Horton

Re: WIP: Faster Expression Processing and Tuple Deforming (including JIT)

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Nico Williams <nico@cryptonector.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, pgsql-hackers@postgresql.org, Heikki Linnakangas <hlinnaka@iki.fi>, Doug Doole <ddoole@salesforce.com>
Date: 2016-12-06T20:27:51Z
Lists: pgsql-hackers 
Hi,

On 2016-12-06 14:19:21 -0600, Nico Williams wrote:
> A bigger concern might be interface stability.  IIRC the LLVM C/C++
> interfaces are not very stable, but bitcode is.

The C API is a lot more stable than the C++ bit, that's the primary
reason I ended up using it, despite the C++ docs being better.


> > I concur with your feeling that hand-rolled JIT is right out.  But
> 
> Yeah, that way lies maintenance madness.

I'm not quite that sure about that. I had a lot of fun doing some
hand-rolled x86 JITing. Not that is a ward against me being mad.  But
more seriously: Manually doing a JIT gives you a lot faster compilation
times, which makes JIT applicable in a lot more situations.


> > I'm not sure that whatever performance gain we might get in this
> > direction is worth the costs.
> 
> Byte-/bit-coding query plans then JITting them is very likely to improve
> performance significantly.

Note that what I'm proposing is a far cry away from that - this converts
two (peformance wise two, size wise one) significant subsystems, but far
from all the executors to be JIT able.  I think there's some more low
hanging fruits (particularly aggregate transition functions), but
converting everything seems to hit the wrong spot in the
benefit/effort/maintainability triangle.

- Andres

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.