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
--
system-independent, adj.: Works equally poorly on all systems.
