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• Windows 7 Explorer keeps crashing

  - by Daniel Liang

  I currently have an issue with Windows Explorer. It keeps crashing when I browse through a network drive. This is happening on several computers. I have already obtained a crash dump file but it doesn't state much: Microsoft (R) Windows Debugger Version 6.12.0002.633 X86 Copyright (c) Microsoft Corporation. All rights reserved. Loading Dump File [C:\LocalDumps\explorer.exe.3964.dmp] User Mini Dump File with Full Memory: Only application data is available Symbol search path is: SRV*c:\websymbols*http://msdl.microsoft.com/download/symbols Executable search path is: Windows 7 Version 7601 (Service Pack 1) MP (2 procs) Free x86 compatible Product: WinNt, suite: SingleUserTS Machine Name: Debug session time: Mon Oct 21 11:21:30.000 2013 (UTC - 4:00) System Uptime: 0 days 0:06:20.449 Process Uptime: 0 days 0:05:54.000 ................................................................ ................................................................ .... Loading unloaded module list ............. This dump file has an exception of interest stored in it. The stored exception information can be accessed via .ecxr. (f7c.fe4): Access violation - code c0000005 (first/second chance not available) eax=00000000 ebx=07a3f080 ecx=00000400 edx=00000000 esi=00000002 edi=00000000 eip=76e170f4 esp=07a3f030 ebp=07a3f0cc iopl=0 nv up ei pl zr na pe nc cs=001b ss=0023 ds=0023 es=0023 fs=003b gs=0000 efl=00000246 ntdll!KiFastSystemCallRet: 76e170f4 c3 ret I've already tried removing certain context menu items. I disabled all unnecessary start-up items. Ran memtest86 and it looks fine on that end. It also happens when I browse through my local disk. Can anyone take a look into this? Thanks!

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• Calling Excel from PHP 5 through COM fails on Windows 7 when Apache started through Task Planner

  - by Stefan Pantke

  I currently write an application, which controls Excel through COM: The app creates a COM-based Excel instance, opens some XLS files and reads their contents. Scenario I On Windows 7, I start Apache and mySQL using xmapp-control with system administrator rights. All works as expected. The PHP-based controller script interacts with Excel as expected. Scenario II A problem appears, if I start Apache and mySQL as 'background jobs'. Here is how: I created two jobs using Windows 7 Task Planner. One runs apache_start.bat, the other runs mysql_start.bat. Both tasks run as SYSTEM with elevated privileges when Windows 7 boots. Apache and mySQL work as expected. Specifically, Apache serves HTTP request from clients and PHP is able to talk to mySQL. When I call the PHP controller, which calls and interacts with Excel using COM, I do receive an error. The error seems to come from Excel [not COM itself] and reads like this: Excel can't read the XLS-file Excel failed to save the file due to an ill-name worksheet Interestingly, during the first run of the PHP-based controller script, it takes a few seconds to render the error message. Each subsequent run immediately renders the error message. Windows system logs didn't show a single problem report entry. Note, that the PHP program and the Apache instance didn't change - except the way Apache was started. At least the PHP controller script is perfectly able to read the file-system, since it provides the pathes to the XLS-file through scandir() of a certain directory. Concurrency issues can't be the cause of the problem. A single instance of the specific PHP controller interacts with Excel. Question Could someone provide details, why this happens?

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• Celery daemon as a Ubuntu service does not consume tasks while running from terminal does

  - by Guy

  On Ubuntu 11.10, I have to issue python tasks from django using celery. I'm currently testing on the same machine but eventually the celery worker should run on a remote machine. django uses the following settings: BROKER_HOST = "127.0.0.1" BROKER_PORT = 5672 BROKER_VHOST = "/my_vhost" BROKER_USER = "celery" BROKER_PASSWORD = "celery" I can also see my task queued in http://localhost:55672/#/queues the celery daemon uses the following configuration (celeryconfig.py): BROKER_HOST = "127.0.0.1" BROKER_PORT = 5672 BROKER_USER = "celery" BROKER_PASSWORD = "celery" BROKER_VHOST = "/my_vhost" CELERY_RESULT_BACKEND = "amqp" import os import sys sys.path.append(os.getcwd()) CELERY_IMPORTS = ("tasks", ) running celeryd -l info works well and now I want to run it as a service. I've followed the instructions from http://ask.github.com/celery/cookbook/daemonizing.html and now I'm trying to run it using: sudo /etc/init.d/celeryd start But the message is not being consumed, no error in the celery log either. /etc/default/celeryd CELERYD_NODES="w1" CELERYD_CHDIR="/path/to/django/project" CELERYD_OPTS="--time-limit=300 --concurrency=1" CELERY_CONFIG_MODULE="celeryconfig" # %n will be replaced with the nodename. CELERYD_LOG_FILE="/var/log/celery/%n.log" CELERYD_PID_FILE="/var/run/celery/%n.pid" # Workers should run as an unprivileged user. CELERYD_USER="celery" CELERYD_GROUP="celery" I've also created user celery in Ubuntu not sure if its necessary. Any help will be appreciated, Thanks, Guy

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• Transferring an SQL Processor License to a virtual hosted environment

