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Re: archive log

From: Mike heydon <pgbison_at_iafrica.com>
Date: 1997/12/05
Message-ID: <01bd0145$91585b60$29af0bc4@mheydon>#1/1

> but for some reason, after archivelog is enable the system seems to be
> very slow...
> does the archivelog generally use a lot of system resources?
>
> is there a way to set it so it doesn't uses alot of system resource?

One of the major causes of poor system peformance with archiving is CHECKPOINTS. A checkpoint will occur at every redo log switch or in accordance to the log_checkpoint_interval and log_checkpoint_timeout. When Oracle is performing a checkpoint NOTHING else can happen as it is ensuring that whatever is in memory in the SGA is written out to disk. If checkpoints are happening too frequently then you will have a performance penalty.

How to rectify this ?

Set parameter log_checkpoints_to_alert = true in init ora file. This will give you the interval that checkpoints are occuring in the alert log. They should ideally be occuring every 30-60 minutes. If they are not then your redo log files are probably too small. Increase their size and set log_checkpoint_interval = 0 (Disable timed checkpoints) and set log_checkpoint_interval = xx where xx is a size BIGGER than your redo log size. This will ensure that checkpoints ONLY occur when a redo log switch occurs. The frequency of log switching and checkpoints are now controllable by the size of the redo log files.

Other thingies .....

Make sure checkpoint_process = true in init ora file. This reduces the work LGWR (Log writer) has to do. If this parameter is NOT set the LGWR has to do Checkpoints as well as writing the redo logs.

Check the alert log to ensure that LGWR is NOT waiting for ARCH (Archiver process). If it is then a peformance bottleneck is happenening. The solution to this is to ADD more redo logs so that LGWR is always able to write to a redo log. It cannot write to a redo log if ARCH is busy archiving it. The normal amount of redo logs when Archiving is active is 4 to 5.

Good Luck
Mike Heydon Received on Fri Dec 05 1997 - 00:00:00 CST

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