Re: Multi-threaded LGWR
Date: Tue, 26 Apr 2016 18:25:18 -0400
Message-ID: <D3B8A2DC9D3840A69F902DFCD5365BB9_at_RAMPC>
I am interested in knowing more about this too. We have a 12c RAC database with very high volume of redo generation. Recently on a SR opened with Oracle support, the recommendation was to turn off log writer workers by setting the parameter you mentioned below. We were hesitant to do so, as we did not seem to encounter the bugs, which if I recall correctly was on AIX and we are on SUSE Linux. We typically see around 2 of the 10 workers on our system busy. Others are almost always idle.
Ram
From: Mladen Gogala
Sent: Tuesday, April 26, 2016 5:10 PM
To: oracle-l
Subject: Multi-threaded LGWR
Oracle 12c introduced a new feature, namely multi-threaded LGWR. Of course, as it usually happens, you only find out about the new feature when it doesn't work. The problems I encountered are documented in the following support documents:
a.. 1957710.1
b.. 21915719.8
I was unable to find any controlling parameter in the documentation, short of "_use_single_log_writer" which is not really what I want. Does anyone have any details on that mechanism? How big must LOG_BUFFER be to start an additional thread? How do threads write? My guess is that they split the file into peaces and that each thread writes into its own peace of file. Obviously, there are some issues. In 11G, we saw private redo strands, now we have multi-threaded log writer. Did anyone do any research on that? This is a job for systemtap, but I have been traveling and didn't have much time.
Regards
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Mladen Gogala
Oracle Consultant
http://mgogala.freehostia.com
DISCLAIMER: I am solely responsible for any opinion expressed in this email
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Received on Wed Apr 27 2016 - 00:25:18 CEST