{"id":1089,"date":"2020-02-04T06:30:58","date_gmt":"2020-02-04T14:30:58","guid":{"rendered":"http:\/\/3.209.169.194\/blogs\/erin\/?p=1089"},"modified":"2020-02-04T08:49:12","modified_gmt":"2020-02-04T16:49:12","slug":"are-changes-to-query-store-logged","status":"publish","type":"post","link":"https:\/\/www.sqlskills.com\/blogs\/erin\/are-changes-to-query-store-logged\/","title":{"rendered":"Are Changes to Query Store Logged?"},"content":{"rendered":"

The Query Store feature is a bit unique in that its status can change without user interference, which means it is important to understand how changes to Query Store are logged.\u00a0 A couple weeks ago John Deardurff<\/a> posted a question on Twitter asking specifically whether the SQL Server ERRORLOG is written to when the OPERATION_MODE changes to READ_ONLY because\u00a0 MAX_STORAGE_SIZE_MB is exceeded.\u00a0 I had never tested to confirm, but I know there is an event in Extended Events that will fire when the limit is reached.\u00a0 I also know that when a user makes a change to a Query Store setting, it is logged in the ERRORLOG.<\/p>\n

User Changes<\/h2>\n

With a copy of WideWorldImporters<\/a> restored in my SQL Server 2019 VM, I will create an Extended Events with a few events I think will be relevant:<\/p>\n

CREATE EVENT SESSION [XEStatusChange]
\nON SERVER
\nADD EVENT qds.query_store_db_settings_changed,
\nADD EVENT qds.query_store_disk_size_info,
\nADD EVENT qds.query_store_disk_size_over_limit
\nADD TARGET package0.event_file(SET filename=N’C:\\temp\\XEStatus’,max_file_size=(256))
\nWITH (MAX_MEMORY=4096 KB, EVENT_RETENTION_MODE=ALLOW_SINGLE_EVENT_LOSS, MAX_DISPATCH_LATENCY=30 SECONDS, MAX_EVENT_SIZE=0 KB, MEMORY_PARTITION_MODE=NONE,&nbsp; TRACK_CAUSALITY=OFF, STARTUP_STATE=OFF);
\nGO<\/p>\n

 <\/p>\n

Next, we will change the MAX_STORAGE_SIZE_MB to just 5MB.\u00a0 Note that this is an extremely low value that I do not recommend.<\/p>\n

USE [master];
\nGO
\nALTER DATABASE [WideWorldImporters]
\nSET QUERY_STORE (
\nOPERATION_MODE = READ_WRITE,
\nMAX_STORAGE_SIZE_MB = 5
\n);
\nGO<\/p>\n

 <\/p>\n

If we look at the output from Extended Events, we can see that my change to Query Store is logged:<\/p>\n

\"Extended<\/a>
Extended Events output after Query Store MAX_STORAGE_SIZE changed to 5MB via TSQL<\/figcaption><\/figure>\n

 <\/p>\n

If we check the ERRORLOG, information about the change exists there as well:<\/p>\n

\"ERRORLOG<\/a>
ERRORLOG entry showing Query Store setting change<\/figcaption><\/figure>\n

<\/h2>\n

Finally, a quick peek of the Query Store pane in SSMS confirms the settings:<\/p>\n

\"Query<\/a>
Query Store Settings<\/figcaption><\/figure>\n

Another quick note: these are not the values I would recommend for a production system<\/em>.\u00a0 For more information on settings, check out my Query Store Settings<\/a> post.<\/p>\n

System Changes<\/h2>\n

Now we will explore what gets logged when the OPERATION_MODE setting changes from READ_WRITE to READ_ONLY.\u00a0 We will introduce this by running a very ad hoc workload that generates thousands of queries with different literal values.\u00a0 The code exists in the post, Examining the Performance Impact of an Ad Hoc Workload<\/a>, and we will run usp_RandomSelects from multiple threads with the Extended Events session still running.<\/p>\n

Within a few minutes, the following events show up in the Live Data View:<\/p>\n

\"Extended<\/a>
Extended Events output after MAX_STORAGE_SIZE is exceeded<\/figcaption><\/figure>\n

 <\/p>\n

If we check the ERRORLOG, there are no<\/strong> new entries related to Query Store settings.<\/p>\n

Summary<\/h2>\n

As you can see, changes to Query Store are logged differently, depending on the type of change.\u00a0 Any Query Store option that is changed by a user using the ALTER DATABASE command is captured in the ERRORLOG.\u00a0 The query_store_db_settings_changed event also fires. When the OPERATION_MODE is changed by the system, because the storage allocated to Query Store is exceeded, the change is not captured in the ERRORLOG, but it is captured with the query_store_disk_size_over_limit event. In addition, the query_store_disk_size_info event, which fires on a regular basis, will also report the max and current size values. If you want to know when Query Store changes to a READ_ONLY state, you will need to set up an Extended Events session to capture it. To be more proactive, I recommend setting up an Agent job that runs on a regular basis to monitor the space used<\/a>, and sends an email if it exceeds a certain percentage.<\/p>\n","protected":false},"excerpt":{"rendered":"

The Query Store feature is a bit unique in that its status can change without user interference, which means it is important to understand how changes to Query Store are logged.\u00a0 A couple weeks ago John Deardurff posted a question on Twitter asking specifically whether the SQL Server ERRORLOG is written to when the OPERATION_MODE […]<\/p>\n","protected":false},"author":7,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[42,46],"tags":[],"yoast_head":"\nAre Changes to Query Store Logged? - Erin Stellato<\/title>\n<meta name=\"description\" content=\"Changes to Query Store are logged differently, depending whether they are user or system initiated, and you'll want to know what to check to monitor changes\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.sqlskills.com\/blogs\/erin\/are-changes-to-query-store-logged\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Are Changes to Query Store Logged? 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