I know what Vacuum full and truncate are supposed to do. My confusion lies in the fact that we empty table C after Function D finishes. There aren't any current data or records To touch on the table. The MVCC leftovers are all purely dead Rows that should be deleted. Given this, I thought that Vacuum full and truncate should provide exactly the same result. I've attached my original memo to the bottom. -----Original Message----- From: pgsql-performance-owner@xxxxxxxxxxxxxx [mailto:pgsql-performance-owner@xxxxxxxxxxxxxx] On Behalf Of Chris Sent: Tuesday, March 18, 2008 9:11 PM To: Mark Steben Cc: pgsql-performance@xxxxxxxxxxxxxx Subject: Re: question on TRUNCATE vs VACUUM FULL > > So my question is this: Shouldn't VACUUM FULL clean Table C and reclaim > all its space? You've got concepts mixed up. TRUNCATE deletes all of the data from a particular table (and works in all dbms's). http://www.postgresql.org/docs/8.3/interactive/sql-truncate.html VACUUM FULL is a postgres-specific thing which does work behind the scenes to clean up MVCC left-overs. It does not touch any current data or records in the table, it's purely behind the scenes work. http://www.postgresql.org/docs/current/interactive/sql-vacuum.html The two have completely different uses and nothing to do with each other what-so-ever. -- Postgresql & php tutorials http://www.designmagick.com/ -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance [Mark Steben] Table A houses info on all emails that have ever been created for the purpose of being delivered to our end customers. Big table. About 23 million rows. Table B, the 'holding' table is populated with Table A key information via an after trigger whenever Table A is updated or inserted to. Table C, the 'work' table is populated by function D from table B. It is configured exactly like table B. PLPGSQL Function D inserts a predefined number of rows from table B to table C. For purposes of discussion, say 500. Function D, after it does its thing, then deletes the 500 rows it processed from table B, and ALL 500 rows from table C. This entire process, after a sleep period of 10 seconds, repeats itself all day. After each fifth iteration of function D, we perform a VACUUM FULL on both tables B and C. Takes less than 5 seconds. In terms of transaction processing: Table A is processed by many transactions (some read, some update), Table B is processed by - any transaction updating or inserting to Table A via the after trigger (insert, update) - Function D (insert, update, delete) Table C is processed ONLY by function D (insert, update, delete). Nothing else touches it; PG_LOCKS table verifies that that this table is totally free of any transaction Between iterations of function D. -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
