You control the amount of historical
AWR statistics by setting a retention period and a snapshot interval. In
general, snapshots are removed automatically in chronological order. Snapshots
that belong to baselines are retained until their baselines are removed or expire. On a typical system with
10 active sessions, AWR collections require 200 MB to 300 MB of space if the
data is kept for seven days. The space consumption depends mainly on the number
of active sessions in the system. A sizing script, utlsyxsz.sql, includes factors such as the size of
the current occupants of the SYSAUX tablespace, number of
active sessions, frequency of snapshots, and retention time. The awrinfo.sql script produces a report of
the estimated growth rates of various occupants of the SYSAUX tablespace. Both scripts are located
in the $ORACLE_HOME/rdbms/admin directory.
AWR handles space management for the
snapshots. Every night the MMON process purges snapshots that are older than
the retention period. If AWR detects that SYSAUX
is out of space, it automatically reuses the space occupied by the oldest set
of snapshots by deleting them. An alert is then sent to the DBA to indicate
that SYSAUX is under space pressure.
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