Horton

Thread

Commits

  1. Do execGrouping.c via expression eval machinery, take two.

  2. Do execGrouping.c via expression eval machinery.

  3. Introduce ExecQualAndReset() helper.

  1. Expression based grouping equality implementation

    Andres Freund <andres@anarazel.de> — 2017-11-29T08:09:34Z

    Hi,

Similar to [1] (Expression based aggregate transition / combine function
invocation), this patch provides small-medium performance benefits in
order to later enable larger performance benefits with JIT compilation.

What this basically does is to move execGrouping.c functions that
compare tuples for equality (i.e. execTuplesMatch() and the tuplehash
tables themselves) to use the expression evaluation engine. That turns
out to be beneficial on its own because it makes sure we deform all
needed tuples at once, avoid repeated slot_getattr() calls, and because
the branch prediction is better.   Instead of, as previously done,
calling execTuplesMatch() one calls ExecQual(), and sets up the tuples
in the ExprContext.

I'm not yet 100% happy with this:
- currently the function building the comparator is named
  execTuplesMatchPrepare - which ain't quite apt anymore.
- there's now a bit of additional code at callsites to reset the
  ExprContext - was tempted to put that that in a ExecQualAndReset()
  inline wrapper, but that's not entirely trivial because executor.h
  doesn't include memutils.h and ResetExprContext() is declared late.
- I wonder if the APIs for execGrouping.h should get whacked around a
  bit more aggressively - it'd probably be better if the TupleHashTable
  struct were created once instead of being recreated during every
  rescan.
- currently only equality is done via the expression mechanism, I've for
  now just moved execTuplesUnequal() to it's only caller. The semantics
  seems so closely matched to NOT IN() that I don't reallyexpect other
  users.
- A bunch of the pointers to ExprStates are still named *function - that
  seems ok to me, but somebody else might protest.
- some cleanup.

But some comments would be welcome!

I've included the work from [1] here as the patches do conflict.

Greetings,

Andres Freund

[1] https://www.postgresql.org/message-id/20171128003121.nmxbm2ounxzb6n2t@alap3.anarazel.de

  2. Re: Expression based grouping equality implementation

    Andres Freund <andres@anarazel.de> — 2018-01-09T22:25:44Z

    Hi,

On 2017-11-29 00:09:34 -0800, Andres Freund wrote:
> Similar to [1] (Expression based aggregate transition / combine function
> invocation), this patch provides small-medium performance benefits in
> order to later enable larger performance benefits with JIT compilation.

Here's an updated version of the patch.


> - there's now a bit of additional code at callsites to reset the
>   ExprContext - was tempted to put that that in a ExecQualAndReset()
>   inline wrapper, but that's not entirely trivial because executor.h
>   doesn't include memutils.h and ResetExprContext() is declared late.

I've now added ExecQualAndReset(), in patch 0001, and solved the above
problems by including memutils.h and "inlining" ResetExprContext() to
avoid the ordering issue. Not pretty, but seems better than the
alternatives.


I'm not yet quite happy with this, but I thought it'be good to send an
updated version...

- Andres