Re: vacuum full, why multiple times ?

Michael Fuhr wrote:
> On Wed, Mar 09, 2005 at 02:02:13AM +0100, Gaetano Mendola wrote:
>
>
>>Basically I'm noticing that a simple vacuum full is not enough to
>>shrink completelly the table:
>>
>># vacuum full verbose url;
>>INFO: vacuuming "public.url"
>>INFO: "url": found 268392 removable, 21286 nonremovable row versions in 8563 pages
>>DETAIL: 22 dead row versions cannot be removed yet.
>
>
> How busy is the database? I'd guess that each time you run VACUUM,
> there are still open transactions that have visibility to the dead
> rows, so VACUUM doesn't touch them. Those transactions eventually
> complete, and eventually VACUUM FULL does what you're expecting.
> I don't know if that's the only possible cause, but I get results
> similar to yours if I have transactions open when I run VACUUM.
>

That was my first tough but it seem strange that 2 dead rows where
grabbing 7883 pages, don't you think ?

# vacuum full verbose url;
INFO: vacuuming "public.url"
INFO: "url": found 74 removable, 21266 nonremovable row versions in 8550 pages
DETAIL: 2 dead row versions cannot be removed yet.
[SNIP]
INFO: "url": moved 11 row versions, truncated 8550 to 8504 pages

and in the next run:

# vacuum full verbose url;
INFO: vacuuming "public.url"
INFO: "url": found 13 removable, 21264 nonremovable row versions in 8504 pages
DETAIL: 0 dead row versions cannot be removed yet.
[SNIP]
INFO: "url": moved 5666 row versions, truncated 8504 to 621 pages

Regards
Gaetano Mendola