiting rows returned in the query

  - by Diakonia7

  In SQL Compact Edition 3.5 , note that it is the Compact Edition I am talking about- Is there a way to limit the amount of rows to only 2? Something like using LIMIT or TOP. I really don't want to use anything with a SqlCEDataReader, or SqlCEResultSet. I want to do all the limiting in the query. Is this possible now? I have looked around and it doesn't seem so. EDIT- In response to Dave Swersky's request for data and using Min()/Max() on some columns as a means to get the top 2 lines, here is some sample (sterilized) data: Line Site Function Status 1010 Las Vegas new 4 1020 DC send 1 1030 Portland copy 1 1040 SF copy 1 1050 Portland copy 1 1060 DC send 1 *There are more columns than this but these are the significant ones. Sorry for the lack of intuitive data (but the actual data is even less intuitive!), but for security i need to change the data. So- i need to determine: what site the record was at in the preceding line to determine where it needs to be picked up. The site on any given line (except the first line with function = 'new') corresponds to where the item is going next. So simply grabbing that site off the same line wont tell me where it came from. The status will always be 1 or 4. The 4 corresponds to a where it has been delivered already and so i dont want to include those records in the result. But it might be useful in getting the pickup site. For this table of data i want the query to return the site corresponding to the line just above the first line with status 1. So- for this it would be Las Vegas.

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• How to enable and use HTTP PUT and DELETE with Apache2 and PHP?

  - by Andreas Jansson

  Hi, It should be so simple. I've followed every tutorial and forum I could find, yet I can't get it to work. I simply want to build a RESTful API in PHP on Apache2. In my VirtualHost directive I say: <Directory /> AllowOverride All <Limit GET HEAD POST PUT DELETE OPTIONS> Order Allow,Deny Allow from all </Limit> </Directory> Yet every PUT request I make to the server, I get 405 method not supported. Someone advocated using the Script directive, but since I use mod_php, as opposed to CGI, I don't see why that would work. People mention using WebDAV, but to me that seems like overkill. After all, I don't need DAV locking, a DAV filesystem, etc. All I want to do is pass the request on to a PHP script and handle everything myself. I only want to enable PUT and DELETE for the clean semantics. Thanks, Andreas

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• Array: mathematical sequence

  - by VaioIsBorn

  An array of integers A[i] (i 1) is defined in the following way: an element A[k] ( k 1) is the smallest number greater than A[k-1] such that the sum of its digits is equal to the sum of the digits of the number 4* A[k-1] . You need to write a program that calculates the N th number in this array based on the given first element A[1] . INPUT: In one line of standard input there are two numbers seperated with a single space: A[1] (1 <= A[1] <= 100) and N (1 <= N <= 10000). OUTPUT: The standard output should only contain a single integer A[N] , the Nth number of the defined sequence. Input: 7 4 Output: 79 Explanation: Elements of the array are as follows: 7, 19, 49, 79... and the 4th element is solution. I tried solving this by coding a separate function that for a given number A[k] calculates the sum of it's digits and finds the smallest number greater than A[k-1] as it says in the problem, but with no success. The first testing failed because of a memory limit, the second testing failed because of a time limit, and now i don't have any possible idea how to solve this. One friend suggested recursion, but i don't know how to set that. Anyone who can help me in any way please write, also suggest some ideas about using recursion/DP for solving this problem. Thanks.

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• How to avoid "Illegal type in constant pool" using "ldc_w <classname>" in Jasmin?

