From: | Jeff Frost <jeff(at)frostconsultingllc(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Simon Riggs <simon(at)2ndquadrant(dot)com>, pgsql-admin(at)postgresql(dot)org |
Subject: | Re: does wal archiving block the current client connection? |
Date: | 2006-05-17 05:09:53 |
Message-ID: | Pine.LNX.4.64.0605162157150.32485@discord.home.frostconsultingllc.com |
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Lists: | pgsql-admin pgsql-hackers |
On Wed, 17 May 2006, Tom Lane wrote:
>
> I have a lurking feeling that the still-hypothetical connection between
> archiver and foreground operations might come into operation at pg_clog
> page boundaries (which require emitting XLOG events) --- that is, every
> 32K transactions something special happens. The time delay between
> archiver wedging and foreground wedging would then correspond to how
> long it took the XID counter to reach the next 32K multiple. (Jeff,
> what transaction rate do you see on that server --- is that a plausible
> delay for some thousands of transactions to pass?)
>
> This is just a guess, but if you check the archives for Chris K-L's
> out-of-disk-space server meltdown a year or three ago, you'll see
> something similar.
This sounds interesting and I'll go have a look for this thread in the
archives.
It looks like it's running about 3,000 transactions per minute right now
(around 10pm). I got that by doing the following...tell me if this is
reasonable:
db3:~ $ echo select xact_commit from pg_stat_database where datname =
\'vb_web\'\; | psql vb_web ; sleep 60 ; echo select xact_commit from
pg_stat_database where datname = \'vb_web\'\; | psql vb_web
xact_commit
-------------
806325
(1 row)
xact_commit
-------------
809414
(1 row)
So, doing a little subtraction, I got 3,089 transactions for the 60 second
period I ran it. I would guess it's quite a bit more during the day. That
means it would hit 32k transactions around 10-11 minutes...does that fit in
with our timing from above? (Tom, I'm not sure which timing you're
using.)
--
Jeff Frost, Owner <jeff(at)frostconsultingllc(dot)com>
Frost Consulting, LLC http://www.frostconsultingllc.com/
Phone: 650-780-7908 FAX: 650-649-1954
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