Bruce Momjian wrote: > Tom Lane wrote: > > Heikki Linnakangas <[EMAIL PROTECTED]> writes: > > > We wouldn't clean up tuples that are visible to a transaction, but if > > > you have one long-running transaction like pg_dump in a database with > > > otherwise short transaction, you'll have a lot of tuples that are not > > > vacuumable because of the long-running process, but are not in fact > > > visible to any transaction. > > > > It sounds to me like you are proposing to remove the middles of update > > chains, which would break READ-COMMITTED updates initiated by the older > > transactions. Now admittedly pg_dump isn't going to issue any such > > updates, but VACUUM doesn't know that. > > Since a multi-statement transaction can't change its transaction > isolation level after its first statement, would adding a boolean to > PGPROC help VACUUM be more aggressive about removing rows? I am > thinking something like PGPROC.cannot_be_serializable.
In researching, I found we already do this by updating PGPROC.xid for every command in non-serialzable transactions: * GetTransactionSnapshot * Get the appropriate snapshot for a new query in a transaction. * * The SerializableSnapshot is the first one taken in a transaction. * In serializable mode we just use that one throughout the transaction. * In read-committed mode, we take a new snapshot each time we are called. -- Bruce Momjian <[EMAIL PROTECTED]> http://momjian.us EnterpriseDB http://www.enterprisedb.com + If your life is a hard drive, Christ can be your backup. + ---------------------------(end of broadcast)--------------------------- TIP 6: explain analyze is your friend
