Horton

Re: [HACKERS] Parallel tuplesort (for parallel B-Tree index creation)

Te <nospam-abuse@bloodgate.com>

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From: "Tels" <nospam-abuse@bloodgate.com>
To: "Robert Haas" <robertmhaas@gmail.com>
Cc: "Peter Geoghegan" <pg@bowt.ie>, "Andres Freund" <andres@anarazel.de>, "Amit Kapila" <amit.kapila16@gmail.com>, "Thomas Munro" <thomas.munro@enterprisedb.com>, "Rushabh Lathia" <rushabh.lathia@gmail.com>, "Heikki Linnakangas" <hlinnaka@iki.fi>, "Pg Hackers" <pgsql-hackers@postgresql.org>, "Corey Huinker" <corey.huinker@gmail.com>
Date: 2018-02-05T21:39:07Z
Lists: pgsql-hackers 
On Mon, February 5, 2018 4:27 pm, Robert Haas wrote:
> On Mon, Feb 5, 2018 at 1:03 PM, Peter Geoghegan <pg@bowt.ie> wrote:
>> It certainly is common. In the case of logtape.c, we almost always
>> write out some garbage bytes, even with serial sorts. The only
>> difference here is the *sense* in which they're garbage: they're
>> uninitialized bytes, which Valgrind cares about, rather than byte from
>> previous writes that are left behind in the buffer, which Valgrind
>> does not care about.
>
> /me face-palms.
>
> So, I guess another option might be to call VALGRIND_MAKE_MEM_DEFINED
> on the buffer.  "We know what we're doing, trust us!"
>
> In some ways, that seems better than inserting a suppression, because
> it only affects the memory in the buffer.
>
> Anybody else want to express an opinion here?

Are the uninitialized bytes that are written out "whatever was in the
memory previously" or just some "0x00 bytes from the allocation but not
yet overwritten from the PG code"?

Because the first sounds like it could be a security problem - if random
junk bytes go out to the disk, and stay there, information could
inadvertedly leak to permanent storage.

Best regards,

Tels

Commits

  1. Support parallel btree index builds.

  2. Report an ERROR if a parallel worker fails to start properly.

  3. Transfer state pertaining to pending REINDEX operations to workers.

  4. Add a barrier primitive for synchronizing backends.

  5. Allow DML commands that create tables to use parallel query.

  6. Refactor GetOldestXmin() to use flags

  7. Fix regression in parallel planning against inheritance tables.

  8. Don't create "holes" in BufFiles, in the new logtape code.

  9. Simplify the code for logical tape read buffers.

  10. Fix excessive memory consumption in the new sort pre-reading code.

  11. Implement binary heap replace-top operation in a smarter way.

  12. Cosmetic code cleanup in commands/extension.c.

  13. Speed up planner's scanning for parallel-query hazards.

  14. Read from the same worker repeatedly until it returns no tuple.

  15. Improve tuplesort.c to support variable merge order. The original coding