Обсуждение: AW: Adding index flag showing tuple status
> I am looking at adding an index tuple flag to indicate when a > heap tuple is expired so the index code can skip looking up the heap tuple. > > The problem is that I can't figure out how be sure that the heap tuple > doesn't need to be looked at by _any_ backend. Right now, we update the > transaction commit flags in the heap tuple to prevent a pg_log lookup, > but that is not enough because some transactions may still see that heap > tuple as visible. If you are only marking those, that need not be visible anymore, can you not simply delete that key (slot) from the index ? I know vacuum then shows a count mismatch, but that could probably be accounted for. Andreas
>> I am looking at adding an index tuple flag to indicate when a >> heap tuple is expired so the index code can skip looking up the heap tuple. >> >> The problem is that I can't figure out how be sure that the heap tuple >> doesn't need to be looked at by _any_ backend. Right now, we update the >> transaction commit flags in the heap tuple to prevent a pg_log lookup, >> but that is not enough because some transactions may still see that heap >> tuple as visible. > If you are only marking those, that need not be visible anymore, can you not > simply delete that key (slot) from the index ? I know vacuum then shows a count > mismatch, but that could probably be accounted for. I am not sure we need this, if we implement a lightweight VACUUM per my proposal in a nearby thread. The conditions that you could mark or delete an index tuple under are exactly the same that VACUUM would be looking for (viz, tuple dead as far as all remaining transactions are concerned). regards, tom lane
[ Charset ISO-8859-1 unsupported, converting... ] > > > I am looking at adding an index tuple flag to indicate when a > > heap tuple is expired so the index code can skip looking up the heap tuple. > > > > The problem is that I can't figure out how be sure that the heap tuple > > doesn't need to be looked at by _any_ backend. Right now, we update the > > transaction commit flags in the heap tuple to prevent a pg_log lookup, > > but that is not enough because some transactions may still see that heap > > tuple as visible. > > If you are only marking those, that need not be visible anymore, can you not > simply delete that key (slot) from the index ? I know vacuum then shows a count > mismatch, but that could probably be accounted for. I wasn't going to delete it, just add a flag to index scans know they don't need to look at the heap table. -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 853-3000+ If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill, Pennsylvania19026