Shopping Around for Query Optimizations? Try the Query Store!

INTELLIGENT DATA SOLUTIONS WWW.PRAGMATICWORKS.COM
SQL Server 2016
The Query Store
Author: Sean Werick
Company: Pragmatic Works

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About Pragmatic Works

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• Email: SWerick@pragmaticworks.com
About Sean

SQL Server 2016
New Innovations

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What is the Query Store?
A SQL Server 2016 (and SQL DB) Feature that can be Enabled
• Provides insight on query plan choice and performance
• Simplifies performance troubleshooting by quickly finding performance differences
caused by query plan changes
• Automatically captures a history of queries, plans, and runtime statistics, and retains
these for review
• Separates data by time windows to better illustrate database usage patterns and
understand when query plan changes happened on the server

Why Use the Query Store?
Query Performance Insight Helps Satisfy 2 Main Goals
Performance Cost

WHAT IS THE REAL COST?
Why Use the Query Store?
All about the DTUs (PaaS)
A Database Transaction Unit (DTU) is a
blended measure of the resources allocated at
each performance level.
• Processor - % Processor Time
• Logical Disk - Disk Reads/sec
• Logical Disk - Disk Writes/sec
• Database - Log Bytes Flushed/sec
• Review the list of top resource-consuming
queries
• Select an individual query to view its details
• Click Settings to customize how data is
displayed or to show a different time period
• Open Index Advisor* (PaaS) and check if any
recommendations are available
Performance Cost
* Index Advisor - https://azure.microsoft.com/en-us/documentation/articles/sql-database-index-advisor/

How the Query Store “Works”

Does It Work with In-Memory OLTP?
• SQL Server Query Store allows you to monitor the
performance of natively compiled code for workloads
running in-memory OLTP
• Compile and runtime statistics are collected and
exposed the same way as for disk-based workloads
• When you migrate to in-memory OLTP you can
continue using Query Store views in SQL Server
Management Studio as well as custom scripts you have
developed for disk-based workloads before migration
• This saves your investment in learning Query Store
technology and makes it generally usable for
troubleshooting all type of workloads

How to Use the Query Store
In Just 3 Easy Steps, You TOO can be a DBA!!
Okay, okay. This may take a bit more effort and knowledge.

There are 2 Ways to Enable Query Store
By Using the Query Store Page in SSMS
Setting up the Query Store
In Object Explorer, right-click a database, and then click
Properties

By Using the Query Store Page in SSMS
In the Database Properties dialog box, select the Query
Store page
Select related attributes
• General
o Operation Mode (Read or Read/Write)
• Monitoring
o Data Flush Interval (Manual Entry in Minutes)
o Statistics Collection (5 mins, 10 mins, 15 mins, 30 mins, 1 hr,
1 day)
• Max Size
o Query Store Capture Mode (All or Auto)
o Size Based Cleanup Mode (Off or Auto)
o Stale Query Threshold (Manual Entry in Days)

By Using T-SQL Statements
• Use the ALTER DATABASE statement
ALTER DATABASE AdventureWorks2012
SET QUERY_STORE = ON;
Ability to

GUI Option T-SQL Option
Operation Mode (Requested) OPERATION_MODE
Data Flush Interval (Minutes) DATA_FLUSH_INTERVAL_SECONDS
Statistics Collection Interval INTERVAL_LENGTH_MINUTES
Max Size (MB) MAX_STORAGE_SIZE_MB
Query Store Capture Mode QUERY_CAPTURE_MODE
Size Based Cleanup Mode SIZE_BASED_CLEANUP_MODE
Stale Query Threshold (Days) CLEANUP_POLICY (STALE_QUERY_THRESHOLD_DAYS)
MAX_PLANS_PER_QUERY
Query Store Options with T-SQL
ALTER DATABASE [db_name]
SET QUERY_STORE
(
[Query Store options]
);
-- Example
ALTER DATABASE AdventureWorks
SET QUERY_STORE
(
MAX_STORAGE_SIZE_MB = 250
);

sys.query_store_plansys.query_store_runtime_stats
sys.query_context_settings
sys.query_store_runtime_stats_interval
sys.query_store_query
sys.query_store_query_text
plan_id
runtime_stats_interval_id
query_id
context_settings_id
query_text_id
DATA MODEL
sys.database_query_store_options
What Information Does It Provide?

What Information Does It Provide?
*Additional Detail - https://msdn.microsoft.com/en-us/library/dn818146.aspx
Query Store View Description
sys.database_query_store_options Query Store options for this database
sys.query_context_settings Semantics affecting context settings associated with a query (The same
query text compiled under different settings may produce different
results [depending on the underlying data])
sys.query_store_plan Each execution plan associated with a query
sys.query_store_query Information about the query and its associated overall aggregated
runtime execution statistics
sys.query_store_query_text Transact-SQL text and the SQL handle of the query
sys.query_store_runtime_stats Information about runtime execution statistics information for the query
sys.query_store_runtime_stats_interval Information about the start and end time of each interval over which
runtime execution statistics information for a query has been collected

