I pushed 0002 after some makeup, since it's just cosmetic and not
controversial. Here's 0003 rebased on top of it.
(Also, I took out the gin and gist changes: it would be wrong to change
that unconditionally, because the 0xFFFF pattern appears in indexes that
would be pg_upgraded. We need a different strategy, if we want to
enable WARM on GiST/GIN indexes.)
--
Álvaro Herrera https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
>From f6ba238dd46416eb29ac43dadac0c69a75f106fe Mon Sep 17 00:00:00 2001
From: Alvaro Herrera <alvhe...@alvh.no-ip.org>
Date: Tue, 28 Mar 2017 17:39:26 -0300
Subject: [PATCH] Free 3 bits of ItemPointerData.ip_posid
Since we limit block size to 32 kB, the highest offset number used in a
bufpage.h-organized page is 5461, which can be represented with 13 bits.
Therefore, the upper 3 bits in 16-bit ItemPointerData.ip_posid are
unused and this commit reserves them for other purposes.
Author: Pavan Deolasee
---
src/include/access/htup_details.h | 2 +-
src/include/storage/itemptr.h | 30 +++++++++++++++++++++++++++---
src/include/storage/off.h | 11 ++++++++++-
3 files changed, 38 insertions(+), 5 deletions(-)
diff --git a/src/include/access/htup_details.h
b/src/include/access/htup_details.h
index 7b6285d..d3cc0ad 100644
--- a/src/include/access/htup_details.h
+++ b/src/include/access/htup_details.h
@@ -282,7 +282,7 @@ struct HeapTupleHeaderData
* than MaxOffsetNumber, so that it can be distinguished from a valid
* offset number in a regular item pointer.
*/
-#define SpecTokenOffsetNumber 0xfffe
+#define SpecTokenOffsetNumber OffsetNumberPrev(OffsetNumberMask)
/*
* HeapTupleHeader accessor macros
diff --git a/src/include/storage/itemptr.h b/src/include/storage/itemptr.h
index c21d2ad..74eed4e 100644
--- a/src/include/storage/itemptr.h
+++ b/src/include/storage/itemptr.h
@@ -57,7 +57,7 @@ typedef ItemPointerData *ItemPointer;
* True iff the disk item pointer is not NULL.
*/
#define ItemPointerIsValid(pointer) \
- ((bool) (PointerIsValid(pointer) && ((pointer)->ip_posid != 0)))
+ ((bool) (PointerIsValid(pointer) && (((pointer)->ip_posid &
OffsetNumberMask) != 0)))
/*
* ItemPointerGetBlockNumberNoCheck
@@ -84,7 +84,7 @@ typedef ItemPointerData *ItemPointer;
*/
#define ItemPointerGetOffsetNumberNoCheck(pointer) \
( \
- (pointer)->ip_posid \
+ ((pointer)->ip_posid & OffsetNumberMask) \
)
/*
@@ -98,6 +98,30 @@ typedef ItemPointerData *ItemPointer;
)
/*
+ * Get the flags stored in high order bits in the OffsetNumber.
+ */
+#define ItemPointerGetFlags(pointer) \
+( \
+ ((pointer)->ip_posid & ~OffsetNumberMask) >> OffsetNumberBits \
+)
+
+/*
+ * Set the flag bits. We first left-shift since flags are defined starting 0x01
+ */
+#define ItemPointerSetFlags(pointer, flags) \
+( \
+ ((pointer)->ip_posid |= ((flags) << OffsetNumberBits)) \
+)
+
+/*
+ * Clear all flags.
+ */
+#define ItemPointerClearFlags(pointer) \
+( \
+ ((pointer)->ip_posid &= OffsetNumberMask) \
+)
+
+/*
* ItemPointerSet
* Sets a disk item pointer to the specified block and offset.
*/
@@ -105,7 +129,7 @@ typedef ItemPointerData *ItemPointer;
( \
AssertMacro(PointerIsValid(pointer)), \
BlockIdSet(&((pointer)->ip_blkid), blockNumber), \
- (pointer)->ip_posid = offNum \
+ (pointer)->ip_posid = (offNum) \
)
/*
diff --git a/src/include/storage/off.h b/src/include/storage/off.h
index fe8638f..f058fe1 100644
--- a/src/include/storage/off.h
+++ b/src/include/storage/off.h
@@ -26,7 +26,16 @@ typedef uint16 OffsetNumber;
#define InvalidOffsetNumber ((OffsetNumber) 0)
#define FirstOffsetNumber ((OffsetNumber) 1)
#define MaxOffsetNumber ((OffsetNumber) (BLCKSZ /
sizeof(ItemIdData)))
-#define OffsetNumberMask (0xffff) /* valid uint16
bits */
+
+/*
+ * The biggest BLCKSZ we support is 32kB, and each ItemId takes 6 bytes.
+ * That limits the number of line pointers in a page to 32kB/6B = 5461.
+ * Therefore, 13 bits in OffsetNumber are enough to represent all valid
+ * on-disk line pointers. Hence, we can reserve the high-order bits in
+ * OffsetNumber for other purposes.
+ */
+#define OffsetNumberBits 13
+#define OffsetNumberMask ((((uint16) 1) << OffsetNumberBits) - 1)
/* ----------------
* support macros
--
2.1.4
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