Subject: [PATCH 07/10] Index skip scan

From: Dmitrii Dolgov <[email-masked]>
Date: Mon, 8 Jun 2020 20:39:13 +0200

Implementation of basic Index Skip Scan (see Loose Index Scan in the
wiki [1]) infrastructure on top of IndexOnlyScan and IndexScan.
Introduces a new index am function amskip to allow advance past
duplicate key values in a scan. This innocently looking description
could be a bit tricky on the edge between am specific and common parts
of the implementation, mostly due to different information available at
each level, e.g. visibility. This means the common parts should apply
skipping multiple times if necessary.

Original patch and design were proposed by Thomas Munro [2], revived and
improved by Dmitry Dolgov and Jesper Pedersen.

[1] https://wiki.postgresql.org/wiki/Loose_indexscan
[2] https://www.postgresql.org/message-id/flat/CADLWmXXbTSBxP-MzJuPAYSsL_2f0iPm5VWPbCvDbVvfX93FKkw%40mail.gmail.com

Author: Jesper Pedersen, Dmitry Dolgov
Reviewed-by: Thomas Munro, David Rowley, Floris Van Nee, Kyotaro Horiguchi, Tomas Vondra, Peter Geoghegan
---
 contrib/bloom/blutils.c                       |   1 +
 doc/src/sgml/indexam.sgml                     |   1 +
 src/backend/access/brin/brin.c                |   1 +
 src/backend/access/gin/ginutil.c              |   1 +
 src/backend/access/gist/gist.c                |   1 +
 src/backend/access/hash/hash.c                |   1 +
 src/backend/access/index/indexam.c            |  18 ++
 src/backend/access/spgist/spgutils.c          |   1 +
 src/backend/commands/explain.c                |  25 +++
 src/backend/executor/nodeIndexonlyscan.c      |  97 ++++++++-
 src/backend/executor/nodeIndexscan.c          |  56 ++++-
 src/backend/nodes/copyfuncs.c                 |   2 +
 src/backend/nodes/outfuncs.c                  |   2 +
 src/backend/nodes/readfuncs.c                 |   2 +
 src/backend/optimizer/path/costsize.c         |   1 +
 src/backend/optimizer/path/indxpath.c         | 196 +++++++++++++++++-
 src/backend/optimizer/path/pathkeys.c         |  54 ++++-
 src/backend/optimizer/plan/createplan.c       |  20 +-
 src/backend/optimizer/util/pathnode.c         |  37 ++++
 src/backend/optimizer/util/plancat.c          |   1 +
 src/backend/utils/misc/guc.c                  |   9 +
 src/backend/utils/misc/postgresql.conf.sample |   1 +
 src/include/access/amapi.h                    |   7 +
 src/include/access/genam.h                    |   2 +
 src/include/access/sdir.h                     |   7 +
 src/include/nodes/execnodes.h                 |   6 +
 src/include/nodes/pathnodes.h                 |   4 +
 src/include/nodes/plannodes.h                 |   4 +
 src/include/optimizer/cost.h                  |   1 +
 src/include/optimizer/pathnode.h              |   4 +
 src/include/optimizer/paths.h                 |   5 +-
 src/test/regress/expected/sysviews.out        |   3 +-
 32 files changed, 554 insertions(+), 17 deletions(-)

diff --git a/contrib/bloom/blutils.c b/contrib/bloom/blutils.c
index 1e505b1da5..a58bdf7604 100644
--- a/contrib/bloom/blutils.c
+++ b/contrib/bloom/blutils.c
@@ -134,6 +134,7 @@ blhandler(PG_FUNCTION_ARGS)
 	amroutine->ambulkdelete = blbulkdelete;
 	amroutine->amvacuumcleanup = blvacuumcleanup;
 	amroutine->amcanreturn = NULL;
+	amroutine->amskip = NULL;
 	amroutine->amcostestimate = blcostestimate;
 	amroutine->amoptions = bloptions;
 	amroutine->amproperty = NULL;
diff --git a/doc/src/sgml/indexam.sgml b/doc/src/sgml/indexam.sgml
index ec5741df6d..3442ae816b 100644
--- a/doc/src/sgml/indexam.sgml
+++ b/doc/src/sgml/indexam.sgml
@@ -151,6 +151,7 @@ typedef struct IndexAmRoutine
     amendscan_function amendscan;
     ammarkpos_function ammarkpos;       /* can be NULL */
     amrestrpos_function amrestrpos;     /* can be NULL */
+    amskip_function amskip;             /* can be NULL */
 
     /* interface functions to support parallel index scans */
     amestimateparallelscan_function amestimateparallelscan;    /* can be NULL */
diff --git a/src/backend/access/brin/brin.c b/src/backend/access/brin/brin.c
index 27ba596c6e..1ec10ec513 100644
--- a/src/backend/access/brin/brin.c
+++ b/src/backend/access/brin/brin.c
@@ -115,6 +115,7 @@ brinhandler(PG_FUNCTION_ARGS)
 	amroutine->ambulkdelete = brinbulkdelete;
 	amroutine->amvacuumcleanup = brinvacuumcleanup;
 	amroutine->amcanreturn = NULL;
+	amroutine->amskip = NULL;
 	amroutine->amcostestimate = brincostestimate;
 	amroutine->amoptions = brinoptions;
 	amroutine->amproperty = NULL;
diff --git a/src/backend/access/gin/ginutil.c b/src/backend/access/gin/ginutil.c
index 6b9b04cf42..d776d2732f 100644
--- a/src/backend/access/gin/ginutil.c
+++ b/src/backend/access/gin/ginutil.c
@@ -66,6 +66,7 @@ ginhandler(PG_FUNCTION_ARGS)
 	amroutine->ambulkdelete = ginbulkdelete;
 	amroutine->amvacuumcleanup = ginvacuumcleanup;
 	amroutine->amcanreturn = NULL;
+	amroutine->amskip = NULL;
 	amroutine->amcostestimate = gincostestimate;
 	amroutine->amoptions = ginoptions;
 	amroutine->amproperty = NULL;
diff --git a/src/backend/access/gist/gist.c b/src/backend/access/gist/gist.c
index 0683f42c25..fed061184e 100644
--- a/src/backend/access/gist/gist.c
+++ b/src/backend/access/gist/gist.c
@@ -87,6 +87,7 @@ gisthandler(PG_FUNCTION_ARGS)
 	amroutine->ambulkdelete = gistbulkdelete;
 	amroutine->amvacuumcleanup = gistvacuumcleanup;
 	amroutine->amcanreturn = gistcanreturn;
+	amroutine->amskip = NULL;
 	amroutine->amcostestimate = gistcostestimate;
 	amroutine->amoptions = gistoptions;
 	amroutine->amproperty = gistproperty;
diff --git a/src/backend/access/hash/hash.c b/src/backend/access/hash/hash.c
index 0752fb38a9..fd7c13ee4c 100644
--- a/src/backend/access/hash/hash.c
+++ b/src/backend/access/hash/hash.c
@@ -84,6 +84,7 @@ hashhandler(PG_FUNCTION_ARGS)
 	amroutine->ambulkdelete = hashbulkdelete;
 	amroutine->amvacuumcleanup = hashvacuumcleanup;
 	amroutine->amcanreturn = NULL;
+	amroutine->amskip = NULL;
 	amroutine->amcostestimate = hashcostestimate;
 	amroutine->amoptions = hashoptions;
 	amroutine->amproperty = NULL;
diff --git a/src/backend/access/index/indexam.c b/src/backend/access/index/indexam.c
index 3d2dbed708..2544ea24f1 100644
--- a/src/backend/access/index/indexam.c
+++ b/src/backend/access/index/indexam.c
@@ -33,6 +33,7 @@
  *		index_can_return	- does index support index-only scans?
  *		index_getprocid - get a support procedure OID
  *		index_getprocinfo - get a support procedure's lookup info
+ *		index_skip		- advance past duplicate key values in a scan
  *
  * NOTES
  *		This file contains the index_ routines which used
@@ -739,6 +740,23 @@ index_can_return(Relation indexRelation, int attno)
 	return indexRelation->rd_indam->amcanreturn(indexRelation, attno);
 }
 
