cache issues from t-sql-generated plans and how to manage them
DESCRIPTION
Cache issues from T-SQL-generated plans and how to manage them. Webcast by Richard Douglas. To view the recorded webcast, click here:http://dell.to/1fVgKSp Looking for a foolproof way to improve SQL Server performance? You’ll find it by intelligently managing cashed plans that T-SQL code generates. T-SQL code is different from many other languages; you tell it "what" to do and the optimisation engine interprets that command into "how" to do it, then files that information away. Join Dell SQL Server experts as they explain the concepts that support the storage of these “how-to” plans, ways to determine what has been stored, and how to create efficiency at both the database and all-important server level. This educational session will cover: •Concepts behind cashed plans •How to find out what’s been stored •How to create efficiencies at both query and server levels •And much moreTRANSCRIPT
Managing SQL Server’s Plan Cache
Richard Douglas
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Agenda
• Introductions
• What is the plan Cache?
• Plan Cache Memory Usage
• Finding problem plans in the cache
• Events near you
• Q&A
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Your host
• Richard Douglas
• Systems Consultant
• SQL Server MCITPro
• Maidenhead SQL User Group Leader
• Blog: http://SQL.RichardDouglas.co.uk
• Twitter: @SQLRich
• Email: [email protected]
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What is the plan cache?
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Query optimization explained simply
1. Query submitted
2. Magic happens
3. Shedload of data returned
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Plan cache simplified
Query submitted
Run with planCompile
Check for plan in cache
Doesn’t exist Exists
CPU Intensive
Stored in memory
The more plans, the longer this takes. Be mindful of “cache bloating”
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Recompilation Process
From “Plan Caching in SQL Server 2008” by Greg Low
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Finding Compiles / Recompiles
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(Re)Compile Tip
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Call & Hit Rates in SoSSE
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Recompilations• If schema changes are made to any dependencies of code then a
recompilation will occur. This includes:– Tables– Views– Procedures– Indices
• Reaching statistics thresholds:
• An explicit call to sp_recompile.
• Executing a stored procedure using the WITH RECOMPILE option.
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Plan Cache Memory Usage
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Plan Cache Memory Usage
SQL Server Version Cache Pressure Limit
SQL Server 2012, SQL Server 2008 and SQL Server 2005 SP2
75% of visible target memory from 0-4GB + 10% of visible target memory from 4Gb-64GB + 5% of visible target memory > 64GB
SQL Server 2005 RTM and SQL Server 2005 SP1
75% of visible target memory from 0-8GB + 50% of visible target memory from 8Gb-64GB + 25% of visible target memory > 64GB
SQL Server 2000 SQL Server 2000 4GB upper cap on the plan cache
32gb = 5.8gb cache64gb = 9gb cache128gb = 12.2gb cache
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Ageing out plans
Cost = I/O cost + context switch cost (a measure of CPU cost) + memory cost
The individual parts of the cost are calculated as follows.
• Two I/O’s cost 1 tick, maximum of 19 ticks.
• Two context switches cost 1 tick, maximum of 8 ticks.
• Sixteen memory pages (128 KB) cost 1 tick, maximum of 4 ticks.
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Finding problem plans in the cache
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Finding Problem Plans in the Cache
In this section:
• Examples of cache bloat
• Finding IO intensive queries
• Finding CPU Intensive queries
• Looking for certain plan operations
• Looking at Individual plans
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Summary
• The reason for the plan cache.
• Monitoring the plan cache.
• Plan cache memory utilisation.
• Demonstrated how to find:– Cache bloat– Particular operators– High resource queries
Pg. 18© 2012 Quest Software Inc. All rights reserved.
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SQL Rally
Amsterdam (Holland): 6 – 8th Nov
http://www.sqlpass.org/sqlrally/2013/amsterdam/Home.aspx
Stockholm (Sweden): 4-6th Nov
http://www.sqlpass.org/sqlrally/2013/nordic/Home.aspx
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What Do Developers Need to Know About SQL Server?
Join Microsoft Certified Master Brent Ozar & Richard Douglas:
The database comes with a manual, but let's be honest: nobody's got time for that. Database administrators - let's distill the most important concepts and rules for developers down to 140-character chunks on Twitter on Thursday, October 24th from 10AM to 11AM Eastern.
Microsoft Certified Master Brent Ozar will lead the discussion at #dellsql.
Register now - http://bit.ly/H6XeDU
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What would you like to see?
• Best Practices– DBA– Developer
• Indexing
• Baselining
• SSAS
• SSIS
• SSRS
• Always On Availability Groups
• Backups
• Clustering
• Database Mirroring
• Performance Monitoring
• Performance Tuning
• Installation & Configuration
Next Webcast: 19th November 2013
23 Global MarketingUnderstanding Query Execution Plans
Any questions?
