Re: Deleting millions of rows

On Mon, Feb 2, 2009 at 1:17 PM, Brian Cox <brian(dot)cox(at)ca(dot)com> wrote:
> I'm using 8.3.5. Table ts_defects has 48M rows. Through psql: delete from
> ts_defects;
> Result: out of memory/Can't allocate size: 32
> I then did 10 or so deletes to get rid of the rows. Afterwards, inserts into
> or queries on this
> table performed significantly slower. I tried a vacuum analyze, but this
> didn't help. To fix this,
> I dumped and restored the database.
>
> 1) why can't postgres delete all rows in a table if it has millions of rows?
> 2) is there any other way to restore performance other than restoring the
> database?

Does the table have triggers on it? Does it have indexes? What is the
result of pg_relation_size() on that table?

How much memory do you have in your machine? What is work_mem set to?

Did you try VACUUM FULL instead of just plain VACUUM to recover
performance? You might also need to REINDEX.

Or you could TRUNCATE the table.

...Robert