  - by Andrew Shepherd

  My company is currently hosting a service in-house, and we want to move to an externally hosted environment. We would then be using a virtual server. I understand that this might be spread across multiple machines, but from my perspective as a customer, this layer is abstracted away - I shouldn't know or care about the hardware that the OS is hosted on. We have a licensed edition of SQL Server 2008. This is one Processor license. Will it be a violation of the licensing agreement to use this in a virtual environment. From the reference guide here it says When licensed Per Processor With Workgroup, Web, and Standard editions, for each server to which you have assigned the required number of per processor licenses, you may run, at any one time, any number of instances of the server software in physical and virtual operating system environments on the licensed server. However, the total number of physical and virtual processors used by those operating system environments cannot exceed the number of software licenses assigned to that server For enterprise edition there is an added option: if all physical processors in a machine have been licensed, then you may run unlimited instances of SQL server 2008 in one physical and an unlimited number of virtual operating environments on that same machine. I'm having trouble getting my head around this. Would I theoretically have to get a license for every processor in this virtual environment (which is effectively impossible because I have no way of knowing how many processors there actually are)? Or can I just say that it's hosted on one "virtual" server, so that's OK?

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• Server Recovery from Denial of Service

  - by JMC

  I'm looking at a server that might be misconfigured to handle Denial of Service. The database was knocked offline after the attack, and was unable to restart itself after it failed to restart when the attack subsided. Details of the Attack: The Attacker either intentionally or unintentionally sent 1000's of search queries using the applications search query url within a couple of seconds. It looks like the server was overwhelmed and it caused the database to log this message: Server Specs: 1.5GB of dedicated memory Are there any obvious mis-configurations here that I'm missing? **mysql.log** 121118 20:28:54 mysqld_safe Number of processes running now: 0 121118 20:28:54 mysqld_safe mysqld restarted 121118 20:28:55 [Warning] option 'slow_query_log': boolean value '/var/log/mysqld.slow.log' wasn't recognized. Set to OFF. 121118 20:28:55 [Note] Plugin 'FEDERATED' is disabled. 121118 20:28:55 InnoDB: The InnoDB memory heap is disabled 121118 20:28:55 InnoDB: Mutexes and rw_locks use GCC atomic builtins 121118 20:28:55 InnoDB: Compressed tables use zlib 1.2.3 121118 20:28:55 InnoDB: Using Linux native AIO 121118 20:28:55 InnoDB: Initializing buffer pool, size = 512.0M InnoDB: mmap(549453824 bytes) failed; errno 12 121118 20:28:55 InnoDB: Completed initialization of buffer pool 121118 20:28:55 InnoDB: Fatal error: cannot allocate memory for the buffer pool 121118 20:28:55 [ERROR] Plugin 'InnoDB' init function returned error. 121118 20:28:55 [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed. 121118 20:28:55 [ERROR] Unknown/unsupported storage engine: InnoDB 121118 20:28:55 [ERROR] Aborting **ulimit -a** core file size (blocks, -c) 0 data seg size (kbytes, -d) unlimited scheduling priority (-e) 0 file size (blocks, -f) unlimited pending signals (-i) 13089 max locked memory (kbytes, -l) 64 max memory size (kbytes, -m) unlimited open files (-n) 1024 pipe size (512 bytes, -p) 8 POSIX message queues (bytes, -q) 819200 real-time priority (-r) 0 stack size (kbytes, -s) 8192 cpu time (seconds, -t) unlimited max user processes (-u) 1024 virtual memory (kbytes, -v) unlimited file locks (-x) unlimited **httpd.conf** StartServers 10 MinSpareServers 8 MaxSpareServers 12 ServerLimit 256 MaxClients 256 MaxRequestsPerChild 4000 **my.cnf** innodb_buffer_pool_size=512M # Increase Innodb Thread Concurrency = 2 * [numberofCPUs] + 2 innodb_thread_concurrency=4 # Set Table Cache table_cache=512 # Set Query Cache_Size query_cache_size=64M query_cache_limit=2M # A sort buffer is used for optimizing sorting sort_buffer_size=8M # Log slow queries slow_query_log=/var/log/mysqld.slow.log long_query_time=2 #performance_tweak join_buffer_size=2M **php.ini** memory_limit = 128M post_max_size = 8M

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• Apache https is slsow

  - by raucous12

  Hey, I've set apache up to use SSL with a self signed certificate. With http (KeepAlive off), I can get over 5000 requests per second. However, with https, I can only get 13 requests per second. I know there is supposed to be a bit of an overhead, but this seems abnormal. Can anyone suggest how I might go about debugging this. Here is the ab log for https: Server Software: Apache/2.2.3 Server Hostname: 127.0.0.1 Server Port: 443 SSL/TLS Protocol: TLSv1/SSLv3,DHE-RSA-AES256-SHA,4096,256 Document Path: /hello.html Document Length: 29 bytes Concurrency Level: 5 Time taken for tests: 30.49425 seconds Complete requests: 411 Failed requests: 0 Write errors: 0 Total transferred: 119601 bytes HTML transferred: 11919 bytes Requests per second: 13.68 [#/sec] (mean) Time per request: 365.565 [ms] (mean) Time per request: 73.113 [ms] (mean, across all concurrent requests) Transfer rate: 3.86 [Kbytes/sec] received Connection Times (ms) min mean[+/-sd] median max Connect: 190 347 74.3 333 716 Processing: 0 14 24.0 1 166 Waiting: 0 11 21.6 0 165 Total: 191 361 80.8 345 716 Percentage of the requests served within a certain time (ms) 50% 345 66% 377 75% 408 80% 421 90% 468 95% 521 98% 578 99% 596 100% 716 (longest request)

