Collect quals for outer-join reduction on demand To prove that a forced-null Var is non-nullable in every matching row, reduce_outer_joins() uses the strict quals that hold for every row a subtree emits. The first pass currently gathers those quals into each subtree's state, so that the second pass need not re-walk the jointree at decision time.
That duplicates find_subquery_safe_quals(), which already performs this traversal for query_outputs_are_not_nullable(), and it charges every query containing an outer join for a list build at every FromExpr and every inner or semi join, whether or not any upper qual turns out to force a Var null. Since each level copies what its children collected, the space required grows quadratically with the depth of nested inner joins. What it buys is small even then: the walk it avoids is cheap enough to be called on demand. So rename find_subquery_safe_quals() to find_safe_quals(), export it, and drop safe_quals from the first pass's state in favor of the subtree's jointree node. The second pass calls find_safe_quals() at the point where it needs the proof. Also stop treating a semijoin there like a left join: semijoins are reachable from the new caller, and a semijoin emits only matched left-hand rows, so its ON quals do hold for every output row. Author: Richard Guo <[email protected]> Discussion: https://postgr.es/m/cambws4-6fazy7+vcovr0-vqnuaxozic8o4d4zrwmm2woi+q...@mail.gmail.com Branch ------ master Details ------- https://git.postgresql.org/pg/commitdiff/31c002aa89787e4bbe237e36f51dead96b674998 Modified Files -------------- src/backend/optimizer/prep/prepjointree.c | 61 ++++++------------------------- src/backend/optimizer/util/clauses.c | 54 ++++++++++++++++----------- src/include/optimizer/clauses.h | 1 + 3 files changed, 45 insertions(+), 71 deletions(-)
