Ms sql updating statistics
The database engine employs statistics when generating execution plans that are used to access data stored within the database.
For that reason, having accurate and up-to-date statistics is crucial.
Auto create statistics and auto update statistics Each database has two options related to statistics: auto create statistics and auto update statistics.
Typically, both should be left enabled for databases.
Statistics are automatically updated when certain thresholds within SQL Server are met, i.e., the number of rows in the table increases or decreases by 10% of the number of rows the statistic was based on.
Additional Information ------------------------------- In SQL 2000 Auto Update stats monitors the rowmodctr value of sysindexes which records number of data changes.
In contrast, if you have invalid or out-of-date statistics, it can lead the SQL Server engine to take the wrong path to the data, and taking the wrong path means that an index scan is made when an index seek would have been appropriate or a seek is performed against the wrong index.
Even worse, it would perform a table scan instead of any index operation at all.
Also, the next time AUTO runs it will overwrite the all the statistics generated from the FULL SCAN.
Rememer, both FULL SCAN and AUTO STATS are updating the same data in sysindexes, so whomever runs last are stats used by the Query Optimizer. -------------------- Use Update Stats with full scan and disable Auto Stats when doing large batch updates and minimal to none ongoing updates.