Oracle ASH report Overview

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What is ASH report?

Active session history

Sampled active session for into memory buffer every second (V$ACTIVE_SESSION_HISTORY)

Collect active session data only

Writing to disk by AWR snapshots (DBA_HIST_ACTIVE_SESS_HISTORY)

Part of oracle 10g database 

How ASH work?

If example oracle standard program used to run in 5-second now which taking mort hen 10-min need to check that particular sql query why taking 10-min. For AWR report never show this type of performance issue. Awr report showing only top SQL

We can find this kind of issues in ASH report.

Using ASH report can perform detailed analysis V$ACTIVE_SESSION_HISTORY view and DBA_HIST_ACTIVE_SESS_HISTORY view

 

V$ACTIVE_SESSION_HISTORY

displays sampled session activity in the database.

It contains snapshots of active database sessions taken once a second.

For V$Activite_session_history table holed data for only one hour

Whatever data in v$activie_session_history will write DBA_HIST_ACTIVE_SESS_HISTORY in every 10-min.

If user said 30-min back query not running properly we can find v$active_session_history table

DBA_HIST_ACTIVE_SESS_HISTORY

displays the history of the contents of the in-memory active session history of recent system activity.

This view contains snapshots of V$ACTIVE_SESSION_HISTORY.


How to find ASH buffer size and minimum and max sample:

select * from v$sgastat where name like 'ASH_buffers';

select min(sample_time),max(sample_time) from v$active_session_history;


ASH: Dimensions:

1)Session

2)Wait

Event, P1, P2, P3, blocking_sid

3)SQL

Sql_id, Plan_hash,ect

4)Plsql

Top level, Current call

5)Objects

Object#, File#, Block#

6)Application

Program, Module, Action, Client_id, Service


Using ASH data

V$Activite_session_history

DBA_HIST_ACTIVE_SESS_HISTORY

ADDM

ASH report

How to generate ASH report?

@ /oracle/product/12.1.0.2/db/rdbms/admin/ ashrpt.sql

Rac:

@$ORACLE_HOME/rdbms/admin/ashrpti.sql

 

Refer

How to Generate an ASH Report (Doc ID 1433973.1)

How to Identify Tuning opportunity

Important views and terminologies in performance Tuning

Overview of oracle AWR report

Overview of Oracle SQL-Tuning Adviser

Performance tuning basic OS analysis

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