TRUNCATE pg_largeobject

Hey Tamas,

2011/7/25 Tamas Vincze <vincze@neb.com>

Is it safe?

This table is around 500GB and because of performance reasons
I slowly moved all large objects to regular files on a NetApp
share.

Now it shows 0 records:

# select count(*) from pg_largeobject;
count
-------
0
(1 row)

but disk space and RAM by the free space map is still occupied.
I'd like to clean it up.
A VACUUM FULL would probably do it, but it would take several
hours with heavy I/O and I'd like to avoid that on a production
server.

Can I safely issue a "TRUNCATE pg_largeobject"?
It is v8.1.9.

Thanks!

I think that SELECT lo_unlink(loid) FROM (SELECT DISTINCT loid FROM
pg_largeobject) AS foo
would be better than direct truncation.

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--
// Dmitriy.

Hi Dmitriy,

pg_largeobject is already empty, I have lo_unlink()'ed everything
from it, but it still takes up the same disk space and memory for
the free page maps. I'm looking at the best way to reclaim the
disk/memory from this otherwise empty table.
Normal VACUUM didn't help and I'd like some advice whether to use
VACUUM FULL or TRUNCATE.

-Tamas