+/* ----------------
+ *		index_skip
+ *
+ *		Skip past all tuples where the first 'prefix' columns have the
+ *		same value as the last tuple returned in the current scan.
+ * ----------------
+ */
+bool
+index_skip(IndexScanDesc scan, ScanDirection direction,
+		   ScanDirection indexdir, bool scanstart, int prefix)
+{
+	SCAN_CHECKS;
+
+	return scan->indexRelation->rd_indam->amskip(scan, direction,
+												 indexdir, prefix);
+}
+
 /* ----------------
  *		index_getprocid
  *
diff --git a/src/backend/access/spgist/spgutils.c b/src/backend/access/spgist/spgutils.c
index d8b1815061..b2ed0712f2 100644
--- a/src/backend/access/spgist/spgutils.c
+++ b/src/backend/access/spgist/spgutils.c
@@ -69,6 +69,7 @@ spghandler(PG_FUNCTION_ARGS)
 	amroutine->ambulkdelete = spgbulkdelete;
 	amroutine->amvacuumcleanup = spgvacuumcleanup;
 	amroutine->amcanreturn = spgcanreturn;
+	amroutine->amskip = NULL;
 	amroutine->amcostestimate = spgcostestimate;
 	amroutine->amoptions = spgoptions;
 	amroutine->amproperty = spgproperty;
diff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c
index afc45429ba..a160de5493 100644
--- a/src/backend/commands/explain.c
+++ b/src/backend/commands/explain.c
@@ -149,6 +149,7 @@ static void ExplainXMLTag(const char *tagname, int flags, ExplainState *es);
 static void ExplainIndentText(ExplainState *es);
 static void ExplainJSONLineEnding(ExplainState *es);
 static void ExplainYAMLLineStarting(ExplainState *es);
+static void ExplainIndexSkipScanKeys(int skipPrefixSize, ExplainState *es);
 static void escape_yaml(StringInfo buf, const char *str);

@@ -1098,6 +1099,22 @@ ExplainPreScanNode(PlanState *planstate, Bitmapset **rels_used)
 	return planstate_tree_walker(planstate, ExplainPreScanNode, rels_used);
 }
 
+/*
+ * ExplainIndexSkipScanKeys -
+ *	  Append information about index skip scan to es->str.
+ *
+ * Can be used to print the skip prefix size.
+ */
+static void
+ExplainIndexSkipScanKeys(int skipPrefixSize, ExplainState *es)
+{
+	if (skipPrefixSize > 0)
+	{
+		if (es->format != EXPLAIN_FORMAT_TEXT)
+			ExplainPropertyInteger("Distinct Prefix", NULL, skipPrefixSize, es);
+	}
+}
+
 /*
  * ExplainNode -
  *	  Appends a description of a plan tree to es->str
@@ -1439,6 +1456,8 @@ ExplainNode(PlanState *planstate, List *ancestors,
 			{
 				IndexScan  *indexscan = (IndexScan *) plan;
 
+				ExplainIndexSkipScanKeys(indexscan->indexskipprefixsize, es);
+
 				ExplainIndexScanDetails(indexscan->indexid,
 										indexscan->indexorderdir,
 										es);
@@ -1449,6 +1468,8 @@ ExplainNode(PlanState *planstate, List *ancestors,
 			{
 				IndexOnlyScan *indexonlyscan = (IndexOnlyScan *) plan;
 
+				ExplainIndexSkipScanKeys(indexonlyscan->indexskipprefixsize, es);
+
 				ExplainIndexScanDetails(indexonlyscan->indexid,
 										indexonlyscan->indexorderdir,
 										es);
@@ -1709,6 +1730,8 @@ ExplainNode(PlanState *planstate, List *ancestors,
 	switch (nodeTag(plan))
 	{
 		case T_IndexScan:
+			if (((IndexScan *) plan)->indexskipprefixsize > 0)
+				ExplainPropertyBool("Skip scan", true, es);
 			show_scan_qual(((IndexScan *) plan)->indexqualorig,
 						   "Index Cond", planstate, ancestors, es);
 			if (((IndexScan *) plan)->indexqualorig)
@@ -1722,6 +1745,8 @@ ExplainNode(PlanState *planstate, List *ancestors,
 										   planstate, es);
 			break;
 		case T_IndexOnlyScan:
+			if (((IndexOnlyScan *) plan)->indexskipprefixsize > 0)
+				ExplainPropertyBool("Skip scan", true, es);
 			show_scan_qual(((IndexOnlyScan *) plan)->indexqual,
 						   "Index Cond", planstate, ancestors, es);
 			if (((IndexOnlyScan *) plan)->indexqual)
diff --git a/src/backend/executor/nodeIndexonlyscan.c b/src/backend/executor/nodeIndexonlyscan.c
index 0754e28a9a..0fad258202 100644
--- a/src/backend/executor/nodeIndexonlyscan.c
+++ b/src/backend/executor/nodeIndexonlyscan.c
@@ -41,6 +41,7 @@
 #include "miscadmin.h"
 #include "storage/bufmgr.h"
 #include "storage/predicate.h"
+#include "storage/itemptr.h"
 #include "utils/memutils.h"
 #include "utils/rel.h"
 
