The stats
redo synch writes
redo synch time
appear for a session that sends a "sync" call
to the log writer.
The stats redo writes redo write time appear for LGWR and record the number and duration of writes.
Regards
Jonathan Lewis http://www.oracle.com/technology/community/oracle_ace/ace1.html#lewis
The Co-operative Oracle Users' FAQ http://www.jlcomp.demon.co.uk/faq/ind_faq.html
Cost Based Oracle: Fundamentals http://www.jlcomp.demon.co.uk/cbo_book/ind_book.html
Subject: Log file sync spike Date: Fri, 9 Jun 2006 16:01:03 -0000 From: "Laimutis Nedzinskas" <Laimutis.Nedzinskas@xxxxxxxxxxxxx>
I am trying to understand what is causing "log file sync" 5-15 minutes duration spike in my db. What puzzles me is that I can not see spike in the other activities on my db.
It is strange that:
- "redo write time" statistics does not follow "redo synch time" at the
time of the spike - v$sysstat value of "redo write time" is half of the "redo synch
time".
If "redo synch time" spike happens because of hw problems then why
"redo write time" does not follow it?
If it is not hw issue then what else LGWR can be doing 50% of time(see
the difference between redo write time and redo synch time) ? Or am I hitting yet another V$-bug?
Database statistics in centiseconds follows:
56,105,687 cs redo synch time from v$sysstat 54,796,921 cs log file sync from v$system_event
24,163,771 cs redo write time from v$sysstat
162,672 cs log file switch completion from v$system_event
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