Re: WIP: generalized index constraints
От | Jeff Davis |
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Тема | Re: WIP: generalized index constraints |
Дата | |
Msg-id | 1253400834.23353.228.camel@jdavis обсуждение исходный текст |
Ответ на | Re: WIP: generalized index constraints (Tom Lane <tgl@sss.pgh.pa.us>) |
Ответы |
Re: WIP: generalized index constraints
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Список | pgsql-hackers |
On Sat, 2009-09-19 at 18:00 -0400, Tom Lane wrote: > Well, you can't do it *exactly* the same way btree does, but what > I would envision is first insert the index tuple and then do a > dirty-snapshot search for conflicting tuples. The interlock against > conflicting concurrent inserts doesn't need all this new infrastructure > you propose; just wait to see if conflicting transactions commit, same > as we do now. And I do maintain that that sort of code has a high risk > of undetected bugs. How do you prevent deadlocks in the following case? T1: inserts into index T2: inserts into index T1: checks index for conflicts, finds T2 T2: checks index for conflicts, finds T1 We can't say "only wait if your xid is higher" because xid 200 may both insert and check the index before xid 100 even inserts. The way I solve this in my current patch is by assigning a sequence number in a shared memory table for each insert. The sequence number works because a higher sequence number will always be able to see a lower sequence number's tuple, so we can safely say "only wait if you have a higher sequence number". I can tack the same solution onto your idea, but I would need to keep my shared memory table and probably some other infrastructure. It may be less complex than it is currently, however. Simpler ideas welcome. And to clarify the syntax issue, I assume this means that: ((a||b)::circle &&) would look for the column in the index that matches that expression, and then use that attribute number when scanning the index? I'm OK with that; I don't see a lot of obvious value in having separate expressions for the constraint and the index (even if it did have value, it would take some real creativity to find it ;) Regards,Jeff Davis
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