@@ -62,9 +63,26 @@ IndexOnlyNext(IndexOnlyScanState *node)
 	EState	   *estate;
 	ExprContext *econtext;
 	ScanDirection direction;
+	ScanDirection readDirection;
 	IndexScanDesc scandesc;
 	TupleTableSlot *slot;
 	ItemPointer tid;
+	ItemPointerData startTid;
+	IndexOnlyScan *indexonlyscan = (IndexOnlyScan *) node->ss.ps.plan;
+
+	/*
+	 * Tells if the current position was reached via skipping. In this case
+	 * there is no nead for the index_getnext_tid
+	 */
+	bool skipped = false;
+
+	/*
+	 * Index only scan must be aware that in case of skipping we can return to
+	 * the starting point due to visibility checks. In this situation we need
+	 * to jump further, and number of skipping attempts tell us how far do we
+	 * need to do so.
+	 */
+	int skipAttempts = 0;
 
 	/*
 	 * extract necessary information from index scan node
@@ -72,7 +90,7 @@ IndexOnlyNext(IndexOnlyScanState *node)
 	estate = node->ss.ps.state;
 	direction = estate->es_direction;
 	/* flip direction if this is an overall backward scan */
-	if (ScanDirectionIsBackward(((IndexOnlyScan *) node->ss.ps.plan)->indexorderdir))
+	if (ScanDirectionIsBackward(indexonlyscan->indexorderdir))
 	{
 		if (ScanDirectionIsForward(direction))
 			direction = BackwardScanDirection;
@@ -114,16 +132,87 @@ IndexOnlyNext(IndexOnlyScanState *node)
 						 node->ioss_OrderByKeys,
 						 node->ioss_NumOrderByKeys);
 	}
+	else
+	{
+		ItemPointerCopy(&scandesc->xs_heaptid, &startTid);
+	}
+
+	/*
+	 * Check if we need to skip to the next key prefix, because we've been
+	 * asked to implement DISTINCT.
+	 *
+	 * When fetching a cursor in the direction opposite to a general scan
+	 * direction, the result must be what normal fetching should have
+	 * returned, but in reversed order. In other words, return the last or
+	 * first scanned tuple in a DISTINCT set, depending on a cursor direction.
+	 * Due to that we skip also when the first tuple wasn't emitted yet, but
+	 * the directions are opposite.
+	 */
+	if (node->ioss_SkipPrefixSize > 0 &&
+		(node->ioss_FirstTupleEmitted ||
+		 ScanDirectionsAreOpposite(direction, indexonlyscan->indexorderdir)))
+	{
+		if (!index_skip(scandesc, direction, indexonlyscan->indexorderdir,
+						!node->ioss_FirstTupleEmitted, node->ioss_SkipPrefixSize))
+		{
+			/*
+			 * Reached end of index. At this point currPos is invalidated, and
+			 * we need to reset ioss_FirstTupleEmitted, since otherwise after
+			 * going backwards, reaching the end of index, and going forward
+			 * again we apply skip again. It would be incorrect and lead to an
+			 * extra skipped item.
+			 */
+			node->ioss_FirstTupleEmitted = false;
+			return ExecClearTuple(slot);
+		}
+		else
+		{
+			skipAttempts = 1;
+			skipped = true;
+			tid = &scandesc->xs_heaptid;
+		}
+	}
+
+	readDirection = skipped ? indexonlyscan->indexorderdir : direction;
 
 	/*
 	 * OK, now that we have what we need, fetch the next tuple.
 	 */
-	while ((tid = index_getnext_tid(scandesc, direction)) != NULL)
+	while (skipped || (tid = index_getnext_tid(scandesc, readDirection)) != NULL)
 	{
 		bool		tuple_from_heap = false;
 
 		CHECK_FOR_INTERRUPTS();
 
+		/*
+		 * If we already emitted first tuple, while doing index only skip scan
+		 * with advancing and reading in different directions we can return to
+		 * the same position where we started after visibility check. Recognize
+		 * such situations and skip more.
+		 */
+		if ((readDirection != direction) && node->ioss_FirstTupleEmitted &&
+			ItemPointerIsValid(&startTid) && ItemPointerEquals(&startTid, tid))
+		{
+			int i;
+			skipAttempts += 1;
+
+			for (i = 0; i < skipAttempts; i++)
+			{
+				if (!index_skip(scandesc, direction,
+								indexonlyscan->indexorderdir,
+								!node->ioss_FirstTupleEmitted,
+								node->ioss_SkipPrefixSize))
+				{
+					node->ioss_FirstTupleEmitted = false;
+					return ExecClearTuple(slot);
+				}
+			}
+
+			tid = &scandesc->xs_heaptid;
+		}
+
+		skipped = false;
+
 		/*
 		 * We can skip the heap fetch if the TID references a heap page on
 		 * which all tuples are known visible to everybody.  In any case,
@@ -250,6 +339,8 @@ IndexOnlyNext(IndexOnlyScanState *node)
 							  ItemPointerGetBlockNumber(tid),
 							  estate->es_snapshot);
 
+		node->ioss_FirstTupleEmitted = true;
+
 		return slot;
 	}
 
@@ -504,6 +595,8 @@ ExecInitIndexOnlyScan(IndexOnlyScan *node, EState *estate, int eflags)
 	indexstate->ss.ps.plan = (Plan *) node;
 	indexstate->ss.ps.state = estate;
 	indexstate->ss.ps.ExecProcNode = ExecIndexOnlyScan;
+	indexstate->ioss_SkipPrefixSize = node->indexskipprefixsize;
+	indexstate->ioss_FirstTupleEmitted = false;
 
 	/*
 	 * Miscellaneous initialization
diff --git a/src/backend/executor/nodeIndexscan.c b/src/backend/executor/nodeIndexscan.c
index 2fffb1b437..71aac4493d 100644
--- a/src/backend/executor/nodeIndexscan.c
+++ b/src/backend/executor/nodeIndexscan.c
@@ -85,6 +85,13 @@ IndexNext(IndexScanState *node)
 	ScanDirection direction;
 	IndexScanDesc scandesc;
 	TupleTableSlot *slot;
+	IndexScan *indexscan = (IndexScan *) node->ss.ps.plan;
+
+	/*
+	 * tells if the current position was reached via skipping. In this case
+	 * there is no nead for the index_getnext_tid
+	 */
+	bool skipped = false;
 
 	/*
 	 * extract necessary information from index scan node
@@ -92,7 +99,7 @@ IndexNext(IndexScanState *node)
 	estate = node->ss.ps.state;
 	direction = estate->es_direction;
 	/* flip direction if this is an overall backward scan */
-	if (ScanDirectionIsBackward(((IndexScan *) node->ss.ps.plan)->indexorderdir))
+	if (ScanDirectionIsBackward(indexscan->indexorderdir))
 	{
 		if (ScanDirectionIsForward(direction))
 			direction = BackwardScanDirection;
@@ -117,6 +124,12 @@ IndexNext(IndexScanState *node)
 
 		node->iss_ScanDesc = scandesc;
 
