Reduce the number of pallocs when building partition bounds

Enterprise / PostgreSQL - David Rowley [postgresql.org] - 6 July 2021 00:24 UTC

In each of the create_*_bound() functions for LIST, RANGE and HASH partitioning, there were a large number of palloc calls which could be reduced down to a much smaller number.

In each of these functions, an array was built so that we could qsort it before making the PartitionBoundInfo. For LIST and HASH partitioning, an array of pointers was allocated then each element was allocated within that array. Since the number of items of each dimension is known beforehand, we can just allocate a single chunk of memory for this.

Similarly, with all partition strategies, we're able to reduce the number of allocations to build the ->datums field. This is an array of Datum pointers, but there's no need for the Datums that each element points to to be singly allocated. One big chunk will do. For RANGE partitioning, the PartitionBoundInfo->kind field can get the same treatment.

We can apply the same optimizations to partition_bounds_copy(). Doing this might have a small effect on cache performance when searching for the correct partition during partition pruning or DML on a partitioned table. However, that's likely to be small and this is mostly about reducing palloc overhead.

Author: Nitin Jadhav, Justin Pryzby, David Rowley

53d86957e9 Reduce the number of pallocs when building partition bounds
src/backend/partitioning/partbounds.c | 194 +++++++++++++++++++++-------------
1 file changed, 123 insertions(+), 71 deletions(-)

Upstream: git.postgresql.org


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