Tom Lane wrote: > Bruce Momjian <[EMAIL PROTECTED]> writes: > > Tom Lane wrote: > >>> * Order duplicate index entries by tid for faster heap lookups > > > >> I don't know why that TODO entry exists, but I think the idea is > >> counterproductive. > > > I assume you are talking about a unique index that probably only has a > > few non-expired rows (in which case the newer rows first is better). > > The TODO deals with cases where you have lots of valid duplicate index > > rows, and you want to spin through all the matching rows in heap order > > rather than randomly. > > Maybe so, but it would degrade the performance in the unique-index case > if we do it as the TODO is worded.
Yes, the wording is just a guide. > My own opinion is that the bitmap-index-lookup approach will be superior > to trying to keep the index entries in TID order. (That's the idea > we've been discussing for awhile of separating the heap-fetch stage from > the index-scan stage: scan the index, make a sparse bitmap of the TIDs > we need to visit, possibly AND or OR this bitmap with maps derived from > other indexes, and finally visit the rows in heap order.) Oh, yes. -- 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 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