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Rename MaxTupleSize to MaxHeapTupleSize to clarify that it's not meant to

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describe the maximum size of index tuples (which is typically AM-dependent
anyway); and consequently remove the bogus deduction for "special space"
that was built into it.

Adjust TOAST_TUPLE_THRESHOLD and TOAST_MAX_CHUNK_SIZE to avoid wasting two
bytes per toast chunk, and to ensure that the calculation correctly tracks any
future changes in page header size.  The computation had been inaccurate in a
way that didn't cause any harm except space wastage, but future changes could
have broken it more drastically.

Fix the calculation of BTMaxItemSize, which was formerly computed as 1 byte
more than it could safely be.  This didn't cause any harm in practice because
it's only compared against maxalign'd lengths, but future changes in the size
of page headers or btree special space could have exposed the problem.

initdb forced because of change in TOAST_MAX_CHUNK_SIZE, which alters the
storage of toast tables.
This commit is contained in:
Tom Lane
2007-02-05 04:22:18 +00:00
parent a2e092e1c7
commit 23c4978e6c
8 changed files with 65 additions and 47 deletions
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13
src/include/access/nbtree.h
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@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/access/nbtree.h,v 1.109 2007/01/20 18:43:35 neilc Exp $
* $PostgreSQL: pgsql/src/include/access/nbtree.h,v 1.110 2007/02/05 04:22:18 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -99,13 +99,18 @@ typedef struct BTMetaPageData
#define BTREE_VERSION 2 /* current version number */
/*
* Maximum size of a btree index entry, including its tuple header.
*
* We actually need to be able to fit three items on every page,
* so restrict any one item to 1/3 the per-page available space.
*
* Note: sizeof(PageHeaderData) includes the first ItemId, but we have
* to allow for 2 more, as well as the end-of-page special space.
*/
#define BTMaxItemSize(page) \
((PageGetPageSize(page) - \
sizeof(PageHeaderData) - \
MAXALIGN(sizeof(BTPageOpaqueData))) / 3 - sizeof(ItemIdData))
MAXALIGN_DOWN((PageGetPageSize(page) - \
MAXALIGN(sizeof(PageHeaderData) + 2*sizeof(ItemIdData)) - \
MAXALIGN(sizeof(BTPageOpaqueData))) / 3)
/*
* The leaf-page fillfactor defaults to 90% but is user-adjustable.