Thread: pgsql: HashAgg: use better cardinality estimate for recursive spilling.
HashAgg: use better cardinality estimate for recursive spilling. Use HyperLogLog to estimate the group cardinality in a spilled partition. This estimate is used to choose the number of partitions if we recurse. The previous behavior was to use the number of tuples in a spilled partition as the estimate for the number of groups, which lead to overpartitioning. That could cause the number of batches to be much higher than expected (with each batch being very small), which made it harder to interpret EXPLAIN ANALYZE results. Reviewed-by: Peter Geoghegan Discussion: https://postgr.es/m/a856635f9284bc36f7a77d02f47bbb6aaf7b59b3.camel@j-davis.com Backpatch-through: 13 Branch ------ master Details ------- https://git.postgresql.org/pg/commitdiff/9878b643f37b1e4167f64a9941244bfabed60623 Modified Files -------------- src/backend/executor/nodeAgg.c | 64 +++++++++++++++++++++++++++--------------- src/include/executor/nodeAgg.h | 2 +- 2 files changed, 43 insertions(+), 23 deletions(-)