| From: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
|---|---|
| To: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
| Cc: | Itagaki Takahiro <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Jeff Davis <pgsql(at)j-davis(dot)com>, Alvaro Herrera <alvherre(at)commandprompt(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: New VACUUM FULL |
| Date: | 2009-12-21 12:56:41 |
| Message-ID: | 4B2F7089.6090703@enterprisedb.com |
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| 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
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