I am concerned this is getting beyond my capabilities for 7.4 --- anyone want to help?
--------------------------------------------------------------------------- Tom Lane wrote: > Manfred Koizar <[EMAIL PROTECTED]> writes: > > Maybe. The whole point of my approach is: If we can limit the active > > range of transactions requiring parent xid lookups to a small fraction > > of the range needing pg_clog lookups, then it makes sense to store > > status bits and parent xids in different files. Otherwise keeping > > them together in one file clearly is faster. > > Hmm ... I'm not sure that that's possible. > > But wait a moment. The child xid is by definition always greater than > (newer than) its parent. So if we consult pg_clog and find the > transaction marked committed, *and* the xid is before the window of XIDs > in our snapshot, then even if it's not a top-level xid, the parent must > be before our window too. Therefore we can conclude the transaction is > visible in our snapshot. So indeed there is a good-size range of xids > for which we'll never need to chase the parent link: everything before > the RecentGlobalXmin computed by GetSnapshotData. (We do have to set > subtransactions to committed during parent commit to make this true; > we can't update them lazily. But I think that's okay.) > > Maybe you're right --- we could probably truncate pg_subtrans faster > than pg_clog, and we could definitely expect to keep less of it in > memory than pg_clog. > > regards, tom lane > > ---------------------------(end of broadcast)--------------------------- > TIP 3: if posting/reading through Usenet, please send an appropriate > subscribe-nomail command to [EMAIL PROTECTED] so that your > message can get through to the mailing list cleanly > -- Bruce Momjian | http://candle.pha.pa.us [EMAIL PROTECTED] | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073 ---------------------------(end of broadcast)--------------------------- TIP 4: Don't 'kill -9' the postmaster
