Ignore BRIN indexes when checking for HOT udpates

When determining whether an index update may be skipped by using HOT, we
can ignore attributes indexed only by BRIN indexes. There are no index
pointers to individual tuples in BRIN, and the page range summary will
be updated anyway as it relies on visibility info.

This also removes rd_indexattr list, and replaces it with rd_attrsvalid
flag. The list was not used anywhere, and a simple flag is sufficient.

Patch by Josef Simanek, various fixes and improvements by me.

Author: Josef Simanek
Reviewed-by: Tomas Vondra, Alvaro Herrera
Discussion: https://postgr.es/m/CAFp7QwpMRGcDAQumN7onN9HjrJ3u4X3ZRXdGFT0K5G2JWvnbWg%40mail.gmail.com

doc/src/sgml/indexam.sgml

@@ -126,6 +126,8 @@ typedef struct IndexAmRoutine
     bool        amcaninclude;
     /* does AM use maintenance_work_mem? */
     bool        amusemaintenanceworkmem;
+    /* does AM block HOT update? */
+    bool        amhotblocking;
     /* OR of parallel vacuum flags */
     uint8       amparallelvacuumoptions;
     /* type of data stored in index, or InvalidOid if variable */
@@ -246,6 +248,15 @@ typedef struct IndexAmRoutine
    null, independently of <structfield>amoptionalkey</structfield>.
   </para>
 
+  <para>
+   The <structfield>amhotblocking</structfield> flag indicates whether the
+   access method blocks <acronym>HOT</acronym> when an indexed attribute is
+   updated. Access methods without pointers to individual tuples (like
+   <acronym>BRIN</acronym>) may allow <acronym>HOT</acronym> even in this
+   case. This does not apply to attributes referenced in index predicates,
+   an update of such attribute always disables <acronym>HOT</acronym>.
+  </para>
+
  </sect1>
 
  <sect1 id="index-functions">

src/backend/access/brin/brin.c

@@ -108,6 +108,7 @@ brinhandler(PG_FUNCTION_ARGS)
 	amroutine->amcanparallel = false;
 	amroutine->amcaninclude = false;
 	amroutine->amusemaintenanceworkmem = false;
+	amroutine->amhotblocking = false;
 	amroutine->amparallelvacuumoptions =
 		VACUUM_OPTION_PARALLEL_CLEANUP;
 	amroutine->amkeytype = InvalidOid;

src/backend/access/gin/ginutil.c

@@ -56,6 +56,7 @@ ginhandler(PG_FUNCTION_ARGS)
 	amroutine->amcanparallel = false;
 	amroutine->amcaninclude = false;
 	amroutine->amusemaintenanceworkmem = true;
+	amroutine->amhotblocking = true;
 	amroutine->amparallelvacuumoptions =
 		VACUUM_OPTION_PARALLEL_BULKDEL | VACUUM_OPTION_PARALLEL_CLEANUP;
 	amroutine->amkeytype = InvalidOid;

src/backend/access/gist/gist.c

@@ -77,6 +77,7 @@ gisthandler(PG_FUNCTION_ARGS)
 	amroutine->amcanparallel = false;
 	amroutine->amcaninclude = true;
 	amroutine->amusemaintenanceworkmem = false;
+	amroutine->amhotblocking = true;
 	amroutine->amparallelvacuumoptions =
 		VACUUM_OPTION_PARALLEL_BULKDEL | VACUUM_OPTION_PARALLEL_COND_CLEANUP;
 	amroutine->amkeytype = InvalidOid;

src/backend/access/hash/hash.c

@@ -74,6 +74,7 @@ hashhandler(PG_FUNCTION_ARGS)
 	amroutine->amcanparallel = false;
 	amroutine->amcaninclude = false;
 	amroutine->amusemaintenanceworkmem = false;
+	amroutine->amhotblocking = true;
 	amroutine->amparallelvacuumoptions =
 		VACUUM_OPTION_PARALLEL_BULKDEL;
 	amroutine->amkeytype = INT4OID;

