Understanding When SQL Server statistics will automatically update. During the PASS Summit in November I presented a session on Demystifying Database Statistics (if you attended Summit but missed it, you can stream it from here). During the session I went through a demo that showed the automatic update of a statistic. The database had the Auto Update Statistics option enabled, and I had added almost 2. ![]() Is there a way to restore a SQL Server 2012 database backup to a SQL Server 2008? I tried to attach file, it does not work. Is there a way to update multiple columns in SQL server the same way an insert statement is used? Something like: Update table1 set (a,b,c,d,e,f,g,h,i,j,k)= (t2.a,t2. In this post I am going to explain the importance of recovery models and backup types. Why I am writing this post? Because, when I was teaching about the topic to my. Bulk Import and Export of Data Examples of Bulk Import and Export of XML Documents. Erin, we are running SQL Server 2008 R2 Sp2 and the AUTO update Statistics feature has been enabled, but we still get instances where the statistics were not updated. From this article, developers will get some useful guidelines on bulk data insertion in SQL Server.; Author: Ashrafur Rahaman; Updated:; Section. SQL SERVER 2005 uses ALTER INDEX syntax to reindex database. SQL SERVER 2005 supports DBREINDEX but it will be deprecated in future versions. I can't seem to figure out how this is happening. Here's an example of the file that I'm attempting to bulk insert into SQL server 2005: ***A NICE HEADER HERE. An issue that affected Cumulative Update 1 for Microsoft SQL Server 2014 had previously caused us to remove the update from the download server. ![]() ![]() The number of rows added via the bulk import was just over the limit to trigger an auto- update of statistics for the next query, which I showed. I had many people ask why statistics did not update immediately after the bulk load of the 2. I want to step through the demo that I did at Summit to clarify when an automatic update will occur. The Setup. Start with a copy of the Adventure. Works. 20. 12 database, which you can download from Code. Plex. Ensure that the Auto Update Statistics option is enabled. ![]() IF (SELECT COUNT(*) FROM . After we create the table, we will check to see when statistics last updated. We can use various methods to check statistics date, such as DBCC SHOW. I just created the table, so the Last Updated date is current, and I have not made any changes so the modification count is 0. Invalidating Statistics. For my demo I want to bulk insert enough rows to invalidate the statistics. SQL Server has pre- determined thresholds where it considers statistics to be out- of- date and therefore invalid. The technical article, Statistics Used by the Query Optimizer in Microsoft SQL Server 2. For a regular table, statistics are out of date when: o The table size has gone from 0 to > 0 rows (test 1). The number of rows in the table when the statistics were gathered was 5. The table had more than 5. The Sales. Sales. Order. Detail table has 1. The bulk insert below loads 2. Download the . txt file for the bulk insert here. The statistics are now out of date based on the threshold defined previously, and we would expect that a query or data modification against Sales. Test. Sales. Order. Detail would trigger an update of statistics. But before we try that, let. When a query is executed and its plan is in the cache, the statistics the plan depends on are checked to see if they are out of date. If so, the plan is removed from the cache, and during recompilation of the query, the statistics are updated. The plan also is removed from the cache if any of the statistics it depends on have changed. To be clear, if a query plan exists in cache and that plan uses specific statistics, when the query executes SQL Server checks to see if any of the statistics used in the plan are out of date. If they are, then the automatic update of those statistics occurs. If a plan does not exist in cache for a query, then if the optimizer uses a statistics object that is out of date when the plan compiles, SQL Server will automatically update those statistics. Invoking the Automatic Update. We have not run any query against Sales. Test. Sales. Order. Detail except our bulk insert. At the time that the query compiled for the bulk insert, no statistics for Sales. Test. Sales. Order. Detail were out of date; therefore no statistics required an automatic update. Now let. We could simply assume that the optimizer used this object in the plan. However, in SQL Server 2. XML and confirm this. In his post, Statistics used in a cached query plan, Fabiano Neves Amorim describes a method to capture statistics information from the plan. Please note the following: This information is only available in SQL Server 2. This query requires use of an undocumented trace flag. I do not recommend using this trace flag in a Production environment. This query interrogates the plan cache. The plan cache may be very large for your system, depending on the amount of memory on the server. Before querying the plan, I recommend setting the transaction isolation level to READ UNCOMMITTED, and also recommend using OPTION (MAXDOP 1) to limit CPU utilization. The query may take longer to execute, but it reduces the impact on other queries executing concurrently. If we query the plan cache using Fabio. Paul White has an excellent post, How to Find the Statistics Used to Compile an Execution Plan, which I recommend reading if you. Even though the statement modified Product. ID for three rows (the modification counter for the statistic increased from 2. If the plan does not use a statistic, the statistic will not automatically update, even if the query modifies columns in said statistic key. Summary. As I stated initially, I wanted to write this post to clear up any confusion surrounding automatic updates for statistics. Even if a statistic becomes outdated as the result of a modification, it will not automatically update after the modification completes. The statistic will automatically update the next time a query plan uses it. To reiterate (yes, this might be overkill), SQL Server will automatically update a statistic when: A query compiles for the first time, and a statistic used in the plan is out of date. A query has an existing query plan, but a statistic in the plan is out of date. For those that attended my session at Summit, I hope this helps address any questions you might have still had. If not, please leave a comment and I will get back to you!
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