Re: pgsql: Add parallel-aware hash joins.

On Thu, Dec 21, 2017 at 10:29 PM, Andres Freund <andres@anarazel.de> wrote:
> On 2017-12-21 08:49:46 +0000, Andres Freund wrote:
>> Add parallel-aware hash joins.
>
> There's to relatively mundane failures:
> https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=tern&dt=2017-12-21%2008%3A48%3A12
> https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=termite&dt=2017-12-21%2008%3A50%3A08

Right, it looks like something takes more space on ppc systems causing
a batch increase that doesn't happen on amd64.  I'll come back to
that.

> but also one that's a lot more interesting:
> https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=capybara&dt=2017-12-21%2008%3A50%3A08
>
> which shows an assert failure:
>
> #2  0x00000000008687d1 in ExceptionalCondition (conditionName=conditionName@entry=0xa76a98
"!(!accessor->sts->participants[i].writing)",errorType=errorType@entry=0x8b2c49 "FailedAssertion",
fileName=fileName@entry=0xa76991"sharedtuplestore.c", lineNumber=lineNumber@entry=273) at assert.c:54 
> #3  0x000000000089883e in sts_begin_parallel_scan (accessor=0xfaf780) at sharedtuplestore.c:273
> #4  0x0000000000634de4 in ExecParallelHashRepartitionRest (hashtable=0xfaec18) at nodeHash.c:1369
> #5  ExecParallelHashIncreaseNumBatches (hashtable=0xfaec18) at nodeHash.c:1198
> #6  0x000000000063546b in ExecParallelHashTupleAlloc (hashtable=hashtable@entry=0xfaec18, size=40,
shared=shared@entry=0x7ffee26a8868)at nodeHash.c:2778 
> #7  0x00000000006357c8 in ExecParallelHashTableInsert (hashtable=hashtable@entry=0xfaec18, slot=slot@entry=0xfa76f8,
hashvalue=<optimizedout>) at nodeHash.c:1696 
> #8  0x0000000000635b5f in MultiExecParallelHash (node=0xf7ebc8) at nodeHash.c:288
> #9  MultiExecHash (node=node@entry=0xf7ebc8) at nodeHash.c:112
>
> which seems to suggest that something in the state machine logic is
> borked. ExecParallelHashIncreaseNumBatches() should've ensured that
> everyone has called sts_end_write()...

Hmm.  This looks the same as the one-off single assertion failure that
I mentioned[1] and had not been able to reproduce.  Investigating.

[1] https://www.postgresql.org/message-id/CAEepm%3D0oE%3DyO0Kam86W1d-iJoasWByYkcrkDoJu6t5mRhFGHkQ%40mail.gmail.com

--
Thomas Munro
http://www.enterprisedb.com