• Heikki Linnakangas's avatar
    Remove obsolete heap_formtuple/modifytuple/deformtuple functions. · 72611724
    Heikki Linnakangas authored
    These variants used the old-style 'n'/' ' NULL indicators. The new-style
    functions have been available since version 8.1. That should be long enough
    that if there is still any old external code using these functions, they
    can just switch to the new functions without worrying about backwards
    compatibility
    
    Peter Geoghegan
    72611724
htup_details.h 27.2 KB
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/*-------------------------------------------------------------------------
 *
 * htup_details.h
 *	  POSTGRES heap tuple header definitions.
 *
 *
 * Portions Copyright (c) 1996-2015, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/access/htup_details.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef HTUP_DETAILS_H
#define HTUP_DETAILS_H

#include "access/htup.h"
#include "access/tupdesc.h"
#include "access/tupmacs.h"
#include "access/transam.h"
#include "storage/bufpage.h"

/*
 * MaxTupleAttributeNumber limits the number of (user) columns in a tuple.
 * 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 upper limit without making t_hoff wider would be a little
 * over 1700.  We use round numbers here and for MaxHeapAttributeNumber
 * so that alterations in HeapTupleHeaderData layout won't change the
 * supported max number of columns.
 */
#define MaxTupleAttributeNumber 1664	/* 8 * 208 */

/*
 * MaxHeapAttributeNumber limits the number of (user) columns in a table.
 * This should be somewhat less than MaxTupleAttributeNumber.  It must be
 * at least one less, else we will fail to do UPDATEs on a maximal-width
 * table (because UPDATE has to form working tuples that include CTID).
 * In practice we want some additional daylight so that we can gracefully
 * support operations that add hidden "resjunk" columns, for example
 * SELECT * FROM wide_table ORDER BY foo, bar, baz.
 * In any case, depending on column data types you will likely 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 */

/*
 * Heap tuple header.  To avoid wasting space, the fields should be
 * laid out in such a way as to avoid structure padding.
 *
 * Datums of composite types (row types) share the same general structure
 * as on-disk tuples, so that the same routines can be used to build and
 * examine them.  However the requirements are slightly different: a Datum
 * does not need any transaction visibility information, and it does need
 * a length word and some embedded type information.  We can achieve this
 * by overlaying the xmin/cmin/xmax/cmax/xvac fields of a heap tuple
 * with the fields needed in the Datum case.  Typically, all tuples built
 * in-memory will be initialized with the Datum fields; but when a tuple is
 * about to be inserted in a table, the transaction fields will be filled,
 * overwriting the datum fields.
 *
 * The overall structure of a heap tuple looks like:
 *			fixed fields (HeapTupleHeaderData struct)
 *			nulls bitmap (if HEAP_HASNULL is set in t_infomask)
 *			alignment padding (as needed to make user data MAXALIGN'd)
 *			object ID (if HEAP_HASOID is set in t_infomask)
 *			user data fields
 *
 * We store five "virtual" fields Xmin, Cmin, Xmax, Cmax, and Xvac in three
 * physical fields.  Xmin and Xmax are always really stored, but Cmin, Cmax
 * and Xvac share a field.  This works because we know that Cmin and Cmax
 * are only interesting for the lifetime of the inserting and deleting
 * transaction respectively.  If a tuple is inserted and deleted in the same
 * transaction, we store a "combo" command id that can be mapped to the real
 * cmin and cmax, but only by use of local state within the originating
 * backend.  See combocid.c for more details.  Meanwhile, Xvac is only set by
 * old-style VACUUM FULL, which does not have any command sub-structure and so
 * does not need either Cmin or Cmax.  (This requires that old-style VACUUM
 * FULL never try to move a tuple whose Cmin or Cmax is still interesting,
 * ie, an insert-in-progress or delete-in-progress tuple.)
 *
 * A word about t_ctid: whenever a new tuple is stored on disk, its t_ctid
 * is initialized with its own TID (location).  If the tuple is ever updated,
 * its t_ctid is changed to point to the replacement version of the tuple.
 * Thus, a tuple is the latest version of its row iff XMAX is invalid or
 * t_ctid points to itself (in which case, if XMAX is valid, the tuple is
 * either locked or deleted).  One can follow the chain of t_ctid links
 * to find the newest version of the row.  Beware however that VACUUM might
 * erase the pointed-to (newer) tuple before erasing the pointing (older)
 * tuple.  Hence, when following a t_ctid link, it is necessary to check
 * to see if the referenced slot is empty or contains an unrelated tuple.
 * Check that the referenced tuple has XMIN equal to the referencing tuple's
 * XMAX to verify that it is actually the descendant version and not an
 * unrelated tuple stored into a slot recently freed by VACUUM.  If either
 * check fails, one may assume that there is no live descendant version.
 *
 * t_ctid is sometimes used to store a speculative insertion token, instead
 * of a real TID.  A speculative token is set on a tuple that's being
 * inserted, until the inserter is sure that it wants to go ahead with the
 * insertion.  Hence a token should only be seen on a tuple with an XMAX
 * that's still in-progress, or invalid/aborted.  The token is replaced with
 * the tuple's real TID when the insertion is confirmed.  One should never
 * see a speculative insertion token while following a chain of t_ctid links,
 * because they are not used on updates, only insertions.
 *
 * Following the fixed header fields, the nulls bitmap is stored (beginning
 * at t_bits).  The bitmap is *not* stored if t_infomask shows that there
 * are no nulls in the tuple.  If an OID field is present (as indicated by
 * t_infomask), then it is stored just before the user data, which begins at
 * the offset shown by t_hoff.  Note that t_hoff must be a multiple of
 * MAXALIGN.
 */