+		/* Index skip scan assumes xs_want_itup, so set it to true */
+		if (indexscan->indexskipprefixsize > 0)
+			node->iss_ScanDesc->xs_want_itup = true;
+		else
+			node->iss_ScanDesc->xs_want_itup = false;
+
 		/*
 		 * If no run-time keys to calculate or they are ready, go ahead and
 		 * pass the scankeys to the index AM.
@@ -127,12 +140,48 @@ IndexNext(IndexScanState *node)
 						 node->iss_OrderByKeys, node->iss_NumOrderByKeys);
 	}
 
+	/*
+	 * Check if we need to skip to the next key prefix, because we've been
+	 * asked to implement DISTINCT.
+	 *
+	 * When fetching a cursor in the direction opposite to a general scan
+	 * direction, the result must be what normal fetching should have
+	 * returned, but in reversed order. In other words, return the last or
+	 * first scanned tuple in a DISTINCT set, depending on a cursor direction.
+	 * Due to that we skip also when the first tuple wasn't emitted yet, but
+	 * the directions are opposite.
+	 */
+	if (node->iss_SkipPrefixSize > 0 &&
+		(node->iss_FirstTupleEmitted ||
+		 ScanDirectionsAreOpposite(direction, indexscan->indexorderdir)))
+	{
+		if (!index_skip(scandesc, direction, indexscan->indexorderdir,
+					   !node->iss_FirstTupleEmitted, node->iss_SkipPrefixSize))
+		{
+			/*
+			 * Reached end of index. At this point currPos is invalidated, and
+			 * we need to reset iss_FirstTupleEmitted, since otherwise after
+			 * going backwards, reaching the end of index, and going forward
+			 * again we apply skip again. It would be incorrect and lead to an
+			 * extra skipped item.
+			 */
+			node->iss_FirstTupleEmitted = false;
+			return ExecClearTuple(slot);
+		}
+		else
+		{
+			skipped = true;
+			index_fetch_heap(scandesc, slot);
+		}
+	}
+
 	/*
 	 * ok, now that we have what we need, fetch the next tuple.
 	 */
-	while (index_getnext_slot(scandesc, direction, slot))
+	while (skipped || index_getnext_slot(scandesc, direction, slot))
 	{
 		CHECK_FOR_INTERRUPTS();
+		skipped = false;
 
 		/*
 		 * If the index was lossy, we have to recheck the index quals using
@@ -149,6 +198,7 @@ IndexNext(IndexScanState *node)
 			}
 		}
 
+		node->iss_FirstTupleEmitted = true;
 		return slot;
 	}
 
@@ -910,6 +960,8 @@ ExecInitIndexScan(IndexScan *node, EState *estate, int eflags)
 	indexstate->ss.ps.plan = (Plan *) node;
 	indexstate->ss.ps.state = estate;
 	indexstate->ss.ps.ExecProcNode = ExecIndexScan;
+	indexstate->iss_SkipPrefixSize = node->indexskipprefixsize;
+	indexstate->iss_FirstTupleEmitted = false;
 
 	/*
 	 * Miscellaneous initialization
diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index 9d832ddc03..78500efd7d 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -491,6 +491,7 @@ _copyIndexScan(const IndexScan *from)
 	COPY_NODE_FIELD(indexorderbyorig);
 	COPY_NODE_FIELD(indexorderbyops);
 	COPY_SCALAR_FIELD(indexorderdir);
+	COPY_SCALAR_FIELD(indexskipprefixsize);
 
 	return newnode;
 }
@@ -516,6 +517,7 @@ _copyIndexOnlyScan(const IndexOnlyScan *from)
 	COPY_NODE_FIELD(indexorderby);
 	COPY_NODE_FIELD(indextlist);
 	COPY_SCALAR_FIELD(indexorderdir);
+	COPY_SCALAR_FIELD(indexskipprefixsize);
 
 	return newnode;
 }
diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c
index 13905e6037..2b6c007398 100644
--- a/src/backend/nodes/outfuncs.c
+++ b/src/backend/nodes/outfuncs.c
@@ -560,6 +560,7 @@ _outIndexScan(StringInfo str, const IndexScan *node)
 	WRITE_NODE_FIELD(indexorderbyorig);
 	WRITE_NODE_FIELD(indexorderbyops);
 	WRITE_ENUM_FIELD(indexorderdir, ScanDirection);
+	WRITE_INT_FIELD(indexskipprefixsize);
 }
 
 static void
@@ -574,6 +575,7 @@ _outIndexOnlyScan(StringInfo str, const IndexOnlyScan *node)
 	WRITE_NODE_FIELD(indexorderby);
 	WRITE_NODE_FIELD(indextlist);
 	WRITE_ENUM_FIELD(indexorderdir, ScanDirection);
+	WRITE_INT_FIELD(indexskipprefixsize);
 }
 
 static void
diff --git a/src/backend/nodes/readfuncs.c b/src/backend/nodes/readfuncs.c
index 8830c8df99..8a207332fc 100644
--- a/src/backend/nodes/readfuncs.c
+++ b/src/backend/nodes/readfuncs.c
@@ -1872,6 +1872,7 @@ _readIndexScan(void)
 	READ_NODE_FIELD(indexorderbyorig);
 	READ_NODE_FIELD(indexorderbyops);
 	READ_ENUM_FIELD(indexorderdir, ScanDirection);
+	READ_INT_FIELD(indexskipprefixsize);
 
 	READ_DONE();
 }
@@ -1891,6 +1892,7 @@ _readIndexOnlyScan(void)
 	READ_NODE_FIELD(indexorderby);
 	READ_NODE_FIELD(indextlist);
 	READ_ENUM_FIELD(indexorderdir, ScanDirection);
+	READ_INT_FIELD(indexskipprefixsize);
 
 	READ_DONE();
 }
diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c
index a25b674a19..658bacabf4 100644
--- a/src/backend/optimizer/path/costsize.c
+++ b/src/backend/optimizer/path/costsize.c
@@ -132,6 +132,7 @@ int			max_parallel_workers_per_gather = 2;
 bool		enable_seqscan = true;
 bool		enable_indexscan = true;
 bool		enable_indexonlyscan = true;
+bool		enable_indexskipscan = true;
 bool		enable_bitmapscan = true;
 bool		enable_tidscan = true;
 bool		enable_sort = true;
diff --git a/src/backend/optimizer/path/indxpath.c b/src/backend/optimizer/path/indxpath.c
index ff536e6b24..bd0a073998 100644
--- a/src/backend/optimizer/path/indxpath.c
+++ b/src/backend/optimizer/path/indxpath.c
@@ -784,6 +784,16 @@ get_index_paths(PlannerInfo *root, RelOptInfo *rel,
 	{
 		IndexPath  *ipath = (IndexPath *) lfirst(lc);
 
+		/*
+		 * To prevent unique paths from index skip scans being potentially used
+		 * when not needed scan keep them in a separate pathlist.
+		*/
+		if (ipath->indexskipprefix != 0)
+		{
+			add_unique_path(rel, (Path *) ipath);
+			continue;
+		}
+
 		if (index->amhasgettuple)
 			add_path(rel, (Path *) ipath);
 
