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• Javascript performance issue

  - by Daniel

  Hello, I've built a top menu based on superfish, but the amount of displayed items in the menu is huge. And there is also alot of jquery on the top menu. Now to the problem, everytime I load any page that has the menu, the browser(ie7) feels like it looks it locks it self for about 1-2 seconds while the page is being loaded. I'm sure that the top menu is the issue, and I would like to improve the performance of the page.(besides removing the menu and removing the menu items) I've used firebug to see which calls take most of the times, and I the calls are standard jquery or superfish. The top menu is a ascx control. Are they any good ways to let the page load first and the menu later or any other goods ideas to improve the performance?

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• What is a good motivating example for dataflow concurrency?

  - by Alex Miller

  I understand the basics of dataflow programming and have encountered it a bit in Clojure APIs, talks from Jonas Boner, GPars in Groovy, etc. I know it's prevalent in languages like Io (although I have not studied Io). What I am missing is a compelling reason to care about dataflow as a paradigm when building a concurrent program. Why would I use a dataflow model instead of a mutable state+threads+locks model (common in Java, C++, etc) or an actor model (common in Erlang or Scala) or something else? In particular, while I know of library support in the languages above (and Scala and Ruby), I don't know of a single program or library that is a poster child user of this model. Who is using it? Why do they find it better than the other models I mentioned?

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• Multiple complete HTTP requests stuck in TCP CLOSE_WAIT state

  - by Sean Owen

  I have a Java and Tomcat-based server application which initiates many outbound HTTP requests to other web sites. We use Jakarta's HTTP Core/Client libraries, very latest versions. The server locks up at some point since all its worker threads are stuck trying to close completed HTTP connections. Using 'lsof' reveals a bunch of sockets stuck in TCP CLOSE_WAIT state. This doesn't happen for all, or even most connections. In fact, I saw it before and resolved it by making sure to set the Connection: Close response header. So that makes me think it may be bad behavior of remote servers. It may have come up again since I moved the app to a totally new service provider -- different OS, network situation. But, I am still at a loss as to what I could do, if anything, to work around this. Some poking around on the internet didn't turn up anything I'm not already doing. Just thought I'd ask if anyone has seen and solved this?

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• Any way to select without causing locking in MySQL?

  - by Shore

  Query: SELECT COUNT(online.account_id) cnt from online; But online table is also modified by an event, so frequently I can see lock by running show processlist. Is there any grammar in MySQL that can make select statement not causing locks? And I've forgotten to mention above that it's on a MySQL slave database. After I added into my.cnf:transaction-isolation = READ-UNCOMMITTED the slave will meet with error: Error 'Binary logging not possible. Message: Transaction level 'READ-UNCOMMITTED' in InnoDB is not safe for binlog mode 'STATEMENT'' on query So, is there a compatible way to do this?

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• Why use SyncLocks in .NET for simple operations when Interlocked class is available?

  - by rwmnau

  I've been doing simple multi-threading in VB.NET for a while, and have just gotten into my first large multi-threaded project. I've always done everything using the Synclock statement because I didn't think there was a better way. I just learned about the Interlocked Class - it makes it look as though all this: Private SomeInt as Integer Private SomeInt_LockObject as New Object Public Sub IntrementSomeInt Synclock SomeInt_LockObject SomeInt += 1 End Synclock End Sub Can be replaced with a single statement: Interlocked.Increment(SomeInt) This handles all the locking internally and modifies the number. This would be much simpler than writing my own locks for simple operations (longer-running or more complicated operations obviously still need their own locking). Is there a reason why I'd rolling my own locking, using dedicated locking objects, when I can accomplish the same thing using the Interlocked methods?

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• SQLite multi process access

  - by Nicolas

  Hello, We are using SQLite in a multi processes and multi threaded application. The SQLite database files are encrypted using the embedded SQLite encryption. The FAQ states that SQLite should be able to manage multi process accesses using locks mechanism. We are experiencing a strange problem: When many threads are accessing the same database file, sometime constrains violations occur, more specifically - a field with a unique constrain is getting duplicate values after calling "insert or replace" statement. It happens quite often now, that we are using the encryption. Before we started using SQLite encryption we did not notice such a behavior. Are there any specific known issues with this?