  - by jazzdev

  I'm writing a compiler that generates Jasmin code and want to invoke a method that takes a Class as a parameter. public class CTest { public static void main(String[] args) throws Exception { java.lang.reflect.Array.newInstance(CTest.class, 0); } } So in Jasmin, I think that should be: .class public CTest2 .super java/lang/Object .method public static main([Ljava/lang/String;)V .limit stack 2 .limit locals 1 ldc_w CTest2 iconst_0 invokestatic java/lang/reflect/Array/newInstance(Ljava/lang/Class;I)Ljava/lang/Object; pop return .end method When I assemble it and run it I get: Exception in thread "main" java.lang.VerifyError: (class: CTest2, method: main signature: ([Ljava/lang/String;)V) Illegal type in constant pool Looking at the disassembled code for both CTest.class (the Java version) and CTest2.class (the Jasmin version) with "javap -c -verbose" they both appear to set up the constant pool the same way: const #2 = class #16; // CTest const #16 = Asciz CTest; 0: ldc_w #2; //class CTest const #14 = Asciz CTest2; const #17 = class #14; // CTest2 0: ldc_w #17; //class CTest2 I've fixed two bugs in Jasmin already, but I can't see what it's doing wrong when putting the class in the constant pool for "ldc_w" it puts classes in the constant pool for other instructions, like "new" and "anewarray" correctly. I've tried looking at the .class files with TraceClassVisitor in ASM, but it doesn't dump the constant pool. Any ideas what I can try next?

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• Project Euler 7 Scala Problem

  - by Nishu

  I was trying to solve Project Euler problem number 7 using scala 2.8 First solution implemented by me takes ~8 seconds def problem_7:Int = { var num = 17; var primes = new ArrayBuffer[Int](); primes += 2 primes += 3 primes += 5 primes += 7 primes += 11 primes += 13 while (primes.size < 10001){ if (isPrime(num, primes)) primes += num if (isPrime(num+2, primes)) primes += num+2 num += 6 } return primes.last; } def isPrime(num:Int, primes:ArrayBuffer[Int]):Boolean = { // if n == 2 return false; // if n == 3 return false; var r = Math.sqrt(num) for (i <- primes){ if(i <= r ){ if (num % i == 0) return false; } } return true; } Later I tried the same problem without storing prime numbers in array buffer. This take .118 seconds. def problem_7_alt:Int = { var limit = 10001; var count = 6; var num:Int = 17; while(count < limit){ if (isPrime2(num)) count += 1; if (isPrime2(num+2)) count += 1; num += 6; } return num; } def isPrime2(n:Int):Boolean = { // if n == 2 return false; // if n == 3 return false; var r = Math.sqrt(n) var f = 5; while (f <= r){ if (n % f == 0) { return false; } else if (n % (f+2) == 0) { return false; } f += 6; } return true; } I tried using various mutable array/list implementations in Scala but was not able to make solution one faster. I do not think that storing Int in a array of size 10001 can make program slow. Is there some better way to use lists/arrays in scala?

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• Why can't I get a TRUE return in this prepared statement?

  - by Cortopasta

  I can't seem to get this to do anything but return false. My best guess is that the prepared statement isn't executing, but I have no idea why. private function check_credentials($plain_username, $md5_password) { global $dbcon; $ac = new ac(); $ac->dbconnect(); $userid = $dbcon->prepare('SELECT id FROM users WHERE username = :username AND password = :password LIMIT 1'); $userid->bindParam(':username', $plain_username); $userid->bindParam(':password', $md5_password); $userid->execute(); $id = $userid->fetch(); Return $id; } *EDIT:*I've even tried hard coding the username and password into the function itself to try and isolate the problem like this: private function check_credentials($plain_username, $md5_password) { global $dbcon; $plain_username = "jim"; $md5_username = "waffles"; $ac = new ac(); $ac->dbconnect(); $userid = $dbcon->prepare('SELECT id FROM users WHERE username = :username AND password = :password LIMIT 1'); $userid->bindParam(':username', $plain_username); $userid->bindParam(':password', $md5_password); $userid->execute(); print_r($dbcon->errorInfo()); $id = $userid->fetch(); Return $id; } Still nothing :-/

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• Controlling ASP.NET output cache memory usage