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• Bonnie does not provide speed for Sequential Input / Block

  - by Lqp1

  I'm using ProxmoxVE and I would like to run some benchmarks regarding performances of this product. One of these benchmarks is bonnie++ ; it runs very well in a VM (qemu-kvm) but when I run it in a conainer (openVZ), it does not provide me reading speed (only writing). I don't understand why... Does anyone know what's happenning ? VMs ans Containers are Debian 7.4. Here's the output of bonnie in the container: root@ct2:/# bonnie++ -u root Using uid:0, gid:0. Writing a byte at a time...done Writing intelligently...done Rewriting...done Reading a byte at a time...done Reading intelligently...done start 'em...done...done...done...done...done... Create files in sequential order...done. Stat files in sequential order...done. Delete files in sequential order...done. Create files in random order...done. Stat files in random order...done. Delete files in random order...done. Version 1.96 ------Sequential Output------ --Sequential Input- --Random- Concurrency 1 -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks-- Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP ct2 1G 843 99 59116 8 60351 4 4966 99 +++++ +++ 2745 8 Latency 9558us 3582ms 527ms 1672us 936us 5248us Version 1.96 ------Sequential Create------ --------Random Create-------- ct2 -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete-- files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP 16 +++++ +++ +++++ +++ +++++ +++ +++++ +++ +++++ +++ +++++ +++ Latency 19567us 358us 368us 107us 59us 25us 1.96,1.96,ct2,1,1401810323,1G,,843,99,59116,8,60351,4,4966,99,+++++,+++,2745,8,16,,,,,+++++,+++,+++++,+++,+++++,+++,+++++,+++,+++++,+++,+++++,+++,9558us,3582ms,527ms,1672us,936us,5248us,19567us,358us,368us,107us,59us,25us The filesystem for / is of type "simfs", which is a pseudo filesystem for openVZ. Maybe it's related to this issue but I can't find anyone with the same issue with bonnie and openVZ... Thanks for your help. Regards, Thomas.

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• Apache https is slow

  - by raucous12

  Hey, I've set apache up to use SSL with a self signed certificate. With https (KeepAlive on), I can get over 3000 requests per second. However, with https (KeepAlive off), I can only get 13 requests per second. I know there is supposed to be a bit of an overhead, but this seems abnormal. Can anyone suggest how I might go about debugging this. Here is the ab log for https: Server Software: Apache/2.2.3 Server Hostname: 127.0.0.1 Server Port: 443 SSL/TLS Protocol: TLSv1/SSLv3,DHE-RSA-AES256-SHA,4096,256 Document Path: /hello.html Document Length: 29 bytes Concurrency Level: 5 Time taken for tests: 30.49425 seconds Complete requests: 411 Failed requests: 0 Write errors: 0 Total transferred: 119601 bytes HTML transferred: 11919 bytes Requests per second: 13.68 [#/sec] (mean) Time per request: 365.565 [ms] (mean) Time per request: 73.113 [ms] (mean, across all concurrent requests) Transfer rate: 3.86 [Kbytes/sec] received Connection Times (ms) min mean[+/-sd] median max Connect: 190 347 74.3 333 716 Processing: 0 14 24.0 1 166 Waiting: 0 11 21.6 0 165 Total: 191 361 80.8 345 716 Percentage of the requests served within a certain time (ms) 50% 345 66% 377 75% 408 80% 421 90% 468 95% 521 98% 578 99% 596 100% 716 (longest request)

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• amazon ec2-medium apache requests per second terrible

  - by TheDayIsDone

  EDITED -- test running from localhost now to rule out network... i have a c1.medium using EBS. when i do an apache benchmark and i'm just printing a "hello" for the test from localhost - no database hits, it's very slow. i can repeat this test many times with the same results. any thoughts? thanks in advance. ab -n 1000 -c 100 http://localhost/home/test/ Benchmarking localhost (be patient) Completed 100 requests Completed 200 requests Completed 300 requests Completed 400 requests Completed 500 requests Completed 600 requests Completed 700 requests Completed 800 requests Completed 900 requests Completed 1000 requests Finished 1000 requests Server Software: Apache/2.2.23 Server Hostname: localhost Server Port: 80 Document Path: /home/test/ Document Length: 5 bytes Concurrency Level: 100 Time taken for tests: 25.300 seconds Complete requests: 1000 Failed requests: 0 Write errors: 0 Total transferred: 816000 bytes HTML transferred: 5000 bytes Requests per second: 39.53 [#/sec] (mean) Time per request: 2530.037 [ms] (mean) Time per request: 25.300 [ms] (mean, across all concurrent requests) Transfer rate: 31.50 [Kbytes/sec] received Connection Times (ms) min mean[+/-sd] median max Connect: 0 7 21.0 0 73 Processing: 81 2489 665.7 2500 4057 Waiting: 80 2443 654.0 2445 4057 Total: 85 2496 653.5 2500 4057 Percentage of the requests served within a certain time (ms) 50% 2500 66% 2651 75% 2842 80% 2932 90% 3301 95% 3506 98% 3762 99% 3838 100% 4057 (longest request)

