On Mon, Mar 14, 2011 at 8:52 AM, Robert Haas <robertmh...@gmail.com> wrote: > On Fri, Mar 11, 2011 at 8:07 PM, Bruce Momjian <br...@momjian.us> wrote: >> Currently, if you create a temporary table with the ON COMMIT action of >> DELETE ROWS, the table will truncated for every commit, whether there is >> any data in the table or not. >> >> I measured the overhead using this test: >> >> $ (echo 'CREATE TEMPORARY TABLE TEST2 (x int);'; jot -b 'SELECT 1;' >> 10000) | time psql test > /dev/null >> 6.93 real 0.93 user 0.78 sys >> $ (echo 'CREATE TEMPORARY TABLE TEST2 (x int) ON COMMIT DELETE ROWS;'; >> jot -b 'SELECT 1;' 10000) | time psql test > /dev/null >> 7.93 real 1.02 user 0.72 sys >> >> The overhead measures 14%. Is there a simple way to avoid the repeated >> truncation overhead of such cases? Is this a TODO? > > We might be able to make PreCommit_on_commit_actions() exit quickly > without doing anything if MyXactAccessedTempRel is false. I haven't > tested that solution and am not 100% confident that it's safe, but if > it is I believe it would address your concern.
aside: I find 'on commit drop' tables to be quite useless, especially in plpgsql due to performance issues. it's much better to organize data around a permanent table organized around txid_current(), with something swooping along periodically and cleaning it up. merlin -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