Query Store Best Practices
 Information and performance are generally a give and take, but there ARE some
best practices
 Every single setting in the Query Store has associated costs and benefits
• Treat Query Store performance tuning like an agile project with Sprints
o Sprint 1 – Keep Operation Mode in READ/WRITE mode for information collection
 This reduces write time, and subsequent overall database performance, for data
collection as no reporting is occurring
o Sprint 2 – Change Operation Mode to READ mode for analysis and actual performance
tuning
 This it increases report performance because no writes are occurring. This also results
in no “dirty reads” because of the asynchronous writes

Query Store Best Practices
• Flush the data at specific business case intervals. For example, if performance of the DB
seems to be poor around end of the month due financial reporting, consider using the Agile
methodology to complete one iteration, then flush the data before the next iteration.
• Keep the Max Size small enough to keep the reporting relatively snappy, however, keep
enough data to capture all of the business needs
• Keep an accurate Cleanup Policy as the business and reporting solution evolves
• Collect statistics as frequently as possible to see exactly which execution plans are being
executed. If the statistics are not updated for some time, you may be looking at an old
execution plan because the statistics have changed
 Information and performance are generally a give and take, and it ultimately
relies on each and every business and its processes

Query Store Reporting
Azure SQL DB
• Cloud offering (PaaS)
• Learn and adapt dynamically with your app
• Scale performance on the fly, without app
downtime
• Build multitenant apps with customer isolation
and efficiency
• Work within your preferred development
environments
• Help protect and secure your app data

The top queries view opens and the
top CPU consuming queries are listed
• The top line shows overall DTU% for the
database, while the bars show CPU%
consumed by the selected queries
during the selected interval
• The bottom grid represents aggregated
information for the visible queries
o Average CPU per query during
observable interval
o Total duration per query
o Total number of executions for a
particular query

Viewing Individual Query Details
Click any query in the list of top queries.
The details view opens and the queries CPU consumption is broken
down over time.
Click around the chart for details.
The top line is overall DTU%, and the bars are CPU% consumed by
the selected query.
Review the data to see detailed metrics including duration, number
of executions, and resource utilization percentage for each interval
the query was running.

Query Store On Premise Reporting
On Premise Solution?

Query Store Dashboards
SSMS

Custom Views and SQL
HOW?
sys.query_store_plansys.query_store_runtime_stats
sys.query_context_settings
sys.query_store_runtime_stats_interval
sys.query_store_query
sys.query_store_query_text
plan_id
runtime_stats_interval_id
query_id
context_settings_id
query_text_id
sys.database_query_store_options

Query Store Admin with T-SQL
Stored Procedure Description
sp_query_store_flush_db Flushes the in-memory portion of the Query Store data to disk
sp_query_store_reset_exec_stats Clears the runtime stats for a specific query plan from the query store
sp_query_store_force_plan Enables forcing a particular plan for a particular query.
When a plan is forced for a particular query, every time SQL Server encounters
the query, it tries to force the plan in the optimizer. If plan forcing fails, a
XEvent is fired and the optimizer is instructed to optimize in the normal way.
sp_query_store_unforce_plan Enables unforcing a particular plan for a particular query
sp_query_store_remove_plan Removes a single plan from the query store
sp_query_store_remove_query Removes the query, as well as all associated plans and runtime stats from the
query store

Forcing Execution Plans
OLD WAY
1. Run SET SHOWPLAN_XML ON to return the XML
Execution Plan, or alternatively, grab the XML Plan
from the sys.dm_exec_text_query_plan DMF)
2. Create the Plan Guide using the
sp_create_plan_guide Stored Procedure

Forcing Execution Plans
NEW WAY
1. Click the “Force Plan” button inside one of the
Query Store reports
2. Use the sp_query_store_force_plan SP.
EXEC sp_query_store_force_plan 136, 146;

Error State
Remember to verify intermittently that the Query Store is still collecting data
SELECT actual_state_desc, desired_state_desc, current_storage_size_mb,
max_storage_size_mb, readonly_reason, interval_length_minutes,
stale_query_threshold_days, size_based_cleanup_mode_desc,
query_capture_mode_desc
FROM sys.database_query_store_options;
If there is a difference between the actual_state_desc and desired_state_desc, this indicates that a change of
operations mode occurred automatically.
The most common change is for the Query Store to silently switch to read-only mode. In extremely rarely
circumstances, Query Store can end up in the ERROR state because of internal errors.
When the actual state is read-only, use the readonly_reason column to determine the root cause. Typically, the
Query Store transitioned to read-only mode because the size quota was exceeded. In that case the
readonly_reason is set to 65536.

Error State
How to Fix
Reactive
Increase the maximum storage size by using the
MAX_STORAGE_SIZE_MB option of ALTER DATABASE
Clean up Query Store data
ALTER DATABASE [QueryStoreDB]
SET QUERY_STORE CLEAR;
Change Operation Mode back to READ/WRITE
ALTER DATABASE [QueryStoreDB]
SET QUERY_STORE (OPERATION_MODE = READ_WRITE);
Proactive
Apply best practices, specifically related to Query
Store size
Make sure that most recent data is retained,
configure time-based policy to remove stale
information regularly
Consider setting Query Capture Mode to Auto as it
filters out queries that are usually less relevant for
your workload

Questions and Answers

Shopping Around for Query Optimizations? Try the Query Store!

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Shopping Around for Query Optimizations? Try the Query Store!

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