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Re: Setting visibility map in VACUUM's second phase

From: Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Setting visibility map in VACUUM's second phase
Date: 2012-12-07 03:51:50
Message-ID: CABOikdNnhhpG-fM_g9+2o+m4jKJ_WD00Oyhi5yWkYye4-UGUgg@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Thu, Dec 6, 2012 at 11:31 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

>
> I think taking a second whack at setting the visibility bit is a fine
> idea, but let's drop all the rest of this premature optimization.
>

Fair enough. I thought about doing it that way but was worried that an
additional page scan will raise eyebrows. While it does not affect the
common case because we would have done that scan anyways in the
subsequent vacuum, but in the worst case where most of the pages not
remain all-visible by the time we come back to the second phase of
vacuum, this additional line pointer scan will add some overhead. With
couple of pluses for the approach, I won't mind doing it this way
though.

Thanks,
Pavan

-- 
Pavan Deolasee
http://www.linkedin.com/in/pavandeolasee


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