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• NetApp erroring with: STATUS_NOLOGON_WORKSTATION_TRUST_ACCOUNT

  - by Sobrique

  Since a sitewide upgrade to Windows 7 on desktop, I've started having a problem with virus checking. Specifically - when doing a rename operation on a (filer hosted) CIFS share. The virus checker seems to be triggering a set of messages on the filer: [filerB: auth.trace.authenticateUser.loginTraceIP:info]: AUTH: Login attempt by user server-wk8-r2$ of domain MYDOMAIN from client machine 10.1.1.20 (server-wk8-r2). [filerB: auth.dc.trace.DCConnection.statusMsg:info]: AUTH: TraceDC- attempting authentication with domain controller \\MYDC. [filerB: auth.trace.authenticateUser.loginRejected:info]: AUTH: Login attempt by user rejected by the domain controller with error 0xc0000199: STATUS_NOLOGON_WORKSTATION_TRUST_ACCOUNT. [filerB: auth.trace.authenticateUser.loginTraceMsg:info]: AUTH: Delaying the response by 5 seconds due to continuous failed login attempts by user server-wk8-r2$ of domain MYDOMAIN from client machine 10.1.1.20. This seems to specifically trigger on a rename so what we think is going on is the virus checker is seeing a 'new' file, and trying to do an on-access scan. The virus checker - previously running as LocalSystem and thus sending null as it's authentication request is now looking rather like a DOS attack, and causing the filer to temporarily black list. This 5s lock out each 'access attempt' is a minor nuisance most of the time, and really quite significant for some operations - e.g. large file transfers, where every file takes 5s Having done some digging, this seems to be related to NLTM authentication: Symptoms Error message: System error 1808 has occurred. The account used is a computer account. Use your global user account or local user account to access this server. A packet trace of the failure will show the error as: STATUS_NOLOGON_WORKSTATION_TRUST_ACCOUNT (0xC0000199) Cause Microsoft has changed the functionality of how a Local System account identifies itself during NTLM authentication. This only impacts NTLM authentication. It does not impact Kerberos Authentication. Solution On the host, please set the following group policy entry and reboot the host. Network Security: Allow Local System to use computer identity for NTLM: Disabled Defining this group policy makes Windows Server 2008 R2 and Windows 7 function like Windows Server 2008 SP1. So we've now got a couple of workaround which aren't particularly nice - one is to change this security option. One is to disable virus checking, or otherwise exempt part of the infrastructure. And here's where I come to my request for assistance from ServerFault - what is the best way forwards? I lack Windows experience to be sure of what I'm seeing. I'm not entirely sure why NTLM is part of this picture in the first place - I thought we were using Kerberos authentication. I'm not sure how to start diagnosing or troubleshooting this. (We are going cross domain - workstation machine accounts are in a separate AD and DNS domain to my filer. Normal user authentication works fine however.) And failing that, can anyone suggest other lines of enquiry? I'd like to avoid a site wide security option change, or if I do go that way I'll need to be able to supply detailed reasoning. Likewise - disabling virus checking works as a short term workaround, and applying exclusions may help... but I'd rather not, and don't think that solves the underlying problem. EDIT: Filers in AD ldap have SPNs for: nfs/host.fully.qualified.domain nfs/host HOST/host.fully.qualified.domain HOST/host (Sorry, have to obfuscate those). Could it be that without a 'cifs/host.fully.qualified.domain' it's not going to work? (or some other SPN? ) Edit: As part of the searching I've been doing I've found: http://itwanderer.wordpress.com/2011/04/14/tread-lightly-kerberos-encryption-types/ Which suggests that several encryption types were disabled by default in Win7/2008R2. This might be pertinent, as we've definitely had a similar problem with Keberized NFSv4. There is a hidden option which may help some future Keberos users: options nfs.rpcsec.trace on (This hasn't given me anything yet though, so may just be NFS specific). Edit: Further digging has me tracking it back to cross domain authentication. It looks like my Windows 7 workstation (in one domain) is not getting Kerberos tickets for the other domain, in which my NetApp filer is CIFS joined. I've done this separately against a standalone server (Win2003 and Win2008) and didn't get Kerberos tickets for those either. Which means I think Kerberos might be broken, but I've no idea how to troubleshoot further. Edit: A further update: It looks like this may be down Kerberos tickets not being issued cross domain. This then triggers NTLM fallback, which then runs into this problem (since Windows 7). First port of call will be to investigate the Kerberos side of things, but in neither case do we have anything pointing at the Filer being the root cause. As such - as the storage engineer - it's out of my hands. However, if anyone can point me in the direction of troubleshooting Kerberos spanning two Windows AD domains (Kerberos Realms) then that would be appreciated. Options we're going to be considering for resolution: Amend policy option on all workstations via GPO (as above). Talking to AV vendor about the rename triggering scanning. Talking to AV vendor regarding running AV as service account. investigating Kerberos authentication (why it's not working, whether it should be).

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• SSL and mod_rewrite error

  - by wnoveno

  Hi, I have https on my site. Pages with rewritten URL in my site are inaccessible while direct urls (folders). here's the htaccess ## 2009-12-17 16:52 JGC [START] ## Enable http compression for this site <IfModule mod_deflate.c> SetOutputFilter DEFLATE ## Directive "DeflateCompressionLevel" not allowed in .htaccess, only valid in server config and virtual hosts # DeflateCompressionLevel 9 # file-types indicated will not be compressed SetEnvIfNoCase Request_URI \.(?:gif|jpe?g|png)$ no-gzip dont-vary SetEnvIfNoCase Request_URI \.(?:swf|flv|pdf)$ no-gzip dont-vary SetEnvIfNoCase Request_URI \.(?:exe|t?gz|zip|gz2|sit|rar)$ no-gzip dont-vary <IfModule mod_headers.c> Header append Vary User-Agent </IfModule> </IfModule> ## 2009-12-17 16:52 JGC [END] ## 2010-03-05 16:05 JGC [START] #<IfModule mod_alias.c> #RedirectMatch 301 ^(/)$ /online-casino-poker-register.html #RedirectMatch 301 ^(/en)$ /en/online-casino-poker-register.html #RedirectMatch 301 ^(/en/)$ /en/online-casino-poker-register.html #RedirectMatch 301 ^(/en\.html)$ /en/online-casino-poker-register.html #RedirectMatch 301 ^(/sc)$ /sc/online-casino-poker-register.html #RedirectMatch 301 ^(/sc/)$ /sc/online-casino-poker-register.html #RedirectMatch 301 ^(/sc\.html)$ /sc/online-casino-poker-register.html #RedirectMatch 301 ^(/ch)$ /ch/online-casino-poker-register.html #RedirectMatch 301 ^(/ch/)$ /ch/online-casino-poker-register.html #RedirectMatch 301 ^(/ch\.html)$ /ch/online-casino-poker-register.html #</IfModule> ## 2010-03-05 16:05 JGC [END] ## # @version $Id: htaccess.txt 10492 2008-07-02 06:38:28Z ircmaxell $ # @package Joomla # @copyright Copyright (C) 2005 - 2008 Open Source Matters. All rights reserved. # @license http://www.gnu.org/copyleft/gpl.html GNU/GPL # Joomla! is Free Software ## ##################################################### # READ THIS COMPLETELY IF YOU CHOOSE TO USE THIS FILE # # The line just below this section: 'Options +FollowSymLinks' may cause problems # with some server configurations. It is required for use of mod_rewrite, but may already # be set by your server administrator in a way that dissallows changing it in # your .htaccess file. If using it causes your server to error out, comment it out (add # to # beginning of line), reload your site in your browser and test your sef url's. If they work, # it has been set by your server administrator and you do not need it set here. # ##################################################### ## Can be commented out if causes errors, see notes above. Options +FollowSymLinks # # mod_rewrite in use RewriteEngine On #RewriteLog "/var/www/html/dafa888/rewrite.log" #RewriteLogLevel 3 RewriteCond %{HTTP_COOKIE} !jfcookie\[lang\] [NC] RewriteCond %{HTTP:Accept-Language} ^zh-cn [NC] RewriteRule ^$ /sc/ [L,R=301] RewriteCond %{HTTP_COOKIE} !jfcookie\[lang\] [NC] RewriteCond %{HTTP:Accept-Language} ^zh-tw [NC] RewriteRule ^$ /ch/ [L,R=301] #RewriteCond %{HTTP_COOKIE} !jfcookie[lang] [NC] #RewriteCond %{HTTP_COOKIE} jfcookie\[lang\] [NC] #RewriteCond %{HTTP_COOKIE} jfcookie\[lang\]=([^;]+) [NC] #RewriteRule ^(.*)$ /%1/$1 [NC,QSA] ########## Begin - Rewrite rules to block out some common exploits ## If you experience problems on your site block out the operations listed below ## This attempts to block the most common type of exploit `attempts` to Joomla! # # Block out any script trying to set a mosConfig value through the URL RewriteCond %{QUERY_STRING} mosConfig_[a-zA-Z_]{1,21}(=|\%3D) [OR] # Block out any script trying to base64_encode crap to send via URL RewriteCond %{QUERY_STRING} base64_encode.*\(.*\) [OR] # Block out any script that includes a <script> tag in URL RewriteCond %{QUERY_STRING} (\<|%3C).*script.*(\>|%3E) [NC,OR] # Block out any script trying to set a PHP GLOBALS variable via URL RewriteCond %{QUERY_STRING} GLOBALS(=|\[|\%[0-9A-Z]{0,2}) [OR] # Block out any script trying to modify a _REQUEST variable via URL RewriteCond %{QUERY_STRING} _REQUEST(=|\[|\%[0-9A-Z]{0,2}) # Send all blocked request to homepage with 403 Forbidden error! RewriteRule ^(.*)$ index.php [F,L] # ########## End - Rewrite rules to block out some common exploits # Uncomment following line if your webserver's URL # is not directly related to physical file paths. # Update Your Joomla! Directory (just / for root) RewriteBase / #RewriteCond %{HTTP_HOST} ^(.*)$ [NC] #RewriteRule ^(.*)$ http://www.%1/$1 [R=301] ########## Begin - Joomla! core SEF Section # RewriteCond %{REQUEST_FILENAME} !-f RewriteCond %{REQUEST_FILENAME} !-d RewriteCond %{REQUEST_URI} !^/index.php RewriteCond %{REQUEST_URI} (/|\.php|\.html|\.htm|\.feed|\.pdf|\.raw|/[^.]*)$ [NC] RewriteRule (.*) index.php RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization},L] # ########## End - Joomla! core SEF Section

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• What is the coolest thing you can do in <10 lines of simple code? Help me inspire beginners!

