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Distinguish between MaxHeapAttributeNumber and MaxTupleAttributeNumber,
where the latter is made slightly larger to allow for in-memory tuples containing resjunk attributes. Responds to today's complaint that one cannot UPDATE a table containing the allegedly-legal maximum number of columns. Also, apply Manfred Koizar's recent patch to avoid extra alignment padding when there is a null bitmap. This saves bytes in some cases while not creating any backward-compatibility problem AFAICS.
This commit is contained in:
Tom Lane
@@ -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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*
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* $Id: htup.h,v 1.51 2001/11/05 17:46:31 momjian Exp $
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* $Id: htup.h,v 1.52 2002/05/27 19:53:33 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@@ -17,25 +17,44 @@
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#include "storage/bufpage.h"
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#include "storage/relfilenode.h"
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#define MinHeapTupleBitmapSize 32 /* 8 * 4 */
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/*
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* MaxHeapAttributeNumber limits the number of (user) columns in a table.
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* MaxTupleAttributeNumber limits the number of (user) columns in a tuple.
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* The key limit on this value is that the size of the fixed overhead for
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* a tuple, plus the size of the null-values bitmap (at 1 bit per column),
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* plus MAXALIGN alignment, must fit into t_hoff which is uint8. On most
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* machines the absolute upper limit without making t_hoff wider would be
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* about 1700. Note, however, that depending on column data types you will
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* likely also be running into the disk-block-based limit on overall tuple
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* size if you have more than a thousand or so columns. TOAST won't help.
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* machines the upper limit without making t_hoff wider would be a little
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* over 1700. We use round numbers here and for MaxHeapAttributeNumber
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* so that alterations in HeapTupleHeaderData layout won't change the
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* supported max number of columns.
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*/
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#define MaxTupleAttributeNumber 1664 /* 8 * 208 */
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/*----------
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* MaxHeapAttributeNumber limits the number of (user) columns in a table.
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* This should be somewhat less than MaxTupleAttributeNumber. It must be
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* at least one less, else we will fail to do UPDATEs on a maximal-width
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* table (because UPDATE has to form working tuples that include CTID).
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* In practice we want some additional daylight so that we can gracefully
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* support operations that add hidden "resjunk" columns, for example
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* SELECT * FROM wide_table ORDER BY foo, bar, baz.
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* In any case, depending on column data types you will likely be running
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* into the disk-block-based limit on overall tuple size if you have more
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* than a thousand or so columns. TOAST won't help.
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*----------
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*/
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#define MaxHeapAttributeNumber 1600 /* 8 * 200 */
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/*
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* This is the on-disk copy of the tuple.
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* On-disk heap tuple header. Currently this is also used as the header
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* format for tuples formed in memory, although in principle they could
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* be different.
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*
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* To avoid wasting space, the attributes should be layed out in such a
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* way to reduce structure padding.
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* way to reduce structure padding. Note that t_hoff is the offset to
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* the start of the user data, and so must be a multiple of MAXALIGN.
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* Also note that we omit the nulls bitmap if t_infomask shows that there
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* are no nulls in the tuple.
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*/
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typedef struct HeapTupleHeaderData
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{
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@@ -51,14 +70,13 @@ typedef struct HeapTupleHeaderData
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int16 t_natts; /* number of attributes */
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uint16 t_infomask; /* various infos */
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uint16 t_infomask; /* various flag bits, see below */
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uint8 t_hoff; /* sizeof() tuple header */
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uint8 t_hoff; /* sizeof header incl. bitmap, padding */
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/* ^ - 31 bytes - ^ */
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bits8 t_bits[MinHeapTupleBitmapSize / 8];
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/* bit map of NULLs */
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bits8 t_bits[1]; /* bitmap of NULLs -- VARIABLE LENGTH */
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/* MORE DATA FOLLOWS AT END OF STRUCT */
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} HeapTupleHeaderData;
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@@ -183,7 +201,7 @@ typedef struct xl_heap_clean
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#define FirstLowInvalidHeapAttributeNumber (-8)
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/*
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* This is the in-memory copy of the tuple.
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* HeapTupleData is an in-memory data structure that points to a tuple.
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*
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* This new HeapTuple for version >= 6.5 and this is why it was changed:
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*
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@@ -222,11 +240,9 @@ typedef HeapTupleData *HeapTuple;
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/*
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* BITMAPLEN(NATTS) -
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* Computes minimum size of bitmap given number of domains.
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* Computes size of null bitmap given number of data columns.
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*/
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#define BITMAPLEN(NATTS) \
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((((((int)(NATTS) - 1) >> 3) + 4 - (MinHeapTupleBitmapSize >> 3)) \
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& ~03) + (MinHeapTupleBitmapSize >> 3))
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#define BITMAPLEN(NATTS) (((int)(NATTS) + 7) / 8)
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/*
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* HeapTupleIsValid
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@@ -240,26 +256,26 @@ typedef HeapTupleData *HeapTuple;
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#define HEAP_HASNULL 0x0001 /* has null attribute(s) */
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#define HEAP_HASVARLENA 0x0002 /* has variable length
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* attribute(s) */
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#define HEAP_HASEXTERNAL 0x0004 /* has external stored */
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/* attribute(s) */
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#define HEAP_HASCOMPRESSED 0x0008 /* has compressed stored */
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/* attribute(s) */
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#define HEAP_HASEXTERNAL 0x0004 /* has external stored
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* attribute(s) */
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#define HEAP_HASCOMPRESSED 0x0008 /* has compressed stored
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* attribute(s) */
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#define HEAP_HASEXTENDED 0x000C /* the two above combined */
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#define HEAP_XMAX_UNLOGGED 0x0080 /* to lock tuple for update */
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/* without logging */
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#define HEAP_XMAX_UNLOGGED 0x0080 /* to lock tuple for update
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* without logging */
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#define HEAP_XMIN_COMMITTED 0x0100 /* t_xmin committed */
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#define HEAP_XMIN_INVALID 0x0200 /* t_xmin invalid/aborted */
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#define HEAP_XMAX_COMMITTED 0x0400 /* t_xmax committed */
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#define HEAP_XMAX_INVALID 0x0800 /* t_xmax invalid/aborted */
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#define HEAP_MARKED_FOR_UPDATE 0x1000 /* marked for UPDATE */
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#define HEAP_UPDATED 0x2000 /* this is UPDATEd version of row */
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#define HEAP_MOVED_OFF 0x4000 /* removed or moved to another
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* place by vacuum */
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#define HEAP_MOVED_OFF 0x4000 /* moved to another place by
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* vacuum */
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#define HEAP_MOVED_IN 0x8000 /* moved from another place by
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* vacuum */
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#define HEAP_XACT_MASK 0xFFF0 /* */
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#define HEAP_XACT_MASK 0xFFF0 /* visibility-related bits */
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#define HeapTupleNoNulls(tuple) \
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(!(((HeapTuple) (tuple))->t_data->t_infomask & HEAP_HASNULL))
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