| From: | "Graeme B(dot) Bell" <grb(at)skogoglandskap(dot)no> |
|---|---|
| To: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Merlin Moncure <mmoncure(at)gmail(dot)com>, "Josh Berkus" <josh(at)agliodbs(dot)com>, postgres performance list <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: Yet another abort-early plan disaster on 9.3 |
| Date: | 2014-09-30 11:34:48 |
| Message-ID: | 9E62E5EE-3E0E-4871-84B4-34E82E1C8AC9@skogoglandskap.no |
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| Lists: | pgsql-hackers pgsql-performance |
>> The existing cost estimation
>> code effectively assumes that they're perfectly uniformly distributed;
>> which is a good average-case assumption but can be horribly wrong in
>> the worst case.
Sorry, just an outsider jumping in with a quick comment.
Every year or two the core count goes up. Can/should/does postgres ever attempt two strategies in parallel, in cases where strategy A is generally good but strategy B prevents bad worst case behaviour? Kind of like a Schrödinger's Cat approach to scheduling. What problems would it raise?
Graeme.
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