  - by Tom Ritter

  I'm looking for the coolest thing you can do in a few lines of simple code. I'm sure you can write a Mandelbrot set in Haskell in 15 lines but it's difficult to follow. My goal is to inspire students that programming is cool. We know that programming is cool because you can create anything you imagine - it's the ultimate creative outlet. I want to inspire these beginners and get them over as many early-learning humps as I can. Now, my reasons are selfish. I'm teaching an Intro to Computing course to a group of 60 half-engineering, half business majors; all freshmen. They are the students who came from underprivileged High schools. From my past experience, the group is generally split as follows: a few rock-stars, some who try very hard and kind of get it, the few who try very hard and barely get it, and the few who don't care. I want to reach as many of these groups as effectively as I can. Here's an example of how I'd use a computer program to teach: Here's an example of what I'm looking for: a 1-line VBS script to get your computer to talk to you: CreateObject("sapi.spvoice").Speak InputBox("Enter your text","Talk it") I could use this to demonstrate order of operations. I'd show the code, let them play with it, then explain that There's a lot going on in that line, but the computer can make sense of it, because it knows the rules. Then I'd show them something like this: 4(5*5) / 10 + 9(.25 + .75) And you can see that first I need to do is (5*5). Then I can multiply for 4. And now I've created the Object. Dividing by 10 is the same as calling Speak - I can't Speak before I have an object, and I can't divide before I have 100. Then on the other side I first create an InputBox with some instructions for how to display it. When I hit enter on the input box it evaluates or "returns" whatever I entered. (Hint: 'oooooo' makes a funny sound) So when I say Speak, the right side is what to Speak. And I get that from the InputBox. So when you do several things on a line, like: x = 14 + y; You need to be aware of the order of things. First we add 14 and y. Then we put the result (what it evaluates to, or returns) into x. That's my goal, to have a bunch of these cool examples to demonstrate and teach the class while they have fun. I tried this example on my roommate and while I may not use this as the first lesson, she liked it and learned something. Some cool mathematica programs that make beautiful graphs or shapes that are easy to understand would be good ideas and I'm going to look into those. Here are some complicated actionscript examples but that's a bit too advanced and I can't teach flash. What other ideas do you have?

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• Is C# slower than VB.NET?

  - by Matt Winckler

  Believe it or not, despite the title, this is not a troll. Running some benchmarks this morning, my colleagues and I have discovered some strange things concerning performance, and I am wondering if we're doing something horribly wrong. We started out comparing C# vs. Delphi Prism calculating prime numbers, and found that Prism was about 30% faster. I figured maybe CodeGear did more optimization when generating IL (the exe was about twice as big as C#'s and had all sorts of different IL in it.) So I decided to write a test in VB.NET as well, assuming that Microsoft's compilers would end up writing essentially the same IL for each language. However, the result there was more shocking: C# was more than three times slower than VB running the same operations. The generated IL was different, but not extremely so, and I'm not good enough at reading it to understand the differences. As a fan of C#, this apparent slowness wounds me horribly, and I am left wondering: what in the world is going on here? Is it time to pack it all in and go write web apps in Ruby? ;-) I've included the code for each below--just copy it into a new VB or C# console app, and run. On my machine, VB finds 348513 primes in about 6.36 seconds. C# finds the same number of primes in 21.76 seconds. (I've got an Intel Core2 Quad Q6600 @2.4Ghz; on another Intel machine in the office the code for both runs much faster but the ratio is about the same; on an AMD machine here the timing is ~10 seconds for VB and ~13 for C#--much less difference, but C# is still always slower.) Both of the console applications were compiled in Release mode, but otherwise no project settings were changed from the defaults generated by Visual Studio 2008. Is it a generally-known fact that C#'s generated IL is worse than VB's? Or is this a strange edge case? Or is my code flawed somehow (most likely)? Any insights are appreciated. VB code Imports System.Diagnostics Module Module1 Private temp As List(Of Int32) Private sw As Stopwatch Private totalSeconds As Double Sub Main() serialCalc() End Sub Private Sub serialCalc() temp = New List(Of Int32)() sw = Stopwatch.StartNew() For i As Int32 = 2 To 5000000 testIfPrimeSerial(i) Next sw.Stop() totalSeconds = sw.Elapsed.TotalSeconds Console.WriteLine(String.Format("{0} seconds elapsed.", totalSeconds)) Console.WriteLine(String.Format("{0} primes found.", temp.Count)) Console.ReadKey() End Sub Private Sub testIfPrimeSerial(ByVal suspectPrime As Int32) For i As Int32 = 2 To Math.Sqrt(suspectPrime) If (suspectPrime Mod i = 0) Then Exit Sub End If Next temp.Add(suspectPrime) End Sub End Module C# Code using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Diagnostics; namespace FindPrimesCSharp { class Program { List<Int32> temp = new List<Int32>(); Stopwatch sw; double totalSeconds; static void Main(string[] args) { new Program().serialCalc(); } private void serialCalc() { temp = new List<Int32>(); sw = Stopwatch.StartNew(); for (Int32 i = 2; i <= 5000000; i++) { testIfPrimeSerial(i); } sw.Stop(); totalSeconds = sw.Elapsed.TotalSeconds; Console.WriteLine(string.Format("{0} seconds elapsed.", totalSeconds)); Console.WriteLine(string.Format("{0} primes found.", temp.Count)); Console.ReadKey(); } private void testIfPrimeSerial(Int32 suspectPrime) { for (Int32 i = 2; i <= Math.Sqrt(suspectPrime); i++) { if (suspectPrime % i == 0) return; } temp.Add(suspectPrime); } } }

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• Is SQL Server DRI (ON DELETE CASCADE) slow?

  - by Aaronaught

  I've been analyzing a recurring "bug report" (perf issue) in one of our systems related to a particularly slow delete operation. Long story short: It seems that the CASCADE DELETE keys were largely responsible, and I'd like to know (a) if this makes sense, and (b) why it's the case. We have a schema of, let's say, widgets, those being at the root of a large graph of related tables and related-to-related tables and so on. To be perfectly clear, deleting from this table is actively discouraged; it is the "nuclear option" and users are under no illusions to the contrary. Nevertheless, it sometimes just has to be done. The schema looks something like this: Widgets | +--- Anvils (1:1) | | | +--- AnvilTestData (1:N) | +--- WidgetHistory (1:N) | +--- WidgetHistoryDetails (1:N) Nothing too scary, really. A Widget can be different types, an Anvil is a special type, so that relationship is 1:1 (or more accurately 1:0..1). Then there's a large amount of data - perhaps thousands of rows of AnvilTestData per Anvil collected over time, dealing with hardness, corrosion, exact weight, hammer compatibility, usability issues, and impact tests with cartoon heads. Then every Widget has a long, boring history of various types of transactions - production, inventory moves, sales, defect investigations, RMAs, repairs, customer complaints, etc. There might be 10-20k details for a single widget, or none at all, depending on its age. So, unsurprisingly, there's a CASCADE DELETE relationship at every level here. If a Widget needs to be deleted, it means something's gone terribly wrong and we need to erase any records of that widget ever existing, including its history, test data, etc. Again, nuclear option. Relations are all indexed, statistics are up to date. Normal queries are fast. The system tends to hum along pretty smoothly for everything except deletes. Getting to the point here, finally, for various reasons we only allow deleting one widget at a time, so a delete statement would look like this: DELETE FROM Widgets WHERE WidgetID = @WidgetID Pretty simple, innocuous looking delete... that takes over 2 minutes to run, for a widget with no data! After slogging through execution plans I was finally able to pick out the AnvilTestData and WidgetHistoryDetails deletes as the sub-operations with the highest cost. So I experimented with turning off the CASCADE (but keeping the actual FK, just setting it to NO ACTION) and rewriting the script as something very much like the following: DECLARE @AnvilID int SELECT @AnvilID = AnvilID FROM Anvils WHERE WidgetID = @WidgetID DELETE FROM AnvilTestData WHERE AnvilID = @AnvilID DELETE FROM WidgetHistory WHERE HistoryID IN ( SELECT HistoryID FROM WidgetHistory WHERE WidgetID = @WidgetID) DELETE FROM Widgets WHERE WidgetID = @WidgetID Both of these "optimizations" resulted in significant speedups, each one shaving nearly a full minute off the execution time, so that the original 2-minute deletion now takes about 5-10 seconds - at least for new widgets, without much history or test data. Just to be absolutely clear, there is still a CASCADE from WidgetHistory to WidgetHistoryDetails, where the fanout is highest, I only removed the one originating from Widgets. Further "flattening" of the cascade relationships resulted in progressively less dramatic but still noticeable speedups, to the point where deleting a new widget was almost instantaneous once all of the cascade deletes to larger tables were removed and replaced with explicit deletes. I'm using DBCC DROPCLEANBUFFERS and DBCC FREEPROCCACHE before each test. I've disabled all triggers that might be causing further slowdowns (although those would show up in the execution plan anyway). And I'm testing against older widgets, too, and noticing a significant speedup there as well; deletes that used to take 5 minutes now take 20-40 seconds. Now I'm an ardent supporter of the "SELECT ain't broken" philosophy, but there just doesn't seem to be any logical explanation for this behaviour other than crushing, mind-boggling inefficiency of the CASCADE DELETE relationships. So, my questions are: Is this a known issue with DRI in SQL Server? (I couldn't seem to find any references to this sort of thing on Google or here in SO; I suspect the answer is no.) If not, is there another explanation for the behaviour I'm seeing? If it is a known issue, why is it an issue, and are there better workarounds I could be using?

