Horton

Re: SegFault on 9.6.14

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: Thomas Munro <thomas.munro@gmail.com>, vignesh C <vignesh21@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>, Jerry Sievers <gsievers19@comcast.net>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2019-08-12T21:42:21Z
Lists: pgsql-hackers 
On Mon, Aug 12, 2019 at 3:07 PM Alvaro Herrera <alvherre@2ndquadrant.com> wrote:
> How likely is it that we would ever be able to release memory from a
> Sort (or, say, a hashjoin hash table) when it's done being read, but
> before completing the whole plan?  As I understand, right now we hold
> onto a lot of memory after such plans have been fully read, for no good
> reason other than executor being unaware of this.  This might not be
> directly related to the problem at hand, since it's not just parallel
> plans that are affected.

Being able to do that sort of thing was one of my goals in designing
the ExecShutdownNode stuff.  Unfortunately, it's clear from this bug
report that it's still a few bricks short of a load, and Tom doesn't
seem real optimistic about how easy it will be to buy those bricks at
discount prices. But I hope we persist in trying to get there, because
I don't like the idea of saying that we'll never be smart enough to
know we're done with any part of the plan until we're definitely done
with the whole thing. I think that's leaving too much money on the
table.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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.