Обсуждение: pgsql: Relax overly strict rules in select_outer_pathkeys_for_merge()
Relax overly strict rules in select_outer_pathkeys_for_merge() The select_outer_pathkeys_for_merge function made an attempt to build the merge join pathkeys in the same order as query_pathkeys. This was done as it may have led to no sort being required for an ORDER BY or GROUP BY clause in the upper planner. However, this restriction seems overly strict as it required that we match the query_pathkeys entirely or we don't bother putting the merge join pathkeys in that order. Here we relax this rule so that we use a prefix of the query_pathkeys providing that prefix matches all of the join quals. This may provide the upper planner with partially sorted input which will allow the use of incremental sorts instead of full sorts. Author: David Rowley Reviewed-by: Richard Guo Discussion: https://postgr.es/m/CAApHDvrtZu0PHVfDPFM4Yx3jNR2Wuwosv+T2zqa7LrhhBr2rRg@mail.gmail.com Branch ------ master Details ------- https://git.postgresql.org/pg/commitdiff/b592422095655a64d638f541df784b19b8ecf8ad Modified Files -------------- src/backend/optimizer/path/pathkeys.c | 40 +++++++++++++++++++++++++++++------ src/test/regress/expected/join.out | 31 +++++++++++++++++++++++++++ src/test/regress/sql/join.sql | 18 ++++++++++++++++ 3 files changed, 82 insertions(+), 7 deletions(-)