Tag Archives: Performance Tuning

Performance Tuning in SQL Server

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One of the frequently asked questions in forums, interviews and during general discussions, is performance tuning. In fact, a friend of mine, (who knows a little bit of SQL Server) when speaking about my blogs, asked me why I had not written any blog on performance tuning. I gave a pause and said, do you know that heavy usage of cursors result in poor performance, Database partitioning results in slightly better performance and Database Snapshots cause a performance overhead? Then I continued, though you see I had a blog on those topics,  it is not noticed that they are related to performance of the SQL Server.

The point is, there are many actions or the usage of certain features which directly or indirectly affect the performance of a SQL Server. I would like to post blogs on performance tuning SQL Server, it may be Query Tuning such as rewriting the query to perform better or looking at Indexes and ensure that there are proper Indexes that help the query. It can be related to locking / blocking happening on the database or improper settings of the database options.

There are certain other things to look at when looking to tune a SQL Server apart from those mentioned above. An improper placement of the database files can lead a performance degradation or excessive usage of cursors. There can be system bottlenecks such as Memory, Processor, Disk or Network that is the prime cause for a system slowness. 

Many of these shall be addressed individually in the forth-coming blogs.

— Bru Medishetty

Enable AWE Option in SQL Server

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In this article we will look at the steps to enable AWE Option in SQL Server. When enabled, the Advanced Windowing Extensions gives the ability to SQL Server to utilize Memory more than 4 GB. AWE enabling for SQL Server is valid in 32 Bit Systems only, on 64 bit systems AWE is not required to be enabled.

Steps to enable AWE

In the SSMS, right click on the SQL Instance in Object Explorer, and select properties. the following Properties Dialog Box is displayed.

In the left Pane of the Box, Select the Memory Page and Under Server Memory options check the box as shown in the picture below to use AWE to allocate memory. You can also specify a Minimum and Maximum Memory SQL Server can utilize on the machine. So that incase of Memory available to SQL Server it does not complete utilize and resulting in no or less memory to the Operating System and other application running on the Server.

 

Select OK in the Properties page. The change in the setting will not be effective upon restarting SQL Server.

Alternately, you can also enable using sp_configure. The following scripts provide the alternate steps to
perform to enable AWE option.

As always, I suggest referring other technical information before enabling AWE and other system settings that need to be enabled on the Server for this to be successful, such as enabling /3GB switch or /pae switch in Boot.ini etc.

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–Bru Medishetty

Cursors in SQL Server

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Cursors in SQL Server enable you to work with each of records in a record set, so that you can sequentially work with those records and carry out the required task.

The best example that I can recollect to quote here is when you have a table with 100 rows, with one of the columns as email address. You are required to send an email to all valid records in that column and each record is some way or the other has its own condition, then a Cursor would be a good way to implement this.

What cursor does is, it enables you to fetch the data into the memory and then for each of the row in the data set, you can look at the row, can implement any custom logic that is needed and move on to the next row until you reach the end of the records.

There are different types of cursors available and based on the one you choose, you can actually move back and forth with the records.

One other example I can give is, when you need to run a backup for all the databases in a SQL Instance, it is very easy to implement using cursors and has been used by me and many SQL DBA’s before the introduction of the DTS and SSIS technologies.

That is the main benefit of cursors, but the flip side to it is, they are avoided in situations where the dataset is large, due to performance issues with cursors. Since they have this unique ability to traverse through the dataset, they occupy a high amount of memory in the Server.

You should be able to find many examples on this topic and I shall try to publish an article with more details in one of my next blogs.

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–Bru Medishetty