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• Error Handling without Exceptions

  - by James

  While searching SO for approaches to error handling related to business rule validation , all I encounter are examples of structured exception handling. MSDN and many other reputable development resources are very clear that exceptions are not to be used to handle routine error cases. They are only to be used for exceptional circumstances and unexpected errors that may occur from improper use by the programmer (but not the user.) In many cases, user errors such as fields that are left blank are common, and things which our program should expect, and therefore are not exceptional and not candidates for use of exceptions. QUOTE: Remember that the use of the term exception in programming has to do with the thinking that an exception should represent an exceptional condition. Exceptional conditions, by their very nature, do not normally occur; so your code should not throw exceptions as part of its everyday operations. Do not throw exceptions to signal commonly occurring events. Consider using alternate methods to communicate to a caller the occurrence of those events and leave the exception throwing for when something truly out of the ordinary happens. For example, proper use: private void DoSomething(string requiredParameter) { if (requiredParameter == null) throw new ArgumentExpcetion("requiredParameter cannot be null"); // Remainder of method body... } Improper use: // Renames item to a name supplied by the user. Name must begin with an "F". public void RenameItem(string newName) { // Items must have names that begin with "F" if (!newName.StartsWith("F")) throw new RenameException("New name must begin with /"F/""); // Remainder of method body... } In the above case, according to best practices, it would have been better to pass the error up to the UI without involving/requiring .NET's exception handling mechanisms. Using the same example above, suppose one were to need to enforce a set of naming rules against items. What approach would be best? Having the method return a enumerated result? RenameResult.Success, RenameResult.TooShort, RenameResult.TooLong, RenameResult.InvalidCharacters, etc. Using an event in a controller class to report to the UI class? The UI calls the controller's RenameItem method, and then handles an AfterRename event that the controller raises and that has rename status as part of the event args? The controlling class directly references and calls a method from the UI class that handles the error, e.g. ReportError(string text). Something else... ? Essentially, I want to know how to perform complex validation in classes that may not be the Form class itself, and pass the errors back to the Form class for display -- but I do not want to involve exception handling where it should not be used (even though it seems much easier!) Based on responses to the question, I feel that I'll have to state the problem in terms that are more concrete: UI = User Interface, BLL = Business Logic Layer (in this case, just a different class) User enters value within UI. UI reports value to BLL. BLL performs routine validation of the value. BLL discovers rule violation. BLL returns rule violation to UI. UI recieves return from BLL and reports error to user. Since it is routine for a user to enter invalid values, exceptions should not be used. What is the right way to do this without exceptions?

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• Can someone explain the "use-cases" for the default munin graphs?

  - by exhuma

  When installing munin, it activates a default set of plugins (at least on ubuntu). Alternatively, you can simply run munin-node-configure to figure out which plugins are supported on your system. Most of these plugins plot straight-forward data. My question is not to explain the nature of the data (well... maybe for some) but what is it that you look for in these graphs? It is easy to install munin and see fancy graphs. But having the graphs and not being able to "read" them renders them totally useless. I am going to list standard plugins which are enabled by default on my system. So it's going to be a long list. For completeness, I am also going to list plugins which I think to understand and give a short explanation as to what I think it's used for. Pleas correct if I am wrong with any of them. So let me split this questions in three parts: Plugins where I don't even understand the data Plugins where I understand the data but don't know what I should look out for Plugins which I think to understand Plugins where I don't even understand the data These may contain questions that are not necessarily aimed at munin alone. Not understanding the data usually mean a gap in fundamental knowledge on operating systems/hardware.... ;) Feel free to respond with a "giyf" answer. These are plugins where I can only guess what's going on... I hardly want to look at these "guessing"... Disk IOs per device (IOs/second)What's an IO. I know it stands for input/output. But that's as far as it goes. Disk latency per device (Average IO wait)Not a clue what an "IO wait" is... IO Service TimeThis one is a huge mess, and it's near impossible to see something in the graph at all. Plugins where I understand the data but don't know what I should look out for IOStat (blocks/second read/written)I assume, the thing to look out for in here are spikes? Which would mean that the device is in heavy use? Available entropy (bytes)I assume that this is important for random number generation? Why would I graph this? So far the value has always been near constant. VMStat (running/I/O sleep processes)What's the difference between this one and the "processes" graph? Both show running/sleeping processes, whereas the "Processes" graph seems to have more details. Disk throughput per device (bytes/second read/written) What's thedifference between this one and the "IOStat" graph? inode table usageWhat should I look for in this graph? Plugins which I think to understand I'll be guessing some things here... correct me if I am wrong. Disk usage in percent (percent)How much disk space is used/remaining. As this is approaching 100%, you should consider cleaning up or extend the partition. This is extremely important for the root partition. Firewall Throughput (packets/second)The number of packets passing through the firewall. If this is spiking for a longer period of time, it could be a sign of a DOS attack (or we are simply recieving a large file). It can also give you an idea about your firewall performance. If it's levelling out and you need more "power" you should consider load balancing. If it's levelling out and see a correlation with your CPU load, it could also mean that your hardware is not fast enough. Correlations with disk usage could point to excessive LOG targets in you FW config. eth0 errors (packets in/out)Network errors. If this value is increasing, it could be a sign of faulty hardware. eth0 traffic (bits/second in/out)Raw network traffic. This should correlate with Firewall throughput. number of threadsAn ever-increasing value might point to a process not properly closing threads. Investigate! processesBreakdown of active processes (including sleeping). A quick spike in here might point to a fork-bomb. A slowly, but ever-increasing value might point to an application spawning sub-processes but not properly closing them. Investigate using ps faux. process priorityThis shows the distribution of process priorities. Having only high-priority processes is not of much use. Consider de-prioritizing some. cpu usageFairly straight-forward. If this is spiking, you may have an attack going on, or a process is hogging the CPU. Idf it's slowly increasing and approaching max in normal operations, you should consider upgrading your hardware (or load-balancing). file table usageNumber of actively open files. If this is reaching max, you may have a process opening, but not properly releasing files. load averageShows an summarized value for the system load. Should correlate with CPU usage. Increasing values can come from a number of sources. Look for correlations with other graphs. memory usageA graphical representation of you memory. As long as you have a lot of unused+cache+buffers you are fine. swap in/outShows the activity on your swap partition. This should always be 0. If you see activity on this, you should add more memory to your machine!

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• Java Synchronized List Deadlock

  - by portoalet

  From Effective Java 2nd edition item 67 page 266-268: The background thread calls s.removeObserver, which attempts to lock observers, but it can’t acquire the lock, because the main thread already has the lock. All the while, the main thread is waiting for the background thread to finish removing the observer, which explains the deadlock. I am trying to find out which threads deadlock in the main method by using ThreadMXBean (http://stackoverflow.com/questions/1102359/programmatic-deadlock-detection-in-java) , but why does it not return the deadlocked threads? I used a new Thread to run the ThreadMXBean detection. public class ObservableSet<E> extends ForwardingSet<E> { public ObservableSet(Set<E> set) { super(set); } private final List<SetObserver<E>> observers = new ArrayList<SetObserver<E>>(); public void addObserver(SetObserver<E> observer) { synchronized(observers) { observers.add(observer); } } public boolean removeObserver(SetObserver<E> observer) { synchronized(observers) { return observers.remove(observer); } } private void notifyElementAdded(E element) { synchronized(observers) { for (SetObserver<E> observer : observers) observer.added(this, element); } } @Override public boolean add(E element) { boolean added = super.add(element); if (added) notifyElementAdded(element); return added; } @Override public boolean addAll(Collection<? extends E> c) { boolean result = false; for (E element : c) result|=add(element); //callsnotifyElementAdded return result; } public static void main(String[] args) { ObservableSet<Integer> set = new ObservableSet<Integer>(new HashSet<Integer>()); final ThreadMXBean threadMxBean = ManagementFactory.getThreadMXBean(); Thread t = new Thread(new Runnable() { @Override public void run() { while( true ) { long [] threadIds = threadMxBean.findDeadlockedThreads(); if( threadIds != null) { ThreadInfo[] infos = threadMxBean.getThreadInfo(threadIds); for( ThreadInfo threadInfo : infos) { StackTraceElement[] stacks = threadInfo.getStackTrace(); for( StackTraceElement stack : stacks ) { System.out.println(stack.toString()); } } } try { System.out.println("Sleeping.."); TimeUnit.MILLISECONDS.sleep(1000); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } } } }); t.start(); set.addObserver(new SetObserver<Integer>() { public void added(ObservableSet<Integer> s, Integer e) { ExecutorService executor = Executors.newSingleThreadExecutor(); final SetObserver<Integer> observer = this; try { executor.submit(new Runnable() { public void run() { s.removeObserver(observer); } }).get(); } catch (ExecutionException ex) { throw new AssertionError(ex.getCause()); } catch (InterruptedException ex) { throw new AssertionError(ex.getCause()); } finally { executor.shutdown(); } } }); for (int i = 0; i < 100; i++) set.add(i); } } public interface SetObserver<E> { // Invoked when an element is added to the observable set void added(ObservableSet<E> set, E element); } // ForwardingSet<E> simply wraps another Set and forwards all operations to it.

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• java - BigDecimal

  - by Mk12

  I was trying to make my own class for currencies using longs, but Apparently I should use BigDecimal (and then whenever I print it just add the $ sign before it). Could someone please get me started? What would be the best way to use BigDecimals for Dollar currencies, like making it at least but no more than 2 decimal places for the cents, etc. The api for BigDecimal is huge, and I don't know which methods to use. Also, BigDecimal has better precision, but isn't that all lost if it passes through a double? if I do new BigDecimal(24.99), how will it be different than using a double? Or should I use the constructor that uses a String instead? EDIT: I decided to use BigDecimals, and then use: private static final java.text.NumberFormat moneyt = java.text.NumberFormat.getCurrencyInstance(); { money.setRoundingMode(RoundingMode.HALF_EVEN); } and then whenever I display the BigDecimals, to use money.format(theBigDecimal). Is this alright? Should I have the BigDecimal rounding it too? Because then it doesn't get rounded before it does another operation.. if so, could you show me how? And how should I create the BigDecimals? new BigDecimal("24.99") ? Well, after many comments to Vineet Reynolds (thanks for keeping coming back and answering), this is what I have decided. I use BigDecimals and a NumberFormat. Here is where I create the NumberFormat instance. private static final NumberFormat money; static { money = NumberFormat.getCurrencyInstance(Locale.CANADA); money.setRoundingMode(RoundingMode.HALF_EVEN); } Here is my BigDecimal: private final BigDecimal price; Whenever I want to display the price, or another BigDecimal that I got through calculations of price, I use: money.format(price) to get the String. Whenever I want to store the price, or a calculation from price, in a database or in a field or anywhere, I use (for a field): myCalculatedResult = price.add(new BigDecimal("34.58")).setScale(2, RoundingMode.HALF_EVEN); .. but I'm thinking now maybe I should not have the NumberFormat round, but when I want to display do this: System.out.print(money.format(price.setScale(2, RoundingMode.HALF_EVEN); That way to ensure the model and things displayed in the view are the same. I don't do: price = price.setScale(2, RoundingMode.HALF_EVEN); Because then it would always round to 2 decimal places and wouldn't be as precise in calculations. So its all solved now, I guess. But is there any shortcut to typing calculatedResult.setScale(2, RoundingMode.HALF_EVEN) all the time? All I can think of is static importing HALF_EVEN... EDIT: I've changed my mind a bit, I think if I store a value, I won't round it unless I have no more operations to do with it, e.g. if it was the final total that will be charged to someone. I will only round things at the end, or whenever necessary, and I will still use NumberFormat for the currency formatting, but since I always want rounding for display, I made a static method for display: public static String moneyFormat(BigDecimal price) { return money.format(price.setScale(2, RoundingMode.HALF_EVEN)); } So values stored in variables won't be rounded, and I'll use that method to display prices.