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• Strange 3-second tcp connection latencies (Linux, HTTP)

  - by user25417

  Our webservers with static content are experiencing strange 3 second latencies occasionally. Typically, an ApacheBench run ( 10000 requests, concurrency 1 or 40, no difference, but keepalive off) looks like this: Connection Times (ms) min mean[+/-sd] median max Connect: 2 10 152.8 3 3015 Processing: 2 8 34.7 3 663 Waiting: 2 8 34.7 3 663 Total: 4 19 157.2 6 3222 Percentage of the requests served within a certain time (ms) 50% 6 66% 7 75% 7 80% 7 90% 9 95% 11 98% 223 99% 225 100% 3222 (longest request) I have tried many things: - Apache2 2.2.9 with worker or prefork MPM, no difference (with KeepAliveTimeout 10-15) - Nginx 0.6.32 - various tcp parameters (net.core.somaxconn=3000, net.ipv4.tcp_sack=0, net.ipv4.tcp_dsack=0) - putting the files/DocumentRoot on tmpfs - shorewall on or off (i.e. empty iptables or not) - AllowOverride None is on for /, so no .htaccess checks (verified with strace) - the problem persists whether the webservers are accessed directly or through a Foundry load balancer Kernel is 2.6.32 (Debian Lenny backports), but it occurred with 2.6.26 also. IPv6 is enabled, but not used. Does the issue look familiar to anyone? Help/suggestions are much appreciated. It sounds a bit like a SYN,ACK packet getting lost or ignored.

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• Spring Security: session expiration without redirect to expired-url?

  - by Kdeveloper

  I'm using Spring Security 3.0.2 form based authentication. But I can't figure out how I can configure it so that when a session expires that the request is not redirect to an other page (expired-url) or displays a 'session expires' message. I don't want any redirect or messages, I want that a anonymous session is started just like when a user without a session enters the website. My current configuration: <http> <intercept-url pattern="/login.action*" filters="none"/> <intercept-url pattern="/admin/**" access="ROLE_ADMIN" /> <intercept-url pattern="/**" access="IS_AUTHENTICATED_ANONYMOUSLY"/> <form-login login-page="/login.action" authentication-failure-url="/login.action?error=failed" login-processing-url="/login-handler.action"/> <logout logout-url="/logoff-execute.action" logout-success-url="/logoff.action?done=1"/> <remember-me key="remember-me-security" services-ref="rememberMeServices"/> <session-management > <concurrency-control max-sessions="1" error-if-maximum-exceeded="false" expired-url="/login.action?error=expired.url"/> </session-management> </http>

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• EF 4, POCO and AddOrUpdate

  - by Eric J.

  I'm trying to create a method on an EF 4 POCO repository called AddOrUpdate. The idea is that the business layer can pass in a POCO object and the persistence framework will add the object if it is new (not yet in the database), else will update the database (once SaveChanges() is called) with the new value. This is similar to some other questions I have asked about EF, but I'm only about 80% there in understanding this so please forgive partial duplication. The part I'm missing is how to update the object graph in my ObjectContext/associated ObjectSet for the passed-in business object once I have determined that the business object indeed already exists in the database (and now has been loaded thanks to TryGetObjectByKey). ApplyCurrentValues sounds sort of like what I want, but it only copies scalar values and doesn't seem intended to update the object graph in the ObjectContext/ObjectSet. Because of my particular use case I don't care about concurrency right now. public void AddOrUpdate(BO biz) { object obj; EntityKey ek = Ctx.CreateEntityKey(mySetName, biz); bool found = Ctx.TryGetObjectByKey(ek, out obj); if (found) { // How do I do what this method name implies? Biz is a parent with children. mySet.TellTheSetToUpdateThisObject(biz); } else { mySet.AddObject(biz); } Ctx.DetectChanges(); }

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• How can I beta test web Perl modules under Apache/mod_perl on production web server?

  - by DVK

  We have a setup where most code, before being promoted to full production, is deployed in BETA mode - meaning, it runs in full production environment (using production database - usually production data; and production web server). We call that stage BETA testing. One of the main requirements is that BETA code promotion to production must be a simple "cp" command from beta to production directory - no code/filename changes. For non-web Perl code, achieving seamless BETA test is quite doable (see details here): Perl programs live in a standard location under production root (/usr/code/scripts) with production perl modules living under the same root (/usr/code/lib/perl) The BETA code has 100% same code paths except under beta root (/usr/code/beta/) A special module manipulates @INC of any script based on whether the script was called from /usr/code/scripts or /usr/code/test/scripts, to include beta libraries for beta scripts. This setup works fine up till we need to beta test our web Perl code (the setup is EmbPerl and Apache/mod_perl). The hang-up is as follows: if both a production Perl module and BETA Perl module have the same name (e.g. /usr/code/lib/perl/MyLib1.pm and /usr/code/beta/lib/perl/MyLib1.pm), then mod_perl will only be able to load ONE of these modules into memory - and there's no way we are aware of for a particular web page to affect which version of the module is currently loaded due to concurrency issues. Leaving aside the obvious non-programming solution (get a bloody BETA web server) which for political/organizational reasons is not feasible, is there any way we can somehow hack around this problem in either Perl or mod_perl? I played around with various approaches to unloading Perl modules that %INC has listed, but the problem remains that another user might load a beta page at just the right (or rather wrong) moment and have the beta module loaded which will be used for my production page.

