RE: intermittent long "log file sync" waits

From: Noveljic Nenad <>
Date: Thu, 2 Jul 2020 08:13:40 +0000
Message-ID: <>

Hi Chris,

>we did that and still experienced the long LFS.

Could you produce ash_wait_chains2 “event2||’ ‘||program2” “event=’log file sync’ for a case with the single log writer and switched off adaptive LFS?

From: <> On Behalf Of Chris Stephens Sent: Montag, 10. Februar 2020 23:16
To: oracle-l <> Subject: Re: intermittent long "log file sync" waits

I was able to capture x$trace output from session w/ 10005:4 for a session experiencing > 1 sec LFS wait.

$ awk '$0 ~ /^*** SESSION ID/ || ($7 > 1000000 && $0 ~ /log file sync/) {print $0}' lsst2db3_ora_1100.trc *** SESSION ID:(8.36700) 2020-02-10T14:26:43.346885-06:00 WAIT #0: nam='log file sync' ela= 1165317 buffer#=18314 sync scn=1014204133 p3=0 obj#=-1 tim=534257573876

however i don't see rows with "data like '%log file%':

SQL> select count(*) from xt_snaps where sid = 8 and serial# = 36700; COUNT(*)


SQL> select count(*) from xt_snaps where sid = 8 and serial# = 36700 and data like '%log file%'; COUNT(*)


Here is a gist of all data corresponding to that sid,serial# (i didn't see anything interesting):

I ran the following (generated from a script executing every 5 seconds looking for new sessions running this workload) to enable that 10005:4 event so i think i got things right:

alter tracing enable "10005:4:8";

Oracle support recommended we set the following and test:

Here are additional steps I would like you to try.

alter system set "_high_priority_processes"='LMS*|LGWR|PMON' scope=spfile;ex
ALTER SYSTEM SET "_use_single_log_writer"=TRUE scope=spfile; <<-- restart required.
ALTER SYSTEM SET "_use_adaptive_log_file_sync"= false;

we did that and still experienced the long LFS.

not sure where to go from here except to the fridge to grab a beer.

On Fri, Feb 7, 2020 at 9:41 AM Priit Piipuu <<>> wrote: Hi,

19c RAC and "log file sync" without associated dbwr activity rings a bell. I noticed similar thing while investigating DRM related problems. In our case GRD gets locked for a few seconds during remastering, and that totally wrecks certain DML heavy workloads. But it looked like a collateral damage and I didn't bother to investigate further. Of course, with remastering going wrong there would be "gcs drm freeze in server mode" wait events, and probably some other gcs related stuff from "Other" wait class. That's not apparent from the traces below.

On Tue, 28 Jan 2020 at 17:11, Chris Stephens <<>> wrote: 3-node Oracle 19.3 RAC
Centos 7

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Received on Thu Jul 02 2020 - 10:13:40 CEST

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