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• Thread Synchronisation 101

  - by taspeotis

  Previously I've written some very simple multithreaded code, and I've always been aware that at any time there could be a context switch right in the middle of what I'm doing, so I've always guarded access the shared variables through a CCriticalSection class that enters the critical section on construction and leaves it on destruction. I know this is fairly aggressive and I enter and leave critical sections quite frequently and sometimes egregiously (e.g. at the start of a function when I could put the CCriticalSection inside a tighter code block) but my code doesn't crash and it runs fast enough. At work my multithreaded code needs to be a tighter, only locking/synchronising at the lowest level needed. At work I was trying to debug some multithreaded code, and I came across this: EnterCriticalSection(&m_Crit4); m_bSomeVariable = true; LeaveCriticalSection(&m_Crit4); Now, m_bSomeVariable is a Win32 BOOL (not volatile), which as far as I know is defined to be an int, and on x86 reading and writing these values is a single instruction, and since context switches occur on an instruction boundary then there's no need for synchronising this operation with a critical section. I did some more research online to see whether this operation did not need synchronisation, and I came up with two scenarios it did: The CPU implements out of order execution or the second thread is running on a different core and the updated value is not written into RAM for the other core to see; and The int is not 4-byte aligned. I believe number 1 can be solved using the "volatile" keyword. In VS2005 and later the C++ compiler surrounds access to this variable using memory barriers, ensuring that the variable is always completely written/read to the main system memory before using it. Number 2 I cannot verify, I don't know why the byte alignment would make a difference. I don't know the x86 instruction set, but does mov need to be given a 4-byte aligned address? If not do you need to use a combination of instructions? That would introduce the problem. So... QUESTION 1: Does using the "volatile" keyword (implicity using memory barriers and hinting to the compiler not to optimise this code) absolve a programmer from the need to synchronise a 4-byte/8-byte on x86/x64 variable between read/write operations? QUESTION 2: Is there the explicit requirement that the variable be 4-byte/8-byte aligned? I did some more digging into our code and the variables defined in the class: class CExample { private: CRITICAL_SECTION m_Crit1; // Protects variable a CRITICAL_SECTION m_Crit2; // Protects variable b CRITICAL_SECTION m_Crit3; // Protects variable c CRITICAL_SECTION m_Crit4; // Protects variable d // ... }; Now, to me this seems excessive. I thought critical sections synchronised threads between a process, so if you've got one you can enter it and no other thread in that process can execute. There is no need for a critical section for each variable you want to protect, if you're in a critical section then nothing else can interrupt you. I think the only thing that can change the variables from outside a critical section is if the process shares a memory page with another process (can you do that?) and the other process starts to change the values. Mutexes would also help here, named mutexes are shared across processes, or only processes of the same name? QUESTION 3: Is my analysis of critical sections correct, and should this code be rewritten to use mutexes? I have had a look at other synchronisation objects (semaphores and spinlocks), are they better suited here? QUESTION 4: Where are critical sections/mutexes/semaphores/spinlocks best suited? That is, which synchronisation problem should they be applied to. Is there a vast performance penalty for choosing one over the other? And while we're on it, I read that spinlocks should not be used in a single-core multithreaded environment, only a multi-core multithreaded environment. So, QUESTION 5: Is this wrong, or if not, why is it right? Thanks in advance for any responses :)

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• How to use objects as modules/functors in Scala?

  - by Jeff

  Hi. I want to use object instances as modules/functors, more or less as shown below: abstract class Lattice[E] extends Set[E] { val minimum: E val maximum: E def meet(x: E, y: E): E def join(x: E, y: E): E def neg(x: E): E } class Calculus[E](val lat: Lattice[E]) { abstract class Expr case class Var(name: String) extends Expr {...} case class Val(value: E) extends Expr {...} case class Neg(e1: Expr) extends Expr {...} case class Cnj(e1: Expr, e2: Expr) extends Expr {...} case class Dsj(e1: Expr, e2: Expr) extends Expr {...} } So that I can create a different calculus instance for each lattice (the operations I will perform need the information of which are the maximum and minimum values of the lattice). I want to be able to mix expressions of the same calculus but not be allowed to mix expressions of different ones. So far, so good. I can create my calculus instances, but problem is that I can not write functions in other classes that manipulate them. For example, I am trying to create a parser to read expressions from a file and return them; I also was trying to write an random expression generator to use in my tests with ScalaCheck. Turns out that every time a function generates an Expr object I can't use it outside the function. Even if I create the Calculus instance and pass it as an argument to the function that will in turn generate the Expr objects, the return of the function is not recognized as being of the same type of the objects created outside the function. Maybe my english is not clear enough, let me try a toy example of what I would like to do (not the real ScalaCheck generator, but close enough). def genRndExpr[E](c: Calculus[E], level: Int): Calculus[E]#Expr = { if (level > MAX_LEVEL) { val select = util.Random.nextInt(2) select match { case 0 => genRndVar(c) case 1 => genRndVal(c) } } else { val select = util.Random.nextInt(3) select match { case 0 => new c.Neg(genRndExpr(c, level+1)) case 1 => new c.Dsj(genRndExpr(c, level+1), genRndExpr(c, level+1)) case 2 => new c.Cnj(genRndExpr(c, level+1), genRndExpr(c, level+1)) } } } Now, if I try to compile the above code I get lots of error: type mismatch; found : plg.mvfml.Calculus[E]#Expr required: c.Expr case 0 = new c.Neg(genRndExpr(c, level+1)) And the same happens if I try to do something like: val boolCalc = new Calculus(Bool) val e1: boolCalc.Expr = genRndExpr(boolCalc) Please note that the generator itself is not of concern, but I will need to do similar things (i.e. create and manipulate calculus instance expressions) a lot on the rest of the system. Am I doing something wrong? Is it possible to do what I want to do? Help on this matter is highly needed and appreciated. Thanks a lot in advance. After receiving an answer from Apocalisp and trying it. Thanks a lot for the answer, but there are still some issues. The proposed solution was to change the signature of the function to: def genRndExpr[E, C <: Calculus[E]](c: C, level: Int): C#Expr I changed the signature for all the functions involved: getRndExpr, getRndVal and getRndVar. And I got the same error message everywhere I call these functions and got the following error message: error: inferred type arguments [Nothing,C] do not conform to method genRndVar's type parameter bounds [E,C genRndVar(c) Since the compiler seemed to be unable to figure out the right types I changed all function call to be like below: case 0 => new c.Neg(genRndExpr[E,C](c, level+1)) After this, on the first 2 function calls (genRndVal and genRndVar) there were no compiling error, but on the following 3 calls (recursive calls to genRndExpr), where the return of the function is used to build a new Expr object I got the following error: error: type mismatch; found : C#Expr required: c.Expr case 0 = new c.Neg(genRndExpr[E,C](c, level+1)) So, again, I'm stuck. Any help will be appreciated.

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• Windows NT Service shutdown issues

  - by Jeremiah Gowdy

  I have developed middleware that provides RPC functionality to multiple client applications on multiple platforms within our organization. The middleware is written in C# and runs as a Windows NT Service. It handles things like file access to network shares, database access, etc. The middleware is hosted on two high end systems running Windows Server 2008 R2. When one of our server administrators goes to reboot the machine, primarily to do Windows Updates, there are serious problems with how the system behaves in regards to my NT Service. My service is designed to immediately stop listening for new connections, immediately start refusing new requests on existing connections, and otherwise shut down as rapidly as possible in the case of an OnStop or OnShutdown request from the SCM. Still, to maintain system integrity, operations that are currently in progress are allowed to continue for a reasonable time. Usually the server shuts down inside of 30 seconds (when the service is manually stopped for example). However, when the system is instructed to restart, my service immediately loses access to network drives and UNC paths, causing data integrity problems for any open files and partial writes to those locations. My service does list Workstation (and thus SMB Redirector) as a dependency, so I would think that my service would need to be stopped prior to Workstation/Redirector being stopped if Windows were honoring those dependencies. Basically, my application is forced to crash and burn, failing remote procedure calls and eventually being forced to terminate by the operating system after a timeout period has elapsed (seems to be on the order of 20-30 seconds). Unlike a Windows application, my Windows NT Service doesn't seem to have any power to stop a system shutdown in progress, delay the system shutdown, or even just the opportunity to save out any pending network share disk writes before being forcibly disconnected and shutdown. How is an NT Service developer supposed to have any kind of application integrity in this environment? Why is it that Forms Applications get all of the opportunity to finish their business prior to shutdown, while services seem to get no such benefits? I have tried: Calling SetProcessShutdownParameters via p/invoke to try to notify my application of the shutdown sooner to avoid Redirector shutting down before I do. Calling ServiceBase.RequestAdditionalTime with a value less than or equal to the two minute limit. Tweaking the WaitToKillServiceTimeout Everything I can think of to make my service shutdown faster. But in the end, I still get ~30 seconds of problematic time in which my service doesn't even seem to have been notified of an OnShutdown event yet, but requests are failing due to redirector no longer servicing my network share requests. How is this issue meant to be resolved? What can I do to delay or stop the shutdown, or at least be allowed to shut down my active tasks without Redirector services disappearing out from under me? I can understand what Microsoft is trying to do to prevent services from dragging their feet and showing shutdowns, but that seems like a great goal for Windows client operating systems, not for servers. I don't want my servers to shutdown fast, I want operational integrity and graceful shutdowns. Thanks in advance for any help you can provide. PS in regards to writing my own middleware, this is for a telephony application with sub-second "soft-realtime" response time requirements. It does make sense, and it's not a point I'm looking to debate. :)

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• Is this way the best solution to read and save images from Rss Feeds?

