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TOAST mop-up work: update comments for tuple-size-related symbols such

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as MaxHeapAttributeNumber.  Increase MaxAttrSize to something more
reasonable (given what it's used for, namely checking char(n) declarations,
I didn't make it the full 1G that it could theoretically be --- 10Mb
seemed a more reasonable number).  Improve calculation of MaxTupleSize.
This commit is contained in:
Tom Lane
2000-08-07 20:16:13 +00:00
parent d2165a4a5d
commit 0224177400
8 changed files with 96 additions and 63 deletions
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43
src/include/access/htup.h
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@@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2000, PostgreSQL, Inc
* Portions Copyright (c) 1994, Regents of the University of California
*
* $Id: htup.h,v 1.33 2000/07/04 01:49:43 vadim Exp $
* $Id: htup.h,v 1.34 2000/08/07 20:15:40 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -18,8 +18,16 @@
#define MinHeapTupleBitmapSize 32 /* 8 * 4 */
/* check these, they are likely to be more severely limited by t_hoff */
/*
* MaxHeapAttributeNumber limits the number of (user) columns in a table.
* The key limit on this value is that the size of the fixed overhead for
* a tuple, plus the size of the null-values bitmap (at 1 bit per column),
* plus MAXALIGN alignment, must fit into t_hoff which is uint8. On most
* machines the absolute upper limit without making t_hoff wider would be
* about 1700. Note, however, that depending on column data types you will
* likely also be running into the disk-block-based limit on overall tuple
* size if you have more than a thousand or so columns. TOAST won't help.
*/
#define MaxHeapAttributeNumber 1600 /* 8 * 200 */
/*
@@ -130,13 +138,32 @@ typedef struct xl_heap_move
#endif /* XLOG */
#define MinTupleSize (MAXALIGN(sizeof (PageHeaderData)) + \
MAXALIGN(sizeof(HeapTupleHeaderData)) + \
MAXALIGN(sizeof(char)))
#define MaxTupleSize (BLCKSZ - MinTupleSize)
/*
* MaxTupleSize is the maximum allowed size of a tuple, including header and
* MAXALIGN alignment padding. Basically it's BLCKSZ minus the other stuff
* that has to be on a disk page. The "other stuff" includes access-method-
* dependent "special space", which we assume will be no more than
* MaxSpecialSpace bytes (currently, on heap pages it's actually zero).
*
* NOTE: we do not need to count an ItemId for the tuple because
* sizeof(PageHeaderData) includes the first ItemId on the page.
*/
#define MaxSpecialSpace 32
#define MaxTupleSize \
(BLCKSZ - MAXALIGN(sizeof(PageHeaderData) + MaxSpecialSpace))
/*
* MaxAttrSize is a somewhat arbitrary upper limit on the declared size of
* data fields of char(n) and similar types. It need not have anything
* directly to do with the *actual* upper limit of varlena values, which
* is currently 1Gb (see struct varattrib in postgres.h). I've set it
* at 10Mb which seems like a reasonable number --- tgl 8/6/00.
*/
#define MaxAttrSize (10 * 1024 * 1024)
#define MaxAttrSize (MaxTupleSize - MAXALIGN(sizeof(HeapTupleHeaderData)))
#define SelfItemPointerAttributeNumber (-1)
#define ObjectIdAttributeNumber (-2)