Re: SegFault on 9.6.14

Amit Kapila <amit.kapila16@gmail.com>

From: Amit Kapila <amit.kapila16@gmail.com>
To: Thomas Munro <thomas.munro@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Jerry Sievers <gsievers19@comcast.net>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, pgsql-hackers <pgsql-hackers@postgresql.org>, Robert Haas <robertmhaas@gmail.com>
Date: 2019-07-26T04:13:24Z
Lists: pgsql-hackers
On Tue, Jul 23, 2019 at 5:28 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Tue, Jul 23, 2019 at 9:11 AM Thomas Munro <thomas.munro@gmail.com> wrote:
> >
>
> > Another idea from the band-aid-solutions-that-are-easy-to-back-patch
> > department: in ExecutePlan() where we call ExecShutdownNode(), we
> > could write EXEC_FLAG_DONE into estate->es_top_eflags, and then have
> > ExecGatherShutdown() only run ExecParallelCleanup() if it sees that
> > flag.  That's not beautiful, but it's less churn that the 'bool final'
> > argument we discussed before, and could be removed in master when we
> > have a better way.
> >
>
> Right, that will be lesser code churn and it can also work.  However,
> one thing that needs some thought is till now es_top_eflags is only
> set in ExecutorStart and same is mentioned in comments where it is
> declared and it seems we are going to change that with this idea.  How
> about having a separate function ExecBlahShutdown which will clean up
> resources as parallel context and can be called only from ExecutePlan
> where we are calling ExecShutdownNode?  I think both these and the
> other solution we have discussed are on similar lines and another idea
> could be to relax the assert which again is not a superb idea.
>

It seems we don't have a clear preference for any particular solution
among these and neither there appears to be any better idea.  I guess
we can wait for a few days to see if Robert has any views on this,
otherwise, pick one of the above and move ahead.

Robert, let us know if you have any preference or better idea to fix
this problem?

-- 
With Regards,
Amit Kapila.
EnterpriseDB: http://www.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.