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Make PlaceHolderInfo lookup O(1).

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Up to now we've just searched the placeholder_list when we want to
find the PlaceHolderInfo with a given ID.  While there's no evidence
of that being a problem in the field, an upcoming patch will add
find_placeholder_info() calls in build_joinrel_tlist(), which seems
likely to make it more of an issue: a joinrel emitting lots of
PlaceHolderVars would incur O(N^2) cost, and we might be building
a lot of joinrels in complex queries.  Hence, add an array that
can be indexed directly by phid to make the lookups constant-time.

Discussion: https://postgr.es/m/1405792.1660677844@sss.pgh.pa.us
This commit is contained in:
Tom Lane
2022-08-17 15:35:51 -04:00
parent efd0c16bec
commit 6569ca4397
5 changed files with 50 additions and 14 deletions
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5
src/include/nodes/pathnodes.h
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@@ -357,6 +357,11 @@ struct PlannerInfo
/* list of PlaceHolderInfos */
List *placeholder_list;
/* array of PlaceHolderInfos indexed by phid */
struct PlaceHolderInfo **placeholder_array pg_node_attr(read_write_ignore, array_size(placeholder_array_size));
/* allocated size of array */
int placeholder_array_size pg_node_attr(read_write_ignore);
/* list of ForeignKeyOptInfos */
List *fkey_list;