Strip PlaceHolderVars from index operands When pulling up a subquery, we may need to wrap its targetlist items in PlaceHolderVars to enforce separate identity or as a result of outer joins. However, this causes any upper-level WHERE clauses referencing these outputs to contain PlaceHolderVars, which prevents indxpath.c from recognizing that they could be matched to index columns or index expressions, potentially affecting the planner's ability to use indexes.
To fix, explicitly strip PlaceHolderVars from index operands. A PlaceHolderVar appearing in a relation-scan-level expression is effectively a no-op. Nevertheless, to play it safe, we strip only PlaceHolderVars that are not marked nullable. The stripping is performed recursively to handle cases where PlaceHolderVars are nested or interleaved with other node types. To minimize performance impact, we first use a lightweight walker to check for the presence of strippable PlaceHolderVars. The expensive mutator is invoked only if a candidate is found, avoiding unnecessary memory allocation and tree copying in the common case where no PlaceHolderVars are present. Back-patch to v18. Although this issue exists before that, changes in this version made it common enough to notice. Given the lack of field reports for older versions, I am not back-patching further. Reported-by: Haowu Ge <[email protected]> Author: Richard Guo <[email protected]> Discussion: https://postgr.es/m/[email protected] Backpatch-through: 18 Branch ------ REL_18_STABLE Details ------- https://git.postgresql.org/pg/commitdiff/b4cf7442058f0b0f525b5df36f4bbfc73a97ed0c Modified Files -------------- src/backend/optimizer/path/indxpath.c | 109 +++++++++++++++++++++++++++-- src/backend/optimizer/plan/createplan.c | 14 ++-- src/include/optimizer/paths.h | 1 + src/test/regress/expected/groupingsets.out | 95 +++++++++++++++++++++++++ src/test/regress/sql/groupingsets.sql | 46 ++++++++++++ 5 files changed, 256 insertions(+), 9 deletions(-)