  - by Keyne

  Hi, I've build a "RSS Feed Reader" module to my application, and for every post with images in the content, I get the first that matches a specific size and then I save for future use as reference to the posts. When processing, everything works properly except when more then 10 images are saved at the same time (This value is variable). I got an 404 error after a while saving the images. Some images are saved, but not all of them. If I run the app in my local server, everything work as expected (using set_timeout(0) to avoid timeout errors). Currently my application is hosted at dreamhost and I'm using Zend Framework. I'm not sure if the problem is specif for Zend Framework applications, so I didn't put any tags about. I've had this problem another time with other projects hosted at dreamhost. They seems to limitate memory for operations like that. My question is: There is a better way to save images then this (maybe in background? a limited amount per operation?): require_once(APPLICATION_PATH . '/../library/simplehtmldom/simple_html_dom.php'); $TableFeeds = new Model_DbTable_Feeds(); $Feeds = $TableFeeds->fetchAll(); foreach($Feeds as $Feed) { $entries = Zend_Feed_Reader::import($Feed->link); $lastEntry = $this->getLastEntry($Feed->id); if($lastEntry) { $lastDate = new Zend_Date($lastEntry->created_at, Zend_Date::ISO_8601); } foreach ($entries as $entry) { if($lastDate) { if(strtotime($lastDate->get('y-M-d H:m:s')) >= strtotime($entry->getDateCreated()->get('y-M-d H:m:s'))) { break; } } $Category = new Model_DbTable_Categorias(); $availableCategories = $Category->getList('slug'); $categoria_id = false; foreach ($categories as $cat) { if(!empty($cat) && !$categoria_id) { $slug = Zf_Convert::slugfy($cat); if($availableCategories[$Feed->categoria_id] == $slug) { $categoria_id = $Feed->categoria_id; break; } if(in_array($slug,$availableCategories)) { $categoria_id = array_search($slug,$availableCategories); break; } } } if(!$categoria_id) { $categoria_id = $Feed->categoria_id; } // Cadastra a entrada $data = array( 'categoria_id' => $categoria_id, 'feed_id' => $Feed->id, 'titulo' => $entry->getTitle(), 'slug' => Zf_Convert::slugfy($entry->getTitle()), 'created_at' => $entry->getDateCreated()->get(Zend_Date::ISO_8601), 'link' => $entry->getLink(), 'html' => $entry->getContent(), 'tags' => $tags ); $entry_id = $this->insert($data); if($categoria_id == 2) { set_time_limit(0); $post_dom = str_get_dom($entry->getContent()); $img_tags = $post_dom->find('img'); $images = array(); foreach($img_tags as $image) { $images[] = $image->src; } if(count($images)) { $i = 0; $saved = false; while($images[$i] && !$saved) { $src = $images[$i]; $imagem = Zf_Image::create($src); $size = $imagem->getCurrentDimensions(); if($size['width'] >= 150 && $size['height'] >= 200) { $imagem->adaptiveResize(200,200); $imagem->save(PUBLIC_PATH . '/img/feeds/manchetes/' . $entry_id . '.jpg'); $saved = true; $this->update(array('imagemChamada' => 1),'id =' . $entry_id); } $i++; } } } } } }

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• Template problems: No matching function for call

  - by Nick Sweet

  I'm trying to create a template class, and when I define a non-member template function, I get the "No matching function for call to randvec()" error. I have a template class defined as: template <class T> class Vector { T x, y, z; public: //constructors Vector(); Vector(const T& x, const T& y, const T& z); Vector(const Vector& u); //accessors T getx() const; T gety() const; T getz() const; //mutators void setx(const T& x); void sety(const T& y); void setz(const T& z); //operations void operator-(); Vector plus(const Vector& v); Vector minus(const Vector& v); Vector cross(const Vector& v); T dot(const Vector& v); void times(const T& s); T length() const; //Vector<T>& randvec(); //operators Vector& operator=(const Vector& rhs); friend std::ostream& operator<< <T>(std::ostream&, const Vector<T>&); }; and the function in question, which I've defined after all those functions above, is: //random Vector template <class T> Vector<double>& randvec() { const int min=-10, max=10; Vector<double>* r = new Vector<double>; int randx, randy, randz, temp; const int bucket_size = RAND_MAX/(max-min +1); temp = rand(); //voodoo hackery do randx = (rand()/bucket_size)+min; while (randx < min || randx > max); r->setx(randx); do randy = (rand()/bucket_size)+min; while (randy < min || randy > max); r->sety(randy); do randz = (rand()/bucket_size)+min; while (randz < min || randz > max); r->setz(randz); return *r; } Yet, every time I call it in my main function using a line like: Vector<double> a(randvec()); I get that error. However, if I remove the template and define it using 'double' instead of 'T', the call to randvec() works perfectly. Why doesn't it recognize randvec()? P.S. Don't mind the bit labeled voodoo hackery - this is just a cheap hack so that I can get around another problem I encountered.

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• XSLT Select all nodes containing a specific substing

  - by Mike

  I'm trying to write an XPath that will select certain nodes that contain a specific word. In this case the word is, "Lockwood". The correct answer is 3. Both of these paths give me 3. count(//*[contains(./*,'Lockwood')]) count(BusinessLetter/*[contains(../*,'Lockwood')]) But when I try to output the text of each specific node //*[contains(./*,'Lockwood')][1] //*[contains(./*,'Lockwood')][2] //*[contains(./*,'Lockwood')][3] Node 1 ends up containing all the text and nodes 2 and 3 are blank. Can some one please tell me what's happening or what I'm doing wrong. Thanks. <?xml version="1.0" encoding="UTF-8"?> <?xml-stylesheet type="text/xsl" href="XPathFunctions.xsl"?> <BusinessLetter> <Head> <SendDate>November 29, 2005</SendDate> <Recipient> <Name Title="Mr."> <FirstName>Joshua</FirstName> <LastName>Lockwood</LastName> </Name> <Company>Lockwood &amp; Lockwood</Company> <Address> <Street>291 Broadway Ave.</Street> <City>New York</City> <State>NY</State> <Zip>10007</Zip> <Country>United States</Country> </Address> </Recipient> </Head> <Body> <List> <Heading>Along with this letter, I have enclosed the following items:</Heading> <ListItem>two original, execution copies of the Webucator Master Services Agreement</ListItem> <ListItem>two original, execution copies of the Webucator Premier Support for Developers Services Description between Lockwood &amp; Lockwood and Webucator, Inc.</ListItem> </List> <Para>Please sign and return all four original, execution copies to me at your earliest convenience. Upon receipt of the executed copies, we will immediately return a fully executed, original copy of both agreements to you.</Para> <Para>Please send all four original, execution copies to my attention as follows: <Person> <Name> <FirstName>Bill</FirstName> <LastName>Smith</LastName> </Name> <Address> <Company>Webucator, Inc.</Company> <Street>4933 Jamesville Rd.</Street> <City>Jamesville</City> <State>NY</State> <Zip>13078</Zip> <Country>USA</Country> </Address> </Person> </Para> <Para>If you have any questions, feel free to call me at <Phone>800-555-1000 x123</Phone> or e-mail me at <Email>[email protected]</Email>.</Para> </Body> <Foot> <Closing> <Name> <FirstName>Bill</FirstName> <LastName>Smith</LastName> </Name> <JobTitle>VP of Operations</JobTitle> </Closing> </Foot> </BusinessLetter>

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• Python: Memory usage and optimization when modifying lists

  - by xApple

  The problem My concern is the following: I am storing a relativity large dataset in a classical python list and in order to process the data I must iterate over the list several times, perform some operations on the elements, and often pop an item out of the list. It seems that deleting one item out of a Python list costs O(N) since Python has to copy all the items above the element at hand down one place. Furthermore, since the number of items to delete is approximately proportional to the number of elements in the list this results in an O(N^2) algorithm. I am hoping to find a solution that is cost effective (time and memory-wise). I have studied what I could find on the internet and have summarized my different options below. Which one is the best candidate ? Keeping a local index: while processingdata: index = 0 while index < len(somelist): item = somelist[index] dosomestuff(item) if somecondition(item): del somelist[index] else: index += 1 This is the original solution I came up with. Not only is this not very elegant, but I am hoping there is better way to do it that remains time and memory efficient. Walking the list backwards: while processingdata: for i in xrange(len(somelist) - 1, -1, -1): dosomestuff(item) if somecondition(somelist, i): somelist.pop(i) This avoids incrementing an index variable but ultimately has the same cost as the original version. It also breaks the logic of dosomestuff(item) that wishes to process them in the same order as they appear in the original list. Making a new list: while processingdata: for i, item in enumerate(somelist): dosomestuff(item) newlist = [] for item in somelist: if somecondition(item): newlist.append(item) somelist = newlist gc.collect() This is a very naive strategy for eliminating elements from a list and requires lots of memory since an almost full copy of the list must be made. Using list comprehensions: while processingdata: for i, item in enumerate(somelist): dosomestuff(item) somelist[:] = [x for x in somelist if somecondition(x)] This is very elegant but under-the-cover it walks the whole list one more time and must copy most of the elements in it. My intuition is that this operation probably costs more than the original del statement at least memory wise. Keep in mind that somelist can be huge and that any solution that will iterate through it only once per run will probably always win. Using the filter function: while processingdata: for i, item in enumerate(somelist): dosomestuff(item) somelist = filter(lambda x: not subtle_condition(x), somelist) This also creates a new list occupying lots of RAM. Using the itertools' filter function: from itertools import ifilterfalse while processingdata: for item in itertools.ifilterfalse(somecondtion, somelist): dosomestuff(item) This version of the filter call does not create a new list but will not call dosomestuff on every item breaking the logic of the algorithm. I am including this example only for the purpose of creating an exhaustive list. Moving items up the list while walking while processingdata: index = 0 for item in somelist: dosomestuff(item) if not somecondition(item): somelist[index] = item index += 1 del somelist[index:] This is a subtle method that seems cost effective. I think it will move each item (or the pointer to each item ?) exactly once resulting in an O(N) algorithm. Finally, I hope Python will be intelligent enough to resize the list at the end without allocating memory for a new copy of the list. Not sure though. Abandoning Python lists: class Doubly_Linked_List: def __init__(self): self.first = None self.last = None self.n = 0 def __len__(self): return self.n def __iter__(self): return DLLIter(self) def iterator(self): return self.__iter__() def append(self, x): x = DLLElement(x) x.next = None if self.last is None: x.prev = None self.last = x self.first = x self.n = 1 else: x.prev = self.last x.prev.next = x self.last = x self.n += 1 class DLLElement: def __init__(self, x): self.next = None self.data = x self.prev = None class DLLIter: etc... This type of object resembles a python list in a limited way. However, deletion of an element is guaranteed O(1). I would not like to go here since this would require massive amounts of code refactoring almost everywhere.

