GATHERDATABASESTATS

GATHERDATABASESTATS is a database maintenance operation designed to collect statistics about database objects in order to support the query optimizer's ability to generate efficient execution plans. It updates metadata about tables, indexes, and other objects, which the optimizer uses to estimate cardinalities, selectivity, and plan costs.

In Oracle databases, the closest built-in equivalent is DBMS_STATS.GATHER_DATABASE_STATS, which gathers statistics across all schemas and objects in the database. Other database systems offer similar utilities with different names.

Scope and data collected: It gathers table and index statistics such as number of rows, number of blocks, and space usage; column statistics including density, number of distinct values, and histograms; and, in some implementations, system statistics like I/O or CPU measurements. It may also collect frozen statistics or incremental statistics depending on options.

Usage: Typically run by database administrators as part of regular maintenance or after large data changes. It can be run across the entire database, for a single schema, or for individual objects. Options may control sampling rate, whether dependent objects are included (cascade), and whether existing plans should be invalidated immediately.

Impact and best practices: The operation is resource-intensive and can temporarily affect performance. It is usually scheduled during off-peak times, and many environments use incremental or automatic statistics gathering to balance freshness with overhead. After a stats refresh, applications may observe plan changes; testing is recommended when statistics are updated.

See also: DBMS_STATS, Oracle Database, optimizer statistics, histogram statistics.