typedef struct HeapTupleFields
{
	TransactionId t_xmin;		/* inserting xact ID */
	TransactionId t_xmax;		/* deleting or locking xact ID */

	union
	{
		CommandId	t_cid;		/* inserting or deleting command ID, or both */
		TransactionId t_xvac;	/* old-style VACUUM FULL xact ID */
	}			t_field3;
} HeapTupleFields;

typedef struct DatumTupleFields
{
	int32		datum_len_;		/* varlena header (do not touch directly!) */

	int32		datum_typmod;	/* -1, or identifier of a record type */

	Oid			datum_typeid;	/* composite type OID, or RECORDOID */

	/*
	 * Note: field ordering is chosen with thought that Oid might someday
	 * widen to 64 bits.
	 */
} DatumTupleFields;

struct HeapTupleHeaderData
{
	union
	{
		HeapTupleFields t_heap;
		DatumTupleFields t_datum;
	}			t_choice;

	ItemPointerData t_ctid;		/* current TID of this or newer tuple (or a
								 * speculative insertion token) */

	/* Fields below here must match MinimalTupleData! */

	uint16		t_infomask2;	/* number of attributes + various flags */

	uint16		t_infomask;		/* various flag bits, see below */

	uint8		t_hoff;			/* sizeof header incl. bitmap, padding */

	/* ^ - 23 bytes - ^ */

	bits8		t_bits[FLEXIBLE_ARRAY_MEMBER];	/* bitmap of NULLs */

	/* MORE DATA FOLLOWS AT END OF STRUCT */
};

/* typedef appears in tupbasics.h */

#define SizeofHeapTupleHeader offsetof(HeapTupleHeaderData, t_bits)

/*
 * information stored in t_infomask:
 */
#define HEAP_HASNULL			0x0001	/* has null attribute(s) */
#define HEAP_HASVARWIDTH		0x0002	/* has variable-width attribute(s) */
#define HEAP_HASEXTERNAL		0x0004	/* has external stored attribute(s) */
#define HEAP_HASOID				0x0008	/* has an object-id field */
#define HEAP_XMAX_KEYSHR_LOCK	0x0010	/* xmax is a key-shared locker */
#define HEAP_COMBOCID			0x0020	/* t_cid is a combo cid */
#define HEAP_XMAX_EXCL_LOCK		0x0040	/* xmax is exclusive locker */
#define HEAP_XMAX_LOCK_ONLY		0x0080	/* xmax, if valid, is only a locker */

 /* xmax is a shared locker */
#define HEAP_XMAX_SHR_LOCK	(HEAP_XMAX_EXCL_LOCK | HEAP_XMAX_KEYSHR_LOCK)

