Allow HOT updates for some expression indexes

If the value of an index expression is unchanged after UPDATE,
allow HOT updates where previously we disallowed them, giving
a significant performance boost in those cases.

Particularly useful for indexes such as JSON->>field where the
JSON value changes but the indexed value does not.

Submitted as "surjective indexes" patch, now enabled by use
of new "recheck_on_update" parameter.

Author: Konstantin Knizhnik
Reviewer: Simon Riggs, with much wordsmithing and some cleanup

1 files changed, 11 insertions, 1 deletions

diff --git a/src/include/utils/rel.h b/src/include/utils/rel.h
index aa8add544a1..c26c395b0bd 100644
--- a/src/include/utils/rel.h
+++ b/src/include/utils/rel.h
@@ -141,10 +141,12 @@ typedef struct RelationData
 	List	   *rd_statlist;	/* list of OIDs of extended stats */
 
 	/* data managed by RelationGetIndexAttrBitmap: */
-	Bitmapset  *rd_indexattr;	/* identifies columns used in indexes */
+	Bitmapset  *rd_indexattr;	/* columns used in non-projection indexes */
+	Bitmapset  *rd_projindexattr;	/* columns used in projection indexes */
 	Bitmapset  *rd_keyattr;		/* cols that can be ref'd by foreign keys */
 	Bitmapset  *rd_pkattr;		/* cols included in primary key */
 	Bitmapset  *rd_idattr;		/* included in replica identity index */
+	Bitmapset  *rd_projidx;     /* Oids of projection indexes */
 
 	PublicationActions *rd_pubactions;	/* publication actions */
 
@@ -245,6 +247,14 @@ typedef struct ForeignKeyCacheInfo
 	Oid			conpfeqop[INDEX_MAX_KEYS];	/* PK = FK operator OIDs */
 } ForeignKeyCacheInfo;
 
+/*
+ * Options common for all all indexes
+ */
+typedef struct GenericIndexOpts
+{
+	int32		vl_len_;
+	bool        recheck_on_update;
+} GenericIndexOpts;
 
 /*
  * StdRdOptions