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• Play! Framework 1.2.4 --- C3P0 settings to avoid Communications link failure do to idle time

  - by HelpMeStackOverflowMyOnlyHope

  I'm trying to customize my C3P0 settings to avoid the error shown at the bottom of this post. It was suggested at this url --- http://make-it-open.blogspot.com/2008/12/sql-error-0-sqlstate-08s01.html --- to adjust the settings as follows: In hibernate.cfg.xml, write <property name="c3p0.min_size">5</property> <property name="c3p0.max_size">20</property> <property name="c3p0.timeout">1800</property> <property name="c3p0.max_statements">50</property> Then create "c3p0.properties" in your root classpath folder and write c3p0.testConnectionOnCheckout=true c3p0.acquireRetryDelay=1000 c3p0.acquireRetryAttempts=1 I've tried to make those adjustments following the direction of the Play! Framework documentation, where they say use "db.pool..." as follows: db.pool.timeout=1800 db.pool.maxSize=15 db.pool.minSize=5 db.pool.initialSize=5 db.pool.acquireRetryAttempts=1 db.pool.preferredTestQuery=SELECT 1 db.pool.testConnectionOnCheckout=true db.pool.acquireRetryDelay=1000 db.pool.maxStatements=50 Are those settings not going to work? Should I be trying to set them in a different way? With those settings I still get the error shown below, that is due to to long of a idle time. Complete Stack Trace of Error: 23:00:44,932 WARN ~ SQL Error: 0, SQLState: 08S01 2012-04-13T23:00:44+00:00 app[web.1]: 23:00:44,932 ERROR ~ Communications link failure 2012-04-13T23:00:44+00:00 app[web.1]: 2012-04-13T23:00:44+00:00 app[web.1]: The last packet successfully received from the server was 274,847 milliseconds ago. The last packet sent successfully to the server was 7 milliseconds ago. 2012-04-13T23:00:44+00:00 app[web.1]: 23:00:44,934 ERROR ~ Why the driver complains here? 2012-04-13T23:00:44+00:00 app[web.1]: com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: No operations allowed after connection closed.Connection was implicitly closed by the driver. 2012-04-13T23:00:44+00:00 app[web.1]: at com.mysql.jdbc.Util.handleNewInstance(Util.java:407) 2012-04-13T23:00:44+00:00 app[web.1]: at com.mysql.jdbc.Util.getInstance(Util.java:382) 2012-04-13T23:00:44+00:00 app[web.1]: at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1013) 2012-04-13T23:00:44+00:00 app[web.1]: at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:987) 2012-04-13T23:00:44+00:00 app[web.1]: at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:982) 2012-04-13T23:00:44+00:00 app[web.1]: at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:927) 2012-04-13T23:00:44+00:00 app[web.1]: at com.mysql.jdbc.ConnectionImpl.throwConnectionClosedException(ConnectionImpl.java:1213) 2012-04-13T23:00:44+00:00 app[web.1]: at com.mysql.jdbc.ConnectionImpl.getMutex(ConnectionImpl.java:3101) 2012-04-13T23:00:44+00:00 app[web.1]: at com.mysql.jdbc.ConnectionImpl.setAutoCommit(ConnectionImpl.java:4975) 2012-04-13T23:00:44+00:00 app[web.1]: at org.hibernate.jdbc.BorrowedConnectionProxy.invoke(BorrowedConnectionProxy.java:74) 2012-04-13T23:00:44+00:00 app[web.1]: at $Proxy49.setAutoCommit(Unknown Source) 2012-04-13T23:00:44+00:00 app[web.1]: at play.db.jpa.JPAPlugin.closeTx(JPAPlugin.java:368) 2012-04-13T23:00:44+00:00 app[web.1]: at play.db.jpa.JPAPlugin.onInvocationException(JPAPlugin.java:328) 2012-04-13T23:00:44+00:00 app[web.1]: at play.plugins.PluginCollection.onInvocationException(PluginCollection.java:447) 2012-04-13T23:00:44+00:00 app[web.1]: at play.Invoker$Invocation.onException(Invoker.java:240) 2012-04-13T23:00:44+00:00 app[web.1]: at play.jobs.Job.onException(Job.java:124) 2012-04-13T23:00:44+00:00 app[web.1]: at play.jobs.Job.call(Job.java:163) 2012-04-13T23:00:44+00:00 app[web.1]: at play.jobs.Job$1.call(Job.java:66) 2012-04-13T23:00:44+00:00 app[web.1]: at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334) 2012-04-13T23:00:44+00:00 app[web.1]: at java.util.concurrent.FutureTask.run(FutureTask.java:166) 2012-04-13T23:00:44+00:00 app[web.1]: at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$101(ScheduledThreadPoolExecutor.java:165) 2012-04-13T23:00:44+00:00 app[web.1]: at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:266) 2012-04-13T23:00:44+00:00 app[web.1]: at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110) 2012-04-13T23:00:44+00:00 app[web.1]: at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603) 2012-04-13T23:00:44+00:00 app[web.1]: at java.lang.Thread.run(Thread.java:636) 2012-04-13T23:00:44+00:00 app[web.1]: Caused by: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

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• Undefined referencec to ...

  - by Patrick LaChance

  I keep getting this error message every time I try to compile, and I cannot find out what the problem is. any help would be greatly appreciated: C:\DOCUME~1\Patrick\LOCALS~1\Temp/ccL92mj9.o:main.cpp:(.txt+0x184): undefined reference to 'List::List()' C:\DOCUME~1\Patrick\LOCALS~1\Temp/ccL92mj9.o:main.cpp:(.txt+0x184): undefined reference to 'List::add(int)' collect2: ld returned 1 exit status code: //List.h ifndef LIST_H define LIST_H include //brief Definition of linked list class class List { public: /** \brief Exception for operating on empty list */ class Empty : public std::exception { public: virtual const char* what() const throw(); }; /** \brief Exception for invalid operations other than operating on an empty list */ class InvalidOperation : public std::exception { public: virtual const char* what() const throw(); }; /** \brief Node within List */ class Node { public: /** data element stored in this node */ int element; /** next node in list / Node next; /** previous node in list / Node previous; Node (int element); ~Node(); void print() const; void printDebug() const; }; List(); ~List(); void add(int element); void remove(int element); int first()const; int last()const; int removeFirst(); int removeLast(); bool isEmpty()const; int size()const; void printForward() const; void printReverse() const; void printDebug() const; /** enables extra output for debugging purposes */ static bool traceOn; private: /** head of list */ Node* head; /** tail of list */ Node* tail; /** count of number of nodes */ int count; }; endif //List.cpp I only included the parts of List.cpp that might be the issue include "List.h" include include using namespace std; List::List() { //List::size = NULL; head = NULL; tail = NULL; } List::~List() { Node* current; while(head != NULL) { current = head- next; delete current-previous; if (current-next!=NULL) { head = current; } else { delete current; } } } void List::add(int element) { Node* newNode; Node* current; newNode-element = element; if(newNode-element head-element) { current = head-next; } else { head-previous = newNode; newNode-next = head; newNode-previous = NULL; return; } while(newNode-element current-element) { current = current-next; } if(newNode-element <= current-element) { newNode-previous = current-previous; newNode-next = current; } } //main.cpp include "List.h" include include using namespace std; //void add(int element); int main (char** argv, int argc) { List* MyList = new List(); bool quit = false; string value; int element; while(quit==false) { cinvalue; if(value == "add") { cinelement; MyList-add(element); } if(value=="quit") { quit = true; } } return 0; } I'm doing everything I think I'm suppose to be doing. main.cpp isn't complete yet, just trying to get the add function to work first. Any help will be greatly appreciated.

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• this program runs but not correctly:brief decription of what i am trying to do can someone tell me i

  - by user320950

  this is what i have to do: write a program that determines the grade dispersal for 100 students You are to read the exam scores into three arrays, one array for each exam. You must then calculate how many students scored A’s (90 or above), B’s (80 or above), C’s (70 or above), D’s (60 or above), and F’s (less than 60). Do this for each exam and write the distribution to the screen. // basic file operations #include <iostream> #include <fstream> using namespace std; int read_file_in_array(double exam[100][3]); double calculate_total(double exam1[], double exam2[], double exam3[]); // function that calcualates grades to see how many 90,80,70,60 //void display_totals(); double exam[100][3]; int main() { double go,go2,go3; double exam[100][3],exam1[100],exam2[100],exam3[100]; go=read_file_in_array(exam); go2=calculate_total(exam1,exam2,exam3); //go3=display_totals(); cout << go,go2,go3; return 0; } /* int display_totals() { int grade_total; grade_total=calculate_total(exam1,exam2,exam3); return 0; } */ double calculate_total(double exam1[],double exam2[],double exam3[]) { int calc_tot,above90=0, above80=0, above70=0, above60=0,i,j, fail=0; double exam[100][3]; calc_tot=read_file_in_array(exam); for(i=0;i<100;i++) { for (j=0; j<3; j++) { exam1[i]=exam[100][0]; exam2[i]=exam[100][1]; exam3[i]=exam[100][2]; if(exam[i][j] <=90 && exam[i][j] >=100) { above90++; { if(exam[i][j] <=80 && exam[i][j] >=89) { above80++; { if(exam[i][j] <=70 && exam[i][j] >=79) { above70++; { if(exam[i][j] <=60 && exam[i][j] >=69) { above60++; { if(exam[i][j] >=59) { fail++; } } } } } } } } } } } return 0; } int read_file_in_array(double exam[100][3]) { ifstream infile; int exam1[100]; int exam2[100]; int exam3[100]; infile.open("grades.txt");// file containing numbers in 3 columns if(infile.fail()) // checks to see if file opended { cout << "error" << endl; } int num, i=0,j=0; while(!infile.eof()) // reads file to end of line { for(i=0;i<100;i++) // array numbers less than 100 { for(j=0;j<3;j++) // while reading get 1st array or element infile >> exam[i][j]; infile >> exam[i][j]; infile >> exam[i][j]; cout << exam[i][j] << endl; { if (! (infile >> exam[i][j]) ) cout << exam[i][j] << endl; } exam[i][j]=exam1[i]; exam[i][j]=exam2[i]; exam[i][j]=exam3[i]; } infile.close(); } return 0; }

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• REST web service keeps first POST parametrs

