Re: does wal archiving block the current client connection?

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.)


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Jeff Frost, Owner     <jeff@frostconsultingllc.com>
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