src/backend/access/heap/heapam.c

@@ -3223,7 +3223,7 @@ heap_update(Relation relation, ItemPointer otid, HeapTuple newtup,
 	 * Note that we get copies of each bitmap, so we need not worry about
 	 * relcache flush happening midway through.
 	 */
-	hot_attrs = RelationGetIndexAttrBitmap(relation, INDEX_ATTR_BITMAP_ALL);
+	hot_attrs = RelationGetIndexAttrBitmap(relation, INDEX_ATTR_BITMAP_HOT_BLOCKING);
 	key_attrs = RelationGetIndexAttrBitmap(relation, INDEX_ATTR_BITMAP_KEY);
 	id_attrs = RelationGetIndexAttrBitmap(relation,
 										  INDEX_ATTR_BITMAP_IDENTITY_KEY);

src/backend/access/nbtree/nbtree.c

@@ -113,6 +113,7 @@ bthandler(PG_FUNCTION_ARGS)
 	amroutine->amcanparallel = true;
 	amroutine->amcaninclude = true;
 	amroutine->amusemaintenanceworkmem = false;
+	amroutine->amhotblocking = true;
 	amroutine->amparallelvacuumoptions =
 		VACUUM_OPTION_PARALLEL_BULKDEL | VACUUM_OPTION_PARALLEL_COND_CLEANUP;
 	amroutine->amkeytype = InvalidOid;

src/backend/access/spgist/spgutils.c

@@ -62,6 +62,7 @@ spghandler(PG_FUNCTION_ARGS)
 	amroutine->amcanparallel = false;
 	amroutine->amcaninclude = true;
 	amroutine->amusemaintenanceworkmem = false;
+	amroutine->amhotblocking = true;
 	amroutine->amparallelvacuumoptions =
 		VACUUM_OPTION_PARALLEL_BULKDEL | VACUUM_OPTION_PARALLEL_COND_CLEANUP;
 	amroutine->amkeytype = InvalidOid;

src/backend/utils/cache/relcache.c

@@ -2428,10 +2428,10 @@ RelationDestroyRelation(Relation relation, bool remember_tupdesc)
 	list_free_deep(relation->rd_fkeylist);
 	list_free(relation->rd_indexlist);
 	list_free(relation->rd_statlist);
-	bms_free(relation->rd_indexattr);
 	bms_free(relation->rd_keyattr);
 	bms_free(relation->rd_pkattr);
 	bms_free(relation->rd_idattr);
+	bms_free(relation->rd_hotblockingattr);
 	if (relation->rd_pubactions)
 		pfree(relation->rd_pubactions);
 	if (relation->rd_options)
@@ -5105,10 +5105,10 @@ RelationGetIndexPredicate(Relation relation)
 Bitmapset *
 RelationGetIndexAttrBitmap(Relation relation, IndexAttrBitmapKind attrKind)
 {
-	Bitmapset  *indexattrs;		/* indexed columns */
 	Bitmapset  *uindexattrs;	/* columns in unique indexes */
 	Bitmapset  *pkindexattrs;	/* columns in the primary index */
 	Bitmapset  *idindexattrs;	/* columns in the replica identity */
+	Bitmapset  *hotblockingattrs;   /* columns with HOT blocking indexes */
 	List	   *indexoidlist;
 	List	   *newindexoidlist;
 	Oid			relpkindex;
@@ -5117,18 +5117,18 @@ RelationGetIndexAttrBitmap(Relation relation, IndexAttrBitmapKind attrKind)
 	MemoryContext oldcxt;
 