@@ -866,12 +876,15 @@ build_index_paths(PlannerInfo *root, RelOptInfo *rel,
 	double		loop_count;
 	List	   *orderbyclauses;
 	List	   *orderbyclausecols;
-	List	   *index_pathkeys;
+	List	   *index_pathkeys = NIL;
 	List	   *useful_pathkeys;
+	List	   *index_pathkeys_pos = NIL;
 	bool		found_lower_saop_clause;
 	bool		pathkeys_possibly_useful;
 	bool		index_is_ordered;
 	bool		index_only_scan;
+	bool		not_empty_qual = false;
+	bool		can_skip;
 	int			indexcol;
 
 	/*
@@ -989,7 +1002,8 @@ build_index_paths(PlannerInfo *root, RelOptInfo *rel,
 	if (index_is_ordered && pathkeys_possibly_useful)
 	{
 		index_pathkeys = build_index_pathkeys(root, index,
-											  ForwardScanDirection);
+											  ForwardScanDirection,
+											  &index_pathkeys_pos);
 		useful_pathkeys = truncate_useless_pathkeys(root, rel,
 													index_pathkeys);
 		orderbyclauses = NIL;
@@ -1021,6 +1035,129 @@ build_index_paths(PlannerInfo *root, RelOptInfo *rel,
 	index_only_scan = (scantype != ST_BITMAPSCAN &&
 					   check_index_only(rel, index));
 
+	/* Check if an index skip scan is possible. */
+	can_skip = enable_indexskipscan & index->amcanskip;
+
+	if (can_skip)
+	{
+		/*
+		 * Skip scan is not supported when there are qual conditions, which are
+		 * not covered by index. The reason for that is that those conditions
+		 * are evaluated later, already after skipping was applied.
+		 *
+		 * TODO: This implementation is too restrictive, and doesn't allow e.g.
+		 * index expressions. For that we need to examine index_clauses too.
+		 */
+		if (root->parse->jointree != NULL)
+		{
+			ListCell *lc;
+
+			foreach(lc, (List *) root->parse->jointree->quals)
+			{
+				Node *expr, *qual = (Node *) lfirst(lc);
+				OpExpr *expr_op;
+				Var *var;
+				bool found = false;
+
+				if (!is_opclause(qual))
+				{
+					not_empty_qual = true;
+					break;
+				}
+
+				expr = get_leftop(qual);
+				expr_op = (OpExpr *) qual;
+
+				if (!IsA(expr, Var))
+				{
+					not_empty_qual = true;
+					break;
+				}
+
+				var = (Var *) expr;
+
+				/*
+				 * Check if the qual operator is indexable by any columns of
+				 * the index, test collation and opfamily.
+				 */
+				for (int i = 0; i < index->ncolumns; i++)
+				{
+					if (index->indexkeys[i] == var->varattno &&
+						IndexCollMatchesExprColl(index->indexcollations[i],
+												 expr_op->inputcollid) &&
+						op_in_opfamily(expr_op->opno, index->opfamily[i]))
+					{
+						found = true;
+						break;
+					}
+				}
+
+				if (!found)
+				{
+					not_empty_qual = true;
+					break;
+				}
+			}
+		}
+
+		/*
+		 * For an index scan verify that index fully covers distinct
+		 * expressions, otherwise there is not enough information for skipping
+		 */
+		if (!index_only_scan && root->query_uniquekeys != NULL)
+		{
+			ListCell *lc;
+
+			foreach(lc, root->query_uniquekeys)
+			{
+				UniqueKey *uniqueKey = (UniqueKey *) lfirst(lc);
+				ListCell *lc1;
+
+				foreach(lc1, uniqueKey->exprs)
+				{
+					Expr *expr = (Expr *) lfirst(lc1);
+					bool found = false;
+
+					if (!IsA(expr, Var))
+					{
+						ListCell *lc2;
+
+						foreach(lc2, index->indexprs)
+						{
+							if(equal(lfirst(lc1), lfirst(lc2)))
+							{
+								found = true;
+								break;
+							}
+						}
+					}
+					else
+					{
+						Var *var = (Var *) expr;
+
+						for (int i = 0; i < index->ncolumns; i++)
+						{
+							if (index->indexkeys[i] == var->varattno)
+							{
+								found = true;
+								break;
+							}
+						}
+					}
+
+					if (!found)
+					{
+						can_skip = false;
+						break;
+					}
+				}
+
+				if (!can_skip)
+					break;
+			}
+		}
+	}
+
 	/*
 	 * 4. Generate an indexscan path if there are relevant restriction clauses
 	 * in the current clauses, OR the index ordering is potentially useful for
@@ -1044,6 +1181,32 @@ build_index_paths(PlannerInfo *root, RelOptInfo *rel,
 								  false);
 		result = lappend(result, ipath);
 
+		/* Consider index skip scan as well */
+		if (root->query_uniquekeys != NULL && can_skip && !not_empty_qual)
+		{
+			int numusefulkeys = list_length(useful_pathkeys);
+			int numsortkeys = list_length(root->query_pathkeys);
+
+			if (numusefulkeys == numsortkeys)
+			{
+				int prefix;
+				if (list_length(root->distinct_pathkeys) > 0)
+					prefix = find_index_prefix_for_pathkey(index_pathkeys,
+														   index_pathkeys_pos,
+														   llast_node(PathKey,
+														   root->distinct_pathkeys));
+				else
+					/* all are distinct keys are constant and optimized away.
+					 * skipping with 1 is sufficient as all are constant anyway
+					 */
+					prefix = 1;
+
+				result = lappend(result,
+								 create_skipscan_unique_path(root, index,
+															 (Path *) ipath, prefix));
+			}
+		}
+
 		/*
 		 * If appropriate, consider parallel index scan.  We don't allow
 		 * parallel index scan for bitmap index scans.
@@ -1082,7 +1245,8 @@ build_index_paths(PlannerInfo *root, RelOptInfo *rel,
 	if (index_is_ordered && pathkeys_possibly_useful)
 	{
 		index_pathkeys = build_index_pathkeys(root, index,
-											  BackwardScanDirection);
+											  BackwardScanDirection,
+											  &index_pathkeys_pos);
 		useful_pathkeys = truncate_useless_pathkeys(root, rel,
 													index_pathkeys);
 		if (useful_pathkeys != NIL)
@@ -1099,6 +1263,32 @@ build_index_paths(PlannerInfo *root, RelOptInfo *rel,
 									  false);
 			result = lappend(result, ipath);
 
