SQL Server 2016 Query Store

SQL Server 2016 Query Store Sergio Govoni @segovoni www.sqlblog.com/blogs/sergio_govoni

Sponsors

Speaker BIO SQL Server MVP sqlblog.com/blogs/sergio_govoni @segovoni ugiss.org manning.com/delaney segovoni@gmail.com

Agenda Query plan change Can cause performance issues Why do plan changes happen? Problems you face for slow running queries What does the Query Store do for you? Live Query Statistics

QP changes can cause performance issues Web site is down Temporary perf. issues SQL Server upgrade Database is not working How to fix it ASAP? Impossible to predict the root cause Performance regression caused by the new version

Fixing query plan regression is hard Problems you face for slow running queries Time of the day and compiled parameters Has the Data Collector been activated? Plan cache may not be suitable for troubleshooting You have to find out why it is show When you have the issue on you hands Can you modify the query text? Do you know the SP to create the Plan Guide?

Let s do a quiz Who is the author of this painting? A. Pablo Picasso B. Vincent Van Gogh C. Claude Monet D. Pierre-Auguste Renoir E. Query Optimizer P 1 P 2 P 3 P 4

Why do plan changes happen? Query Optimizer generates and evaluates many plans for the same query Data changes every hour, so the QO might select a different plan Generally, boundary plans have the same performance http://dsl.serc.iisc.ernet.in/projects/picasso/

What does the Query Store do for you? It stores all the plan choices and related performance metrics for each query It identifies queries that have become slower recently It allows DBA to force an execution plan easily It makes sure your changes work across server restart, upgrades, failover and query recompiles

How the Query Store captures data

How the Query Store exposes data Each DMV joined In- Memory and On-Disk data When memory pressure occurs, some data In- Memory will be flushed to the disk In-Memory Data On-Disk Data sys.query_store_runtime_stats

How the Query Store interprets the query text Query text starts from the first character of the first token (of the statement) and it ends at the last character of the last token Comments and spaces, before or after, don t change anything Comments and spaces inside count sys.query_store_query_text query_text_id is used to force a plan for a query statement_sql_handle contains the MD5 hash of the query text

Query Store DMV overview ANSI Options Execution plans Metrics: 1 row per plan per time interval 1:N 1:N 1:N Query_Text Query_ANSI Query_Plan Runtime_Stats Context_Settings One row per unique combination of set options Runtime_Stats_Interval One row per time interval

Demo Environment A console application executes this query in a loop on a database where Query Store is enabled Parameters are generated by a randomized function, values are between Zero and 100 Plan cache is cleaned when parameters values are less than 2

SQL Server 2016 Query Store DEMO

Query Store Tuning Because collecting data has always a cost, SQL Server allows you to tune the Query Store with these options of ALTER DATABASE statement INTERVAL_LENGTH_MINUTES MAX_STORAGE_SIZE_MB MAX_PLANS_PER_QUERY (200 by default) QUERY_CAPTURE_MODE (ALL, AUTO, NONE) DATA_FLUSH_INTERVAL_SECONDS

Server Upgrades Are you worried about SQL Server upgrades? This is the way out 1. Restore a copy of the production DBs on a test server 2. Run a significative workload 3. Look at the Query Store for performance regressions Plan forced works across Recompilation Server reboots and failover

Live Query Statistics Allows you to see the live execution plan of an active query It provides a way to better understand the query execution process and the control flow It is extremely useful (and cool ) for debugging query performance It is based on sys.dm_exec_query_profiles You can use it also on SQL Server 2014 (SP1)

Live Query Statistics DEMO

Live Query Statistics on SQL 2014 (SP1) At the server side Download and install the Service Pack 1 for SQL 2014 (if you have not already done) At the client side Download and install the latest version of SSMS (September 2015 preview) Enable the Live Query Statistics Play with it on a test machine.. SQL Server will make some effort to produce the data for this tool!

Summary: With Query Store you can.. Analyze your workload Easily fix plan regressions Find the most expensive queries De-risk SQL Server upgrades

Resources [docs.com] SQL Server Query Store SQL Server 2016 Video Pills Live Query Statistics

Q&A Questions?

Evaluations Don t forget to compile evaluations form here http://speakerscore.com/sqlsat454 This session http://speakerscore.com/qs2016

#sqlsat454 http://speakerscore.com/qs2016 THANKS! Thanks for attending this session. If you have additional questions, please post them on the MSDN SQL Server Forums (ITA ENG)