Managing Version Store Space in SQL Server

 

Managing Version Store Space in SQL Server

 

Introduction:

SQL Server's version store is an important component of its concurrency control mechanism, used to store row versions generated by transactions that use the READ COMMITTED SNAPSHOT or SNAPSHOT isolation levels. However, if the version store runs out of space, it can lead to transaction failures and other issues that can affect the stability and performance of your SQL Server database. In this blog post, we will discuss how to manage version store space in SQL Server and ensure that your database remains stable and performing optimally.

 

Identifying Version Store Space Issues:

The first step in managing version store space is to identify if there are any issues. You can use the sys.dm_tran_version_store_space_usage Dynamic Management View (DMV) to monitor the space usage of the version store and identify if it is running low on space. This DMV returns information about the amount of space reserved and used by the version store in tempdb, which is where the version store resides in SQL Server.

 

Resolving Version Store Space Issues:

If the version store space is full or running low on space, you can take the following steps to resolve the issue:

 

Identify the cause: The first step is to identify why the version store space is full. This could be due to a long-running transaction or an excessive amount of concurrent transactions.

 

Check tempdb size and growth settings: Check the size of the tempdb database and the growth settings to ensure that it is sufficient to accommodate the version store usage. If necessary, increase the size of tempdb and adjust its growth settings.

 

Tune your workload: If your workload is generating excessive versions in the version store, you may need to tune your queries or adjust your application's concurrency control mechanisms to reduce the number of versions generated.

 

Monitor version store space usage: Use sys.dm_tran_version_store_space_usage or other monitoring tools to track the version store space usage over time and ensure that it remains within acceptable limits.

 

Identify transactions using version store space: Use the sys.dm_tran_active_snapshot_database_transactions DMV to identify which transactions are using the version store and how much space they are occupying. This DMV returns information about active transactions that are using the READ COMMITTED SNAPSHOT or SNAPSHOT isolation levels and are generating versions in the version store.

 

Monitor version generation and cleanup: Use the sys.dm_tran_version_generations and sys.dm_tran_current_snapshot DMVs to monitor the generation and cleanup of versions in the version store. These DMVs return information about the versions that are being generated and cleaned up by SQL Server.

 

Restart SQL Server: If the above steps do not resolve the issue, you may need to restart the SQL Server service to clear out the version store and free up space. However, this should be done as a last resort since it can disrupt ongoing transactions and cause downtime for your applications.

 

Conclusion:

Managing version store space is an important aspect of maintaining a stable and performing SQL Server database. By monitoring the space usage of the version store and taking appropriate measures to resolve any issues, you can ensure that your database remains available and responsive to your users' needs. Additionally, by using DMVs such as sys.dm_tran_active_snapshot_database_transactions, sys.dm_tran_version_generations, and sys.dm_tran_current_snapshot, you can gain deeper insights into which transactions are using how much space in the version store, and track the generation and cleanup of versions over time.