#define HEAP_LOCK_MASK	(HEAP_XMAX_SHR_LOCK | HEAP_XMAX_EXCL_LOCK | \
						 HEAP_XMAX_KEYSHR_LOCK)
#define HEAP_XMIN_COMMITTED		0x0100	/* t_xmin committed */
#define HEAP_XMIN_INVALID		0x0200	/* t_xmin invalid/aborted */
#define HEAP_XMIN_FROZEN		(HEAP_XMIN_COMMITTED|HEAP_XMIN_INVALID)
#define HEAP_XMAX_COMMITTED		0x0400	/* t_xmax committed */
#define HEAP_XMAX_INVALID		0x0800	/* t_xmax invalid/aborted */
#define HEAP_XMAX_IS_MULTI		0x1000	/* t_xmax is a MultiXactId */
#define HEAP_UPDATED			0x2000	/* this is UPDATEd version of row */
#define HEAP_MOVED_OFF			0x4000	/* moved to another place by pre-9.0
										 * VACUUM FULL; kept for binary
										 * upgrade support */
#define HEAP_MOVED_IN			0x8000	/* moved from another place by pre-9.0
										 * VACUUM FULL; kept for binary
										 * upgrade support */
#define HEAP_MOVED (HEAP_MOVED_OFF | HEAP_MOVED_IN)

#define HEAP_XACT_MASK			0xFFF0	/* visibility-related bits */

/*
 * A tuple is only locked (i.e. not updated by its Xmax) if the
 * HEAP_XMAX_LOCK_ONLY bit is set; or, for pg_upgrade's sake, if the Xmax is
 * not a multi and the EXCL_LOCK bit is set.
 *
 * See also HeapTupleHeaderIsOnlyLocked, which also checks for a possible
 * aborted updater transaction.
 *
 * Beware of multiple evaluations of the argument.
 */
#define HEAP_XMAX_IS_LOCKED_ONLY(infomask) \
	(((infomask) & HEAP_XMAX_LOCK_ONLY) || \
	 (((infomask) & (HEAP_XMAX_IS_MULTI | HEAP_LOCK_MASK)) == HEAP_XMAX_EXCL_LOCK))

/*
 * Use these to test whether a particular lock is applied to a tuple
 */
#define HEAP_XMAX_IS_SHR_LOCKED(infomask) \
	(((infomask) & HEAP_LOCK_MASK) == HEAP_XMAX_SHR_LOCK)
#define HEAP_XMAX_IS_EXCL_LOCKED(infomask) \
	(((infomask) & HEAP_LOCK_MASK) == HEAP_XMAX_EXCL_LOCK)
#define HEAP_XMAX_IS_KEYSHR_LOCKED(infomask) \
	(((infomask) & HEAP_LOCK_MASK) == HEAP_XMAX_KEYSHR_LOCK)

/* turn these all off when Xmax is to change */
#define HEAP_XMAX_BITS (HEAP_XMAX_COMMITTED | HEAP_XMAX_INVALID | \
						HEAP_XMAX_IS_MULTI | HEAP_LOCK_MASK | HEAP_XMAX_LOCK_ONLY)

/*
 * information stored in t_infomask2:
 */
#define HEAP_NATTS_MASK			0x07FF	/* 11 bits for number of attributes */
/* bits 0x1800 are available */
#define HEAP_KEYS_UPDATED		0x2000	/* tuple was updated and key cols
										 * modified, or tuple deleted */
#define HEAP_HOT_UPDATED		0x4000	/* tuple was HOT-updated */
#define HEAP_ONLY_TUPLE			0x8000	/* this is heap-only tuple */

#define HEAP2_XACT_MASK			0xE000	/* visibility-related bits */

/*
 * HEAP_TUPLE_HAS_MATCH is a temporary flag used during hash joins.  It is
 * only used in tuples that are in the hash table, and those don't need
 * any visibility information, so we can overlay it on a visibility flag
 * instead of using up a dedicated bit.
 */
#define HEAP_TUPLE_HAS_MATCH	HEAP_ONLY_TUPLE /* tuple has a join match */

/*
 * Special value used in t_ctid.ip_posid, to indicate that it holds a
 * speculative insertion token rather than a real TID.  This must be higher
 * than MaxOffsetNumber, so that it can be distinguished from a valid
 * offset number in a regular item pointer.
 */
#define SpecTokenOffsetNumber		0xfffe

/*
 * HeapTupleHeader accessor macros
 *
 * Note: beware of multiple evaluations of "tup" argument.  But the Set
 * macros evaluate their other argument only once.
 */

