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Improve performance of numeric sum(), avg(), stddev(), variance(), etc.

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This patch improves performance of most built-in aggregates that formerly
used a NUMERIC or NUMERIC array as their transition type; this includes
not only aggregates on numeric inputs, but some aggregates on integer
inputs where overflow of an int8 value is a possibility.  The code now
uses a special-purpose data structure to avoid array construction and
deconstruction overhead, as well as packing and unpacking overhead for
numeric values.

These aggregates' transition type is now declared as INTERNAL, since
it doesn't correspond to any SQL data type.  To keep the planner from
thinking that that means a lot of storage will be used, we make use
of the just-added pg_aggregate.aggtransspace feature.  The space estimate
is set to 128 bytes, which is at least in the right ballpark.

Hadi Moshayedi, reviewed by Pavel Stehule and Tomas Vondra
This commit is contained in:
Tom Lane
2013-11-16 18:46:34 -05:00
parent 6cb86143e8
commit 69c8fbac20
7 changed files with 354 additions and 178 deletions
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src/include/utils/builtins.h
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@ -989,6 +989,7 @@ extern Datum int4_accum(PG_FUNCTION_ARGS);
extern Datum int8_accum(PG_FUNCTION_ARGS);
extern Datum int8_avg_accum(PG_FUNCTION_ARGS);
extern Datum numeric_avg(PG_FUNCTION_ARGS);
extern Datum numeric_sum(PG_FUNCTION_ARGS);
extern Datum numeric_var_pop(PG_FUNCTION_ARGS);
extern Datum numeric_var_samp(PG_FUNCTION_ARGS);
extern Datum numeric_stddev_pop(PG_FUNCTION_ARGS);