 	/* Quick exit if we already computed the result. */
-	if (relation->rd_indexattr != NULL)
+	if (relation->rd_attrsvalid)
 	{
 		switch (attrKind)
 		{
-			case INDEX_ATTR_BITMAP_ALL:
-				return bms_copy(relation->rd_indexattr);
 			case INDEX_ATTR_BITMAP_KEY:
 				return bms_copy(relation->rd_keyattr);
 			case INDEX_ATTR_BITMAP_PRIMARY_KEY:
 				return bms_copy(relation->rd_pkattr);
 			case INDEX_ATTR_BITMAP_IDENTITY_KEY:
 				return bms_copy(relation->rd_idattr);
+			case INDEX_ATTR_BITMAP_HOT_BLOCKING:
+				return bms_copy(relation->rd_hotblockingattr);
 			default:
 				elog(ERROR, "unknown attrKind %u", attrKind);
 		}
@@ -5159,7 +5159,7 @@ restart:
 	relreplindex = relation->rd_replidindex;
 
 	/*
-	 * For each index, add referenced attributes to indexattrs.
+	 * For each index, add referenced attributes to appropriate bitmaps.
 	 *
 	 * Note: we consider all indexes returned by RelationGetIndexList, even if
 	 * they are not indisready or indisvalid.  This is important because an
@@ -5168,10 +5168,10 @@ restart:
 	 * CONCURRENTLY is far enough along that we should ignore the index, it
 	 * won't be returned at all by RelationGetIndexList.
 	 */
-	indexattrs = NULL;
 	uindexattrs = NULL;
 	pkindexattrs = NULL;
 	idindexattrs = NULL;
+	hotblockingattrs = NULL;
 	foreach(l, indexoidlist)
 	{
 		Oid			indexOid = lfirst_oid(l);
@@ -5236,8 +5236,9 @@ restart:
 			 */
 			if (attrnum != 0)
 			{
-				indexattrs = bms_add_member(indexattrs,
-											attrnum - FirstLowInvalidHeapAttributeNumber);
+				if (indexDesc->rd_indam->amhotblocking)
+					hotblockingattrs = bms_add_member(hotblockingattrs,
+												 attrnum - FirstLowInvalidHeapAttributeNumber);
 
 				if (isKey && i < indexDesc->rd_index->indnkeyatts)
 					uindexattrs = bms_add_member(uindexattrs,
@@ -5254,10 +5255,15 @@ restart:
 		}
 
 		/* Collect all attributes used in expressions, too */
-		pull_varattnos(indexExpressions, 1, &indexattrs);
+		if (indexDesc->rd_indam->amhotblocking)
+			pull_varattnos(indexExpressions, 1, &hotblockingattrs);
 
-		/* Collect all attributes in the index predicate, too */
-		pull_varattnos(indexPredicate, 1, &indexattrs);
+		/*
+		 * Collect all attributes in the index predicate, too. We have to ignore
+		 * amhotblocking flag, because the row might become indexable, in which
+		 * case we have to add it to the index.
+		 */
+		pull_varattnos(indexPredicate, 1, &hotblockingattrs);
 
 		index_close(indexDesc, AccessShareLock);
 	}
@@ -5285,25 +5291,25 @@ restart:
 		bms_free(uindexattrs);
 		bms_free(pkindexattrs);
 		bms_free(idindexattrs);
-		bms_free(indexattrs);
+		bms_free(hotblockingattrs);
 
 		goto restart;
 	}
 
 	/* Don't leak the old values of these bitmaps, if any */
-	bms_free(relation->rd_indexattr);
-	relation->rd_indexattr = NULL;
 	bms_free(relation->rd_keyattr);
 	relation->rd_keyattr = NULL;
 	bms_free(relation->rd_pkattr);
 	relation->rd_pkattr = NULL;
 	bms_free(relation->rd_idattr);
 	relation->rd_idattr = NULL;
+	bms_free(relation->rd_hotblockingattr);
+	relation->rd_hotblockingattr = NULL;
 
