Add TID Range Scans to support efficient scanning ranges of TIDs

This adds a new executor node named TID Range Scan.  The query planner
will generate paths for TID Range scans when quals are discovered on base
relations which search for ranges on the table's ctid column.  These
ranges may be open at either end. For example, WHERE ctid >= '(10,0)';
will return all tuples on page 10 and over.

To support this, two new optional callback functions have been added to
table AM.  scan_set_tidrange is used to set the scan range to just the
given range of TIDs.  scan_getnextslot_tidrange fetches the next tuple
in the given range.

For AMs were scanning ranges of TIDs would not make sense, these functions
can be set to NULL in the TableAmRoutine.  The query planner won't
generate TID Range Scan Paths in that case.

Author: Edmund Horner, David Rowley
Reviewed-by: David Rowley, Tomas Vondra, Tom Lane, Andres Freund, Zhihong Yu
Discussion: https://postgr.es/m/CAMyN-kB-nFTkF=VA_JPwFNo08S0d-Yk0F741S2B7LDmYAi8eyA@mail.gmail.com

1 files changed, 59 insertions, 0 deletions

diff --git a/src/backend/storage/page/itemptr.c b/src/backend/storage/page/itemptr.c
index 55759c383b6..f40d6c22a02 100644
--- a/src/backend/storage/page/itemptr.c
+++ b/src/backend/storage/page/itemptr.c
@@ -71,3 +71,62 @@ ItemPointerCompare(ItemPointer arg1, ItemPointer arg2)
 	else
 		return 0;
 }
+
+/*
+ * ItemPointerInc
+ *		Increment 'pointer' by 1 only paying attention to the ItemPointer's
+ *		type's range limits and not MaxOffsetNumber and FirstOffsetNumber.
+ *		This may result in 'pointer' becoming !OffsetNumberIsValid.
+ *
+ * If the pointer is already the maximum possible values permitted by the
+ * range of the ItemPointer's types, then do nothing.
+ */
+void
+ItemPointerInc(ItemPointer pointer)
+{
+	BlockNumber blk = ItemPointerGetBlockNumberNoCheck(pointer);
+	OffsetNumber off = ItemPointerGetOffsetNumberNoCheck(pointer);
+
+	if (off == PG_UINT16_MAX)
+	{
+		if (blk != InvalidBlockNumber)
+		{
+			off = 0;
+			blk++;
+		}
+	}
+	else
+		off++;
+
+	ItemPointerSet(pointer, blk, off);
+}
+
+/*
+ * ItemPointerDec
+ *		Decrement 'pointer' by 1 only paying attention to the ItemPointer's
+ *		type's range limits and not MaxOffsetNumber and FirstOffsetNumber.
+ *		This may result in 'pointer' becoming !OffsetNumberIsValid.
+ *
+ * If the pointer is already the minimum possible values permitted by the
+ * range of the ItemPointer's types, then do nothing.  This does rely on
+ * FirstOffsetNumber being 1 rather than 0.
+ */
+void
+ItemPointerDec(ItemPointer pointer)
+{
+	BlockNumber blk = ItemPointerGetBlockNumberNoCheck(pointer);
+	OffsetNumber off = ItemPointerGetOffsetNumberNoCheck(pointer);
+
+	if (off == 0)
+	{
+		if (blk != 0)
+		{
+			off = PG_UINT16_MAX;
+			blk--;
+		}
+	}
+	else
+		off--;
+
+	ItemPointerSet(pointer, blk, off);
+}