Performance - Isolating Waits in a RAC environment

Performance - Isolating Waits in a RAC environment.

Determine the snap IDs you are interested in

For example, to obtain a list of snap IDs from the previous day, execute the following SQL:

SQL> SELECT snap_id, begin_interval_time FROM dba_hist_snapshot WHERE TRUNC(begin_interval_time) = TRUNC(sysdate-1) ;

Step 1 :
--------
Identify the Wait Class

select wait_class_id, wait_class, count(*) cnt
from dba_hist_active_sess_history
where snap_id between &1 and &2
group by wait_class_id, wait_class
order by 3;
2723168908 Idle 1
3290255840 Configuration 9
3386400367 Commit 90
4108307767 System I/O 149
3875070507 Concurrency 182
1740759767 User I/O 184
1893977003 Other 244
4217450380 Application 365
2000153315 Network 475
[NULL] [NULL] 916
3871361733 Cluster 1844

Step 2
-------
Identify the event_id associated with above wait class ID
select event_id, event, count(*) cnt from dba_hist_active_sess_history
where snap_id between 18231 and 18232 and wait_class_id=3871361733
group by event_id, event
order by 3;
EVENT_ID EVENT COUNT(*)
1742950045 gc current retry 1
3897775868 gc current multi block request 1
512320954 gc cr request 4
661121159 gc cr multi block request 9
2685450749 gc current grant 2-way 11
3201690383 gc cr grant 2-way 18
1457266432 gc current split 27
3046984244 gc cr block 3-way 41
111015833 gc current block 2-way 62
3570184881 gc current block 3-way 62
737661873 gc cr block 2-way 67
2277737081 gc current grant busy 95
1520064534 gc cr block busy 235
2701629120 gc current block busy 396
1478861578 gc buffer busy 815

Step 3
-------
Identify the SQL_ID associated with the above event_id
select 'gc buffer busy' ,sql_id, count(*) cnt from dba_hist_active_sess_history
where snap_id between 18231 and 18232
and event_id in (1478861578)
group by sql_id having count(*) > 55
UNION
select 'gc current block busy',sql_id, count(*) cnt from dba_hist_active_sess_history
where snap_id between 18231 and 18232
and event_id in (2701629120)
group by sql_id having count(*) > 55
UNION
select 'gc cr block busy',sql_id, count(*) cnt from dba_hist_active_sess_history
where snap_id between 18231 and 18232
and event_id in (1520064534)
group by sql_id having count(*) > 55
order by 2 ;

Wait Event SQL ID waits
--------------------------------------------------------------------------------------
gc buffer busy 5qwhj3nru2jtq 765
gc current block busy 5qwhj3nru2jtq 332

Step 4 :
--------
Identify the SQL statement associated with the above SQL ID
select sql_id,sql_text from dba_hist_sqltext where sql_id in ('5qwhj3nru2jtq')
Output:
INSERT INTO Component_attrMap (Component_id, key, value) VALUES (:1, :2, :3)
Step 5 :
--------
Identify the object associated with the above statement
select current_obj#, count(*) cnt from dba_hist_active_sess_history
where snap_id between 18231 and 18232
and event_id in (1478861578,2701629120)and sql_id='5qwhj3nru2jtq'
group by current_obj#
order by 2;

Obj # Count(*)
67818 1
67988 1096

Step 6 :
-------
Identify the Object associated with the above Object ID
select object_id, owner, object_name, subobject_name, object_type from dba_objects
where object_id in (67988);
OBJECT_ID OWNER OBJECT_NAME SUBOBJECT_NAME
--------- ----- ------------- --------------
67988 SCOTT COMP_ID_INDX1 INDEX

In this case creating a REVERSE KEY index provided the required solution.