Horton

Re: pgsql: Add parallel-aware hash joins.

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

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: Andres Freund <andres@anarazel.de>, Robert Haas <robertmhaas@gmail.com>, Thomas Munro <thomas.munro@enterprisedb.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2018-01-24T20:36:35Z
Lists: pgsql-hackers 
Alvaro Herrera <alvherre@alvh.no-ip.org> writes:
> Andres Freund wrote:
>> Besides larger groups, starting the next test(s) earlier, another way to
>> gain pretty large improvements would be a test schedule feature that
>> allowed to stat dependencies between tests. So instead of manually
>> grouping the schedule, have 'numerology' state that it depends on int2,
>> int4, int8, float4, float8, which means it can actually be started
>> earlier than it currently can in many cases.

> Yeah, I proposed this a decade ago but never had the wits to write the
> code.

There'd be a lot of followup work to sanitize the tests better.  For
instance, if two tests transiently create tables named "foo", it doesn't
matter as long as they're not in the same group.  It would matter with
this.

There are things we could do to mitigate that --- one attractive idea
is to have each test create its own schema for transient objects.
The limiting factor is that we don't want the test scripts to change
so much that back-patching tests becomes impossible.  (Or at least,
I'd not like that.)

I'm concerned that we'd end up with a higher number of irreproducible
test failures with no good way to investigate them.

> It would be very useful for running tests standalone, too -- much as I
> dislike 'make installcheck' taking half a minute, I dislike much more
> having to take 5 minutes each time to figure out that create_table
> depends on box, polygon, create_function, yadda yadda.

Yeah, if we could say "run just this test and its needed precursors",
that'd be a huge win in a lot of situations.

Definitely seems like an idea worth pursuing.

			regards, tom lane

Commits

  1. Update obsolete sentence in README.parallel.

  2. Rewrite ConditionVariableBroadcast() to avoid live-lock.

  3. Tweak parallel hash join test case in hopes of improving stability.

  4. Rename pg_rewind's copy_file_range() to avoid conflict with new linux syscall.

  5. Fix some minor errors in new PHJ code.

  6. Fix EXPLAIN ANALYZE output for Parallel Hash.

  7. Fix rare assertion failure in parallel hash join.

  8. Cancel CV sleep during subtransaction abort.

  9. Add parallel-aware hash joins.

  10. Fix EXPLAIN ANALYZE of hash join when the leader doesn't participate.

  11. Add some regression tests that exercise hash join code.