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Add appropriately ifdef'd hack to make ARM compiler allocate ItemPointerData

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as six bytes not eight.  This fixes a regression test failure but more
importantly avoids wasting four bytes of pad space in every tuple header.
Also add some commentary about what's going on.
This commit is contained in:
Tom Lane 2001-03-30 05:25:51 +00:00
parent d0f6ae68f5
commit dcbbdb1b3e
1 changed files with 17 additions and 3 deletions
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20
src/include/storage/itemptr.h
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@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group * Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California * Portions Copyright (c) 1994, Regents of the University of California
* *
* $Id: itemptr.h,v 1.17 2001/03/22 04:01:06 momjian Exp $ * $Id: itemptr.h,v 1.18 2001/03/30 05:25:51 tgl Exp $
* *
*------------------------------------------------------------------------- *-------------------------------------------------------------------------
*/ */
@ -20,15 +20,29 @@
/* /*
* ItemPointer: * ItemPointer:
* *
* this is a pointer to an item on another disk page in the same file. * This is a pointer to an item within a disk page of a known file
* (for example, a cross-link from an index to its parent table).
* blkid tells us which block, posid tells us which entry in the linp * blkid tells us which block, posid tells us which entry in the linp
* (ItemIdData) array we want. * (ItemIdData) array we want.
*
* Note: because there is an item pointer in each tuple header and index
* tuple header on disk, it's very important not to waste space with
* structure padding bytes. The struct is designed to be six bytes long
* (it contains three int16 fields) but a few compilers will pad it to
* eight bytes unless coerced. We apply appropriate persuasion where
* possible, and to cope with unpersuadable compilers, we try to use
* "SizeOfIptrData" rather than "sizeof(ItemPointerData)" when computing
* on-disk sizes.
*/ */
typedef struct ItemPointerData typedef struct ItemPointerData
{ {
BlockIdData ip_blkid; BlockIdData ip_blkid;
OffsetNumber ip_posid; OffsetNumber ip_posid;
} ItemPointerData; }
#ifdef __arm__
__attribute__((packed)) /* Appropriate whack upside the head for ARM */
#endif
ItemPointerData;
#define SizeOfIptrData \ #define SizeOfIptrData \
(offsetof(ItemPointerData, ip_posid) + sizeof(OffsetNumber)) (offsetof(ItemPointerData, ip_posid) + sizeof(OffsetNumber))