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• Java: opening and reading from a file without locking it.

  - by rogue780

  I need to be able to mimic 'tail -f' with Java. I'm trying to read a log file as it's being written by another process, but when I open the file to read it, it locks the file and the other process can't write to it anymore. Any help would be greatly appreciated! Here is the code that I'm using currently: public void read(){ Scanner fp = null; try{ fp = new Scanner(new FileReader(this.filename)); fp.useDelimiter("\n"); }catch(java.io.FileNotFoundException e){ System.out.println("java.io.FileNotFoundException e"); } while(true){ if(fp.hasNext()){ this.parse(fp.next()); } } }

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• Guidelines of when to use locking

  - by miguel

  I would like to know if there are any guidelineswhich a developer should follow as to when (and where) to place locks. For instance: I understand that code such as this should be locked, to avoid the possibility of another thread changing the value of SomeHeapValue unexpectedly. class Foo { public SomeHeapObject myObject; public void DoSummat(object inputValue_) { myObject.SomeHeapValue = inputValue_; } } My question is, however, how deep does one go with the locking? For instance, if we have this code: class Foo { public SomeHeapObject myObject; public void DoSummat(object inputValue_) { myObject.SomeHeapValue = GetSomeHeapValue(); } } Should we lock in the DoSummat(...) method, or should we lock in the GetSomeHeapValue() method? Are there any guidelines that you all keep in mind when strcturing multi-threaded code?

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• Obtain Update Table Lock at start of Stored Procedure in SQL Server

  - by Jim Hurne

  I'm writing a SQL Server stored procedure in which I want to lock a table for update before executing the body of the stored procedure. I don't want to prevent other processes from reading the table, but I do want to prevent other processes updating the table. Here is my first attempt: CREATE PROCEDURE someProcedure BEGIN SET TRANSACTION ISOLATION LEVEL READ COMITTED BEGIN TRANSANCTION SELECT COUNT(*) FROM TheTable WITH (UPDLOCK, TABLOCK) -- Pause procedure so that we can view the locks with sp_lock WAITFOR DELAY '00:15' -- Do stuff COMMIT END When I execute the stored procedure, and invoke sp_lock, I see that the table is indeed locked. However, it's locked with an Exclusive lock instead of an update lock: spid | dbid | ObjId | IndId | Type | Resource | Mode | Status ------------------------------------------------------------------ 63 | 10 | 233208031 | 0 | TAB | | X | GRANT How can I get an update (U) lock instead?

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• What to monitor on MSSQL Server

  - by user361434

  Hi all I have been asked to monitor MSSQL Server (2005 & 2008) and am wondering what are good metrics to look at? I can access WMI counters but am slightly lost as to how much depth is going to be useful. Currently I have on my list: user connections logins per second latch waits per second total latch wait time dead locks per second errors per second Log and data file sizes I am looking to be able to monitor values that will indicate a degradation of performance on the machine or a potential serious issue. To this end I am also wondering at what values some of these things would be considered normal vs problematic? As I reckon it would probably be a really good question to have answered for the general community I thought i'd court some of you DBA experts out there (I am certainly not one of them!) Apologies if a rather open ended question. Ry

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• Concurency issues with scheduling app

  - by Sazug

  Our application needs a simple scheduling mechanism - we can schedule only one visit per room for the same time interval (but one visit can be using one or more rooms). Using SQL Server 2005, sample procedure could look like this: CREATE PROCEDURE CreateVisit @start datetime, @end datetime, @roomID int AS BEGIN DECLARE @isFreeRoom INT BEGIN TRANSACTION SELECT @isFreeRoom = COUNT(*) FROM visits V INNER JOIN visits_rooms VR on VR.VisitID = V.ID WHERE @start = start AND @end = [end] AND VR.RoomID = @roomID IF (@isFreeRoom = 0) BEGIN INSERT INTO visits (start, [end]) VALUES (@start, @end) INSERT INTO visits_rooms (visitID, roomID) VALUES (SCOPE_IDENTITY(), @roomID) END COMMIT TRANSACTION END In order to not have the same room scheduled for two visits at the same time, how should we handle this problem in procedure? Should we use SERIALIZABLE transaction isolation level or maybe use table hints (locks)? Which one is better?