/*
 * HeapTupleHeaderGetRawXmin returns the "raw" xmin field, which is the xid
 * originally used to insert the tuple.  However, the tuple might actually
 * be frozen (via HeapTupleHeaderSetXminFrozen) in which case the tuple's xmin
 * is visible to every snapshot.  Prior to PostgreSQL 9.4, we actually changed
 * the xmin to FrozenTransactionId, and that value may still be encountered
 * on disk.
 */
#define HeapTupleHeaderGetRawXmin(tup) \
( \
	(tup)->t_choice.t_heap.t_xmin \
)

#define HeapTupleHeaderGetXmin(tup) \
( \
	HeapTupleHeaderXminFrozen(tup) ? \
		FrozenTransactionId : HeapTupleHeaderGetRawXmin(tup) \
)

#define HeapTupleHeaderSetXmin(tup, xid) \
( \
	(tup)->t_choice.t_heap.t_xmin = (xid) \
)

#define HeapTupleHeaderXminCommitted(tup) \
( \
	(tup)->t_infomask & HEAP_XMIN_COMMITTED \
)

#define HeapTupleHeaderXminInvalid(tup) \
( \
	((tup)->t_infomask & (HEAP_XMIN_COMMITTED|HEAP_XMIN_INVALID)) == \
		HEAP_XMIN_INVALID \
)

#define HeapTupleHeaderXminFrozen(tup) \
( \
	((tup)->t_infomask & (HEAP_XMIN_FROZEN)) == HEAP_XMIN_FROZEN \
)

#define HeapTupleHeaderSetXminCommitted(tup) \
( \
	AssertMacro(!HeapTupleHeaderXminInvalid(tup)), \
	((tup)->t_infomask |= HEAP_XMIN_COMMITTED) \
)

#define HeapTupleHeaderSetXminInvalid(tup) \
( \
	AssertMacro(!HeapTupleHeaderXminCommitted(tup)), \
	((tup)->t_infomask |= HEAP_XMIN_INVALID) \
)

#define HeapTupleHeaderSetXminFrozen(tup) \
( \
	AssertMacro(!HeapTupleHeaderXminInvalid(tup)), \
	((tup)->t_infomask |= HEAP_XMIN_FROZEN) \
)

/*
 * HeapTupleHeaderGetRawXmax gets you the raw Xmax field.  To find out the Xid
 * that updated a tuple, you might need to resolve the MultiXactId if certain
 * bits are set.  HeapTupleHeaderGetUpdateXid checks those bits and takes care
 * to resolve the MultiXactId if necessary.  This might involve multixact I/O,
 * so it should only be used if absolutely necessary.
 */
#define HeapTupleHeaderGetUpdateXid(tup) \
( \
	(!((tup)->t_infomask & HEAP_XMAX_INVALID) && \
	 ((tup)->t_infomask & HEAP_XMAX_IS_MULTI) && \
	 !((tup)->t_infomask & HEAP_XMAX_LOCK_ONLY)) ? \
		HeapTupleGetUpdateXid(tup) \
	: \
		HeapTupleHeaderGetRawXmax(tup) \
)

#define HeapTupleHeaderGetRawXmax(tup) \
( \
	(tup)->t_choice.t_heap.t_xmax \
)

#define HeapTupleHeaderSetXmax(tup, xid) \
( \
	(tup)->t_choice.t_heap.t_xmax = (xid) \
)

/*
 * HeapTupleHeaderGetRawCommandId will give you what's in the header whether
 * it is useful or not.  Most code should use HeapTupleHeaderGetCmin or
 * HeapTupleHeaderGetCmax instead, but note that those Assert that you can
 * get a legitimate result, ie you are in the originating transaction!
 */
#define HeapTupleHeaderGetRawCommandId(tup) \
( \
	(tup)->t_choice.t_heap.t_field3.t_cid \
)

/* SetCmin is reasonably simple since we never need a combo CID */
#define HeapTupleHeaderSetCmin(tup, cid) \
do { \
	Assert(!((tup)->t_infomask & HEAP_MOVED)); \
	(tup)->t_choice.t_heap.t_field3.t_cid = (cid); \
	(tup)->t_infomask &= ~HEAP_COMBOCID; \
} while (0)

