Finally got some breathing space for my first post of the year! In order to get a major client through Christmas which is traditionally their busiest period of the year (where load normally goes up five-fold), we embarked on a major platform refresh where both the back end SQL Server DBMS was upgraded from SQL 2008R2 to SQL Server 2012 and the hardware was upgraded to 2 x Dell PowerEdge R910s with 4 x 10 (physical) cores and 512GB of RAM in each server.
Carrying on my series of posts on SQL Server and Disk IO it’s time to cover the old stalwart that is perfmon (referred to in Windows as Performance Monitor) which I know anyone who has delved into any Windows performance issue will have some familiarity with, so I’m not going to cover what it is or how to use it. The principal reason for this post is to add my own experiences of using perfmon to turn it into a sql performance monitor to track down issues and monitor SQL Server performance.
I’ve finally got around to this, the third part of my SQL Server and Disk IO series of posts: The sys.dm_io_virtual_file_stats DMV and fn_virtualfilestats function are great tools for extracting granular information about SQL Server IO performance, right down to the individual file in each database. It gives details of the number of physical reads/writes, amount of data read/written and how much time was spent reading/writing that data. Traditionally, this has been important because IO access is the slowest part of fulfilling any database queries as RAM and CPU access takes nanoseconds or microseconds, whereas typically access to a spinning disk takes several milliseconds.
Do you have tempdb on Fusion-io (or equivalent) technology? Is your reindexing job left on default settings (re-orgs at 5-15% and full rebuilds at @ 30%)? If so, then you might be interested in the findings in this post. The benefits of flash memory as a replacement for spinning drives in order to boost SQL Server performance is well documented. However, I’m not sure if one particular benefit has been fully exploited.
I’m starting off this series of posts with a discussion about partition offsets. Diving off at the deep end a bit perhaps, but if your disk setup is not based on firm foundations, you’re setting yourself up for one of the most common and easily-avoidable performance issues right from the off, and a IO performance hit of 20-30%. The partition offset issue is relevant to any disk partitions created prior to Windows Server 2008.
Many aspects of a database system’s configuration will affect the performance of queries running on that DBMS. However, there is one single component that has the greatest impact on DBMS performance, and that, of course, is disk (IO) access. It’s a broad topic and all aspects of it are pretty well covered in various blogs and technical articles, but there’s not much out there that gathers it all together. The intention of this series of posts is to try consolidate some of this information and focus in on some of the functions and procedures that can be used to monitor, troubleshoot and configure SQL Server disk configuration and most, importantly, disk performance.