On 9/14/07, Tom Lane <[EMAIL PROTECTED]> wrote: > > > HeapTupleSatisfiesAbort is bogus because it has failed to track recent > changes in tqual.c.
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Oh. I should have been aware. Rather than fix it, though, I question why we need it at all. The only > use of it is in heap_prune_tuplechain() and ISTM that code is redundant, > wrong, or both. > > In the case of a full-page prune, it's redundant because the tuple would > be found anyway by searching its chain from the root tuple. Indeed I > suspect that such a tuple is entered into the newly-dead list twice, > perhaps risking overflow of that array. No, we would never reach an aborted dead tuple from the chain because we would see a live tuple before that. Or the tuple preceding the aborted (first aborted, if there are many) may have been updated again and the chain never reaches to the aborted tuples. Thats the reason why we have HeapTupleSatisfiesAbort to collect any aborted heap-only tuples. In the case of a single-chain prune, it still seems wrong since you'll > eliminate only one of what might be a chain with multiple aborted > entries. If it's OK to leave those other entries for future collection, > then it should be OK to leave this one too. If it's not OK then the > approach needs to be redesigned. Again, since we check every heap-only tuple for aborted dead case we shall collect all such tuples. I think one place where you are confusing (or IOW the code might have confused you ;-)) is that we never reach aborted dead heap-only tuples by following the HOT chain from the root tuple and thats why it needs special treatment. I'm fairly unclear on what the design intention is for recovering from > the case where the last item(s) on a HOT chain are aborted. Please > clarify. > > We don't do anything special. Such a tuple is never reached during HOT chain following because either we would see a visible tuple before that or the older tuple might have been updated again and the chain had moved in a different direction. We only need some special treatment to prune such tuple and hence the business of HeapTupleSatisfiesAbort Having said that, based on our recent discussion about pruning a chain upto and including the latest DEAD tuple in the chain, ISTM that we can get rid of the giving any special treatment to aborted heap-only tuples. Earlier we could not do so for "HOT updated aborted heap-only" because we did not know if its a part of any valid HOT chain. Now (assuming we change the pruning code to always prune everything including the latest DEAD tuple) we guarantee that all DEAD tuples in the chain will be pruned, and hence we can collect any DEAD tuple seen while pruning. I am not sure if I explain this well, may be I should post an example. Need to run now. Thanks, Pavan -- Pavan Deolasee EnterpriseDB http://www.enterprisedb.com