/* SetCmax must be used after HeapTupleHeaderAdjustCmax; see combocid.c */
#define HeapTupleHeaderSetCmax(tup, cid, iscombo) \
do { \
	Assert(!((tup)->t_infomask & HEAP_MOVED)); \
	(tup)->t_choice.t_heap.t_field3.t_cid = (cid); \
	if (iscombo) \
		(tup)->t_infomask |= HEAP_COMBOCID; \
	else \
		(tup)->t_infomask &= ~HEAP_COMBOCID; \
} while (0)

#define HeapTupleHeaderGetXvac(tup) \
( \
	((tup)->t_infomask & HEAP_MOVED) ? \
		(tup)->t_choice.t_heap.t_field3.t_xvac \
	: \
		InvalidTransactionId \
)

#define HeapTupleHeaderSetXvac(tup, xid) \
do { \
	Assert((tup)->t_infomask & HEAP_MOVED); \
	(tup)->t_choice.t_heap.t_field3.t_xvac = (xid); \
} while (0)

#define HeapTupleHeaderIsSpeculative(tup) \
( \
	(tup)->t_ctid.ip_posid == SpecTokenOffsetNumber \
)

#define HeapTupleHeaderGetSpeculativeToken(tup) \
( \
	AssertMacro(HeapTupleHeaderIsSpeculative(tup)), \
	ItemPointerGetBlockNumber(&(tup)->t_ctid) \
)

#define HeapTupleHeaderSetSpeculativeToken(tup, token)	\
( \
	ItemPointerSet(&(tup)->t_ctid, token, SpecTokenOffsetNumber) \
)

#define HeapTupleHeaderGetDatumLength(tup) \
	VARSIZE(tup)

#define HeapTupleHeaderSetDatumLength(tup, len) \
	SET_VARSIZE(tup, len)

#define HeapTupleHeaderGetTypeId(tup) \
( \
	(tup)->t_choice.t_datum.datum_typeid \
)

#define HeapTupleHeaderSetTypeId(tup, typeid) \
( \
	(tup)->t_choice.t_datum.datum_typeid = (typeid) \
)

#define HeapTupleHeaderGetTypMod(tup) \
( \
	(tup)->t_choice.t_datum.datum_typmod \
)

#define HeapTupleHeaderSetTypMod(tup, typmod) \
( \
	(tup)->t_choice.t_datum.datum_typmod = (typmod) \
)

#define HeapTupleHeaderGetOid(tup) \
( \
	((tup)->t_infomask & HEAP_HASOID) ? \
		*((Oid *) ((char *)(tup) + (tup)->t_hoff - sizeof(Oid))) \
	: \
		InvalidOid \
)

#define HeapTupleHeaderSetOid(tup, oid) \
do { \
	Assert((tup)->t_infomask & HEAP_HASOID); \
	*((Oid *) ((char *)(tup) + (tup)->t_hoff - sizeof(Oid))) = (oid); \
} while (0)

/*
 * Note that we stop considering a tuple HOT-updated as soon as it is known
 * aborted or the would-be updating transaction is known aborted.  For best
 * efficiency, check tuple visibility before using this macro, so that the
 * INVALID bits will be as up to date as possible.
 */
#define HeapTupleHeaderIsHotUpdated(tup) \
( \
	((tup)->t_infomask2 & HEAP_HOT_UPDATED) != 0 && \
	((tup)->t_infomask & HEAP_XMAX_INVALID) == 0 && \
	!HeapTupleHeaderXminInvalid(tup) \
)

#define HeapTupleHeaderSetHotUpdated(tup) \
( \
	(tup)->t_infomask2 |= HEAP_HOT_UPDATED \
)

#define HeapTupleHeaderClearHotUpdated(tup) \
( \
	(tup)->t_infomask2 &= ~HEAP_HOT_UPDATED \
)

#define HeapTupleHeaderIsHeapOnly(tup) \
( \
  (tup)->t_infomask2 & HEAP_ONLY_TUPLE \
)

#define HeapTupleHeaderSetHeapOnly(tup) \
( \
  (tup)->t_infomask2 |= HEAP_ONLY_TUPLE \
)

#define HeapTupleHeaderClearHeapOnly(tup) \
( \
  (tup)->t_infomask2 &= ~HEAP_ONLY_TUPLE \
)

