From 6fc50a6a405b8232a935a3d2459b62dec09c570c Mon Sep 17 00:00:00 2001
From: Dmitrii Dolgov <9erthalion6@gmail.com>
Date: Sat, 22 Jan 2022 21:13:42 +0100
Subject: [PATCH v41 5/6] Extend index skip scan with ScanLooseKey

Index skip scan relies on the information about key prefix that needs to
be jumped over, but it's represented in a rather limited fashion only
via the prefix size. This approach is sufficient now, but for the sake
of flexibility introduce a concept of ScanLooseKey to represent
underspecified search keys. At the moment it's inspired by the idea of
skip keys constrained in some range of keyspace, and not used in any
way.
---
 src/backend/executor/nodeIndexonlyscan.c | 14 ++++++++++----
 src/include/access/relscan.h             |  2 ++
 src/include/access/skey.h                |  8 ++++++++
 src/include/nodes/execnodes.h            |  5 ++++-
 4 files changed, 24 insertions(+), 5 deletions(-)

diff --git a/src/backend/executor/nodeIndexonlyscan.c b/src/backend/executor/nodeIndexonlyscan.c
index d5abac20cb..470c364e53 100644
--- a/src/backend/executor/nodeIndexonlyscan.c
+++ b/src/backend/executor/nodeIndexonlyscan.c
@@ -147,12 +147,12 @@ IndexOnlyNext(IndexOnlyScanState *node)
 	 * Due to that we skip also when the first tuple wasn't emitted yet, but
 	 * the directions are opposite.
 	 */
-	if (node->ioss_SkipPrefixSize > 0 &&
+	if (node->ioss_ScanLooseKeys != NULL &&
 		(node->ioss_FirstTupleEmitted ||
 		 ScanDirectionsAreOpposite(direction, indexonlyscan->indexorderdir)))
 	{
 		if (!index_skip(scandesc, direction, indexonlyscan->indexorderdir,
-						!node->ioss_FirstTupleEmitted, node->ioss_SkipPrefixSize))
+						!node->ioss_FirstTupleEmitted, node->ioss_NumScanLooseKeys))
 		{
 			/*
 			 * Reached end of index. At this point currPos is invalidated, and
@@ -202,7 +202,7 @@ IndexOnlyNext(IndexOnlyScanState *node)
 				if (!index_skip(scandesc, direction,
 								indexonlyscan->indexorderdir,
 								!node->ioss_FirstTupleEmitted,
-								node->ioss_SkipPrefixSize))
+								node->ioss_NumScanLooseKeys))
 				{
 					node->ioss_FirstTupleEmitted = false;
 					return ExecClearTuple(slot);
@@ -594,7 +594,6 @@ 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;
 
 	/*
@@ -697,6 +696,13 @@ ExecInitIndexOnlyScan(IndexOnlyScan *node, EState *estate, int eflags)
 						   NULL,	/* no ArrayKeys */
 						   NULL);
 
+	if (node->indexskipprefixsize != 0)
+	{
+		indexstate->ioss_NumScanLooseKeys = node->indexskipprefixsize;
+		indexstate->ioss_ScanLooseKeys =
+			(ScanLooseKey) palloc(node->indexskipprefixsize * sizeof(ScanLooseKeyData));
+	}
+
 	/*
 	 * If we have runtime keys, we need an ExprContext to evaluate them. The
 	 * node's standard context won't do because we want to reset that context
diff --git a/src/include/access/relscan.h b/src/include/access/relscan.h
index 53a93ccbe7..5200a1867d 100644
--- a/src/include/access/relscan.h
+++ b/src/include/access/relscan.h
@@ -119,8 +119,10 @@ typedef struct IndexScanDescData
 	struct SnapshotData *xs_snapshot;	/* snapshot to see */
 	int			numberOfKeys;	/* number of index qualifier conditions */
 	int			numberOfOrderBys;	/* number of ordering operators */
+	int			numberOfLooseKeys;	/* number of loose index qualifier conditions */
 	struct ScanKeyData *keyData;	/* array of index qualifier descriptors */
 	struct ScanKeyData *orderByData;	/* array of ordering op descriptors */
+	struct ScanLooseKeyData *looseKeyData;	/* array of loose index qualifier descriptors */
 	bool		xs_want_itup;	/* caller requests index tuples */
 	bool		xs_temp_snap;	/* unregister snapshot at scan end? */
 
diff --git a/src/include/access/skey.h b/src/include/access/skey.h
index b5ab17f7d9..a711dc353d 100644
--- a/src/include/access/skey.h
+++ b/src/include/access/skey.h
@@ -74,6 +74,14 @@ typedef struct ScanKeyData
 
 typedef ScanKeyData *ScanKey;
 
+typedef struct ScanLooseKeyData
+{
+	ScanKey start;
+	ScanKey end;
+} ScanLooseKeyData;
+
+typedef ScanLooseKeyData *ScanLooseKey;
+
 /*
  * About row comparisons:
  *
diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index cf36e6c0e6..fa6ee25bc6 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -1508,6 +1508,8 @@ typedef struct IndexScanState
  *		NumOrderByKeys	   number of OrderByKeys
  *		RuntimeKeys		   info about Skeys that must be evaluated at runtime
  *		NumRuntimeKeys	   number of RuntimeKeys
+ *		ScanLooseKeys 	   Skey structures for loose index quals
+ *		NumScanLooseKeys   number of ScanLooseKeys
  *		RuntimeKeysReady   true if runtime Skeys have been computed
  *		RuntimeContext	   expr context for evaling runtime Skeys
  *		RelationDesc	   index relation descriptor
@@ -1527,13 +1529,14 @@ typedef struct IndexOnlyScanState
 	int			ioss_NumOrderByKeys;
 	IndexRuntimeKeyInfo *ioss_RuntimeKeys;
 	int			ioss_NumRuntimeKeys;
+	struct ScanLooseKeyData *ioss_ScanLooseKeys;
+	int			ioss_NumScanLooseKeys;
 	bool		ioss_RuntimeKeysReady;
 	ExprContext *ioss_RuntimeContext;
 	Relation	ioss_RelationDesc;
 	struct IndexScanDescData *ioss_ScanDesc;
 	TupleTableSlot *ioss_TableSlot;
 	Buffer		ioss_VMBuffer;
-	int         ioss_SkipPrefixSize;
 	bool		ioss_FirstTupleEmitted;
 	Size		ioss_PscanLen;
 } IndexOnlyScanState;
-- 
2.32.0