| From: | Alvaro Herrera <alvherre(at)commandprompt(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Greg Stark <gsstark(at)mit(dot)edu>, Robert Haas <robertmhaas(at)gmail(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: remove flatfiles.c |
| Date: | 2009-09-02 20:03:19 |
| Message-ID: | 20090902200319.GC5314@alvh.no-ip.org |
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| Thread: | |
| Lists: | pgsql-hackers |
Tom Lane escribió:
> Greg Stark <gsstark(at)mit(dot)edu> writes:
> > It scans pages *backwards* from the end (which does wonderful things
> > on rotating media). Marks each live tuple it finds as "moved off",
> > finds a new place for it (using the free space map I think?).
>
> BTW, VACUUM FULL doesn't use the free space map --- that code predates
> the FSM by a lot. It builds its own map of free space during its
> initial lazy-VACUUM-equivalent scan that just removes dead tuples.
Another weird consequence of this is that it bails out if it finds a
tuple larger than it can fit in one of the earlier pages; if there's
dead space to be compacted before that, it's not compacted.
--
Alvaro Herrera http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.
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