#define HeapTupleHeaderHasMatch(tup) \
( \
  (tup)->t_infomask2 & HEAP_TUPLE_HAS_MATCH \
)

#define HeapTupleHeaderSetMatch(tup) \
( \
  (tup)->t_infomask2 |= HEAP_TUPLE_HAS_MATCH \
)

#define HeapTupleHeaderClearMatch(tup) \
( \
  (tup)->t_infomask2 &= ~HEAP_TUPLE_HAS_MATCH \
)

#define HeapTupleHeaderGetNatts(tup) \
	((tup)->t_infomask2 & HEAP_NATTS_MASK)

#define HeapTupleHeaderSetNatts(tup, natts) \
( \
	(tup)->t_infomask2 = ((tup)->t_infomask2 & ~HEAP_NATTS_MASK) | (natts) \
)

#define HeapTupleHeaderHasExternal(tup) \
		(((tup)->t_infomask & HEAP_HASEXTERNAL) != 0)


/*
 * BITMAPLEN(NATTS) -
 *		Computes size of null bitmap given number of data columns.
 */
#define BITMAPLEN(NATTS)	(((int)(NATTS) + 7) / 8)

/*
 * MaxHeapTupleSize is the maximum allowed size of a heap tuple, including
 * header and MAXALIGN alignment padding.  Basically it's BLCKSZ minus the
 * other stuff that has to be on a disk page.  Since heap pages use no
 * "special space", there's no deduction for that.
 *
 * NOTE: we allow for the ItemId that must point to the tuple, ensuring that
 * an otherwise-empty page can indeed hold a tuple of this size.  Because
 * ItemIds and tuples have different alignment requirements, don't assume that
 * you can, say, fit 2 tuples of size MaxHeapTupleSize/2 on the same page.
 */
#define MaxHeapTupleSize  (BLCKSZ - MAXALIGN(SizeOfPageHeaderData + sizeof(ItemIdData)))
#define MinHeapTupleSize  MAXALIGN(SizeofHeapTupleHeader)

/*
 * MaxHeapTuplesPerPage is an upper bound on the number of tuples that can
 * fit on one heap page.  (Note that indexes could have more, because they
 * use a smaller tuple header.)  We arrive at the divisor because each tuple
 * must be maxaligned, and it must have an associated item pointer.
 *
 * Note: with HOT, there could theoretically be more line pointers (not actual
 * tuples) than this on a heap page.  However we constrain the number of line
 * pointers to this anyway, to avoid excessive line-pointer bloat and not
 * require increases in the size of work arrays.
 */
#define MaxHeapTuplesPerPage	\
	((int) ((BLCKSZ - SizeOfPageHeaderData) / \
			(MAXALIGN(SizeofHeapTupleHeader) + sizeof(ItemIdData))))

/*
 * 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 TOAST structures in postgres.h).  I've set it
 * at 10Mb which seems like a reasonable number --- tgl 8/6/00.
 */
#define MaxAttrSize		(10 * 1024 * 1024)


/*
 * MinimalTuple is an alternative representation that is used for transient
 * tuples inside the executor, in places where transaction status information
 * is not required, the tuple rowtype is known, and shaving off a few bytes
 * is worthwhile because we need to store many tuples.  The representation
 * is chosen so that tuple access routines can work with either full or
 * minimal tuples via a HeapTupleData pointer structure.  The access routines
 * see no difference, except that they must not access the transaction status
 * or t_ctid fields because those aren't there.
 *
 * For the most part, MinimalTuples should be accessed via TupleTableSlot
 * routines.  These routines will prevent access to the "system columns"
 * and thereby prevent accidental use of the nonexistent fields.
 *
 * MinimalTupleData contains a length word, some padding, and fields matching
 * HeapTupleHeaderData beginning with t_infomask2. The padding is chosen so
 * that offsetof(t_infomask2) is the same modulo MAXIMUM_ALIGNOF in both
 * structs.   This makes data alignment rules equivalent in both cases.
 *
 * When a minimal tuple is accessed via a HeapTupleData pointer, t_data is
 * set to point MINIMAL_TUPLE_OFFSET bytes before the actual start of the
 * minimal tuple --- that is, where a full tuple matching the minimal tuple's
 * data would start.  This trick is what makes the structs seem equivalent.
 *
 * Note that t_hoff is computed the same as in a full tuple, hence it includes
 * the MINIMAL_TUPLE_OFFSET distance.  t_len does not include that, however.
 *
 * MINIMAL_TUPLE_DATA_OFFSET is the offset to the first useful (non-pad) data
 * other than the length word.  tuplesort.c and tuplestore.c use this to avoid
 * writing the padding to disk.
 */
#define MINIMAL_TUPLE_OFFSET \
	((offsetof(HeapTupleHeaderData, t_infomask2) - sizeof(uint32)) / MAXIMUM_ALIGNOF * MAXIMUM_ALIGNOF)
#define MINIMAL_TUPLE_PADDING \
	((offsetof(HeapTupleHeaderData, t_infomask2) - sizeof(uint32)) % MAXIMUM_ALIGNOF)
#define MINIMAL_TUPLE_DATA_OFFSET \
	offsetof(MinimalTupleData, t_infomask2)