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• Delete all records that have no foreign key constraints

  - by Rodney Burton

  I have a SQL 2005 table with millions of rows in it that is being hit by users all day and night. This table is referenced by 20 or so other tables that have foreign key constraints. What I am needing to do on a regular basis is delete all records from this table where the "Active" field is set to false AND there are no other records in any of the child tables that reference the parent record. What is the most efficient way of doing this short of trying to delete each one at a time and letting it cause SQL errors on the ones that violate constraints? Also it is not an option to disable the constraints and I cannot cause locks on the parent table for any significant amount of time.

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• When Does the File Download Dialog Open? - HTML, Javascript

  - by sahs-i-muhterem

  Hello, I have a html page, and when I click a file link on the page, the file download dialog pops up, and this file dialog locks the page. I mean without selecting one of the choices(Open, Save, Cancel) I can't do anything on the page (which is normal). What I need is if javascript can check whether the page is locked or not. (or whether the file dialog is popped?) p.s. don't say "put an onclick event to the link", because the server may respond very slowly (like 30 seconds after clicking)

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• PHP Sessions - Locking and Sharing questions

  - by Nuno Peralta

  Hi, I would like to know if it is possible to read $_SESSION attributes without locking it. Currently, session_start() locks SESSION, that means other PHP processes will wait until it is unlocked. But, some processes just want to get some $_SESSION variables, not to write on them. Is that possible to implement some function like session_get(string $id) which doesn't lock SESSION? Also, it is possible to share SESSIONs between browsers, once the user is logged in the same account, for example, using session_id('shared_vars_of_'.$userid). But, is that secure? Is this discouraged? Thanks, Nuno

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• Unable to delete file locked by same process -- weird!

  - by user300266

  I have an application written in PHP that uses a COM dll written in C#. The dll creates an image file by combining two other image files. The PHP script then takes over to do the housekeeping tasks of deleting the two source files and renaming the resulting combined file. The problem is the PHP script can't delete one of the source files because it's locked. The weird thing is that the process that has it locked is itself which in this case is the Apache Web Server. I have tried altering the C# dll to dispose of all bitmap and graphics objects prior to exiting, and yet the lock remains. My question is, what can I do to get the dll to let go and release the file locks. This is very frustrating.

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• Debugging kernel hang

  - by l.thee.a

  I am trying to run an app which is using a kernel mode driver. System locks up every hour and the only way to recover it is a hard reset. Sysrq stops responding, telnet sessions hang and there are no error messages of any kind. Unfortunately the board does not have ejtag support. I have been trying to isolate it functionally, but this is like looking for a needle in a hay stack. Any suggestions? PS: This is a mips linux system (2.6.31).

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• Determining threshold for lock escalation

  - by Davin

  I have a table with around 2.5 millions records and will be updating around 700k of them and want to update these while still allowing other users to see the data. My update statement looks something like this: UPDATE A WITH (UPDLOCK,ROWLOCK) SET A.field = B.field FROM Table_1 A INNER JOIN Table2 B ON A.id = B.id WHERE A.field IS NULL AND B.field IS NOT NULL I was wondering if there was any way to work out at what point sql server will escalate a lock placed on an update statement (as I don't want the whole table to be locked)? I don't have permissions to run a server trace to see how the locks are being applied, so is there any other way of knowing at what point the lock will be escalated to cover the whole table? Thanks!

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• Are there any e-commerce websites that use NoSQL databases

  - by Saif Bechan

  I have read a lot lately about 'NoSQL' databases such as CouchDB, MongoDB etc. Most of the websites I have seen using this are mainly text based websites such as The New York Times and Source forge. I was wondering if you could apply this to websites where payment is a huge issue. I am thinking of the following issues: How well can you secure the data Do these system provide an easy backup/restore machanism How are transactions handled commit/rollback I have read the following articles that cover some aspects: Can I do transactions and locks in CouchDB? Pros/Cons of document based database vs relational database In these posts the aspect of transactions if covered. However the questions of security and backups is not covered. Can someone shed some light on this subject? And if possible, does anyone know of some e-commerce websites that have successfully implemented the document based database.

