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Reduce "Var IS [NOT] NULL" quals during constant folding

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In commit b262ad440, we introduced an optimization that reduces an IS
[NOT] NULL qual on a NOT NULL column to constant true or constant
false, provided we can prove that the input expression of the NullTest
is not nullable by any outer joins or grouping sets.  This deduction
happens quite late in the planner, during the distribution of quals to
rels in query_planner.  However, this approach has some drawbacks: we
can't perform any further folding with the constant, and it turns out
to be prone to bugs.

Ideally, this deduction should happen during constant folding.
However, the per-relation information about which columns are defined
as NOT NULL is not available at that point.  This information is
currently collected from catalogs when building RelOptInfos for base
or "other" relations.

This patch moves the collection of NOT NULL attribute information for
relations before pull_up_sublinks, storing it in a hash table keyed by
relation OID.  It then uses this information to perform the NullTest
deduction for Vars during constant folding.  This also makes it
possible to leverage this information to pull up NOT IN subqueries.

Note that this patch does not get rid of restriction_is_always_true
and restriction_is_always_false.  Removing them would prevent us from
reducing some IS [NOT] NULL quals that we were previously able to
reduce, because (a) the self-join elimination may introduce new IS NOT
NULL quals after constant folding, and (b) if some outer joins are
converted to inner joins, previously irreducible NullTest quals may
become reducible.

Author: Richard Guo <guofenglinux@gmail.com>
Reviewed-by: Robert Haas <robertmhaas@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CAMbWs4-bFJ1At4btk5wqbezdu8PLtQ3zv-aiaY3ry9Ymm=jgFQ@mail.gmail.com
This commit is contained in:
Richard Guo
2025-07-22 11:21:36 +09:00
parent 904f6a593a
commit e2debb6438
17 changed files with 336 additions and 81 deletions
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12
src/include/nodes/pathnodes.h
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@@ -179,6 +179,9 @@ typedef struct PlannerGlobal
/* partition descriptors */
PartitionDirectory partition_directory pg_node_attr(read_write_ignore);
/* hash table for NOT NULL attnums of relations */
struct HTAB *rel_notnullatts_hash pg_node_attr(read_write_ignore);
} PlannerGlobal;
/* macro for fetching the Plan associated with a SubPlan node */
@@ -719,6 +722,9 @@ typedef struct PartitionSchemeData *PartitionScheme;
* the attribute is needed as part of final targetlist
* attr_widths - cache space for per-attribute width estimates;
* zero means not computed yet
* notnullattnums - zero-based set containing attnums of NOT NULL
* columns (not populated for rels corresponding to
* non-partitioned inh==true RTEs)
* nulling_relids - relids of outer joins that can null this rel
* lateral_vars - lateral cross-references of rel, if any (list of
* Vars and PlaceHolderVars)
@@ -952,11 +958,7 @@ typedef struct RelOptInfo
Relids *attr_needed pg_node_attr(read_write_ignore);
/* array indexed [min_attr .. max_attr] */
int32 *attr_widths pg_node_attr(read_write_ignore);
/*
* Zero-based set containing attnums of NOT NULL columns. Not populated
* for rels corresponding to non-partitioned inh==true RTEs.
*/
/* zero-based set containing attnums of NOT NULL columns */
Bitmapset *notnullattnums;
/* relids of outer joins that can null this baserel */
Relids nulling_relids;