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• How to list column headers of a SQL Server table using sp_help perhaps?

  - by Hamish Grubijan

  Hi, I have a few tables with 70-80 columns in them. I would like to populate them with somewhat random data, unless I will not be able to do so due to key violation, etc. The first step would be simply to get the list of all headers. There seem to be two ways: A) Run select * from table_of_interest; in MSFT SQL Server Management Studio 2008. Now, right-click the result and click "Copy With headers". However, I get zero rows back, and when I try to copy nothing + headers, I get: TITLE: Microsoft SQL Server Management Studio ------------------------------ Value cannot be null. Parameter name: data (System.Windows.Forms) ------------------------------ BUTTONS: OK ------------------------------ This looks like a bug ... anyhow ... there is another way. B) I can run sp_help table_of_interest;. However, I end up getting too much back. I get 7 different tables back but I am only interested in the second one. The columns of the second table are: Column_name | Type | Computed | Length | Prec | Scale | Nullable | TrimTrailingBlanks | FixedLenNullInSource | Collation I might be interested in just a Column_name and Type, but maybe other columns. So ... since sp_help probably runs a bunch of queries ... how do I get under the hood? How can I run the second query AND filter down the number of columns that I am interested in? Many Thanks!

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• LINQ To SQL ignore unique constraint exception and continue

  - by Martin

  I have a single table in a database called Users Users ------ ID (PK, Identity) Username (Unique Index) I have setup a unique index on the Username table to prevent duplicates. I am then enumerating through a collection and creating a new user in the database for each item. What I want to do is just insert a new user and ignore the exception if the unique key constraint is violated (as it's clearly a duplicate record in that case). This is to avoid having to craft where not exists kind of queries. First off, is this going to be any more efficient or should my insert code be checking for duplicates instead? I'm drawn more to the database having that logic as this prevents any other type of client from inserting duplicate data. My other issue is related to LINQ To SQL. I have the following code: public class TestRepo { DatabaseDataContext database = new DatabaseDataContext(); public void Add(string username) { database.Users.InsertOnSubmit(new User() { Username = username }); } public void Save() { database.SubmitChanges(); } } And then I iterate over a collection and insert new users, ignoring any exceptions: TestRepo repo = new TestRepo(); foreach (var name in new string[] { "Tim", "Bob", "John" }) { try { repo.Add(name); repo.Save(); } catch { } } The first time this is run, great I have three users in the table. If I remove the second one and run this code again, nothing is inserted. I expected the first insert to fail with the exception, the second to succeed (as I just removed that item from the DB) and the third to then fail. What seems to be happening is that once the SqlException is thrown (even though the loop continues to iterate) all of the next inserts fail - even when there isn't a row in the table that would cause a unique violation. Can anyone explain this? P.S. The only workaround I could find was to instantiate the repo each time before the insert, then it worked exactly as excepted - indicating that it's something to do with the LINQ To SQL DataContext. Thanks.

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• Atomic UPSERT in SQL Server 2005

  - by rabidpebble

  What is the correct pattern for doing an atomic "UPSERT" (UPDATE where exists, INSERT otherwise) in SQL Server 2005? I see a lot of code on SO (e.g. see http://stackoverflow.com/questions/639854/tsql-check-if-a-row-exists-otherwise-insert) with the following two-part pattern: UPDATE ... FROM ... WHERE <condition> -- race condition risk here IF @@ROWCOUNT = 0 INSERT ... or IF (SELECT COUNT(*) FROM ... WHERE <condition>) = 0 -- race condition risk here INSERT ... ELSE UPDATE ... where will be an evaluation of natural keys. None of the above approaches seem to deal well with concurrency. If I cannot have two rows with the same natural key, it seems like all of the above risk inserting rows with the same natural keys in race condition scenarios. I have been using the following approach but I'm surprised not to see it anywhere in people's responses so I'm wondering what is wrong with it: INSERT INTO <table> SELECT <natural keys>, <other stuff...> FROM <table> WHERE NOT EXISTS -- race condition risk here? ( SELECT 1 FROM <table> WHERE <natural keys> ) UPDATE ... WHERE <natural keys> (Note: I'm assuming that rows will not be deleted from this table. Although it would be nice to discuss how to handle the case where they can be deleted -- are transactions the only option? Which level of isolation?) Is this atomic? I can't locate where this would be documented in SQL Server documentation.

