The event filter would be even better - to narrow down the output only for the
affected sessions:
@ash_wait_chains.sql program2||program2 "event='log file sync'"
"to_date('07.10.2019 08:15:21','dd.mm.yyyy hh24:mi:ss')" "to_date('07.10.2019
08:15:34','dd.mm.yyyy hh24:mi:ss')"
From: Noveljic Nenad
Sent: Montag, 7. Oktober 2019 17:27
To: 'dmarc-noreply@xxxxxxxxxxxxx' <dmarc-noreply@xxxxxxxxxxxxx>;
'oracle-l@xxxxxxxxxxxxx' <oracle-l@xxxxxxxxxxxxx>
Subject: RE: LGWR, EMC or app cursors?
Ø Is LGWR waiting on user sessions and user sessions are waiting on LGWR and
all that causes the disk to be 100%? Can I enable some sort of tracing on LGWR
and would that point to exactly what he's waiting on to prove where the problem
is?
Could you post the output of
https://github.com/tanelpoder/tpt-oracle/blob/master/ash/ash_wait_chains.sql ;
for the observed time period to identify what's the root blocker doing?
@ash_wait_chains.sql program2||event2 1=1 "to_date('07.10.2019
08:15:21','dd.mm.yyyy hh24:mi:ss')" "to_date('07.10.2019 08:15:34','dd.mm.yyyy
hh24:mi:ss')"
Best regards,
Nenad
https://nenadnoveljic.com/blog/
From: oracle-l-bounce@xxxxxxxxxxxxx<mailto:oracle-l-bounce@xxxxxxxxxxxxx>
<oracle-l-bounce@xxxxxxxxxxxxx<mailto:oracle-l-bounce@xxxxxxxxxxxxx>> On Behalf
Of Herring, David
Sent: Montag, 7. Oktober 2019 17:18
To: 'oracle-l@xxxxxxxxxxxxx'
<oracle-l@xxxxxxxxxxxxx<mailto:oracle-l@xxxxxxxxxxxxx>>
Subject: LGWR, EMC or app cursors?
Folks, I've got a bit of a mystery with a particular db where we're getting a
periodic 25-30 pause between user sessions and LGWR processes and can't clearly
identify what's the cause.
* The database is 11.2.0.4, RHEL 7.5, running ASM on EMC.
* Sometimes once a day, sometimes more (never more than 5) times a day we
see user processes start waiting on "log file sync". LGWR is waiting on "log
file parallel write".
* At the same time one of the emcpower* devices shows 100% busy and service
time 200+ (from iostat via osw). mpstat shows 1 CPU at 100% on iowait. It's
not always the same disk (emcpowere1, a1, h1, ...), not always the same CPU.
EMC and sysadmins have confirmed there are no disk errors and from their
standpoint the disks are waiting on Oracle.
* During this time LGWR stats in ASH are all 0 - TIME_WAITED, DELTA*
columns. Only after the problem goes away (about 25 secs) these columns are
populated again, obviously the DELTA* columns 1 row later. LGWR's session
state is WAITING so I assume the column value observations are due to LGWR
waiting, as it won't write stats until it can do something.
I am stuck trying to find out, really prove who is the culprit or what exactly
the wait is on. Is LGWR waiting on user sessions and user sessions are waiting
on LGWR and all that causes the disk to be 100%? Can I enable some sort of
tracing on LGWR and would that point to exactly what he's waiting on to prove
where the problem is?
Regards,
Dave
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