Horton

Re: Parallel bitmap heap scan

Tom Lane <tgl@sss.pgh.pa.us>

View thread View on postgr.es
From: Tom Lane <tgl@sss.pgh.pa.us>
To: Thomas Munro <thomas.munro@enterprisedb.com>
Cc: Robert Haas <robertmhaas@gmail.com>, Dilip Kumar <dilipbalaut@gmail.com>, Haribabu Kommi <kommi.haribabu@gmail.com>, Rafia Sabih <rafia.sabih@enterprisedb.com>, tushar <tushar.ahuja@enterprisedb.com>, Amit Khandekar <amitdkhan.pg@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>, Andres Freund <andres@anarazel.de>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2017-02-20T00:49:17Z
Lists: pgsql-hackers 
Thomas Munro <thomas.munro@enterprisedb.com> writes:
> One practical problem that came up was the need for executor nodes to
> get a chance to do that kind of cleanup before the DSM segment is
> detached.  In my patch series I introduced a new node API
> ExecNodeDetach to allow for that.  Andres objected that the need for
> that is evidence that the existing protocol is broken and should be
> fixed instead.  I'm looking into that.

The thing that you really have to worry about for this kind of proposal
is "what if the query errors out and we never get to ExecEndNode"?
It's particularly nasty if you're talking about parallel queries where
maybe only one or some of the processes involved detect an error.

			regards, tom lane

Commits

  1. Pass DSA_ALLOC_HUGE when allocating a shared TIDBitmap.

  2. Support parallel bitmap heap scans.

  3. tidbitmap: Support shared iteration.

  4. Shut down Gather's children before shutting down Gather itself.

  5. Revise the way the element allocator for a simplehash is specified.

  6. Refactor bitmap heap scan estimation of heap pages fetched.

  7. Use more efficient hashtable for tidbitmap.c to speed up bitmap scans.