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• Suggestions for doing async I/O with Task Parallel Library

  - by anelson

  I have some high performance file transfer code which I wrote in C# using the Async Programming Model (APM) idiom (eg, BeginRead/EndRead). This code reads a file from a local disk and writes it to a socket. For best performance on modern hardware, it's important to keep more than one outstanding I/O operation in flight whenever possible. Thus, I post several BeginRead operations on the file, then when one completes, I call a BeginSend on the socket, and when that completes I do another BeginRead on the file. The details are a bit more complicated than that but at the high level that's the idea. I've got the APM-based code working, but it's very hard to follow and probably has subtle concurrency bugs. I'd love to use TPL for this instead. I figured Task.Factory.FromAsync would just about do it, but there's a catch. All of the I/O samples I've seen (most particularly the StreamExtensions class in the Parallel Extensions Extras) assume one read followed by one write. This won't perform the way I need. I can't use something simple like Parallel.ForEach or the Extras extension Task.Factory.Iterate because the async I/O tasks don't spend much time on a worker thread, so Parallel just starts up another task, resulting in potentially dozens or hundreds of pending I/O operations; way too much! You can work around that by Waiting on your tasks, but that causes creation of an event handle (a kernel object), and a blocking wait on a task wait handle, which ties up a worker thread. My APM-based implementation avoids both of those things. I've been playing around with different ways to keep multiple read/write operations in flight, and I've managed to do so using continuations that call a method that creates another task, but it feels awkward, and definitely doesn't feel like idiomatic TPL. Has anyone else grappled with an issue like this with the TPL? Any suggestions?

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• The LoadLibraryA method returns error code 1114 (ERROR_DLL_INIT_FAILED) after more than 1000 cycles

  - by Javier

  Hi, I'm programing on C++, I'm using Visual Studio 2008, Windows XP, and I have the following problem: My application, that is a DLL that can be used from Python, loads an external dll, uses the required methods, and then unloads this external Dll. It's working properly, but after more than 1000 cycles the method "LoadLibraryA" returns a NULL reference. The main steps are: HINSTANCE h = NULL; h = LoadLibraryA(dllfile.c_str()); DWORD dw = GetLastError(); The error got is: ERROR_DLL_INIT_FAILED 1114 (0x45A) A dynamic link library (DLL) initialization routine failed. The Dll is unloaded by using the following: FreeLibrary(mDLL); mDLL = NULL; Where mDLL is defined like this: HINSTANCE mDLL; First alternative tried: Just load the Dll only once, and unloaded it when the application ends. This fix the problem but introduces a new one. When the application ends, instead of first executing the DllMain method of my applicaion, wich unloads the external DLL, is executing first the DllMain method of the other Dll. This cause the following error because my application is trying to unload a Dll that was unload by itself previously. "Unhandled exception at 0x04a00d07 (DllName.DLL) in Python.exe: 0xC0000005: Access violation reading location 0x0000006b". Any suggestion will be welcomed. Thanks in advance. Regards.

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• How to override ATTR_DEFAULT_IDENTIFIER_OPTIONS in Models in Doctrine?

  - by user309083

  Here someone explained that setting a 'primary' attribute for any row in your Model will override Doctrine_Manager's ATTR_DEFAULT_IDENTIFIER_OPTIONS attribute: http://stackoverflow.com/questions/2040675/how-do-you-override-a-constant-in-doctrines-models This works, however if you have a many to many relation whereby the intermediate table is created, even if you have set both columns in the intermediate to primary an error still results when Doctrine tries to place an index on the nonexistant 'id' column upon table creation. Here's my code: //Bootstrap // set the default primary key to be named 'id', integer, 4 bytes Doctrine_Manager::getInstance()->setAttribute( Doctrine_Core::ATTR_DEFAULT_IDENTIFIER_OPTIONS, array('name' => 'id', 'type' => 'integer', 'length' => 4)); //User Model class User extends Doctrine_Record { public function setTableDefinition() { $this->setTableName('users'); } public function setUp() { $this->hasMany('Role as roles', array( 'local' => 'id', 'foreign' => 'user_id', 'refClass' => 'UserRole', 'onDelete' => 'CASCADE' )); } } //Role Model class Role extends Doctrine_Record { public function setTableDefinition() { $this->setTableName('roles'); } public function setUp() { $this->hasMany('User as users', array( 'local' => 'id', 'foreign' => 'role_id', 'refClass' => 'UserRole' )); } } //UserRole Model class UserRole extends Doctrine_Record { public function setTableDefinition() { $this->setTableName('roles_users'); $this->hasColumn('user_id', 'integer', 4, array('primary'=>true)); $this->hasColumn('role_id', 'integer', 4, array('primary'=>true)); } } Resulting error: SQLSTATE[42000]: Syntax error or access violation: 1072 Key column 'id' doesn't exist in table. Failing Query: "CREATE TABLE roles_users (user_id INT UNSIGNED NOT NULL, role_id INT UNSIGNED NOT NULL, INDEX id_idx (id), PRIMARY KEY(user_id, role_id)) ENGINE = INNODB". Failing Query: CREATE TABLE roles_users (user_id INT UNSIGNED NOT NULL, role_id INT UNSIGNED NOT NULL, INDEX id_idx (id), PRIMARY KEY(user_id, role_id)) ENGINE = INNODB I'm creating my tables using Doctrine::createTablesFromModels();

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• code review: Is it subjective or objective(quantifiable) ?