struct MinimalTupleData
{
	uint32		t_len;			/* actual length of minimal tuple */

	char		mt_padding[MINIMAL_TUPLE_PADDING];

	/* Fields below here must match HeapTupleHeaderData! */

	uint16		t_infomask2;	/* number of attributes + various flags */

	uint16		t_infomask;		/* various flag bits, see below */

	uint8		t_hoff;			/* sizeof header incl. bitmap, padding */

	/* ^ - 23 bytes - ^ */

	bits8		t_bits[FLEXIBLE_ARRAY_MEMBER];	/* bitmap of NULLs */

	/* MORE DATA FOLLOWS AT END OF STRUCT */
};

/* typedef appears in htup.h */

#define SizeofMinimalTupleHeader offsetof(MinimalTupleData, t_bits)


/*
 * GETSTRUCT - given a HeapTuple pointer, return address of the user data
 */
#define GETSTRUCT(TUP) ((char *) ((TUP)->t_data) + (TUP)->t_data->t_hoff)

/*
 * Accessor macros to be used with HeapTuple pointers.
 */

#define HeapTupleHasNulls(tuple) \
		(((tuple)->t_data->t_infomask & HEAP_HASNULL) != 0)

#define HeapTupleNoNulls(tuple) \
		(!((tuple)->t_data->t_infomask & HEAP_HASNULL))

#define HeapTupleHasVarWidth(tuple) \
		(((tuple)->t_data->t_infomask & HEAP_HASVARWIDTH) != 0)

#define HeapTupleAllFixed(tuple) \
		(!((tuple)->t_data->t_infomask & HEAP_HASVARWIDTH))

#define HeapTupleHasExternal(tuple) \
		(((tuple)->t_data->t_infomask & HEAP_HASEXTERNAL) != 0)

#define HeapTupleIsHotUpdated(tuple) \
		HeapTupleHeaderIsHotUpdated((tuple)->t_data)

#define HeapTupleSetHotUpdated(tuple) \
		HeapTupleHeaderSetHotUpdated((tuple)->t_data)

#define HeapTupleClearHotUpdated(tuple) \
		HeapTupleHeaderClearHotUpdated((tuple)->t_data)

#define HeapTupleIsHeapOnly(tuple) \
		HeapTupleHeaderIsHeapOnly((tuple)->t_data)

#define HeapTupleSetHeapOnly(tuple) \
		HeapTupleHeaderSetHeapOnly((tuple)->t_data)

#define HeapTupleClearHeapOnly(tuple) \
		HeapTupleHeaderClearHeapOnly((tuple)->t_data)

#define HeapTupleGetOid(tuple) \
		HeapTupleHeaderGetOid((tuple)->t_data)

#define HeapTupleSetOid(tuple, oid) \
		HeapTupleHeaderSetOid((tuple)->t_data, (oid))


/* ----------------
 *		fastgetattr
 *
 *		Fetch a user attribute's value as a Datum (might be either a
 *		value, or a pointer into the data area of the tuple).
 *
 *		This must not be used when a system attribute might be requested.
 *		Furthermore, the passed attnum MUST be valid.  Use heap_getattr()
 *		instead, if in doubt.
 *
 *		This gets called many times, so we macro the cacheable and NULL
 *		lookups, and call nocachegetattr() for the rest.
 * ----------------
 */

#if !defined(DISABLE_COMPLEX_MACRO)

