Horton

Re: SegFault on 9.6.14

Thomas Munro <thomas.munro@gmail.com>

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From: Thomas Munro <thomas.munro@gmail.com>
To: Jerry Sievers <gsievers19@comcast.net>
Cc: Tomas Vondra <tomas.vondra@2ndquadrant.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2019-07-17T00:44:49Z
Lists: pgsql-hackers 
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:

> #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

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.