RE: Log Switches in RAC
- From: Rajesh Rao <Rajesh.Rao@xxxxxxxxxxxx>
- To: K Gopalakrishnan <kaygopal@xxxxxxxxx>, "yong321@xxxxxxxxx" <yong321@xxxxxxxxx>, "kaygopal@xxxxxxxxx" <kaygopal@xxxxxxxxx>
- Date: Thu, 12 Nov 2009 22:42:42 -0500
KG
Thank You. Thank You. Thank You.
I wrote a script to get ahead of the log switches .i.e. predict which ones
gonna happen next when a log switch happens on the node running the batch and
perform pre-mature log switches on them. Works like a charm so far. Been
running with 3 times the load, and no impact to online nodes so far.
Thanks
Raj
-----Original Message-----
From: K Gopalakrishnan [mailto:kaygopal@xxxxxxxxx]
Sent: Wednesday, November 11, 2009 6:18 PM
To: yong321@xxxxxxxxx; kaygopal@xxxxxxxxx; Rajesh Rao
Subject: Re: Log Switches in RAC
Yong, you are correct.It is a simple watch dog mechanism to keep the threads
current. Wequery the start SCN of all the members during the log switch and
compare with archive_change# in V$database (same kccdi structure from
controlfile) and force archive the threads with their start_scn <force_scn. May
be I can include a brief discussion when I review my RAC book..
-Gopal
----- Original Message ----
From: Yong Huang <yong321@xxxxxxxxx>
To: kaygopal@xxxxxxxxx; Rajesh.Rao@xxxxxxxxxxxx
Cc: oracle-l@xxxxxxxxxxxxx
Sent: Wed, 11 November, 2009 5:03:42 PM
Subject: Re: Log Switches in RAC
> If any of the thread is not archived for longer duration
> and if the critical changes are recorded in that thread,
> you may not be able recover the database as the physiological
> logging requires all the changes from ALL the thread to make
> the recovery complete
There is (or was?) the concept "force archive SCN". I know of two sources
where this is talked about. Rama Velpuri's "Oracle(8) Backup and
Recovery Handbook" and Lawrence To's "Archiving Tips and Hints". The
latter can be found at
https://support.oracle.com/cgi-bin/cr/getfile.cgi?p_attid=75071.1:219081
"Threads are kept relatively current by forcing log
switches or kicking idle instances to archive. For an open and enabled
thread, a lock is used to kick an idle instance.
For a closed and enabled thread, the ARCH process for an active instance
will log switch and archive the closed
thread. A force archive SCN is maintained in the control file to implement
this feature.
"OPS: The ARCH process scans the archive link list found in the control
file and archives all inactive redo logs
whose SCN is less than the force archive SCN. Oracle strives to archive
any log that contain less than or equal to the
force archive SCN. Generally, the log with the lowest SCN is archived
first."
Yong Huang
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