Updating statistics sql 2016 r2
If it looks like a significant amount of rows in the column have changed, SQL Server updates the statistic, then optimizes the query.Because why optimize a query on bad data estimates?Prior to 2016, here’s a quick rundown of pros and cons of TF2371: Overall, this is a low risk trace flag.But in general it does NOT pay off to enable trace flags “just in case” for most people.I don’t dig into the internals of statistics and optimization in this post. ⇒ Be a proactive: If you have millions of rows in some of your tables, you can get burned by doing no statistics maintenance at all if query performance stats to get slow and out of date statistics are found to be the cause.If you’re interested in that, head on over and read the fahhhbulous white paper, Statistics Used by the Query Optimizer in SQL Server 2008. Unfortunately, Aristotle was right when it comes to statistics maintenance in SQL Server. This is because you didn’t do any proactive work at all.Statistics are small, and are created super fast– my query isn’t measurably any faster when I run it a second time.Here’s what the statistics look like on the table in Object Explorer. If you want to verify which column is in each auto-created statistic, you can do that with this query: SELECT s.name, s.auto_created, s.user_created, as colname FROM sys.stats AS s JOIN sys.stats_columns as sc on s.stats_id=sc.stats_id and s.object_id=sc.object_id JOIN sys.columns as c on sc.object_id=c.object_id and sc.column_id=c.column_id WHERE s.object_id=OBJECT_ID('agg.
The SQL Server query optimizer uses statistics to estimate how many rows will be returned by parts of your query. By default, the SQL Server optimizer will see that no statistics exists, and wait while two column statistics are created on the First Name Id and Gender columns.
Then wait a couple days and chase it with it’s charming cousin, Optimizing Your Query Plans with the SQL Server 2014 Cardinality Estimator. ⇒ If you’re too proactive, you’ll eventually be sorry: If you set up statistics maintenance too aggressively, your maintenance windows can start to run long.
I’m also not talking about statistics for memory optimized tables in this article. Back when I read philosophy, I found Aristotle a bit annoying because he talked so much about “moderation”. You shouldn’t run statistics maintenance against a database at the same time you’re checking for corruption, rebuilding indexes, or running other IO intensive processes.
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