+			/* Consider index skip scan as well */
+			if (root->query_uniquekeys != NULL && can_skip && !not_empty_qual)
+			{
+				int numusefulkeys = list_length(useful_pathkeys);
+				int numsortkeys = list_length(root->query_pathkeys);
+
+				if (numusefulkeys == numsortkeys)
+				{
+					int prefix;
+					if (list_length(root->distinct_pathkeys) > 0)
+						prefix = find_index_prefix_for_pathkey(index_pathkeys,
+															   index_pathkeys_pos,
+															   llast_node(PathKey,
+															   root->distinct_pathkeys));
+					else
+						/* all are distinct keys are constant and optimized away.
+						 * skipping with 1 is sufficient as all are constant anyway
+						 */
+						prefix = 1;
+
+					result = lappend(result,
+									 create_skipscan_unique_path(root, index,
+																 (Path *) ipath, prefix));
+				}
+			}
+
 			/* If appropriate, consider parallel index scan */
 			if (index->amcanparallel &&
 				rel->consider_parallel && outer_relids == NULL &&
diff --git a/src/backend/optimizer/path/pathkeys.c b/src/backend/optimizer/path/pathkeys.c
index 4c90f63705..e15637b514 100644
--- a/src/backend/optimizer/path/pathkeys.c
+++ b/src/backend/optimizer/path/pathkeys.c
@@ -522,6 +522,47 @@ get_cheapest_parallel_safe_total_inner(List *paths)
  *		NEW PATHKEY FORMATION
  ****************************************************************************/
 
+/*
+ * Find the prefix size for a specific path key in an index. For example, an
+ * index with (a,b,c) finding path key b will return prefix 2. Optionally
+ * pathkeys_positions can be provided, to specify at which position in the
+ * original pathkey list this particular key could be found (this is helpful
+ * when we deal with redundant pathkeys).
+ *
+ * Returns 0 when not found.
+ */
+int
+find_index_prefix_for_pathkey(List *index_pathkeys,
+							  List *pathkeys_positions,
+							  PathKey *target_pathkey)
+{
+	ListCell   *lc;
+	int			i;
+
+	i = 0;
+	foreach(lc, index_pathkeys)
+	{
+		PathKey    *cpathkey = (PathKey *) lfirst(lc);
+
+		if (cpathkey == target_pathkey)
+		{
+			/*
+			 * Prefix expected to start from 1, increment positions since
+			 * they're 0 based.
+			 */
+			if (pathkeys_positions != NIL &&
+				pathkeys_positions->length > i)
+				return list_nth_int(pathkeys_positions, i) + 1;
+			else
+				return i + 1;
+		}
+
+		i++;
+	}
+
+	return 0;
+}
+
 /*
  * build_index_pathkeys
  *	  Build a pathkeys list that describes the ordering induced by an index
@@ -534,7 +575,9 @@ get_cheapest_parallel_safe_total_inner(List *paths)
  * We iterate only key columns of covering indexes, since non-key columns
  * don't influence index ordering.  The result is canonical, meaning that
  * redundant pathkeys are removed; it may therefore have fewer entries than
- * there are key columns in the index.
+ * there are key columns in the index. Since by removing redundant pathkeys the
+ * information about original position is lost, return it via positions
+ * argument.
  *
  * Another reason for stopping early is that we may be able to tell that
  * an index column's sort order is uninteresting for this query.  However,
@@ -545,7 +588,8 @@ get_cheapest_parallel_safe_total_inner(List *paths)
 List *
 build_index_pathkeys(PlannerInfo *root,
 					 IndexOptInfo *index,
-					 ScanDirection scandir)
+					 ScanDirection scandir,
+					 List **positions)
 {
 	List	   *retval = NIL;
 	ListCell   *lc;
@@ -554,6 +598,8 @@ build_index_pathkeys(PlannerInfo *root,
 	if (index->sortopfamily == NULL)
 		return NIL;				/* non-orderable index */
 
+	*positions = NIL;
+
 	i = 0;
 	foreach(lc, index->indextlist)
 	{
@@ -607,7 +653,11 @@ build_index_pathkeys(PlannerInfo *root,
 			 * for this query.  Add it to list, unless it's redundant.
 			 */
 			if (!pathkey_is_redundant(cpathkey, retval))
+			{
 				retval = lappend(retval, cpathkey);
+				*positions = lappend_int(*positions,
+										 foreach_current_index(lc));
+			}
 		}
 		else
 		{
diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index 906cab7053..c2969a0279 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -181,12 +181,14 @@ static IndexScan *make_indexscan(List *qptlist, List *qpqual, Index scanrelid,
 								 Oid indexid, List *indexqual, List *indexqualorig,
 								 List *indexorderby, List *indexorderbyorig,
 								 List *indexorderbyops,
-								 ScanDirection indexscandir);
+								 ScanDirection indexscandir,
+								 int skipprefix);
 static IndexOnlyScan *make_indexonlyscan(List *qptlist, List *qpqual,
 										 Index scanrelid, Oid indexid,
 										 List *indexqual, List *indexorderby,
 										 List *indextlist,
-										 ScanDirection indexscandir);
+										 ScanDirection indexscandir,
+										 int skipprefix);
 static BitmapIndexScan *make_bitmap_indexscan(Index scanrelid, Oid indexid,
 											  List *indexqual,
 											  List *indexqualorig);
@@ -2997,7 +2999,8 @@ create_indexscan_plan(PlannerInfo *root,
 												fixed_indexquals,
 												fixed_indexorderbys,
 												best_path->indexinfo->indextlist,
-												best_path->indexscandir);
+												best_path->indexscandir,
+												best_path->indexskipprefix);
 	else
 		scan_plan = (Scan *) make_indexscan(tlist,
 											qpqual,
@@ -3008,7 +3011,8 @@ create_indexscan_plan(PlannerInfo *root,
 											fixed_indexorderbys,
 											indexorderbys,
 											indexorderbyops,
-											best_path->indexscandir);
+											best_path->indexscandir,
+											best_path->indexskipprefix);
 
 	copy_generic_path_info(&scan_plan->plan, &best_path->path);
 
@@ -5340,7 +5344,8 @@ make_indexscan(List *qptlist,
 			   List *indexorderby,
 			   List *indexorderbyorig,
 			   List *indexorderbyops,
-			   ScanDirection indexscandir)
+			   ScanDirection indexscandir,
+			   int skipPrefixSize)
 {
 	IndexScan  *node = makeNode(IndexScan);
 	Plan	   *plan = &node->scan.plan;
@@ -5357,6 +5362,7 @@ make_indexscan(List *qptlist,
 	node->indexorderbyorig = indexorderbyorig;
 	node->indexorderbyops = indexorderbyops;
 	node->indexorderdir = indexscandir;
+	node->indexskipprefixsize = skipPrefixSize;
 
 	return node;
 }
@@ -5369,7 +5375,8 @@ make_indexonlyscan(List *qptlist,
 				   List *indexqual,
 				   List *indexorderby,
 				   List *indextlist,
-				   ScanDirection indexscandir)
+				   ScanDirection indexscandir,
+				   int skipPrefixSize)
 {
 	IndexOnlyScan *node = makeNode(IndexOnlyScan);
 	Plan	   *plan = &node->scan.plan;
@@ -5384,6 +5391,7 @@ make_indexonlyscan(List *qptlist,
 	node->indexorderby = indexorderby;
 	node->indextlist = indextlist;
 	node->indexorderdir = indexscandir;
+	node->indexskipprefixsize = skipPrefixSize;
 
 	return node;
 }
diff --git a/src/backend/optimizer/util/pathnode.c b/src/backend/optimizer/util/pathnode.c
index c995921c88..a768f43e22 100644
--- a/src/backend/optimizer/util/pathnode.c
+++ b/src/backend/optimizer/util/pathnode.c
@@ -3029,6 +3029,43 @@ create_upper_unique_path(PlannerInfo *root,
 	return pathnode;
 }
 
