Alvaro Herrera wrote: > Hackers, > > I've whacked the subtrans patch enough so that the simple tests (i.e. > non concurrent) for tuple visibility work. I can create a table and > populate it in subtransactions, rollback or commit them selectively and > get the desired effect at the end. Naturally, catalog entries also > behave [somewhat] sanely. Oh, I made pg_subtrans work too. (Though > whether it's relatively bug-free is yet to be proven.) > > I'm now looking at changing the concurrent visibility rules, i.e. > utils/time/tqual.c. It seems to me one of the most important parts is > making TransactionIdIsInProgress() behave, that is, yield true for every > committed and in-progress subtransaction of a current transaction tree. > (Not only the topmost Xid, which is what it currently does.) > > So, the big question is, how do we do this? The most obvious way (to > me) is to keep the whole array inside the PGPROC struct. This would be > nice because it would only need little modification to > access/transam/varsup.c. The main downside is that it potentially > requires a lot of shared memory. Can we afford that? > > I am already keeping the list of committed Xids in a backend-local list, > but of course this is not visible to other backends.
I remember going through this. Other backends will use pg_subtrans to know what transactions are in progress. They have to do the standard lookups to find the status of the parent transaction. The backend-local list of xids is needed so the commit can clean up those subtransaction xids so that later transactions don't have to use pg_subtrans. Does this help? Sorry I haven't gotten your patches in yet. Tom is working on some other back patches. Also, do you have a plan to handle some of the more complex issues like locking in subtransactions? -- 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 2: you can get off all lists at once with the unregister command (send "unregister YourEmailAddressHere" to [EMAIL PROTECTED])
