DROP OPTIMIZER STATISTICS statement
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DROP OPTIMIZER STATISTICS statement
Use this statement to erase all optimizer statistics.
DROP OPTIMIZER STATISTICS
Must have DBA authority.
None.
The Adaptive Server Anywhere optimizer uses statistical information to
decide upon the best strategy for executing each statement. Adaptive Server
Anywhere automatically gathers and updates these statistics. These statistics
are stored permanently in the database in the column statistics registry.
Statistics gathered while processing one statement are available when
searching for efficient ways to execute subsequent statements.
Occasionally, the statistics may become inaccurate or relevant statistics may
be unavailable. This condition is most likely to arise when few queries have
been executed since a large amount of data was added, updated, or deleted.
In this situation, the best approach is to execute statements that allow
Adaptive Server Anywhere to scan the new rows sequentially. The internal
statistics are automatically updated as a side effect, allowing the optimizer to
choose better plans for subsequent queries.
The DROP OPTIMIZER STATISTICS statement deletes all internal
statistical data from the column statistics registry. This drastic step leaves the
optimizer with no access to essential statistical information. Without these
statistics, the optimizer may generate very inefficient data access plans,
causing poor database performance.
This statement should be used only during problem determination or when
reloading data into a database that differs substantially from the original data.
♦
SQL/92 Vendor extension
♦
Sybase Not supported by Adaptive Server Enterprise.
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