+/*
+ * create_skipscan_unique_path
+ *	  Creates a pathnode the same as an existing IndexPath except based on
+ *	  skipping duplicate values.  This may or may not be cheaper than using
+ *	  create_upper_unique_path.
+ *
+ * The input path must be an IndexPath for an index that supports amskip.
+ */
+IndexPath *
+create_skipscan_unique_path(PlannerInfo *root, IndexOptInfo *index,
+							Path *basepath, int prefix)
+{
+	IndexPath 	*pathnode = makeNode(IndexPath);
+	int 		numDistinctRows;
+	UniqueKey *ukey;
+
+	Assert(IsA(basepath, IndexPath));
+
+	/* We don't want to modify basepath, so make a copy. */
+	memcpy(pathnode, basepath, sizeof(IndexPath));
+
+	ukey = linitial_node(UniqueKey, root->query_uniquekeys);
+
+	Assert(prefix > 0);
+	pathnode->indexskipprefix = prefix;
+	pathnode->path.uniquekeys = root->query_uniquekeys;
+
+	numDistinctRows = estimate_num_groups(root, ukey->exprs,
+										  pathnode->path.rows,
+										  NULL);
+
+	pathnode->path.total_cost = pathnode->path.startup_cost * numDistinctRows;
+	pathnode->path.rows = numDistinctRows;
+
+	return pathnode;
+}
+
 /*
  * create_agg_path
  *	  Creates a pathnode that represents performing aggregation/grouping
diff --git a/src/backend/optimizer/util/plancat.c b/src/backend/optimizer/util/plancat.c
index cd703e41ba..bac3cee9d2 100644
--- a/src/backend/optimizer/util/plancat.c
+++ b/src/backend/optimizer/util/plancat.c
@@ -281,6 +281,7 @@ get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
 			info->amoptionalkey = amroutine->amoptionalkey;
 			info->amsearcharray = amroutine->amsearcharray;
 			info->amsearchnulls = amroutine->amsearchnulls;
+			info->amcanskip = (amroutine->amskip != NULL);
 			info->amcanparallel = amroutine->amcanparallel;
 			info->amhasgettuple = (amroutine->amgettuple != NULL);
 			info->amhasgetbitmap = amroutine->amgetbitmap != NULL &&
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 855076b1fd..6354958ed3 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -960,6 +960,15 @@ static struct config_bool ConfigureNamesBool[] =
 		true,
 		NULL, NULL, NULL
 	},
+	{
+		{"enable_indexskipscan", PGC_USERSET, QUERY_TUNING_METHOD,
+			gettext_noop("Enables the planner's use of index-skip-scan plans."),
+			NULL
+		},
+		&enable_indexskipscan,
+		true,
+		NULL, NULL, NULL
+	},
 	{
 		{"enable_bitmapscan", PGC_USERSET, QUERY_TUNING_METHOD,
 			gettext_noop("Enables the planner's use of bitmap-scan plans."),
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index f46c2dd7a8..4eecf2d95d 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -359,6 +359,7 @@
 #enable_hashjoin = on
 #enable_indexscan = on
 #enable_indexonlyscan = on
+#enable_indexskipscan = on
 #enable_material = on
 #enable_mergejoin = on
 #enable_nestloop = on
diff --git a/src/include/access/amapi.h b/src/include/access/amapi.h
index d357ebb559..eacf890dbe 100644
--- a/src/include/access/amapi.h
+++ b/src/include/access/amapi.h
@@ -173,6 +173,12 @@ typedef void (*amrescan_function) (IndexScanDesc scan,
 typedef bool (*amgettuple_function) (IndexScanDesc scan,
 									 ScanDirection direction);
 
+/* skip past duplicates in a given prefix */
+typedef bool (*amskip_function) (IndexScanDesc scan,
+								 ScanDirection dir,
+								 ScanDirection indexdir,
+								 int prefix);
+
 /* fetch all valid tuples */
 typedef int64 (*amgetbitmap_function) (IndexScanDesc scan,
 									   TIDBitmap *tbm);
@@ -275,6 +281,7 @@ typedef struct IndexAmRoutine
 	amendscan_function amendscan;
 	ammarkpos_function ammarkpos;	/* can be NULL */
 	amrestrpos_function amrestrpos; /* can be NULL */
+	amskip_function amskip;				/* can be NULL */
 
 	/* interface functions to support parallel index scans */
 	amestimateparallelscan_function amestimateparallelscan; /* can be NULL */
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index 4515401869..f14baadea0 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -183,6 +183,8 @@ extern IndexBulkDeleteResult *index_bulk_delete(IndexVacuumInfo *info,
 extern IndexBulkDeleteResult *index_vacuum_cleanup(IndexVacuumInfo *info,
 												   IndexBulkDeleteResult *stats);
 extern bool index_can_return(Relation indexRelation, int attno);
+extern bool index_skip(IndexScanDesc scan, ScanDirection direction,
+					   ScanDirection indexdir, bool start, int prefix);
 extern RegProcedure index_getprocid(Relation irel, AttrNumber attnum,
 									uint16 procnum);
 extern FmgrInfo *index_getprocinfo(Relation irel, AttrNumber attnum,
diff --git a/src/include/access/sdir.h b/src/include/access/sdir.h
index 8154adf3b8..6690c2a0b0 100644
--- a/src/include/access/sdir.h
+++ b/src/include/access/sdir.h
@@ -55,4 +55,11 @@ typedef enum ScanDirection
 #define ScanDirectionIsForward(direction) \
 	((bool) ((direction) == ForwardScanDirection))
 
+/*
+ * ScanDirectionsAreOpposite
+ *		True iff scan directions are backward/forward or forward/backward.
+ */
+#define ScanDirectionsAreOpposite(dirA, dirB) \
+	((bool) (dirA != NoMovementScanDirection && dirA == -dirB))
+
 #endif							/* SDIR_H */
diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index e31ad6204e..9982343e8a 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -1427,6 +1427,8 @@ typedef struct IndexScanState
 	ExprContext *iss_RuntimeContext;
 	Relation	iss_RelationDesc;
 	struct IndexScanDescData *iss_ScanDesc;
+	int         iss_SkipPrefixSize;
+	bool		iss_FirstTupleEmitted;
 