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• WPF update binding in a background thread

  - by Mark

  I have a control that has its data bound to a standard ObservableCollection, and I have a background task that calls a service to get more data. I want to, then, update my backing data behind my control, while displaying a "please wait" dialog, but when I add the new items to the collection, the UI thread locks up while it re-binds and updates my controls. Can I get around this so that my animations and stuff keep running on my "please wait" dialog? Or at least give the "appearance" to the user that its not locked up?

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• Trying to right click on code in VS2008 causes lockup.

  - by Adam Haile

  Working on a Win32 DLL using Visual Studio 2008 SP1 and, since yesterday, whenever I try to right click on code, to go to a variable definition for example, VS completely locks up and I have to manually kill the process. To make it even weirder, whenever this happens the devenv.exe process uses exactly 25% of the CPU. And I mean exactly, never 24%, never 26%, always 25% Also, I've run ProcMon to see if devenv is actually doing something, but it's doing absolutely nothing external of the process. No disk, network, registry access. Nothing. This is getting really aggravating because I have a large code base to deal with and the only other way of jumping to the definition is to first search for it. Has anyone run into a similar issue? And, better yet, know a fix?

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• c# multi threaded file processing

  - by user177883

  There is a folder that contains 1000 of small text files. I aim to parse and process all of them while more files are being populated in to the folder. My intention is to multithread this operation as the single threaded prototype took 6 minutes to process 1000 files. I like to have reader and writer thread(s) as following : while the reader thread(s) are reading the files, I d like to have writer thread(s) to process them. Once the reader is started reading a file, I d like to mark it as being processed, such as by renaming it, once it s read, rename it to completed. How to approach such multithreaded application ? Is it better to use a distributed hash table or a queue? Which data structure to use that would avoid locks? Would you have a better approach to this scheme that you like to share?

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• Mutex takes a long while to unlock

  - by l.thee.a

  I have two threads. First one is something like this: while(1) { pthread_mutex_lock(&mutex); //DO WORK pthread_mutex_unlock(&mutex); pthread_yield(); } The second one locks the mutex on user event, change some settings and unlocks. Thread one does ~ 200 iterations a second. However on occasion it takes the second thread up to 3 seconds to get active (to unlock the mutex). How do I ensure faster response?

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• Google Calendar API DoS prevention

  - by Don

  Hi, It appears that the Google calendar API effectively locks you out if you create and delete a few (less than 10) calendars within a short space of time. This has made it basically impossible for me to test my app, because it creates/deletes a calendar for each user that is added/removed from the app. Currently, I'm "working around" this issue by creating a new Google account each time I get locked out of the Calendar API. Clearly, this solution is less than satisfactory. Is there any way I can avoid this over-zealous DoS prevention? Thanks, Don

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• How to index a date column with null values?

  - by Heinz Z.

  How should I index a date column when some rows has null values? We have to select rows between a date range and rows with null dates. We use Oracle 9.2 and higher. Options I found Using a bitmap index on the date column Using an index on date column and an index on a state field which value is 1 when the date is null Using an index on date column and an other granted not null column My thoughts to the options are: to 1: the table have to many different values to use an bitmap index to 2: I have to add an field only for this purpose and to change the query when I want to retrieve the null date rows to 3: locks tricky to add an field to an index which is not really needed What is the best practice for this case? Thanks in advance Some infos I have read: Oracle Date Index When does Oracle index null column values?

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• MySQL Locking Up

  - by Ian

  I've got a innodb table that gets a lot of reads and almost no writes (like, 1 write for every 400,000 reads approx). I'm running into a pretty big problem though when I do INSERT into the table. MySQL completely locks up. It uses 100% cpu, and every single other table (in other databases even) have their statuses set to "Locked" until the INSERT is done. This is a big problem because MySQL stays locked up for up to 4 minutes. I'm using version 5.1.47 (rpm from mysql.com). Any ideas?

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