Re: Doubt w.r.t vacuum

On 28 Jul 2003 at 9:56, Alvaro Herrera wrote:

> On Mon, Jul 28, 2003 at 02:29:36PM +0530, Shridhar Daithankar wrote:
> 
> > I was just wondering over it. This is for difference between vacuum full and 
> > vacuum analyze. Can somebody enlighten,
> 
> Actually, the different concepts are "lazy vacuum" (plain VACUUM
> command, with or without ANALYZE) and full vacuum ("VACUUM FULL"
> command, with or without ANALYZE).
> 
> Lazy vacuum works one page at a time, so it doesn't need to lock the
> entire table.  It is able to recover empty space from both updated and
> deleted tuples -- in fact, they look the same to it.  All free space on
> each page is defragmented.  Pages with free space are recorded in the
> Free Space Map.  The FSM has limited space available, so only the pages
> with the most free space will be recorded.
> 
> Vacuum full locks the entire table and moves tuples between pages.  It
> leaves all pages full of tuples (except, obviously, the last one), so it
> doesn't need to record them in the FSM.  Pages that are empty at the end
> of the table are truncated.  This was the only version of VACUUM present
> in releases previous to 7.2.

OK. So here is my interpretation,

Vacuum full reclaims the space that is spilled to disk due to insufficient 
vacuumi analyze and/or inadequate FSM size.

So to keep your database free from fat, use adequate FSM and use a autovacuum 
daemon..

Am I going overboard here?

ByeShridhar

--
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