 	/*
 	 * Now save copies of the bitmaps in the relcache entry.  We intentionally
-	 * set rd_indexattr last, because that's the one that signals validity of
-	 * the values; if we run out of memory before making that copy, we won't
+	 * set rd_attrsvalid last, because that's what signals validity of the
+	 * values; if we run out of memory before making that copy, we won't
 	 * leave the relcache entry looking like the other ones are valid but
 	 * empty.
 	 */
@@ -5311,20 +5317,21 @@ restart:
 	relation->rd_keyattr = bms_copy(uindexattrs);
 	relation->rd_pkattr = bms_copy(pkindexattrs);
 	relation->rd_idattr = bms_copy(idindexattrs);
-	relation->rd_indexattr = bms_copy(indexattrs);
+	relation->rd_hotblockingattr = bms_copy(hotblockingattrs);
+	relation->rd_attrsvalid = true;
 	MemoryContextSwitchTo(oldcxt);
 
 	/* We return our original working copy for caller to play with */
 	switch (attrKind)
 	{
-		case INDEX_ATTR_BITMAP_ALL:
-			return indexattrs;
 		case INDEX_ATTR_BITMAP_KEY:
 			return uindexattrs;
 		case INDEX_ATTR_BITMAP_PRIMARY_KEY:
 			return pkindexattrs;
 		case INDEX_ATTR_BITMAP_IDENTITY_KEY:
 			return idindexattrs;
+		case INDEX_ATTR_BITMAP_HOT_BLOCKING:
+			return hotblockingattrs;
 		default:
 			elog(ERROR, "unknown attrKind %u", attrKind);
 			return NULL;
@@ -6180,10 +6187,11 @@ load_relcache_init_file(bool shared)
 		rel->rd_indexlist = NIL;
 		rel->rd_pkindex = InvalidOid;
 		rel->rd_replidindex = InvalidOid;
-		rel->rd_indexattr = NULL;
+		rel->rd_attrsvalid = false;
 		rel->rd_keyattr = NULL;
 		rel->rd_pkattr = NULL;
 		rel->rd_idattr = NULL;
+		rel->rd_hotblockingattr = NULL;
 		rel->rd_pubactions = NULL;
 		rel->rd_statvalid = false;
 		rel->rd_statlist = NIL;

src/include/access/amapi.h

@@ -244,6 +244,8 @@ typedef struct IndexAmRoutine
 	bool		amcaninclude;
 	/* does AM use maintenance_work_mem? */
 	bool		amusemaintenanceworkmem;
+	/* does AM block HOT update? */
+	bool        amhotblocking;
 	/* OR of parallel vacuum flags.  See vacuum.h for flags. */
 	uint8		amparallelvacuumoptions;
 	/* type of data stored in index, or InvalidOid if variable */

src/include/utils/rel.h

@@ -155,10 +155,11 @@ typedef struct RelationData
 	List	   *rd_statlist;	/* list of OIDs of extended stats */
 
 	/* data managed by RelationGetIndexAttrBitmap: */
-	Bitmapset  *rd_indexattr;	/* identifies columns used in indexes */
+	bool		rd_attrsvalid;	/* are bitmaps of attrs valid? */
 	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_hotblockingattr;	/* cols blocking HOT update */
 
 	PublicationActions *rd_pubactions;	/* publication actions */
 

src/include/utils/relcache.h

@@ -55,10 +55,10 @@ extern bytea **RelationGetIndexAttOptions(Relation relation, bool copy);
 
 typedef enum IndexAttrBitmapKind
 {
-	INDEX_ATTR_BITMAP_ALL,
 	INDEX_ATTR_BITMAP_KEY,
 	INDEX_ATTR_BITMAP_PRIMARY_KEY,
-	INDEX_ATTR_BITMAP_IDENTITY_KEY
+	INDEX_ATTR_BITMAP_IDENTITY_KEY,
+	INDEX_ATTR_BITMAP_HOT_BLOCKING
 } IndexAttrBitmapKind;
 
