I am trying to debug a performance issue in an ASP.NET application using .NET 4.5, EF5 (with a 2nd level cache and lazy loaded navigation properties) and SQL Server 2014. We are experiencing a number of wait locks in the SQL server. When I look at the locking transactions, they contain a very quick UPDATE, and then a very large SELECT. The UPDATE is ostensibly a necessary one, but I am confused as to why the SELECT is being run in the same transaction (and why anything is being selected at all). The fundamental issue is that the table referenced in the UPDATE statement is locked for the duration of the SELECT statement.
We use repository pattern for getting data from the db, and DbContext.SaveChanges() for committing changes. I cannot figure out how it is possible that EF produces a transaction where there is both a write and a read, and I am not getting relevant results when I try to search Google.
We have a number of interfaces into the system, and a couple of console applications working on the database as well, but they all go through the same setup/versions of .NET and EF.
I figure that it must be through SaveChanges, since this is (AFAIK) the only time that things are written to the database.
Does anyone here have a hint as to how these locking transactions might be produced?
The fundamental issue is that the table referenced in the UPDATE
statement is locked for the duration of the SELECT statement.
The answer is in your question:
the SELECT is being run in the same transaction
X lock is always held until the end of the transaction, i.e. until it commits or rolls back. So if after your quick update there is a long select, all that update locked in your table remains locked until your select ends.
You can separate your update and select if your business rules permit, you can add an appropriate index on the updated table to lock only some rows and not the whole table, or you can optimize your select to execute faster.
Related
Why would the TrackedMessages_Copy_BizTalkMsgBoxDb SQL Agent job start failing with "Query processor could not produce a query plan"?
Query processor could not produce a query plan because of the hints defined in this query. Resubmit the query without specifying any hints and without using SET FORCEPLAN. [SQLSTATE 42000] (Error 8622).
Our SQL guys are talking about amending the stored proc. but we've told them to treat BizTalk db's as a black box
It should go without saying, but before anything, make sure to backup your databases. In fact, if your regular backup jobs are running, you may be able to restore a backup and compare things to when it was working on this server. That said -
Check the SQL Agent Job to make sure no additional steps have been added/no plan has been forced/no hints are being used; it should just have one step called 'Purge' that calls the procedure below with the DB server and DTA database name as parameters.
Check the procedure (BizTalkMsgBoxDb.dbo.bts_CopyTrackedMessagesToDTA) to make sure it hasn't been altered.
If this is a production or otherwise sensitive box, back up the DBs and restore them to a local dev environment before proceeding!
If this is not production, see if you can run the procedure (perhaps in a transaction that you rollback) directly in SSMS. See if you get any better errors. Add print statements to see if you can find out exactly where it's getting conflicting hints.
If the procedure won't run, consider freeing the procedure cache (DBCC FREEPROCCACHE) and seeing if the procedure will run.
If it runs in your dev environment from a backup, you may have to start looking at server/database settings. I can't think of which ones off the top of my head that would cause this error though.
For what it's worth, well intentioned DBAs break BizTalk frequently. They decide that an index is missing or not properly covering, or that security could be improved, or that the database should be treated like other databases they administer are treated. I've seen DBAs do really silly things to the BizTalk databases that get very hard to diagnose.
Did you try updating the statistics on the database table referenced by the stored procedure (which is run by the SQL Server Agent job? The query planner uses those to decide how best to execute your SQL.
I have a QML application which user intract with. There is a timer that listen to server for work order then insert all info to SQLite db in application.Also user make change on data (update,delete etc...) in SQLite.
My question is , How to prevent multi operation on SQLite table. Only one operation must take effect on SQLite(select,delete,insert,update....) I don't know but , Can Mutex.lock structure use for this. Or Is there a something wrong with multiple operation on SQLite
First thing you should do is read up on SQLite locking, they have a section in the docs about it: https://www.sqlite.org/lockingv3.html
The summarisation is that SQLite does locking on modifications such as an insert or update, but won't create a lock when reading. However if a lock exists whilst a modification is in progress the read won't be able to access the database.
I wouldn't worry too much about locking on reading, the state should be fine to be shared at that stage.
I use the sqlite database schema version.
PRAGMA schema_version;
It helps me control upgrades and prevents user from modifying the schema and then reporting a flood of irreproducible bugs.
However, I find the version increments far more often that I expect.
" It is incremented by SQLite whenever the database schema is modified (by creating or dropping a table or index). " http://www.sqlite.org/pragma.html#pragma_schema_version
In particular when I simply connect and disconnect from sqlitestudio, even though I do not change the schema in any way.
Is there any way of preventing this happening ( or at least understanding what is going on ) ?
I am currently testing Tridion 2011 and am having problems creating multimedia components with uploaded content (as opposed to external).
I fill out the title, schema, multimedia type, select a file from my system then click save. I get a Saving item... information message then approximately 30 seconds later I will receive a The wait operation timed out message.
There doesn't appear to be any error messages in the C:\Program Files (x86)\Tridion\log directory. Looking at the event viewer I see the following information relating to the save action
Unable to save Component (tcm:4-738361).
