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Re: archived WALL files question

From: Frederiko Costa <frederiko(at)gmail(dot)com>
To: pgsql-admin(at)postgresql(dot)org
Subject: Re: archived WALL files question
Date: 2010-04-19 17:10:14
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-admin
I have seen new 16 MB segments files created in pg_xlog directory as 
time goes on. Honestly, I did not understand why it got created, because 
I was running it on a VM and there was no activity. I got several new 

If I run the command you asked, this is the output. Neither segment is 
copied, nor a new segment file gets created:

  select pg_switch_xlog();
(1 row)

Wasn't this command supposed to create a new segment file and copy the 
last non-copied segments - using command specified at archive_command - 
to the destination you defined?

I wanted to understand why the newly created wal segment files (with 16 
MB each) did not copied automatically to the new place. What's the 
criteria? They only get copied when I carry out a base backup.

Thanks for the help!

On 04/19/2010 09:41 AM, Kevin Grittner wrote:
> Frederiko Costa<frederiko(at)gmail(dot)com>  wrote:
>> I noticed the new logs files don't get copied to the directory
>> specified on the archive_command. It's only copied when I do the
>> pg_start_backup()/pg_stop_backup() base backup. Is this behaviour
>> only achieved if I set archive_timeout? I did not want to do that,
>> because I thought as soon as the 16MB WAL segment file got created
>> it would be copied to the exported directory.
> Have you actually been filling up any 16MB WAL file segments?  How
> have you determined that?  What happens when you run (as a database
> superuser) this command?:
> SELECT pg_switch_xlog();
> If the reason you don't want to set archive_timeout is that you
> don't want 16MB files piling up when there is little or no activity,
> you might want to consider using pglesslog or pg_clearxlogtail.
> These can eliminate nearly all the cost of the more frequent logs.
> -Kevin

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