| From: | Melanie Plageman <melanieplageman(at)gmail(dot)com> |
|---|---|
| To: | Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, Jeff Davis <pgsql(at)j-davis(dot)com> |
| Cc: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, Jesse Zhang <sbjesse(at)gmail(dot)com>, dkimura(at)pivotal(dot)io, Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, david(dot)g(dot)kimura(at)gmail(dot)com |
| Subject: | Re: Avoiding hash join batch explosions with extreme skew and weird stats |
| Date: | 2020-05-28 02:25:50 |
| Message-ID: | CAAKRu_b0kGNbUy-8-D2BJ54kSd4Hpd_dyeJtc+sChCgCGJQS+Q@mail.gmail.com |
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| Lists: | pgsql-hackers |
I've attached a rebased patch which includes the "provisionally detach"
deadlock hazard fix approach as well as addresses some of the following
feedback from Jeff Davis provided off-list:
> Can you add some high-level comments that describe the algorithm and
> what the terms mean?
I added to the large comment at the top of nodeHashjoin.c. I've also
added comments to a few of the new members in some structs. Plus I've
added some in-line comments to assist the reviewer that may or may not
be overkill in a final version.
> Can you add some comments to describe what's happening when a batch is
> entering fallback mode?
...
> Can you add some comments describing tuple relocation?
...
> Can you describe somewhere what all the bits for outer matches are for?
All three done.
Also, we kept the batch 0 spilling patch David Kimura authored [1]
separate so it could be discussed separately because we still had some
questions.
It would be great to discuss those, however, keeping them separate might
be more confusing -- I'm not sure.
| Attachment | Content-Type | Size |
|---|---|---|
| v8-0001-Implement-Adaptive-Hashjoin.patch | application/octet-stream | 141.4 KB |
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