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

3 files changed, 15 insertions, 2 deletions

diff --git a/src/include/access/reloptions.h b/src/include/access/reloptions.h
index b32c1e9efe5..ef09611e0d6 100644
--- a/src/include/access/reloptions.h
+++ b/src/include/access/reloptions.h
@@ -51,6 +51,7 @@ typedef enum relopt_kind
 	RELOPT_KIND_PARTITIONED = (1 << 11),
 	/* if you add a new kind, make sure you update "last_default" too */
 	RELOPT_KIND_LAST_DEFAULT = RELOPT_KIND_PARTITIONED,
+	RELOPT_KIND_INDEX = RELOPT_KIND_BTREE|RELOPT_KIND_HASH|RELOPT_KIND_GIN|RELOPT_KIND_SPGIST,
 	/* some compilers treat enums as signed ints, so we can't use 1 << 31 */
 	RELOPT_KIND_MAX = (1 << 30)
 } relopt_kind;
@@ -276,6 +277,7 @@ extern bytea *heap_reloptions(char relkind, Datum reloptions, bool validate);
 extern bytea *view_reloptions(Datum reloptions, bool validate);
 extern bytea *index_reloptions(amoptions_function amoptions, Datum reloptions,
 				 bool validate);
+extern bytea *index_generic_reloptions(Datum reloptions, bool validate);
 extern bytea *attribute_reloptions(Datum reloptions, bool validate);
 extern bytea *tablespace_reloptions(Datum reloptions, bool validate);
 extern LOCKMODE AlterTableGetRelOptionsLockLevel(List *defList);
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
diff --git a/src/include/utils/relcache.h b/src/include/utils/relcache.h
index 8a546aba283..dbbf41b0c16 100644
--- a/src/include/utils/relcache.h
+++ b/src/include/utils/relcache.h
@@ -53,7 +53,8 @@ extern List *RelationGetIndexPredicate(Relation relation);
 
 typedef enum IndexAttrBitmapKind
 {
-	INDEX_ATTR_BITMAP_ALL,
+	INDEX_ATTR_BITMAP_HOT,
+	INDEX_ATTR_BITMAP_PROJ,
 	INDEX_ATTR_BITMAP_KEY,
 	INDEX_ATTR_BITMAP_PRIMARY_KEY,
 	INDEX_ATTR_BITMAP_IDENTITY_KEY