Re: To find out the Top process or Top User sessions generating highest number of archive logs

  • From: Lei Zeng <leizeng2003@xxxxxxxxx>
  • To: "mdinh@xxxxxxxxx" <mdinh@xxxxxxxxx>, "'jwilton@xxxxxxxxxxxxx'" <jwilton@xxxxxxxxxxxxx>, "mark.powell2@xxxxxx" <mark.powell2@xxxxxx>
  • Date: Fri, 17 Feb 2012 13:31:12 -0800 (PST)

Tanel's snapper script is very handy for trouble shooting if the issue is 
currently going on. 
I would like to add few points if in case you need to trouble shooting this 
type of issue which happened in the past.
 
1) AWR can nail down 'redo size per second' to service 
level ( DBA_HIST_SERVICE_STAT)
That roughly tells a direction where the user/process comes from. 
 
2) check for objects which went through the highest change rate.
This can be done from AWR â??Top Segment by block changeâ?? (pay attention to 
the '% of capture' for accuracy), or from logminer
select TABLE_NAME, OPERATION, count(1) 
from V$LOGMNR_CONTENTS 
group by TABLE_NAME, OPERATION 
order by  TABLE_NAME, OPERATION;
 
3)  From the object, we can check DBA_HIST_SQL_PLAN and DBA_HIST_SQLSTAT to 
see if we can dig out the sql statement.
Or, sometime it is just some background knowledge of what application or 
process could land on those objects.
 
WITH x AS (
    SELECT DISTINCT DBID, SQL_ID, PLAN_HASH_VALUE
    FROM DBA_HIST_SQL_PLAN
    WHERE DBID=? AND OBJECT_NAME=? AND OBJECT_OWNER=?
 ),
 y AS (
    SELECT DBID, INSTANCE_NUMBER,
    LAG(SNAP_ID, 1) OVER (PARTITION BY DBID,INSTANCE_NUMBER ORDER BY 
SNAP_ID) begin_snap_id,
    SNAP_ID end_snap_id, END_INTERVAL_TIME end_snap_time
    FROM DBA_HIST_SNAPSHOT
    WHERE DBID=? AND INSTANCE_NUMBER=? AND END_INTERVAL_TIME BETWEEN ? and ?
 )
 SELECT /*+ NO_MERGE(x) ORDERED */
 y.begin_snap_id||'-'||y.end_snap_id snap_id, y.end_snap_time, 
z.INSTANCE_NUMBER inst#,
 z.SQL_ID, z.PLAN_HASH_VALUE, ROUND(z.ELAPSED_TIME_DELTA/1000000) 
elapsed_seconds,
 ROUND(z.CPU_TIME_DELTA/1000000) cpu_seconds,
    z.ROWS_PROCESSED_DELTA rows_processed, z.BUFFER_GETS_DELTA buffer_gets, 
z.DISK_READS_DELTA  disk_reads, z.EXECUTIONS_DELTA  executions, 
z.PARSE_CALLS_DELTA parses
 FROM DBA_HIST_SQLSTAT z JOIN y ON (z.DBID=y.dbid AND 
z.INSTANCE_NUMBER=y.instance_number AND z.SNAP_ID=y.end_snap_id)
 JOIN x ON (z.DBID=x.dbid AND z.SQL_ID =x.sql_id AND 
z.PLAN_HASH_VALUE=x.plan_hash_value)
 WHERE y.begin_snap_id IS NOT NULL
 ORDER BY y.begin_snap_id, y.end_snap_id, z.SQL_ID, z.PLAN_HASH_VALUE
 
Lei 
DBspeed  http://www.dbspeed.com/product.html



________________________________
From: Michael Dinh <mdinh@xxxxxxxxx>
To: "'jwilton@xxxxxxxxxxxxx'" <jwilton@xxxxxxxxxxxxx>; "mark.powell2@xxxxxx" 
<mark.powell2@xxxxxx> 
Cc: ORACLE-L <oracle-l@xxxxxxxxxxxxx> 
Sent: Friday, February 17, 2012 9:15 AM
Subject: RE: To find out the Top process or Top User sessions generating 
highest number of archive logs

A little late?

But wanted to share.

//www.freelists.org/post/oracle-l/archived-log-switch-detecting-whos-causing-excessive-redo-generation

Michael Dinh
Disparity Breaks Automation (DBA)

Great minds discuss ideas; average minds discuss events; small minds discuss 
people - Eleanor Roosevelt 
Confidence comes not from always being right but from not fearing to be wrong - 
Peter T Mcintyre
 
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On 
Behalf Of Jeremiah Wilton
Sent: Thursday, February 16, 2012 11:13 AM
To: mark.powell2@xxxxxx
Cc: ORACLE-L
Subject: Re: To find out the Top process or Top User sessions generating 
highest number of archive logs

On Feb 16, 2012, at 11:27 AM, Powell, Mark wrote:

> I note that the query below always seems to return smon as the largest redo 
> generator on the couple of systems where I checked so if you are interested 
> in only user sessions you might want to add "and s.username is not null" as a 
> condition to filter out the Oracle rdbms background sessions.

I don't see a good reason to exclude background processes, especially if one 
choses to sample and delta the redo size over a number of samples. What if one 
of them is somehow generating the large amount of redo that the I am trying to 
track down?

If you do choose to exclude background processes, there's a column for that in 
gv$session.  Just select where type != 'BACKGROUND'.

Another trick to avoid doing deltas (why are we avoiding that when we have 
Tanel's snapper handy?) might be to divide the redo size by the length of time 
the session has been logged in.  That way you get sort of redo size per unit 
time figure, instead of the grand total for the lifetime of the session (which 
is what is making SMON look so large).

Regards,
--
Jeremiah Wilton
http://www.bluegecko.net
Remote DBA Services

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