1. Scott Fallen Sales Engineer, SQL Sentry Twitter: @ScottFallen Blog: scottfallen.blogspot.com

2. About Scott and SQL Sentry o SQL Sentry Plan Explorer Getting Started with Execution Plans o What are plans and why are they important? o How to collect and read plans. o Tuning opportunities to look for starting out. o Plan Demos. Summary, Q&A, and Resources

3. An execution plan is SQL Server’s estimate of how to retrieve the data requested as efficiently as possible. Plans show what SQL Server is doing internally to satisfy your query. Generated by the query optimizer.

4. Query performance and tuning o “Why is my query so slow?” Index utilization or lack thereof Memory use (Plan Cache)

5. What happens when SQL Server receives a query? First, the query is parsed. This determines the validity of the T-SQL and formatting. Second, the parsed query is sent to the algebrizer to have all of the object names and data types identified within the database. This outputs a query processor tree. The query processor tree is passed on to the query optimizer, and its hash is checked against the plans in the plan cache. If a plan is found, it will be used. If not, we go on to plan compilation.

6. The query optimizer creates what SQL Server thinks will be the most efficient execution plan based on the query processor tree and the statistics available for the data. “Efficiency” is based on I/O and CPU costs for each operation required to retrieve the data. Often more than one plan will be created. The one that is fastest and most efficient will be selected and used. Plan creation is expensive, so sometimes SQL Server decides that it will be cheaper to use a sub-optimal plan than to continue generating new plans. SQL Server tries to reuse plans, and stores them in memory.

7. SQL Server stores and maintains statistics about the distribution and selectivity of the data in the columns and indexes stored in a database. Statistics are essential to plan creation, and incorrect or out-of-date statistics are an extremely common reason for the query optimizer to return an inefficient plan. If you have a query that ran fast yesterday and runs slow today, check stats!

8. Estimated Actual o While usually the same, the actual plan may differ from the estimated plan. This can be due to stale statistics, parallelism request, or invalidity of the estimated plan (ex: temporary resource doesn’t exist yet). XML, Graphical, and Text varieties. We will focus on XML plans viewed Graphically

9. Demos: o SSMS/Plan Explorer for Actual and Estimated Plans o Querying DMOs for Estimated Plans in the Plan Cache Other options, we didn’t demo everything. o SET SHOWPLAN TEXT etc. (deprecated) o Trace Capture

10. The basic structure, arrows and operator icons. Right to left! Costs Rowcounts / Data Sizes Number of executions Some information is available at a glance, other data requires looking at tooltips, the Properties Pane in SSMS, or other tabs in Plan Explorer.

11. Logical and Physical Operators (Blue) o Parallel operators (Also Blue) Cursor Operators (Yellow) T-SQL Language Operators (Green) Blocking and Non-Blocking Operators o Non-Blocking operators stream data through. Data goes out even as it’s still coming in and being worked on. o Blocking operators must complete fully before passing data on. Can lead to issues with concurrency. Let’s walk through some of the more common operators.

12. Scan – Bring back everything! o Table Scan o Clustered Index Scan o Nonclustered Index Scan Seek – Navigate the B-tree to get only the required data. o Clustered Index Seek o Non-Clustered Index Seek Generally, seeks are preferable to scans because they retrieve only the requested data. That said don’t worry about a scan that only picks up a handful of rows!

13. Join – Bringing together data from multiple tables. o Nested Loops Join Generally the best type of join, except for very large data sets. o Merge Join Joins data already ordered on join columns, non-blocking operator. o Hash Match Join Blocking Operator, Uses TempDB. Can be inefficient! Bookmark Lookup – Always accompanied by a join. o Key Lookup Go back to the Clustered Index to retrieve other columns. o RID Lookup Same, but using the RID (row ID) for heaps.

14. Sort o Required for some operations and/or because an ORDER BY clause was used. Can spill to TempDB, generating a Sort Warning that can be captured via trace, and plan XML in 2012+. Filter Compute Scalar o Produces a value from a calculation. Hash Match (Aggregate) o Aggregations can be costly, try to limit the amount of data that needs to be aggregated with a WHERE clause.

15. Putting it all together: DEMO

16. Keep in mind that there are some new operators for INSERT, UPDATE, and DELETE statements. The basic concepts for reading the plans remain the same.

17. SQL Server Execution Plans, Second Edition, by Grant Fritchey. o The definitive guide, and the e-book is free! I learned a ton from this book. o https://www.simple-talk.com/books/sql-books/sql-server-execution-plans,- second-edition,-by-grant-fritchey/ https://www.simple-talk.com/books/sql-books/sql-server-execution-plans,- second-edition,-by-grant-fritchey/ Microsoft Books Online o http://technet.microsoft.com/en-us/library/ms178071%28v=sql.105%29.aspx http://technet.microsoft.com/en-us/library/ms178071%28v=sql.105%29.aspx o http://technet.microsoft.com/en-us/library/ms175913%28v=sql.105%29.aspx http://technet.microsoft.com/en-us/library/ms175913%28v=sql.105%29.aspx Paul White’s Blog o http://sqlblog.com/blogs/paul_white/ http://sqlblog.com/blogs/paul_white/ Aaron Bertrand’s Plan Explorer Demo Kit o http://sqlperformance.com/2014/03/t-sql-queries/updated-plan-explorer-demo-kit http://sqlperformance.com/2014/03/t-sql-queries/updated-plan-explorer-demo-kit Contains the demo plans I used for this presentation.

18. Free Plan Explorer download: http://www.sqlsentry.com/products/plan- explorer/sql-server-query-view#download http://www.sqlsentry.com/products/plan- explorer/sql-server-query-view#download Free query tuning consultations: http://answers.sqlperformance.com. http://answers.sqlperformance.com Free new ebook (regularly $10) to attendees. Send request to sales@sqlsentry.com.sales@sqlsentry.com SQL Server educational videos, scripts, and slides: http://SQLSentry.TVhttp://SQLSentry.TV Tuning blog: http://www.sqlperformance.com/http://www.sqlperformance.com/ Monthly eNews tips and tricks: http://www.sqlsentry.net/newsletter-archive.asp http://www.sqlsentry.net/newsletter-archive.asp

19. Please feel free to contact me with questions: sfallen@sqlsentry.com. sfallen@sqlsentry.com Thanks to all of the attendees and organizers!