Horton

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

Tomas Vondra <tomas.vondra@2ndquadrant.com>

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From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: Peter Geoghegan <pg@bowt.ie>
Cc: Robert Haas <robertmhaas@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>, 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: 2018-02-06T21:30:28Z
Lists: pgsql-hackers 

On 02/06/2018 10:14 PM, Peter Geoghegan wrote:
> On Tue, Feb 6, 2018 at 1:04 PM, Tomas Vondra
> <tomas.vondra@2ndquadrant.com> wrote:
>> Did you do a test with "-O0"? In my experience that makes valgrind tests
>> much more reliable and repeatable. Some time ago we've seen cases that
>> were failing for me but not for others, and I suspect it was due to me
>> using "-O0".
> 
> FWIW, I use -O1 when configure is run for Valgrind. I also turn off
> assertions (this is all scripted). According to the Valgrind manual:
> 
> "With -O1 line numbers in error messages can be inaccurate, although
> generally speaking running Memcheck on code compiled at -O1 works
> fairly well, and the speed improvement compared to running -O0 is
> quite significant. Use of -O2 and above is not recommended as Memcheck
> occasionally reports uninitialised-value errors which don’t really
> exist."
> 

OK, although I was suggesting the optimizations may actually have the
opposite effect - valgrind missing some of the invalid memory accesses
(until the compiler decides not use them for some reason, causing sudden
valgrind failures).

> The manual does also say that there might even be some problems with
> -O1 at a later point, but it sounds like it's probably worth it to me.
> Skink uses -Og, FWIW.
> 

I have little idea what -Og exactly means. It seems to be focused on
debugging experience, and so still does some of the optimizations. Which
I think would explain why skink was not detecting some of the failures
for a long time.

regards

-- 
Tomas Vondra                  http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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