Assuming the distribution is constant between customers, adding new rows to the table variation isn't going to change the data distribution. Statistics on a country or region column in a customer table might never need to be updated because the distribution of values doesn't usually change. These additions change the data distribution and make the statistics out of date. Each time new rows are loaded into the data warehouse, new load dates or transaction dates are added.
One best practice is to update statistics on date columns each day as new dates are added. The target is the name of the target index, statistics, or column for which to display statistics information. The table_name is the name of the table that contains the statistics to display, which can't be an external table. You can view already created stats by running the DBCC SHOW_STATISTICS command: DBCC SHOW_STATISTICS (, ) When automatic statistics are created, they'll take the form: WA_Sys_. The creation of stats is logged in sys.dm_pdw_exec_requests under a different user context. This function is used to improve cardinality estimates for the query plan. If statistics are missing, the query optimizer creates statistics on individual columns in the query predicate or join condition. The dedicated SQL pool engine will analyze incoming user queries for missing statistics when the database AUTO_CREATE_STATISTICS option is set to ON. If it estimates that the selected date will return 1 million rows, it will return a different plan. In most cases, it chooses the plan that will execute the fastest.įor example, if the optimizer estimates that the date your query is filtering on will return one row, it will choose one plan. It compares the cost of various query plans, and then chooses the plan with the lowest cost.
The dedicated SQL pool query optimizer is a cost-based optimizer. After loading data into a dedicated SQL pool, collecting statistics on your data is one of the most important things you can do for query optimization.
The more dedicated SQL pool knows about your data, the faster it can execute queries. Statistics in dedicated SQL pool Why use statistics Provided in this article are recommendations and examples for creating and updating query-optimization statistics using the Synapse SQL resources: dedicated SQL pool and serverless SQL pool.
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