  - by Josh Einstein

  I would like to use output caching with WCF Data Services and although there's nothing specifically built in to support caching, there is an OnStartProcessingRequest method that allows me to hook in and set the cacheability of the request using normal ASP.NET mechanisms. But I am worried about the worker process getting recycled due to excessive memory consumption if large responses are cached. Is there a way to specify an upper limit for the ASP.NET output cache so that if this limit is exceeded, items in the cache will be discarded? I've seen the caching configuration settings but I get the impression from the documentation that this is for explicit caching via the Cache object since there is a separate outputCacheSettings which has no memory-related attributes. Here's a code snippet from Scott Hanselman's post that shows how I'm setting the cacheability of the request. protected override void OnStartProcessingRequest(ProcessRequestArgs args) { base.OnStartProcessingRequest(args); //Cache for a minute based on querystring HttpContext context = HttpContext.Current; HttpCachePolicy c = HttpContext.Current.Response.Cache; c.SetCacheability(HttpCacheability.ServerAndPrivate); c.SetExpires(HttpContext.Current.Timestamp.AddSeconds(60)); c.VaryByHeaders["Accept"] = true; c.VaryByHeaders["Accept-Charset"] = true; c.VaryByHeaders["Accept-Encoding"] = true; c.VaryByParams["*"] = true; }

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• How do we greatly optimize our MySQL database (or replace it) when using joins?

  - by jkaz

  Hi there, This is the first time I'm approaching an extremely high-volume situation. This is an ad server based on MySQL. However, the query that is used incorporates a lot of JOINs and is generally just slow. (This is Rails ActiveRecord, btw) sel = Ads.find(:all, :select = '*', :joins = "JOIN campaigns ON ads.campaign_id = campaigns.id JOIN users ON campaigns.user_id = users.id LEFT JOIN countries ON countries.campaign_id = campaigns.id LEFT JOIN keywords ON keywords.campaign_id = campaigns.id", :conditions = [flashstr + "keywords.word = ? AND ads.format = ? AND campaigns.cenabled = 1 AND (countries.country IS NULL OR countries.country = ?) AND ads.enabled = 1 AND campaigns.dailyenabled = 1 AND users.uenabled = 1", kw, format, viewer['country'][0]], :order = order, :limit = limit) My questions: Is there an alternative database like MySQL that has JOIN support, but is much faster? (I know there's Postgre, still evaluating it.) Otherwise, would firing up a MySQL instance, loading a local database into memory and re-loading that every 5 minutes help? Otherwise, is there any way I could switch this entire operation to Redis or Cassandra, and somehow change the JOIN behavior to match the (non-JOIN-able) nature of NoSQL? Thank you!

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• PHP readfile() and large downloads

  - by Nirmal

  While setting up an online file management system, and now I have hit a block. I am trying to push the file to the client using this modified version of readfile: function readfile_chunked($filename,$retbytes=true) { $chunksize = 1*(1024*1024); // how many bytes per chunk $buffer = ''; $cnt =0; // $handle = fopen($filename, 'rb'); $handle = fopen($filename, 'rb'); if ($handle === false) { return false; } while (!feof($handle)) { $buffer = fread($handle, $chunksize); echo $buffer; ob_flush(); flush(); if ($retbytes) { $cnt += strlen($buffer); } } $status = fclose($handle); if ($retbytes && $status) { return $cnt; // return num. bytes delivered like readfile() does. } return $status; } But when I try to download a 13 MB file, it's just breaking at 4 MB. What would be the issue here? It's definitely not the time limit of any kind because I am working on a local network and speed is not an issue. The memory limit in PHP is set to 300 MB. Thank you for any help.

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• Neural Network settings for fast training

  - by danpalmer

  I am creating a tool for predicting the time and cost of software projects based on past data. The tool uses a neural network to do this and so far, the results are promising, but I think I can do a lot more optimisation just by changing the properties of the network. There don't seem to be any rules or even many best-practices when it comes to these settings so if anyone with experience could help me I would greatly appreciate it. The input data is made up of a series of integers that could go up as high as the user wants to go, but most will be under 100,000 I would have thought. Some will be as low as 1. They are details like number of people on a project and the cost of a project, as well as details about database entities and use cases. There are 10 inputs in total and 2 outputs (the time and cost). I am using Resilient Propagation to train the network. Currently it has: 10 input nodes, 1 hidden layer with 5 nodes and 2 output nodes. I am training to get under a 5% error rate. The algorithm must run on a webserver so I have put in a measure to stop training when it looks like it isn't going anywhere. This is set to 10,000 training iterations. Currently, when I try to train it with some data that is a bit varied, but well within the limits of what we expect users to put into it, it takes a long time to train, hitting the 10,000 iteration limit over and over again. This is the first time I have used a neural network and I don't really know what to expect. If you could give me some hints on what sort of settings I should be using for the network and for the iteration limit I would greatly appreciate it. Thank you!

