Optimize WindowAgg's use of tuplestores When WindowAgg finished one partition of a PARTITION BY, it previously would call tuplestore_end() to purge all the stored tuples before again calling tuplestore_begin_heap() and carefully setting up all of the tuplestore read pointers exactly as required for the given frameOptions. Since the frameOptions don't change between partitions, this part does not make much sense. For queries that had very few rows per partition, the overhead of this was very large.
It seems much better to create the tuplestore and the read pointers once and simply call tuplestore_clear() at the end of each partition. tuplestore_clear() moves all of the read pointers back to the start position and deletes all the previously stored tuples. A simple test query with 1 million partitions and 1 tuple per partition has been shown to run around 40% faster than without this change. The additional effort seems to have mostly been spent in malloc/free. Making this work required adding a new bool field to WindowAggState which had the unfortunate effect of being the 9th bool field in a group resulting in the struct being enlarged. Here we shuffle the fields around a little so that the two bool fields for runcondition relating stuff fit into existing padding. Also, move the "runcondition" field to be near those. This frees up enough space with the other bool fields so that the newly added one fits into the padding bytes. This was done to address a very small but apparent performance regression with queries containing a large number of rows per partition. Reviewed-by: Ashutosh Bapat <ashutosh.bapat....@gmail.com> Reviewed-by: Tatsuo Ishii <is...@postgresql.org> Discussion: https://postgr.es/m/CAHoyFK9n-QCXKTUWT_xxtXninSMEv%2BgbJN66-y6prM3f4WkEHw%40mail.gmail.com Branch ------ master Details ------- https://git.postgresql.org/pg/commitdiff/908a968612f9ed61911d8ca0a185b262b82f1269 Modified Files -------------- src/backend/executor/nodeWindowAgg.c | 162 +++++++++++++++++++++++------------ src/include/nodes/execnodes.h | 22 ++--- 2 files changed, 118 insertions(+), 66 deletions(-)
