Oracle Database 10g now collects the Active Session History (ASH) statistics (mostly the wait statistics for different events) for all active sessions every second, and stores them in a circular buffer in the SGA.
The ASH feature uses about 2MB of SGA memory per CPU.
Current Active Session Data
V$ACTIVE_SESSION_HISTORY enables you to access the ASH statistics. A database session is considered active if it was on the CPU or was waiting for an event that didn’t belong to the Idle wait class (indicated by SESSION_STATE column).
DBA_HIST_ACTIVE_SESSION_HISTORY View
This view in fact is a collection of snapshots from the V$ACTIVE_SESSION_HISTORY view. It is populated either by MMON during its regular snapshot capturing or by MMNL when the memory buffer is full.
Generate ASH Reports
In Oracle Release 2, you can generate ASH Report.
Some of the information it shows are top wait events, top SQL, top SQL command types, and top sessions, among others.
On Database Control:
Performance -> Run ASH Report button
On SQL*Plus:
Run the following script
$ORACLE_HOME/rdbms/admin/ashrpt.sql
Source:Link
The ASH feature uses about 2MB of SGA memory per CPU.
Current Active Session Data
V$ACTIVE_SESSION_HISTORY enables you to access the ASH statistics. A database session is considered active if it was on the CPU or was waiting for an event that didn’t belong to the Idle wait class (indicated by SESSION_STATE column).
DBA_HIST_ACTIVE_SESSION_HISTORY View
This view in fact is a collection of snapshots from the V$ACTIVE_SESSION_HISTORY view. It is populated either by MMON during its regular snapshot capturing or by MMNL when the memory buffer is full.
Generate ASH Reports
In Oracle Release 2, you can generate ASH Report.
Some of the information it shows are top wait events, top SQL, top SQL command types, and top sessions, among others.
On Database Control:
Performance -> Run ASH Report button
On SQL*Plus:
Run the following script
$ORACLE_HOME/rdbms/admin/ashrpt.sql
Source:Link
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