RE: archivelog performance issues

  • From: Richard Croasmun <rac_oracledba@xxxxxxx>
  • To: <oracle-l@xxxxxxxxxxxxx>
  • Date: Tue, 7 Jul 2009 17:23:43 +0000




On Tue, 7 Jul 2009 12:31:43 -0400 Mark.Bobak@xxxxxxxxxxxx wrote:
 


     Some things to check before you switch to archive log mode:
 
-                     How frequently are you seeing log switches, at peak load 
time?  
 
                 Size your online redo so that you get a switch about every 
15-30 minutes, at peak.
                  If your load variaes greatly from peak to non-peak, you may 
want to use
                 archive_lag_target to get more frequent switches during 
off-peak times.
 
-                    Make sure you have at least three redo log groups.
 
I agree 100% with those that state log archive mode should be based on 
recoverability, not performance.  In addition, from a performance point of 
view, it seems to me that the only additional overhead is a copy of the online 
redo log to an archive log for each log switch.  I would say that all the 
points about log size, frequency of log switches, number of online logs etc 
would apply even when the DB is NOT in archive log mode.  The only exception 
would be having enough online logs (or large enough logs) such that the copy of 
a particular log finishes before the database wants to use that online redo log 
again.  Obviously, if the DB is in archive log mode, the overhead of the copy 
on the DB could be reduced by placing the archive logs on separate disks from 
the database and online logs to minimize I/O contention. An last, but not 
least, don't let the archive log area fill up!!  ;-)  Am I missing anything 
here?
 
Rick

 

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