On Tue, Dec 21, 2004 at 10:54:27AM -0500, Tom Lane wrote: > Patrick Hatcher <[EMAIL PROTECTED]> writes: > > Curious: Why would a DELETE FROM tablename work while a pg_dump is > > occurring but a TRUNCATE tablename will stay in a lock state until the > > pg_dump is complete? > > TRUNCATE requires an exclusive lock on the table. > > This is pretty much a no-free-lunch situation: if you want the pg_dump > to be able to dump all the rows that existed when it started, you can > hardly expect to be able to physically remove those rows meanwhile.
I'm wondering though, in principle TRUNCATE could be written to simply update relfilenode and create a new file and new indexes. Old transactions will use the old table, new transactions will see an empty table. I guess the main problem with this would knowing when to delete the old table (and assocated indexes, etc...). Basically, it could be equivalent to: DROP TABLE/CREATE TABLE/CREATE INDEXes... I wonder if the file manager can handle multiple tables with the same oid? Have a nice day, -- Martijn van Oosterhout <[EMAIL PROTECTED]> http://svana.org/kleptog/ > Patent. n. Genius is 5% inspiration and 95% perspiration. A patent is a > tool for doing 5% of the work and then sitting around waiting for someone > else to do the other 95% so you can sue them.
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