expression eval: Reduce number of steps for agg transition invocations

Enterprise / PostgreSQL - Andres Freund [] - 24 February 2020 23:09 EST

Do so by combining the various steps that are part of aggregate transition function invocation into one larger step. As some of the current steps are only necessary for some aggregates, have one variant of the aggregate transition step for each possible combination.

To avoid further manual copies of code in the different transition step implementations, move most of the code into helper functions marked as "always inline".

The benefit of this change is an increase in performance when aggregating lots of rows. This comes in part due to the reduced number of indirect jumps due to the reduced number of steps, and in part by reducing redundant setup code across steps. This mainly benefits interpreted execution, but the code generated by JIT is also improved a bit.

As a nice side-effect it also ends up making the code a bit simpler.

A small additional optimization is removing the need to set aggstate->curaggcontext before calling ExecAggInitGroup, choosing to instead passign curaggcontext as an argument. It was, in contrast to other aggregate related functions, only needed to fetch a memory context to copy the transition value into.

Author: Andres Freund Discussion:

2742c45080 expression eval: Reduce number of steps for agg transition invocations.
src/backend/executor/execExpr.c | 105 ++++++------
src/backend/executor/execExprInterp.c | 307 +++++++++++++++++++++-------------
src/backend/executor/nodeAgg.c | 5 +-
src/backend/jit/llvm/llvmjit_expr.c | 229 +++++++++----------------
src/include/executor/execExpr.h | 34 +---
5 files changed, 332 insertions(+), 348 deletions(-)


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