Bruce Momjian wrote: > Tom Lane wrote: > > Alvaro Herrera <[EMAIL PROTECTED]> writes: > > > Here I present the nested transactions patch and the phantom Xids patch > > > that goes with it. > > > > I looked at the phantom XIDs stuff a bit. I still have little confidence > > that the concept is correct :-( but here are some comments on the code > > level. > > > > > + * They are marked immediately in pg_subtrans as direct childs of the topmost > > > + * Xid (no matter how deep we are in the transaction tree), > > > > Why is that a good idea --- won't it cause problems when you > > commit/abort an intermediate level of subtransaction? > > I don't think so. The phantom xid is used only by the outside > transaction waiting for that tuple to be committe or aborted. The > outside tranaction will sleep on the topmost xid completing, then check > the phantom xid status for commit/abort. Within the transaction, I think > he uses command counter to know the creation and destruction sub-xid. > > I think right now phantom xids are used only for making parts of a > subtransaction committed or aborted and only in cases where the tuple is > created and destroyed by parts of the same transaction tree. > > I don't feel too bad about the runtime cost if only subtransactions are > paying that cost. I know we are really stretching the system here but I > would like to try a little more rather than give up and taking a space > hit for all tuples.
Let me add that outside transactions read those phantom xid only when they are doing dirty reads. What I don't understand is when do outside transactions see tuples created inside a transaction? INSERT into a table with a unique key? Once the main transaction commits, these phantom tuples should work just like ordinary tuples except they get their cmin overwritten when they are expired, I think. -- 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])
