Horton

Re: WIP: Faster Expression Processing v4

Andres Freund <andres@anarazel.de>

View thread View on postgr.es
From: Andres Freund <andres@anarazel.de>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Heikki Linnakangas <hlinnaka@iki.fi>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, pgsql-hackers@postgresql.org
Date: 2017-03-24T01:00:19Z
Lists: pgsql-hackers 
On 2017-03-23 20:36:32 -0400, Tom Lane wrote:
> So I think that we have got to fix ExecEvalWholeRowVar so that it doesn't
> clobber the state of the slot.  Right at the moment, the only way to do
> that seems to be to do this instead of ExecFetchSlotTupleDatum:
> 
>     tuple = ExecCopySlotTuple(slot);
>     dtuple = (HeapTupleHeader)
>         DatumGetPointer(heap_copy_tuple_as_datum(tuple,
>                                                  slot->tts_tupleDescriptor));
>     heap_freetuple(tuple);

Hm.  One disadvantage would be that repeated whole-row references to the
same table would be a bit slower, because we'd repeatedly form a tuple
from a virtual one - but I have a hard time coming up with a scenario
where that'd matter.  I'd suspect that in the end it'd probably even
have a *positive* performance impact, because right now the next scalar
access will have to deform the whole tuple again, and that seems like a
lot more likely scenario.

Greetings,

Andres Freund

Commits

  1. Improve performance of ExecEvalWholeRowVar.

  2. Remove unreachable code in expression evaluation.

  3. Faster expression evaluation and targetlist projection.

  4. Avoid syntax error on platforms that have neither LOCALE_T nor ICU.

  5. Add configure test to see if the C compiler has gcc-style computed gotos.

  6. Improve regression test coverage for TID scanning.

  7. Improve expression evaluation test coverage.

  8. Fix two errors with nested CASE/WHEN constructs.