  - by Diego

  I have a web service in REST, designed with Java and deployed on Tomcat. This is the web service structure: @Path("Personas") public class Personas { @Context private UriInfo context; /** * Creates a new instance of ServiceResource */ public Personas() { } @GET @Produces("text/html") public String consultarEdad (@QueryParam("nombre") String nombre) { ConectorCliente c = new ConectorCliente("root", "cafe.sql", "test"); int edad = c.consultarEdad(nombre); if (edad == Integer.MIN_VALUE) return "-1"; return String.valueOf(edad); } @POST @Produces("text/html") public String insertarPersona(@QueryParam("nombre") String msg, @QueryParam("edad") int edad) { ConectorCliente c = new ConectorCliente("usr", "passwd", "dbname"); c.agregar(msg, edad); return "listo"; } } Where ConectorCliente class is MySQL connector and querying class. So, I had tested this with the @GET actually doing POST work, any user inputed data and information from ma Java FX app and it went direct to webservice's database. However, I changed so the CREATE operation was performed through a webservice responding to an actual POST HTTP request. However, when I run the client and add some info, parameters go OK, but in next time I input different parameters it'll input the same. I run this several times and I can't get the reason of it. This is the clients code: public class WebServicePersonasConsumer { private WebTarget webTarget; private Client client; private static final String BASE_URI = "http://localhost:8080/GetSomeRest/serviciosweb/"; public WebServicePersonasConsumer() { client = javax.ws.rs.client.ClientBuilder.newClient(); webTarget = client.target(BASE_URI).path("Personas"); } public <T> T insertarPersona(Class<T> responseType, String nombre, String edad) throws ClientErrorException { String[] queryParamNames = new String[]{"nombre", "edad"}; String[] queryParamValues = new String[]{nombre, edad}; ; javax.ws.rs.core.Form form = getQueryOrFormParams(queryParamNames, queryParamValues); javax.ws.rs.core.MultivaluedMap<String, String> map = form.asMap(); for (java.util.Map.Entry<String, java.util.List<String>> entry : map.entrySet()) { java.util.List<String> list = entry.getValue(); String[] values = list.toArray(new String[list.size()]); webTarget = webTarget.queryParam(entry.getKey(), (Object[]) values); } return webTarget.request().post(null, responseType); } public <T> T consultarEdad(Class<T> responseType, String nombre) throws ClientErrorException { String[] queryParamNames = new String[]{"nombre"}; String[] queryParamValues = new String[]{nombre}; ; javax.ws.rs.core.Form form = getQueryOrFormParams(queryParamNames, queryParamValues); javax.ws.rs.core.MultivaluedMap<String, String> map = form.asMap(); for (java.util.Map.Entry<String, java.util.List<String>> entry : map.entrySet()) { java.util.List<String> list = entry.getValue(); String[] values = list.toArray(new String[list.size()]); webTarget = webTarget.queryParam(entry.getKey(), (Object[]) values); } return webTarget.request(javax.ws.rs.core.MediaType.TEXT_HTML).get(responseType); } private Form getQueryOrFormParams(String[] paramNames, String[] paramValues) { Form form = new javax.ws.rs.core.Form(); for (int i = 0; i < paramNames.length; i++) { if (paramValues[i] != null) { form = form.param(paramNames[i], paramValues[i]); } } return form; } public void close() { client.close(); } } And this this the code when I perform the operations in a Java FX app: String nombre = nombreTextField.getText(); String edad = edadTextField.getText(); String insertToDatabase = consumidor.insertarPersona(String.class, nombre, edad); So, as parameters are taken from TextFields, is quite odd why second, third, fourth and so on POSTS post the SAME.

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• SPF record doesn't work (not sure which DNS server to tweak)

  - by Ion

  Problem: Google (and perhaps others) marks our emails as SPF neutral. Let me give you some background about the setup: initially got a dedicated server (Hetzner) with Plesk installed to host a domain/web application, let's say: bigjaws.com. Plesk automatically creates a DNS zone for it with some records for the various services it provides out of the box, e.g. webmail.bigjaws.com as a CNAME to bigjaws.com to provide Horde/whatever, etc. Let me point out four relevant of these records (where XXX.XXX.XXX.158 is our dedicated IP): bigjaws.com. A XXX.XXX.XXX.158 mail.bigjaws.com. A XXX.XXX.XXX.158 bigjaws.com MX (10) mail.bigjaws.com. bigjaws.com. TXT v=spf1 +a +mx -all The above records are not(?) valid anymore though, because after using this dedicated server for a while, our site got bigger and bigger so we decided to move our operations over to AWS (EC2, RDS, ELB, etc), but we retained the mail functionality as is, i.e. emails from [email protected] are sent by connecting to our dedicated server where Plesk takes care of things. This was decided in order not to setup anything from scratch. Of course for all DNS-related things we now use Route53. In Route53 I have the following records: mail.schoox.com. A XXX.XXX.XXX.158 bigjaws.com. MX (10) mail.bigjaws.com bigjaws.com. SPF "v=spf1 +ip4:XXX.XXX.XXX.158 +mx ~all" From my understanding of SPF, the SPF status should have been passed: I designate that all email being sent by bigjaws.com from XXX.XXX.XXX.158 are valid/not spam (I added +mx there but I'm not sure if needed). When a mail server receives an email, doesn't it lookup the SPF record of the domain and checks against the IP it got the email from? Checking with spfquery: root@box:~# spfquery -ip XXX.XXX.XXX.158 -sender [email protected] -rcpt-to [email protected] StartError Context: Failed to query MAIL-FROM ErrorCode: (2) Could not find a valid SPF record Error: No DNS data for 'bigjaws.com'. EndError noneneutral Please see http://www.openspf.org/Why?id=employee1%40bigjaws.com&ip=XXX.XXX.XXX.158&receiver=spfquery : Reason: default spfquery: XXX.XXX.XXX.158 is neither permitted nor denied by domain of bigjaws.com Received-SPF: neutral (spfquery: XXX.XXX.XXX.158 is neither permitted nor denied by domain of bigjaws.com) client-ip=XXX.XXX.XXX.158; [email protected]; If I go to the address listed above (openspf.org) it tells me that the message should have been accepted(!): spfquery rejected a message that claimed an envelope sender address of [email protected]. spfquery received a message from static.158.XXX.XXX.XXX.clients.your-server.de (XXX.XXX.XXX.158) that claimed an envelope sender address of [email protected]. The domain bigjaws.com has authorized static.158.XXX.XXX.XXX.clients.your-server.de (XXX.XXX.XXX.158) to send mail on its behalf, so the message should have been accepted. It is impossible for us to say why it was rejected. What should I do? If the problem persists, contact the bigjaws.com postmaster. Also, here are some headers from an email sent by one of our [email protected] addresses to a gmail.com address (by the way, bigjaws.de listed in the "Received: from" field was the initial domain hosted on the dedicated server before adding the .com one -- both are still listed as separate subscriptions under Plesk). Delivered-To: [email protected] Received: by 10.14.177.70 with SMTP id c46csp289656eem; Wed, 23 Oct 2013 01:11:00 -0700 (PDT) X-Received: by 10.14.102.66 with SMTP id c42mr306186eeg.47.1382515860386; Wed, 23 Oct 2013 01:11:00 -0700 (PDT) Return-Path: <[email protected]> Received: from bigjaws.de (static.158.XXX.XXX.XXX.clients.your-server.de. [XXX.XXX.XXX.158]) by mx.google.com with ESMTPS id l4si19438578eew.161.2013.10.23.01.10.59 for <[email protected]> (version=TLSv1 cipher=RC4-SHA bits=128/128); Wed, 23 Oct 2013 01:10:59 -0700 (PDT) Received-SPF: neutral (google.com: XXX.XXX.XXX.158 is neither permitted nor denied by best guess record for domain of [email protected]) client-ip=XXX.XXX.XXX.158; Authentication-Results: mx.google.com; spf=neutral (google.com: XXX.XXX.XXX.158 is neither permitted nor denied by best guess record for domain of [email protected]) [email protected] DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=default; d=bigjaws.com; b=WwRAS0WKjp9lO17iMluYPXOHzqRcOueiQT4rPdvy3WFf0QzoXiy6rLfxU/Ra53jL1vlPbwlLNa5gjoJBi7ZwKfUcvs3s02hJI7b3ozl0fEgJtTPKoCfnwl4bLPbtXNFu; h=Received:Received:Message-ID:Date:From:User-Agent:MIME-Version:To:Subject:Content-Type:Content-Transfer-Encoding; Received: (qmail 22722 invoked from network); 23 Oct 2013 10:10:59 +0200 Received: from hostname.static.ISP.com (HELO ?192.168.1.60?) (YYY.YYY.ISP.IP) by static.158.XXX.XXX.XXX.clients.your-server.de. with ESMTPSA (DHE-RSA-AES256-SHA encrypted, authenticated); 23 Oct 2013 10:10:59 +0200 Message-ID: <[email protected]> Date: Wed, 23 Oct 2013 11:11:00 +0300 From: BigJaws Employee <[email protected]> User-Agent: Mozilla/5.0 (Windows NT 6.2; WOW64; rv:24.0) Gecko/20100101 Thunderbird/24.0.1 MIME-Version: 1.0 To: [email protected] Subject: test SPF Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit test SPF Any ideas why SPF is not working correctly? Also, are there any DNS settings that are not needed anymore and create a problem?

