Re: 7.4?

On Tue, Feb 25, 2003 at 09:41:13AM -0500, Ericson Smith wrote:

> I was actually thinking about a VACUUM FULL. Currently we have not

VACUUM FULL will always block.  To make a rather nasty comparison,
it's like defragging your disk under Windows: you can't really access
a file which is being moved around.

> problems doing a regular VACUUM. That said, will the new vacuum free as
> much space like the current vacuum full, without the handicap of table
> locking?

Yes and no.  VACUUM FULL recovers space absolutely.  So if you know
that the table has really shrunk, and shrunk permanently (or similar
cases, like 100% of the table was replaced), then you need VACUUM
FULL.  Non-blocking VACUUM will make the freed space available to
Postgres, but not to the filesystem in general.  In other words, the
regular VACUUM should mean that your table size stabilises, given
that your database is always more or less the same number of tuples;
but it will be slightly larger on disk than that number of tuples
strictly requires.  (Is that clear?  If not, maybe someone else can
make it clearer.)

A
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