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Commitdcbbdb1

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Add appropriately ifdef'd hack to make ARM compiler allocate ItemPointerData
as six bytes not eight. This fixes a regression test failure but moreimportantly avoids wasting four bytes of pad space in every tuple header.Also add some commentary about what's going on.
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‎src/include/storage/itemptr.h

Lines changed: 17 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -7,7 +7,7 @@
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* Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
10-
* $Id: itemptr.h,v 1.17 2001/03/22 04:01:06 momjian Exp $
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* $Id: itemptr.h,v 1.18 2001/03/30 05:25:51 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
@@ -20,15 +20,29 @@
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/*
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* ItemPointer:
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*
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* this is a pointer to an item on another disk page in the same file.
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* This is a pointer to an item within a disk page of a known file
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* (for example, a cross-link from an index to its parent table).
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* blkid tells us which block, posid tells us which entry in the linp
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* (ItemIdData) array we want.
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*
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* Note: because there is an item pointer in each tuple header and index
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* tuple header on disk, it's very important not to waste space with
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* structure padding bytes. The struct is designed to be six bytes long
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* (it contains three int16 fields) but a few compilers will pad it to
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* eight bytes unless coerced. We apply appropriate persuasion where
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* possible, and to cope with unpersuadable compilers, we try to use
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* "SizeOfIptrData" rather than "sizeof(ItemPointerData)" when computing
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* on-disk sizes.
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*/
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typedefstructItemPointerData
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{
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BlockIdDataip_blkid;
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OffsetNumberip_posid;
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}ItemPointerData;
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}
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#ifdef__arm__
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__attribute__((packed))/* Appropriate whack upside the head for ARM */
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#endif
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ItemPointerData;
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#defineSizeOfIptrData\
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(offsetof(ItemPointerData, ip_posid) + sizeof(OffsetNumber))

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