Horton

Re: WIP: [[Parallel] Shared] Hash

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Peter Geoghegan <pg@heroku.com>
Cc: Thomas Munro <thomas.munro@enterprisedb.com>, Haribabu Kommi <kommi.haribabu@gmail.com>, Pg Hackers <pgsql-hackers@postgresql.org>
Date: 2017-01-11T20:05:02Z
Lists: pgsql-hackers 
On Wed, Jan 11, 2017 at 2:20 PM, Peter Geoghegan <pg@heroku.com> wrote:
> You'd probably still want to throw an error when workers ended up not
> deleting BufFile segments they owned, though, at least for parallel
> tuplesort.

Don't see why.

> This idea is something that's much more limited than the
> SharedTemporaryFile() API that you sketched on the parallel sort
> thread, because it only concerns resource management, and not how to
> make access to the shared file concurrency safe in any special,
> standard way.

Actually, I only intended that sketch to be about resource management.
Sounds like I didn't explain very well.

> Instead, they should be passing around some kind of minimal
> private-to-buffile state in shared memory that coordinates backends
> participating in BufFile unification. Private state created by
> buffile.c, and passed back to buffile.c. Everything should be
> encapsulated within buffile.c, IMV, making parallel implementations as
> close as possible to their serial implementations.

That seems reasonable although I haven't studied the details carefully as yet.

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

Commits

  1. Add shared tuplestores.

  2. Remove BufFile's isTemp flag.

  3. Provide DSM segment to ExecXXXInitializeWorker functions.

  4. Optimize joins when the inner relation can be proven unique.

  5. Fix failure to use clamp_row_est() for parallel joins.

  6. Document lack of validation when attaching foreign partitions.

  7. Fix inclusions of c.h from .h files.

  8. Fix inclusions of postgres_fe.h from .h files.

  9. Bring plpgsql into line with header inclusion policy.

  10. Document intentional violations of header inclusion policy.

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

  12. btree: Support parallel index scans.

  13. Add explicit ORDER BY to a few tests that exercise hash-join code.

  14. Revise hash join code so that we can increase the number of batches

  15. Rewrite hash join to use simple linked lists instead of a