General SQL Server Performance Tuning Tips

On very rare occasions, you may get an error similar to this from SQL Server:

[Microsoft SQL-DMO (ODBC SQLState: 42000)] Error 845: [Microsoft][ODBC SQL Server Driver][SQL Server]Time-out occurred while waiting for buffer latch type 3 for page (2:0), database ID 15.

This error message may also be accompanied by additional error messages, such as a file log or database backup that failed.

This error indicates that your disk I/O system is being overloaded and that SQL Server timed out when trying to write data to disk (via the OS). If this error is a rare event, then there is no need to worry.

But if this event becomes frequent, it could mean that your disk I/O subsystem has hit a bottleneck that it can’t overcome, or that your disk I/O subsystem itself is having problems. You need to find out which one of these is the most likely issue, and then deal with it accordingly.

One of the things that you might want to look for is what I/O activity was happening at the time of the error. For example, it is possible that a disk backup, a DBCC command, or other database activity was all happening at the same time, overwhelming the disk I/O. Perhaps the solution to the problem is as simple as rescheduling some scheduled tasks.  

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According to Microsoft, the way to shrink a log file is to use DBCC SHRINKFILE. This process is painfully slow and inefficient. Even after running the procedure numerous times, you may not get much free space.

Here’s another way to shrink your logs that is guaranteed to work every time. First, back up the database and then detach (sp_detach_db) it (you will have to bring the database down to do this). Next, delete the log file and then re-attach (sp_attach_db) the database, not providing the old log file location from within the sp_attach_db command. This will create a new log file with the old log file name in the old location with default size i.e. 512 KB.

To make sure there is no problem during the operation, the old log file can be renamed and kept until the database is reattached successfully. This provides a backup plan if for some reason SQL server fails to attach the database without the old log file.

This trick won’t work if the database has more than one log file, but if you need to, you can alter the database so that it only has a single log file, while will allow you to perform the above steps. After carrying out the detach and attach database activity, the database can be again altered to add more log files.   Contributed by Gaurav Bindlish.  

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In SQL Server’s Query Analyzer, a somewhat hidden, but useful feature exists that you may not be aware off, and that is the Transact-SQL Debugger. The reasons you may not have seen it before in Query Analyzer is that you don’t see this option in any standard menu, making it somewhat hard to find.

To use the Transact-SQL Debugger, you must first ensure that the Object Browser is displayed from within Query Analyzer. Next, using the Object Browser, open up a database that has one or more stored procedures, then right-click on the stored procedure’s name, and then select Debug. This is how you turn on debugging for a stored procedure.

Once you click on Debug, if the stored procedure you selected has one or more input parameters, you will be asked to enter them, and then you can begin the debugging process. The Transact-SQL Debugger has the typical features you find in most any debugging tool, including:

• Go: Puts the stored procedure into the debugging mode.
• Toggle Breakpoint: Sets or removes a breakpoint at the current line in your code. You cannot set a breakpoint on lines containing non-executable code.
• Remove All Breakpoints: Clears all the breakpoints in your code.
• Step Into: Step Into executes the statement at the current execution point, and then executes one code statement at a time. If the statement is a call to another stored procedure, then the next statement displayed is the first statement in the stored procedure.
• Step Over: Executes one code statement at a time. If the current statement contains a call to another stored procedure, Step Over executes the stored procedure as a unit, and then steps to the next statement in the current stored procedure.
• Step Out: Executes the remaining lines of code in which the current execution point lies. The next statement displayed is the statement following the procedure call. All of the code is executed between the current and the final execution points.
• Run to Cursor: Specifies a statement further down in your code where you want execution to end.
• Restart: Restarts execution at the beginning of the stored procedure.
• Stop Debugging: Stops debugging.
• Watch: Displays the current watch expressions.
• Callstack: Lists the procedures calls that have started, but have yet to be completed.
• Auto Rollback: Automatically rolls back all work performed during execution of the stored procedure.

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Have you ever wanted to test the latest beta software, but didn’t want to put it on your “production” desktop because you were afraid it might crash it, and didn’t have a separate test box available to run it on? Or have you wanted more than one test environment, but didn’t have the necessary hardware?

In both of these cases, there is a new option that allows you to do both, while not requiring any more hardware. How? By using Microsoft Virtual PC 2007. This software, which is designed to run on most desktops and Microsoft operating systems, allows you to install virtual servers on your current desktop (assuming your hardware is big enough).

For example, if you are running Windows XP Workstation on your desktop, you can create one or more multiple virtual servers that run almost any other Microsoft operating system, along with your choice of application software, such as SQL Server running under Windows Server, or any combination you like.

Virtual servers don’t have to be active all the time, you can bring them up only when you want to, helping to preserve hardware resources. You can create as many virtual servers as you like, plus you can have as many running as you like, assuming your hardware will handle them.

If you decide to do this, there are two things you may want to keep in mind. First, when you create a virtual server, you must specify how the networking will work. There are several options. You may have to experiment with these options to select the one that works best for you. Also, you will want to install the optional Virtual Machine Additions into your virtual server, after it is built. This will greatly enhance the performance of the virtual software. Information on how to do this is available in the instructions.

Microsoft also offers a “server” version.  

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To quickly identify which, if any, of your procedure is executed when SQL Server starts, you can use the following query:

USE master
GO
SELECT
name
FROM
sysobjects
WHERE
OBJECTPROPERTY(id, ‘ExecIsStartup’) = 1

However, you can also get the same result via the INFORMATION_SCHEMA views, which are generally preferable over directly querying the system tables. Here’s the query:

USE master
GO
SELECT
ROUTINE_NAME
FROM
INFORMATION_SCHEMA.ROUTINES
WHERE
OBJECTPROPERTY(OBJECT_ID(ROUTINE_NAME), ‘ExecIsStartUp’) = 1

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One Response to “General SQL Server Performance Tuning Tips”

  1. “truncate table is not a logged operation”?? that’s not true, every operation is logged, see http://www.sqlperformance.com/2013/05/sql-performance/drop-truncate-log-myth for and excellent explanation

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