 	/* These are needed for re-checking ORDER BY expr ordering */
 	pairingheap *iss_ReorderQueue;
@@ -1456,6 +1458,8 @@ typedef struct IndexScanState
  *		TableSlot		   slot for holding tuples fetched from the table
  *		VMBuffer		   buffer in use for visibility map testing, if any
  *		PscanLen		   size of parallel index-only scan descriptor
+ *		SkipPrefixSize	   number of keys for skip-based DISTINCT
+ *		FirstTupleEmitted  has the first tuple been emitted
  * ----------------
  */
 typedef struct IndexOnlyScanState
@@ -1474,6 +1478,8 @@ typedef struct IndexOnlyScanState
 	struct IndexScanDescData *ioss_ScanDesc;
 	TupleTableSlot *ioss_TableSlot;
 	Buffer		ioss_VMBuffer;
+	int         ioss_SkipPrefixSize;
+	bool		ioss_FirstTupleEmitted;
 	Size		ioss_PscanLen;
 } IndexOnlyScanState;
 
diff --git a/src/include/nodes/pathnodes.h b/src/include/nodes/pathnodes.h
index 27ff639053..01e68fe6db 100644
--- a/src/include/nodes/pathnodes.h
+++ b/src/include/nodes/pathnodes.h
@@ -1241,6 +1241,9 @@ typedef struct Path
  * we need not recompute them when considering using the same index in a
  * bitmap index/heap scan (see BitmapHeapPath).  The costs of the IndexPath
  * itself represent the costs of an IndexScan or IndexOnlyScan plan type.
+ *
+ * 'indexskipprefix' represents the number of columns to consider for skip
+ * scans.
  *----------
  */
 typedef struct IndexPath
@@ -1253,6 +1256,7 @@ typedef struct IndexPath
 	ScanDirection indexscandir;
 	Cost		indextotalcost;
 	Selectivity indexselectivity;
+	int			indexskipprefix;
 } IndexPath;
 
 /*
diff --git a/src/include/nodes/plannodes.h b/src/include/nodes/plannodes.h
index 95292d7573..a23ea622ed 100644
--- a/src/include/nodes/plannodes.h
+++ b/src/include/nodes/plannodes.h
@@ -403,6 +403,8 @@ typedef struct IndexScan
 	List	   *indexorderbyorig;	/* the same in original form */
 	List	   *indexorderbyops;	/* OIDs of sort ops for ORDER BY exprs */
 	ScanDirection indexorderdir;	/* forward or backward or don't care */
+	int			indexskipprefixsize;	/* the size of the prefix for distinct
+										 * scans */
 } IndexScan;
 
 /* ----------------
@@ -430,6 +432,8 @@ typedef struct IndexOnlyScan
 	List	   *indexorderby;	/* list of index ORDER BY exprs */
 	List	   *indextlist;		/* TargetEntry list describing index's cols */
 	ScanDirection indexorderdir;	/* forward or backward or don't care */
+	int			indexskipprefixsize;	/* the size of the prefix for distinct
+										 * scans */
 } IndexOnlyScan;
 
 /* ----------------
diff --git a/src/include/optimizer/cost.h b/src/include/optimizer/cost.h
index 1be93be098..0f22fcef99 100644
--- a/src/include/optimizer/cost.h
+++ b/src/include/optimizer/cost.h
@@ -50,6 +50,7 @@ extern PGDLLIMPORT int max_parallel_workers_per_gather;
 extern PGDLLIMPORT bool enable_seqscan;
 extern PGDLLIMPORT bool enable_indexscan;
 extern PGDLLIMPORT bool enable_indexonlyscan;
+extern PGDLLIMPORT bool enable_indexskipscan;
 extern PGDLLIMPORT bool enable_bitmapscan;
 extern PGDLLIMPORT bool enable_tidscan;
 extern PGDLLIMPORT bool enable_sort;
diff --git a/src/include/optimizer/pathnode.h b/src/include/optimizer/pathnode.h
index aa6c3e439e..872c858a60 100644
--- a/src/include/optimizer/pathnode.h
+++ b/src/include/optimizer/pathnode.h
@@ -210,6 +210,10 @@ extern UpperUniquePath *create_upper_unique_path(PlannerInfo *root,
 												 Path *subpath,
 												 int numCols,
 												 double numGroups);
+extern IndexPath *create_skipscan_unique_path(PlannerInfo *root,
+											  IndexOptInfo *index,
+											  Path *subpath,
+											  int prefix);
 extern AggPath *create_agg_path(PlannerInfo *root,
 								RelOptInfo *rel,
 								Path *subpath,
diff --git a/src/include/optimizer/paths.h b/src/include/optimizer/paths.h
index b571ddec11..45a985e8c1 100644
--- a/src/include/optimizer/paths.h
+++ b/src/include/optimizer/paths.h
@@ -205,8 +205,11 @@ extern Path *get_cheapest_fractional_path_for_pathkeys(List *paths,
 													   Relids required_outer,
 													   double fraction);
 extern Path *get_cheapest_parallel_safe_total_inner(List *paths);
+extern int find_index_prefix_for_pathkey(List *index_pathkeys,
+										 List *pathkey_positions,
+										 PathKey *target_pathkey);
 extern List *build_index_pathkeys(PlannerInfo *root, IndexOptInfo *index,
-								  ScanDirection scandir);
+								  ScanDirection scandir, List **positions);
 extern List *build_partition_pathkeys(PlannerInfo *root, RelOptInfo *partrel,
 									  ScanDirection scandir, bool *partialkeys);
 extern List *build_expression_pathkey(PlannerInfo *root, Expr *expr,
diff --git a/src/test/regress/expected/sysviews.out b/src/test/regress/expected/sysviews.out
index 6d048e309c..eda1b0a3b4 100644
--- a/src/test/regress/expected/sysviews.out
+++ b/src/test/regress/expected/sysviews.out
@@ -102,6 +102,7 @@ select name, setting from pg_settings where name like 'enable%';
  enable_incremental_sort        | on
  enable_indexonlyscan           | on
  enable_indexscan               | on
+ enable_indexskipscan           | on
  enable_material                | on
  enable_mergejoin               | on
  enable_nestloop                | on
@@ -113,7 +114,7 @@ select name, setting from pg_settings where name like 'enable%';
  enable_seqscan                 | on
  enable_sort                    | on
  enable_tidscan                 | on
-(18 rows)
+(21 rows)
 
 -- Test that the pg_timezone_names and pg_timezone_abbrevs views are
 -- more-or-less working.  We can't test their contents in any great detail
-- 
2.30.2

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