 extern Bitmapset *RelationGetIndexAttrBitmap(Relation relation,

src/test/modules/dummy_index_am/dummy_index_am.c

@@ -298,6 +298,7 @@ dihandler(PG_FUNCTION_ARGS)
 	amroutine->amcanparallel = false;
 	amroutine->amcaninclude = false;
 	amroutine->amusemaintenanceworkmem = false;
+	amroutine->amhotblocking = true;
 	amroutine->amparallelvacuumoptions = VACUUM_OPTION_NO_PARALLEL;
 	amroutine->amkeytype = InvalidOid;
 

src/test/regress/expected/brin.out

@@ -567,3 +567,88 @@ SELECT * FROM brintest_3 WHERE b < '0';
 
 DROP TABLE brintest_3;
 RESET enable_seqscan;
+-- test BRIN index doesn't block HOT update
+CREATE TABLE brin_hot (
+        id  integer PRIMARY KEY,
+        val integer NOT NULL
+) WITH (autovacuum_enabled = off, fillfactor = 70);
+INSERT INTO brin_hot SELECT *, 0 FROM generate_series(1, 235);
+CREATE INDEX val_brin ON brin_hot using brin(val);
+CREATE FUNCTION wait_for_hot_stats() RETURNS void AS $$
+DECLARE
+        start_time timestamptz := clock_timestamp();
+        updated bool;
+BEGIN
+        -- we don't want to wait forever; loop will exit after 30 seconds
+        FOR i IN 1 .. 300 LOOP
+                SELECT (pg_stat_get_tuples_hot_updated('brin_hot'::regclass::oid) > 0) INTO updated;
+                EXIT WHEN updated;
+
+                -- wait a little
+                PERFORM pg_sleep_for('100 milliseconds');
+                -- reset stats snapshot so we can test again
+                PERFORM pg_stat_clear_snapshot();
+        END LOOP;
+        -- report time waited in postmaster log (where it won't change test output)
+        RAISE log 'wait_for_hot_stats delayed % seconds',
+          EXTRACT(epoch FROM clock_timestamp() - start_time);
+END
+$$ LANGUAGE plpgsql;
+UPDATE brin_hot SET val = -3 WHERE id = 42;
+-- We can't just call wait_for_hot_stats() at this point, because we only
+-- transmit stats when the session goes idle, and we probably didn't
+-- transmit the last couple of counts yet thanks to the rate-limiting logic
+-- in pgstat_report_stat().  But instead of waiting for the rate limiter's
+-- timeout to elapse, let's just start a new session.  The old one will
+-- then send its stats before dying.
+\c -
+SELECT wait_for_hot_stats();
+ wait_for_hot_stats 
+--------------------
+ 
+(1 row)
+
+SELECT pg_stat_get_tuples_hot_updated('brin_hot'::regclass::oid);
+ pg_stat_get_tuples_hot_updated 
+--------------------------------
+                              1
+(1 row)
+
+DROP TABLE brin_hot;
+DROP FUNCTION wait_for_hot_stats();
+-- Test handling of index predicates - updating attributes in precicates
+-- should block HOT even for BRIN. We update a row that was not indexed
+-- due to the index predicate, and becomes indexable.
+CREATE TABLE brin_hot_2 (a int, b int);
+INSERT INTO brin_hot_2 VALUES (1, 100);
+CREATE INDEX ON brin_hot_2 USING brin (b) WHERE a = 2;
+UPDATE brin_hot_2 SET a = 2;
+EXPLAIN (COSTS OFF) SELECT * FROM brin_hot_2 WHERE a = 2 AND b = 100;
+            QUERY PLAN             
+-----------------------------------
+ Seq Scan on brin_hot_2
+   Filter: ((a = 2) AND (b = 100))
+(2 rows)
+
+SELECT COUNT(*) FROM brin_hot_2 WHERE a = 2 AND b = 100;
+ count 
+-------
+     1
+(1 row)
+
+SET enable_seqscan = off;
+EXPLAIN (COSTS OFF) SELECT * FROM brin_hot_2 WHERE a = 2 AND b = 100;
+                 QUERY PLAN                  
+---------------------------------------------
+ Bitmap Heap Scan on brin_hot_2
+   Recheck Cond: ((b = 100) AND (a = 2))
+   ->  Bitmap Index Scan on brin_hot_2_b_idx
+         Index Cond: (b = 100)
+(4 rows)
+
+SELECT COUNT(*) FROM brin_hot_2 WHERE a = 2 AND b = 100;
+ count 
+-------
+     1
+(1 row)
+