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• Using Spring as a JPA Container

  - by sdoca

  Hi, I found this article which talks about using Spring as a JPA container: http://java.sys-con.com/node/366275 I have never used Spring before this and am trying to make this work and hope someone can help me. In the article it states that you need to annotate a Spring bean with @Transactional and methods/fields with @PersistenceContext in order to provide transaction support and to inject an entity manager. Is there something the defines a bean as a "Spring Bean"? I have a bean class which implements CRUD operations on entities using generics: @Transactional public class GenericCrudServiceBean implements GenericCrudService { @PersistenceContext(unitName="MyData") private EntityManager em; @Override @PersistenceContext public <T> T create(T t) { em.persist(t); return t; } @Override @PersistenceContext public <T> void delete(T t) { t = em.merge(t); em.remove(t); } ... ... ... @Override @PersistenceContext public List<?> findWithNamedQuery(String queryName) { return em.createNamedQuery(queryName).getResultList(); } } Originally I only had this peristence context annotation: @PersistenceContext(unitName="MyData") private EntityManager em; but had a null em when findWithNamedQuery was invoked. Then I annotated the methods as well, but em is still null (no injection?). I was wondering if this had something to do with my bean not being recognized as "Spring". I have done configuration as best I could following the directions in the article including setting the following in my context.xml file: <?xml version="1.0" encoding="UTF-8"?> <beans xmlns:tx="http://www.springframework.org/schema/tx" tx:schemaLocation="http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.0.xsd"> <bean id="entityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean"> <property name="persistenceUnitName" value="MyData" /> <property name="dataSource" ref="dataSource" /> <property name="loadTimeWeaver" class="org.springframework.classloading.ReflectiveLoadTimeWeaver" /> <property name="jpaVendorAdapter" ref="jpaAdapter" /> </bean> <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close"> <property name="driverClassName" value="oracle.jdbc.driver.OracleDriver" /> <property name="url" value="jdbc:oracle:thin:@localhost:1521:MySID" /> <property name="username" value="user" /> <property name="password" value="password" /> <property name="initialSize" value="3" /> <property name="maxActive" value="10" /> </bean> <bean id="jpaAdapter" class="org.springframework.orm.jpa.vendor.EclipseLinkJpaVendorAdapter"> <property name="databasePlatform" value="org.eclipse.persistence.platform.database.OraclePlatform" /> <property name="showSql" value="true" /> </bean> <bean class="org.springframework.ormmjpa.support.PersistenceAnnotationBeanPostProcessor" /> <tx:annotation-driven /> </beans> I guessed that these belonged in the context.xml file because the article never specifically said which file is the "application context" file. If this is wrong, please let me know.

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• Is there a way to delay compilation of a stored procedure's execution plan?

  - by Ian Henry

  (At first glance this may look like a duplicate of http://stackoverflow.com/questions/421275 or http://stackoverflow.com/questions/414336, but my actual question is a bit different) Alright, this one's had me stumped for a few hours. My example here is ridiculously abstracted, so I doubt it will be possible to recreate locally, but it provides context for my question (Also, I'm running SQL Server 2005). I have a stored procedure with basically two steps, constructing a temp table, populating it with very few rows, and then querying a very large table joining against that temp table. It has multiple parameters, but the most relevant is a datetime "@MinDate." Essentially: create table #smallTable (ID int) insert into #smallTable select (a very small number of rows from some other table) select * from aGiantTable inner join #smallTable on #smallTable.ID = aGiantTable.ID inner join anotherTable on anotherTable.GiantID = aGiantTable.ID where aGiantTable.SomeDateField > @MinDate If I just execute this as a normal query, by declaring @MinDate as a local variable and running that, it produces an optimal execution plan that executes very quickly (first joins on #smallTable and then only considers a very small subset of rows from aGiantTable while doing other operations). It seems to realize that #smallTable is tiny, so it would be efficient to start with it. This is good. However, if I make that a stored procedure with @MinDate as a parameter, it produces a completely inefficient execution plan. (I am recompiling it each time, so it's not a bad cached plan...at least, I sure hope it's not) But here's where it gets weird. If I change the proc to the following: declare @LocalMinDate datetime set @LocalMinDate = @MinDate --where @MinDate is still a parameter create table #smallTable (ID int) insert into #smallTable select (a very small number of rows from some other table) select * from aGiantTable inner join #smallTable on #smallTable.ID = aGiantTable.ID inner join anotherTable on anotherTable.GiantID = aGiantTable.ID where aGiantTable.SomeDateField > @LocalMinDate Then it gives me the efficient plan! So my theory is this: when executing as a plain query (not as a stored procedure), it waits to construct the execution plan for the expensive query until the last minute, so the query optimizer knows that #smallTable is small and uses that information to give the efficient plan. But when executing as a stored procedure, it creates the entire execution plan at once, thus it can't use this bit of information to optimize the plan. But why does using the locally declared variables change this? Why does that delay the creation of the execution plan? Is that actually what's happening? If so, is there a way to force delayed compilation (if that indeed is what's going on here) even when not using local variables in this way? More generally, does anyone have sources on when the execution plan is created for each step of a stored procedure? Googling hasn't provided any helpful information, but I don't think I'm looking for the right thing. Or is my theory just completely unfounded? Edit: Since posting, I've learned of parameter sniffing, and I assume this is what's causing the execution plan to compile prematurely (unless stored procedures indeed compile all at once), so my question remains -- can you force the delay? Or disable the sniffing entirely? The question is academic, since I can force a more efficient plan by replacing the select * from aGiantTable with select * from (select * from aGiantTable where ID in (select ID from #smallTable)) as aGiantTable Or just sucking it up and masking the parameters, but still, this inconsistency has me pretty curious.

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• Modern alternatives to Java

  - by Ralph

  I have been a Java developer for 14 years and have written an enterprise-level (~500 kloc) Swing application that uses most of the standard library APIs. Recently, I have become disappointed with the progress that the language has made to "modernize" itself, and am looking for an alternative for ongoing development. I have considered moving to the .NET platform, but I have issues with using something the only runs well in Windows (I know about Mono, but that is still far behind Microsoft). I also plan on buying a new Macbook Pro as soon as Apple releases their new rumored Arrandale-based machines and want to develop in an environment that will feel "at home" in Unix/Linux. I have considered using Python or Ruby, but the standard Java library is arguably the largest of any modern language. In JVM-based languages, I looked at Groovy, but am disappointed with its performance. Rumor has it that with the soon-to-be released JDK7, with its InvokeDynamic instruction, this will improve, but I don't know how much. Groovy is also not truly a functional language, although it provides closures and some of the "functional" features on collections. It does not embrace immutability. I have narrowed my search down to two JVM-based alternatives: Scala and Clojure. Each has its strengths and weaknesses. I am looking for opinions. I am not an expert at either of these languages; I have read 2 1/2 books on Scala and am currently reading Stu Halloway's book on Clojure. Scala is strongly statically typed. I know the dynamic language folks claim that static typing is a crutch for not doing unit testing, but it does provide a mechanism for compile-time location of a whole class of errors. Scala is more concise than Java, but not as much as Clojure. Scala's inter-operation with Java seems to be better than Clojure's, in that most Java operations are easier to do in Scala than in Clojure. For example, I can find no way in Clojure to create a non-static initialization block in a class derived from a Java superclass. For example, I like the Apache commons CLI library for command line argument parsing. In Java and Scala, I can create a new Options object and add Option items to it in an initialization block as follows (Java code): final Options options = new Options() { { addOption(new Option("?", "help", false, "Show this usage information"); // other options } }; I can't figure out how to the same thing in Clojure (except by using (doit...)), although that may reflect my lack of knowledge of the language. Clojure's collections are optimized for immutability. They rarely require copy-on-write semantics. I don't know if Scala's immutable collections are implemented using similar algorithms, but Rich Hickey (Clojure's inventor) goes out of his way to explain how that language's data structures are efficient. Clojure was designed from the beginning for concurrency (as was Scala) and with modern multi-core processors, concurrency takes on more importance, but I occasionally need to write simple non-concurrent utilities, and Scala code probably runs a little faster for these applications since it discourages, but does not prohibit, "simple" mutability. One could argue that one-off utilities do not have to be super-fast, but sometimes they do tasks that take hours or days to complete. I know that there is no right answer to this "question", but I thought I would open it up for discussion. Are there other JVM-based languages that can be used for enterprise level development?

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• Languages and VMs: Features that are hard to optimize and why

  - by mrjoltcola

  I'm doing a survey of features in preparation for a research project. Name a mainstream language or language feature that is hard to optimize, and why the feature is or isn't worth the price paid, or instead, just debunk my theories below with anecdotal evidence. Before anyone flags this as subjective, I am asking for specific examples of languages or features, and ideas for optimization of these features, or important features that I haven't considered. Also, any references to implementations that prove my theories right or wrong. Top on my list of hard to optimize features and my theories (some of my theories are untested and are based on thought experiments): 1) Runtime method overloading (aka multi-method dispatch or signature based dispatch). Is it hard to optimize when combined with features that allow runtime recompilation or method addition. Or is it just hard, anyway? Call site caching is a common optimization for many runtime systems, but multi-methods add additional complexity as well as making it less practical to inline methods. 2) Type morphing / variants (aka value based typing as opposed to variable based) Traditional optimizations simply cannot be applied when you don't know if the type of someting can change in a basic block. Combined with multi-methods, inlining must be done carefully if at all, and probably only for a given threshold of size of the callee. ie. it is easy to consider inlining simple property fetches (getters / setters) but inlining complex methods may result in code bloat. The other issue is I cannot just assign a variant to a register and JIT it to the native instructions because I have to carry around the type info, or every variable needs 2 registers instead of 1. On IA-32 this is inconvenient, even if improved with x64's extra registers. This is probably my favorite feature of dynamic languages, as it simplifies so many things from the programmer's perspective. 3) First class continuations - There are multiple ways to implement them, and I have done so in both of the most common approaches, one being stack copying and the other as implementing the runtime to use continuation passing style, cactus stacks, copy-on-write stack frames, and garbage collection. First class continuations have resource management issues, ie. we must save everything, in case the continuation is resumed, and I'm not aware if any languages support leaving a continuation with "intent" (ie. "I am not coming back here, so you may discard this copy of the world"). Having programmed in the threading model and the contination model, I know both can accomplish the same thing, but continuations' elegance imposes considerable complexity on the runtime and also may affect cache efficienty (locality of stack changes more with use of continuations and co-routines). The other issue is they just don't map to hardware. Optimizing continuations is optimizing for the less-common case, and as we know, the common case should be fast, and the less-common cases should be correct. 4) Pointer arithmetic and ability to mask pointers (storing in integers, etc.) Had to throw this in, but I could actually live without this quite easily. My feelings are that many of the high-level features, particularly in dynamic languages just don't map to hardware. Microprocessor implementations have billions of dollars of research behind the optimizations on the chip, yet the choice of language feature(s) may marginalize many of these features (features like caching, aliasing top of stack to register, instruction parallelism, return address buffers, loop buffers and branch prediction). Macro-applications of micro-features don't necessarily pan out like some developers like to think, and implementing many languages in a VM ends up mapping native ops into function calls (ie. the more dynamic a language is the more we must lookup/cache at runtime, nothing can be assumed, so our instruction mix is made up of a higher percentage of non-local branching than traditional, statically compiled code) and the only thing we can really JIT well is expression evaluation of non-dynamic types and operations on constant or immediate types. It is my gut feeling that bytecode virtual machines and JIT cores are perhaps not always justified for certain languages because of this. I welcome your answers.

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