  - by Ram

  I am putting together some guidelines for code reviews. We do not have one formal process yet, and trying to formalize it. And our team is geographically distributed We are using TFS for source control (used it for tasks/bug tracking/project management as well, but migrated that to JIRA) with VS2008 for development. What are the things you look for when doing a code review ? These are the things I came up with Enforce FXCop rules (we are a Microsoft shop) Check for performance (any tools ?) and security (thinking about using OWASP- code crawler) and thread safety Adhere to naming conventions The code should cover edge cases and boundaries conditions Should handle exceptions correctly (do not swallow exceptions) Check if the functionality is duplicated elsewhere method body should be small(20-30 lines) , and methods should do one thing and one thing only (no side effects/ avoid temporal coupling -) Do not pass/return nulls in methods Avoid dead code Document public and protected methods/properties/variables What other things do you generally look for ? I am trying to see if we can quantify the review process (it would produce identical output when reviewed by different persons) Example: Saying "the method body should be no longer than 20-30 lines of code" as opposed to saying "the method body should be small" Or is code review very subjective ( and would differ from one reviewer to another ) ? The objective is to have a marking system (say -1 point for each FXCop rule violation,-2 points for not following naming conventions,2 point for refactoring etc) so that developers would be more careful when they check in their code.This way, we can identify developers who are consistently writing good/bad code.The goal is to have the reviewer spend about 30 minutes max, to do a review (I know this is subjective, considering the fact that the changeset/revision might include multiple files/huge changes to the existing architecture etc , but you get the general idea, the reviewer should not spend days reviewing someone's code) What other objective/quantifiable system do you follow to identify good/bad code written by developers? Book reference: Clean Code: A handbook of agile software craftmanship by Robert Martin

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• WinForms DataGridView - update database

  - by Geo Ego

  I know this is a basic function of the DataGridView, but for some reason, I just can't get it to work. I just want the DataGridView on my Windows form to submit any changes made to it to the database when the user clicks the "Save" button. I populate the DataGridView according to a function triggered by a user selection in a DropDownList as follows: using (SqlConnection con = new SqlConnection(conString)) { con.Open(); SqlDataAdapter ruleTableDA = new SqlDataAdapter("SELECT rule.fldFluteType AS [Flute], rule.fldKnife AS [Knife], rule.fldScore AS [Score], rule.fldLowKnife AS [Low Knife], rule.fldMatrixScore AS [Matrix Score], rule.fldMatrix AS [Matrix] FROM dbo.tblRuleTypes rule WHERE rule.fldMachine_ID = '1003'", con); DataSet ruleTableDS = new DataSet(); ruleTableDA.Fill(ruleTableDS); RuleTable.DataSource = ruleTableDS.Tables[0]; } In my save function, I basically have the following (I've trimmed out some of the code around it to get to the point): using (SqlDataAdapter ruleTableDA = new SqlDataAdapter("SELECT rule.fldFluteType AS [Flute], rule.fldKnife AS [Knife], rule.fldScore AS [Score], rule.fldLowKnife AS [Low Knife], rule.fldMatrixScore AS [Matrix Score], rule.fldMatrix AS [Matrix] FROM dbo.tblRuleTypes rule WHERE rule.fldMachine_ID = '1003'", con)) { SqlCommandBuilder commandBuilder = new SqlCommandBuilder(ruleTableDA); DataTable dt = new DataTable(); dt = RuleTable.DataSource as DataTable; ruleTableDA.Fill(dt); ruleTableDA.Update(dt); } Okay, so I edited the code to do the following: build the commands, create a DataTable based on the DataGridView (RuleTable), fill the DataAdapter with the DataTable, and update the database. Now ruleTableDA.Update(dt) is throwing the exception "Concurrency violation: the UpdateCommand affected 0 of the expected 1 records."

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• Can I tell Castle Windsor to create a component in a separate AppDomain?

  - by Michael L Perry

  I've created a multi-threaded service that uses Castle Windsor to create components to run on separate threads. I Resolve an component by name with parameters for each thread. I'm running into concurrency problems with a 3rd party library used by the components. I suspect that isolating those components in separate AppDomains will resolve the problem. Is there a way to have Resolve create the component using a different AppDomain? private ActivityThread NewActivityThread(ActivityInstance activityInstance) { // Set up the creation arguments. System.Collections.IDictionary arguments = new Dictionary<string, string>(); activityInstance.Parameters.ForEach(p => arguments.Add(p.Name, p.Value)); // Get the activity handler from the container. IActivity activity = Program.Container.Resolve<IActivity>(activityInstance.Name, arguments); // Create a thread for the activity. ActivityThread thread = new ActivityThread(activity, activityInstance, _nextActivityID++); return thread; } public ActivityThread(IActivity activity, ActivityInstance instance, int id) { _activity = activity; _instance = instance; _id = id; } public void Start() { if (_thread == null) { // Create a new thread to run this activity. _thread = new Thread(delegate() { _activity.Run(); }); _thread.Name = _activity.ToString(); _thread.SetApartmentState(ApartmentState.STA); _thread.Start(); } }

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• Problem calling Request using RequestBuilder

