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Thread: bgwriter update question

bgwriter update question

From
"Mark Steben"
Date:

I'm running on 7.4.5 (pre bgwriter) and moving to 8.2 in 3 weeks. I turn fsync off on my testing server. When I update a table I expect the file in the base directory to remain the same size until the next syncpoint when it would then update. But it increases immediately. I thought updates remain in memory until syncpoint in pre-8.0. Am I missing somethng?

 

Thanks for your time

 

Mark Steben

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@utoRevenue™
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Re: bgwriter update question

From
Tom Lane
Date:
"Mark Steben" <msteben@autorevenue.com> writes:
> I'm running on 7.4.5 (pre bgwriter) and moving to 8.2 in 3 weeks. I turn
> fsync off on my testing server. When I update a table I expect the file in
> the base directory to remain the same size until the next syncpoint when it
> would then update. But it increases immediately. I thought updates remain in
> memory until syncpoint in pre-8.0. Am I missing somethng?

The updates don't go to disk immediately (they didn't in 7.4 either).
But we always allocate disk space immediately when needed, to make sure
it's available.  Otherwise we could face the embarrassing situation of
having noplace to put rows inserted by an already-reported-committed
transaction.

            regards, tom lane

Re: bgwriter update question

From
"Mark Steben"
Date:
Thanks Tom, every piece of new information adds to my education.
I'm going to put to bed this effort of trying to verify BGWRITER,
knowing that it works in 8.2 and move on.

Regards,
Mark Steben

-----Original Message-----
From: Tom Lane [mailto:tgl@sss.pgh.pa.us]
Sent: Monday, October 22, 2007 2:18 PM
To: Mark Steben
Cc: pgsql-admin@postgresql.org
Subject: Re: [ADMIN] bgwriter update question

"Mark Steben" <msteben@autorevenue.com> writes:
> I'm running on 7.4.5 (pre bgwriter) and moving to 8.2 in 3 weeks. I turn
> fsync off on my testing server. When I update a table I expect the file in
> the base directory to remain the same size until the next syncpoint when
it
> would then update. But it increases immediately. I thought updates remain
in
> memory until syncpoint in pre-8.0. Am I missing somethng?

The updates don't go to disk immediately (they didn't in 7.4 either).
But we always allocate disk space immediately when needed, to make sure
it's available.  Otherwise we could face the embarrassing situation of
having noplace to put rows inserted by an already-reported-committed
transaction.

            regards, tom lane