Horton

Re: SegFault on 9.6.14

Jerry Sievers <gsievers19@comcast.net>

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From: Jerry Sievers <gsievers19@comcast.net>
To: Thomas Munro <thomas.munro@gmail.com>
Cc: Jerry Sievers <gsievers19@comcast.net>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2019-07-17T00:57:50Z
Lists: pgsql-hackers 
Thomas Munro <thomas.munro@gmail.com> writes:

> On Wed, Jul 17, 2019 at 12:26 PM Jerry Sievers <gsievers19@comcast.net> wrote:
>
>> Is this the right sequencing?
>>
>> 1. Start client and get backend pid
>> 2. GDB;  handle SIGUSR1, break, cont
>> 3. Run query
>> 4. bt
>
> Perfect, thanks.  I think I just spotted something:

Dig that!  Great big thanks to you and Tomas, et al for jumping on this.

Please let know if there's anything else I can submit that would be
helpful.


>
>> #11 0x000055666e0359df in ExecShutdownNode (node=node@entry=0x55667033a6c8)
>>     at /build/postgresql-9.6-5O8OLM/postgresql-9.6-9.6.14/build/../src/backend/executor/execProcnode.c:830
>> #12 0x000055666e04d0ff in ExecLimit (node=node@entry=0x55667033a428)
>>     at /build/postgresql-9.6-5O8OLM/postgresql-9.6-9.6.14/build/../src/backend/executor/nodeLimit.c:139
>
> https://github.com/postgres/postgres/blob/REL9_6_STABLE/src/backend/executor/nodeLimit.c#L139
>
> Limit thinks it's OK to "shut down" the subtree, but if you shut down a
> Gather node you can't rescan it later because it destroys its shared
> memory.  Oops.  Not sure what to do about that yet.
>
>
> --
> Thomas Munro
> https://enterprisedb.com
>
>
>

-- 
Jerry Sievers
Postgres DBA/Development Consulting
e: postgres.consulting@comcast.net

Commits

  1. Don't shut down Gather[Merge] early under Limit.

  2. Prohibit shutting down resources if there is a possibility of back up.

  3. Fix buffer usage stats for parallel nodes.

  4. Fix crashes on plans with multiple Gather (Merge) nodes.

  5. Separate reinitialization of shared parallel-scan state from ExecReScan.