src/test/regress/sql/brin.sql

@@ -509,3 +509,66 @@ SELECT * FROM brintest_3 WHERE b < '0';
 
 DROP TABLE brintest_3;
 RESET enable_seqscan;
+
+-- test BRIN index doesn't block HOT update
+CREATE TABLE brin_hot (
+        id  integer PRIMARY KEY,
+        val integer NOT NULL
+) WITH (autovacuum_enabled = off, fillfactor = 70);
+
+INSERT INTO brin_hot SELECT *, 0 FROM generate_series(1, 235);
+CREATE INDEX val_brin ON brin_hot using brin(val);
+
+CREATE FUNCTION wait_for_hot_stats() RETURNS void AS $$
+DECLARE
+        start_time timestamptz := clock_timestamp();
+        updated bool;
+BEGIN
+        -- we don't want to wait forever; loop will exit after 30 seconds
+        FOR i IN 1 .. 300 LOOP
+                SELECT (pg_stat_get_tuples_hot_updated('brin_hot'::regclass::oid) > 0) INTO updated;
+                EXIT WHEN updated;
+
+                -- wait a little
+                PERFORM pg_sleep_for('100 milliseconds');
+                -- reset stats snapshot so we can test again
+                PERFORM pg_stat_clear_snapshot();
+        END LOOP;
+        -- report time waited in postmaster log (where it won't change test output)
+        RAISE log 'wait_for_hot_stats delayed % seconds',
+          EXTRACT(epoch FROM clock_timestamp() - start_time);
+END
+$$ LANGUAGE plpgsql;
+
+UPDATE brin_hot SET val = -3 WHERE id = 42;
+
+-- We can't just call wait_for_hot_stats() at this point, because we only
+-- transmit stats when the session goes idle, and we probably didn't
+-- transmit the last couple of counts yet thanks to the rate-limiting logic
+-- in pgstat_report_stat().  But instead of waiting for the rate limiter's
+-- timeout to elapse, let's just start a new session.  The old one will
+-- then send its stats before dying.
+\c -
+
+SELECT wait_for_hot_stats();
+SELECT pg_stat_get_tuples_hot_updated('brin_hot'::regclass::oid);
+
+DROP TABLE brin_hot;
+DROP FUNCTION wait_for_hot_stats();
+
+-- Test handling of index predicates - updating attributes in precicates
+-- should block HOT even for BRIN. We update a row that was not indexed
+-- due to the index predicate, and becomes indexable.
+CREATE TABLE brin_hot_2 (a int, b int);
+INSERT INTO brin_hot_2 VALUES (1, 100);
+CREATE INDEX ON brin_hot_2 USING brin (b) WHERE a = 2;
+
+UPDATE brin_hot_2 SET a = 2;
+
+EXPLAIN (COSTS OFF) SELECT * FROM brin_hot_2 WHERE a = 2 AND b = 100;
+SELECT COUNT(*) FROM brin_hot_2 WHERE a = 2 AND b = 100;
+
+SET enable_seqscan = off;
+
+EXPLAIN (COSTS OFF) SELECT * FROM brin_hot_2 WHERE a = 2 AND b = 100;
+SELECT COUNT(*) FROM brin_hot_2 WHERE a = 2 AND b = 100;