Re: Why does Oracle start another arc process?

From: Howard J. Rogers <dba_at_hjrdba.com>
Date: Sat, 29 Jun 2002 06:32:56 +1000
Message-ID: <afih7g$oqv$1@lust.ihug.co.nz>

"Anton Buijs" <aammbuijs_at_xs4all.nl> wrote in message news:afi2i0$g18$1_at_news1.xs4all.nl...
> The answer is in the values of all the log_arch% parameters from the
> init.ora file or current values from V$PARAMETERS
>

The true answer is that Oracle will dynamically spawn additional archiver processes when it notices that a backlog of online redo logs for archiving is building up. It's trying to do you a favour, and prevent the very nasty system stall you'll get when you try and switch back to an online log which has been checkpointed, but which hasn't yet been archived.

For example, You switch from log 1 to log 2, and then quickly to log 3 and 4. You've only got log 5 between you and switching back to log 1. Meanwhile, the solo archiving process is still plodding along, archiving Log 1. Oracle will notice that 2, 3 and 4 also need to be archived, so spawns additional processes to get them archived. When you finally switch into log 1, you'd discover that logs 2, 3 and 4 have also been archived. There's thus a clear run between you and log 5.

Oracle is then supposed to kill off the additional archiver process, and re-spawn them if needed. But I've rarely seen it do it. The additional processes seem to hang around for ever, idle. Not sure if that's a (minor) bug, or a feature, or operating system dependent.

It is also true that you can set a log_archive_max_processes init.ora parameter. This does not do what it says it will do. It *sounds* as though this will place a *limit* on the number of archivers Oracle is allowed to spawn dynamically. In fact, it indicates the number of archivers you want created at instance startup. Oracle will quite happily spawn processes in excess of this "maximum" if it feels the need.