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Reading the SQL Server Execution Plan

Reading the SQL Server Execution Plan. Denny Cherry mrdenny@mrdenny.com MVP, MCSA , MCDBA, MCTS, MCITP. Agenda. What is an Execution Plan Reading an Execution Plan Execution Plan Operators Changing the Execution Plan Reading the Execution Plan Demo. What is an Execution Plan.

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Reading the SQL Server Execution Plan

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  1. Reading the SQL Server Execution Plan Denny Cherry mrdenny@mrdenny.com MVP, MCSA, MCDBA, MCTS, MCITP

  2. Agenda • What is an Execution Plan • Reading an Execution Plan • Execution Plan Operators • Changing the Execution Plan • Reading the Execution Plan • Demo

  3. What is an Execution Plan • How the SQL Server access the data within the database. • Returned as XML or text when requested. • Displayed in a much more readable graphical form • Can not be edited directly • Can be adjusted with index hints • Can be set by pining Execution Plans • SQL chooses a Good Enough Plan not the perfect plan.

  4. Reading an Execution Plan • Graphical Plan • Read from Right To Left, Top to Bottom • Follow Arrows until next branch from below • Text Plan • Read from Left to Right, Top to Bottom • Each Operator has it’s own CPU and IO Statistics, both Estimates and Actuals

  5. Reading an Execution Plan

  6. Operators Finding Data • Index Seek – Reads the portion of the index which contains the needed data. • Index Scan – Reads the entire index for the needed data. • Table Scan – Reads the entire table for the needed data. • Key Lookup – Looks up values row by row for values which are missing from the index used. • Table Valued Function – Executes a table valued function within the database

  7. Operators Filtering and Sorting • Nested Loops - Performs inner, outer, semi and anti semi join operations. Performs search on the inner table for each row of the outer table. • Hash Match - Creates a hash for required columns for each row. Then creates a hash for second table and finds matches. • TOP - Returns the specified top number of rows. • Sort - Sorts the incoming rows. • Stream Aggregate – groups rows by one or more columns and calculates one or more aggregate expressions.

  8. Changing the Execution Plan • Index hints • NOLOCK • READPAST • FIRSTFAST • INDEX() • Pinning an Execution Plan • sp_create_plan_guide • sp_control_plan_guide • Adding Indexes To Tables • Modify Indexes to remove scan and lookup operations

  9. sp_create_plan_guide

  10. sp_control_plan_guide

  11. Denny Cherry Please fill out the survey at http://speakerrate.com/mrdenny. mrdenny@mrdenny.com http://itke.techtarget.com/sql-server Contact Info Blog Twitter

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