Horton

Re: New VACUUM FULL

Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>

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From: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>
To: Simon Riggs <simon@2ndQuadrant.com>
Cc: Itagaki Takahiro <itagaki.takahiro@oss.ntt.co.jp>, Tom Lane <tgl@sss.pgh.pa.us>, Jeff Davis <pgsql@j-davis.com>, Alvaro Herrera <alvherre@commandprompt.com>, pgsql-hackers@postgresql.org
Date: 2009-12-21T12:56:41Z
Lists: pgsql-hackers 
Simon Riggs wrote:
> I notice that during copy_heap_data() we make no attempt to skip pages
> that are all visible according to the visibilitymap. It seems like it
> would be a substantial win to copy whole blocks if all the
> pre-conditions are met (I see what they are). I'm surprised to see that
> neither CLUSTER nor VACUUM FULL made use of this previously. I think we
> either need to implement that or document that vacuum will not skip
> all-visible pages when running VACUUM FULL.

Unfortunately the visibility map isn't completely crash-safe at the
moment (see comments in visibilitymap.c for details). So it's not safe
to use it for such purposes. I was planning to address that in 8.5 but
it seems I won't have the time.

-- 
  Heikki Linnakangas
  EnterpriseDB   http://www.enterprisedb.com