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• Throttling outbound API calls generated by a Rails app

  - by Sharpie

  I am not a professional web developer, but I like to wrench on websites as a hobby. Recently, I have been playing with developing a Rails app as a project to help me learn the framework. The goal of my toy app is to harvest data from another service through their API and make it available for me to query using a search function. However, the service I want to pull data from imposes a rate limit on the number of API calls that may be executed per minute. I plan on having my app run a daily update which may generate a burst of API calls that far exceeds the limit provided by the external service. I wish to respect the performance of the external site and so would like to throttle the rate at which my app executes the calls. I have done a little bit of searching and the overwhelming amount of tutorial material and pre-built libraries I have found cover throttling inbound API calls to a web app and I can find little discussion of controlling the flow of outbound calls. Being both an amateur web developer and a rails newbie, it is entirely possible that I have been executing the wrong searches in the wrong places. Therefore my questions are: Is there a nice website out there aggregating Rails tutorials that has material related to throttling outbound API requests? Are there any ruby gems or other libraries that would help me throttle the requests? I have some ideas of how I might go about writing a throttling system using a queue-based worker like DelayedJob or Resque to manage the API calls, but I would rather spend my weekends building the rest of the site if there is a good pre-built solution out there already.

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• Destroying nested resources in restful way

  - by Alex

  I'm looking for help destroying a nested resource in Merb. My current method seems near correct, but the controller raise an InternalServerError during the destruction of the nested object. Here comes all the details concerning the request, don't hesitate to ask for more :) Thanks, Alex I'm trying to destroy a nested resources using the following route in router.resources :events, Orga::Events do |event| event.resources :locations, Orga::Locations end Which gives in jQuery request (delete_ method is a implementation of $.ajax with "DELETE"): $.delete_("/events/123/locations/456"); In the Location controller side, I've got: def delete(id) @location = Location.get(id) raise NotFound unless @location if @location.destroy redirect url(:orga_locations) else raise InternalServerError end end And the log: merb : worker (port 4000) ~ Routed to: {"format"=>nil, "event_id"=>"123", "action"=>"destroy", "id"=>"456", "controller"=>"letsmotiv/locations"} merb : worker (port 4000) ~ Params: {"format"=>nil, "event_id"=>"123", "action"=>"destroy", "id"=>"456", "controller"=>"letsmotiv/locations"} ~ (0.000025) SELECT `id`, `class_type`, `name`, `prefix`, `type`, `capacity`, `handicap`, `export_name` FROM `entities` WHERE (`class_type` IN ('Location') AND `id` = 456) ORDER BY `id` LIMIT 1 ~ (0.000014) SELECT `id`, `streetname`, `phone`, `lat`, `lng`, `country_region_city_id`, `location_id`, `organisation_id` FROM `country_region_city_addresses` WHERE `location_id` = 456 ORDER BY `id` LIMIT 1 merb : worker (port 4000) ~ Merb::ControllerExceptions::InternalServerError - (Merb::ControllerExceptions::InternalServerError)

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• how to atomically claim a row or resource using UPDATE in mysql

  - by Igor

  i have a table of resources (lets say cars) which i want to claim atomically. if there's a limit of one resource per one user, i can do the following trick: UPDATE cars SET user = 'bob' WHERE user IS NULL LIMIT 1 SELECT * FROM cars WHERE user IS bob that way, i claim the resource atomically and then i can see which row i just claimed. this doesn't work when 'bob' can claim multiple cars. i realize i can get a list of cars already claimed by bob, claim another one, and then SELECT again to see what's changed, but that feels hackish. What I'm wondering is, is there some way to see which rows i just updated with my last UPDATE? failing that, is there some other trick to atomically claiming a row? i really want to avoid using SERIALIZABLE isolation level. If I do something like this: 1 SELECT id FROM cars WHERE user IS NULL 2 <here, my PHP or whatever picks a car id> 3 UPDATE cars SET user = 'bob' WHERE id = <the one i picked> would REPEATABLE READ be sufficient here? in other words, could i be guaranteed that some other transactions won't claim the row my software has picked during step 2?

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