Hi,

On 9/22/10 3:59 AM, Niblett, David A wrote:
> The only way you can usually get a Postgres DB table to go down to the actual 
> size of the data is to dump and restore.  That's the point of a database, it 
> allocates space, marks unused space and overwrites that old space with new 
> data.  This keeps the database from having to constantly add and remove space.

With Postgresql, there also are the options of VACUUM FULL (bad for 
production, locks the database and can run for ages on a huge DB) and 
Slony replication to a new DB (takes Slony knowledge).

> It's done a calculation and determined that that free row space you have now 
> is a good buffer amount.  So you likely won't see the database grow much 
> (unless you start storing a lot more mail) or decrease in size either.
>
> Unless you have some compelling reason to decrease the size, I wouldn't worry 
> about it.  I think mine has been stuck at 37G for nearly 2 years now.  It 
> just adds and deletes within the spare space.

You are right here.  Perhaps the only practical case when one can really 
want to reduce the filesystem footprint of a DB is after experimenting 
with a copy of a very large table or similar, e.g.:
CREATE TABLE foo AS SELECT ... FROM dbmail_messageblks;
play around with table foo;
DROP TABLE foo.

Yar
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