The wait operation timed out
Error Code:
0x8004033F (-2147220673)
Call stack:
System.Data.SqlClient.SqlConnection.OnError(SqlException,Boolean,Action`1)
System.Data.SqlClient.SqlInternalConnection.OnError(SqlException,Boolean,Action`1)
System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject,Boolean,Boolean)
System.Data.SqlClient.TdsParser.TryRun(RunBehavior,SqlCommand,SqlDataReader,BulkCopySimpleResultSet,TdsParserStateObject,Boolean&)
System.Data.SqlClient.SqlCommand.FinishExecuteReader(SqlDataReader,RunBehavior,String)
System.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior,RunBehavior,Boolean,Boolean,Int32,Task&,Boolean)
System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior,RunBehavior,Boolean,String,TaskCompletionSource`1,Int32,Task&,Boolean)
System.Data.SqlClient.SqlCommand.InternalExecuteNonQuery(TaskCompletionSource`1,String,Boolean,Int32,Boolean)
System.Data.SqlClient.SqlCommand.ExecuteNonQuery()
Tridion.ContentManager.Data.AdoNet.Sql.SqlDatabaseUtilities.SetBinaryContent(Int32,Stream)
Tridion.ContentManager.Data.AdoNet.ContentManagement.ItemDataMapper.Tridion.ContentManager.Data.ContentManagement.IItemDataMapper.SetBinaryContent(Stream,TcmUri)
Tridion.ContentManager.ContentManagement.RepositoryLocalObject.SetBinaryContent(BinaryContent)
Tridion.ContentManager.ContentManagement.Component.OnSaved(SaveEventArgs)
Tridion.ContentManager.IdentifiableObject.Save(SaveEventArgs)
Tridion.ContentManager.ContentManagement.VersionedItem.Save(Boolean)
Tridion.ContentManager.ContentManagement.VersionedItem.Save()
Tridion.ContentManager.BLFacade.ContentManagement.VersionedItemFacade.UpdateAndCheckIn(UserContext,String,Boolean,Boolean)
XMLState.Save
Component.Save
I already have my timeout settings in the Content Manager Snap-In set to high values (more than 10 minutes) due to another issue.
The BINARIES table in the Content Manage Database is 25GB if that helps.
Any ideas? Thanks.
Edit 1
Following suggestions from Bart Koopman, my DBA has rebuilt the indexes but does not reckon the Transaction log has any impact on performance. The problem persists.
Edit 2
I have just found more details of the error
Unable to save Component (tcm:0-0-0).
Timeout expired.
The timeout period elapsed prior to completion of the operation or the server is not responding.
A database error occurred while executing Stored Procedure "EDA_ITEMS_UPDATEBINARYCONTENT".EDA_ITEMS_UPDATEBINARYCONTENT
After taking a look at this procedure it looks like the following statement could be the root cause
SELECT 1 FROM BINARIES WHERE ID = #iBINARY_ID AND CONTENT IS NULL
I execute it manually with #iBINARY_ID as -1 and after 2 minutes it still hasn't completed. I assume that when I insert a new multimedia component the query will be something similar (i.e. the id will not exist in the table).
The BINARIES table currently has a NON-CLUSTERED Primary Key. Maybe the solution would be to change this to a CLUSTERED Primary Key? However, I assume it is NON-CLUSTERED for a reason.
Just had a response from SDL customer support. Apparently this is a known issue related to statistics and the chosen query plan.
Running the following statement manually from SQL Server Management Studio fixes the problem (it didn't even need to complete for me)
SELECT 1 FROM BINARIES WHERE ID = -1 AND CONTENT IS NULL
Hope this helps someone else out!
Timeouts on database operations are usually an indication of a misconfiguration or a lack of maintenance. By increasing the timeout you are just working around the problem rather than solving it.
With a binaries table that big you will want to make sure you have proper database setup with data files that are separated from your log files (separated on different physical partitions/disks) and possibly even multiple data files on multiple physical partitions to take advantage of performance gains.
Next to that you will want to assure that the standard database maintenance is performed daily/hourly. Things like backing up and truncating the transaction log every hour will greatly improve your database performance (on MS SQL Server a transaction log of more than 1GB slows the database down drastically, you should always try to keep it below that size through timely backup/trucate). Updating statistics and rebuilding indexes is also something you should not forget on a regular basis.
I have a Web site live and running now. I am using the Subsonic to handle the database connections etc.
I am getting time out expired error while updating a table (say Employee). When I check sp_who2, I see the suspended connection for the PID which is updating with a block by anothor pid, so I run the profiler and found out when ever this suspended connection occur, the blocked pid is a select statement on the view (say ActiveEmployees, which is the same as the table but with some where conditions).
Anyone know why a Select statement on the view could cause failure in update. If it is other (like select fails due to update) may be reasonable.
Is there any way for me to make select on a view without locking the table?
PS: I am using the Sql server 2005 and subsonic 2.2.
You might add with(nolock) hint to the select statement in the view if you don't care about accuracy of the returned data (it will return uncommited rows possibly).
We encountered timeouts also when the select statements where scanning a table that other thread was inserting into. I resolved the issue by adding appropriate index that is used by our select.