Horton

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

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Peter Geoghegan <pg@bowt.ie>
Cc: Thomas Munro <thomas.munro@enterprisedb.com>, Heikki Linnakangas <hlinnaka@iki.fi>, Pg Hackers <pgsql-hackers@postgresql.org>, Corey Huinker <corey.huinker@gmail.com>
Date: 2017-01-31T15:02:37Z
Lists: pgsql-hackers 
On Tue, Jan 31, 2017 at 12:15 AM, Peter Geoghegan <pg@bowt.ie> wrote:
>> Should this 64KB minimum be mentioned in the documentation?
>
> You mean user-visible documentation, and not just tuplesort.h? I don't
> think that that's necessary. That's a ludicrously low amount of memory
> for a worker to be limited to anyway. It will never come up with
> remotely sensible use of the feature.

I agree.

>> +   if (!btspool->isunique)
>> +   {
>> +       shm_toc_estimate_keys(&pcxt->estimator, 2);
>> +   }
>>
>> Project style: people always tell me to drop the curlies in cases like
>> that.  There are a few more examples in the patch.
>
> I only do this when there is an "else" that must have curly braces,
> too. There are plenty of examples of this from existing code, so I
> think it's fine.

But I disagree on this one.  I think

if (blah)
    stuff();
else
{
    thing();
    gargle();
}

...is much better than

if (blah)
{
    stuff();
}
else
{
    thing();
    gargle();
}

But if there were a comment on a separate line before the call to
stuff(), then I would do it the second way.

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

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