  - by Tushar Ahirrao

  Hi My Code is String url = "http: gd.geobytes.com/gd?after=-1&variables=GeobytesCountry,GeobytesCity"; RequestBuilder builder = new RequestBuilder(RequestBuilder.GET, URL .encode(url)); try { Request request = builder.sendRequest(null, new RequestCallback() { public void onError(Request request, Throwable exception) { Couldn't connect to server (could be timeout, SOP violation, etc.) } public void onResponseReceived(Request request, Response response) { System.out.println(response.getText() + "Response"); if (200 == response.getStatusCode()) { Window.alert(response.getText()); } else { Window.alert(response.getText()); } } }); } catch (RequestException e) { e.printStackTrace(); } i receive following error com.google.gwt.http.client.RequestPermissionException: The URL http://gd.geobytes.com/gd?after=-1&variables=GeobytesCountry,GeobytesCity is invalid or violates the same-origin security restriction at com.google.gwt.http.client.RequestBuilder.doSend(RequestBuilder.java:378) at com.google.gwt.http.client.RequestBuilder.sendRequest(RequestBuilder.java:254) at com.ip.client.IpAddressTest.onModuleLoad(IpAddressTest.java:46) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at com.google.gwt.dev.shell.ModuleSpace.onLoad(ModuleSpace.java:369) at com.google.gwt.dev.shell.OophmSessionHandler.loadModule(OophmSessionHandler.java:185) at com.google.gwt.dev.shell.BrowserChannelServer.processConnection(BrowserChannelServer.java:380) at com.google.gwt.dev.shell.BrowserChannelServer.run(BrowserChannelServer.java:222) at java.lang.Thread.run(Thread.java:619) Caused by: com.google.gwt.http.client.RequestException: (NS_ERROR_DOM_BAD_URI): Access to restricted URI denied

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• How do I eliminate Error 3002?

  - by Andrew

  Say I have the following table definitions in SQL Server 2008: CREATE TABLE Person (PersonId INT IDENTITY NOT NULL PRIMARY KEY, Name VARCHAR(50) NOT NULL, ManyMoreIrrelevantColumns VARCHAR(MAX) NOT NULL) CREATE TABLE Model (ModelId INT IDENTITY NOT NULL PRIMARY KEY, ModelName VARCHAR(50) NOT NULL, Description VARCHAR(200) NULL) CREATE TABLE ModelScore (ModelId INT NOT NULL REFERENCES Model (ModelId), Score INT NOT NULL, Definition VARCHAR(100) NULL, PRIMARY KEY (ModelId, Score)) CREATE TABLE PersonModelScore (PersonId INT NOT NULL REFERENCES Person (PersonId), ModelId INT NOT NULL, Score INT NOT NULL, PRIMARY KEY (PersonId, ModelId), FOREIGN KEY (ModelId, Score) REFERENCES ModelScore (ModelId, Score)) The idea here is that each Person may have only one ModelScore per Model, but each Person may have a score for any number of defined Models. As far as I can tell, this SQL should enforce these constraints naturally. The ModelScore has a particular "meaning," which is contained in the Definition. Nothing earth-shattering there. Now, I try translating this into Entity Framework using the designer. After updating the model from the database and doing some editing, I have a Person object, a Model object, and a ModelScore object. PersonModelScore, being a join table, is not an object but rather is included as an association with some other name (let's say ModelScorePersonAssociation). The mapping details for the association are as follows: - Association - Maps to PersonModelScore - ModelScore ModelId : Int32 <=> ModelId : int Score : Int32 <=> Score : int - Person PersonId : Int32 <=> PersonId : int On the right-hand side, the ModelId and PersonId values have primary key symbols, but the Score value does not. Upon compilation, I get: Error 3002: Problem in Mapping Fragment starting at line 5190: Potential runtime violation of table PersonModelScore's keys (PersonModelScore.ModelId, PersonModelScore.PersonId): Columns (PersonModelScore.PersonId, PersonModelScore.ModelId) are mapped to EntitySet ModelScorePersonAssociation's properties (ModelScorePersonAssociation.Person.PersonId, ModelScorePersonAssociation.ModelScore.ModelId) on the conceptual side but they do not form the EntitySet's key properties (ModelScorePersonAssociation.ModelScore.ModelId, ModelScorePersonAssociation.ModelScore.Score, ModelScorePersonAssociation.Person.PersonId). What have I done wrong in the designer or otherwise, and how can I fix the error? Many thanks!

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• Javascript/CSS rollover menus are patented and subject to licensing?

  - by Scott B

  Very interesting finding that a client brought to my attention today regarding javascript style rollover menus. They got a call from their legal dept that they need to change the manner in which their rollover menu is activated (at the risk of having to pay license to continue using the navigation technique). Its no April fools joke, apparently this is really happening. Apparently a company named Webvention LLC has obtained enforcement rights to a patent, U.S. Patent No. 5,251,294 - "Accessing, assembling, and using bodies of Information." A menu link, that when rolled over, expands to show a list of categorized, related links. Dropdown menus and slide-out menus are examples of this patented navigational methodology. A key component of this patent is that the dropdown/slide-out action must be initiated by a rollover or mouseover event. If the dropdown/slide-out action is initiated by any other event, such as a mouse-click event, then this behavior is not in violation of the patent. Anyone ever heard of this or know of the validity of its claims? Website is here: http://www.webventionllc.com/

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