#define fastgetattr(tup, attnum, tupleDesc, isnull)					\
(																	\
	AssertMacro((attnum) > 0),										\
	(*(isnull) = false),											\
	HeapTupleNoNulls(tup) ?											\
	(																\
		(tupleDesc)->attrs[(attnum)-1]->attcacheoff >= 0 ?			\
		(															\
			fetchatt((tupleDesc)->attrs[(attnum)-1],				\
				(char *) (tup)->t_data + (tup)->t_data->t_hoff +	\
					(tupleDesc)->attrs[(attnum)-1]->attcacheoff)	\
		)															\
		:															\
			nocachegetattr((tup), (attnum), (tupleDesc))			\
	)																\
	:																\
	(																\
		att_isnull((attnum)-1, (tup)->t_data->t_bits) ?				\
		(															\
			(*(isnull) = true),										\
			(Datum)NULL												\
		)															\
		:															\
		(															\
			nocachegetattr((tup), (attnum), (tupleDesc))			\
		)															\
	)																\
)
#else							/* defined(DISABLE_COMPLEX_MACRO) */

extern Datum fastgetattr(HeapTuple tup, int attnum, TupleDesc tupleDesc,
			bool *isnull);
#endif   /* defined(DISABLE_COMPLEX_MACRO) */


/* ----------------
 *		heap_getattr
 *
 *		Extract an attribute of a heap tuple and return it as a Datum.
 *		This works for either system or user attributes.  The given attnum
 *		is properly range-checked.
 *
 *		If the field in question has a NULL value, we return a zero Datum
 *		and set *isnull == true.  Otherwise, we set *isnull == false.
 *
 *		<tup> is the pointer to the heap tuple.  <attnum> is the attribute
 *		number of the column (field) caller wants.  <tupleDesc> is a
 *		pointer to the structure describing the row and all its fields.
 * ----------------
 */
#define heap_getattr(tup, attnum, tupleDesc, isnull) \
	( \
		((attnum) > 0) ? \
		( \
			((attnum) > (int) HeapTupleHeaderGetNatts((tup)->t_data)) ? \
			( \
				(*(isnull) = true), \
				(Datum)NULL \
			) \
			: \
				fastgetattr((tup), (attnum), (tupleDesc), (isnull)) \
		) \
		: \
			heap_getsysattr((tup), (attnum), (tupleDesc), (isnull)) \
	)


/* prototypes for functions in common/heaptuple.c */
extern Size heap_compute_data_size(TupleDesc tupleDesc,
					   Datum *values, bool *isnull);
extern void heap_fill_tuple(TupleDesc tupleDesc,
				Datum *values, bool *isnull,
				char *data, Size data_size,
				uint16 *infomask, bits8 *bit);
extern bool heap_attisnull(HeapTuple tup, int attnum);
extern Datum nocachegetattr(HeapTuple tup, int attnum,
			   TupleDesc att);
extern Datum heap_getsysattr(HeapTuple tup, int attnum, TupleDesc tupleDesc,
				bool *isnull);
extern HeapTuple heap_copytuple(HeapTuple tuple);
extern void heap_copytuple_with_tuple(HeapTuple src, HeapTuple dest);
extern Datum heap_copy_tuple_as_datum(HeapTuple tuple, TupleDesc tupleDesc);
extern HeapTuple heap_form_tuple(TupleDesc tupleDescriptor,
				Datum *values, bool *isnull);
extern HeapTuple heap_modify_tuple(HeapTuple tuple,
				  TupleDesc tupleDesc,
				  Datum *replValues,
				  bool *replIsnull,
				  bool *doReplace);
extern void heap_deform_tuple(HeapTuple tuple, TupleDesc tupleDesc,
				  Datum *values, bool *isnull);
extern void heap_freetuple(HeapTuple htup);
extern MinimalTuple heap_form_minimal_tuple(TupleDesc tupleDescriptor,
						Datum *values, bool *isnull);
extern void heap_free_minimal_tuple(MinimalTuple mtup);
extern MinimalTuple heap_copy_minimal_tuple(MinimalTuple mtup);
extern HeapTuple heap_tuple_from_minimal_tuple(MinimalTuple mtup);
extern MinimalTuple minimal_tuple_from_heap_tuple(HeapTuple htup);

#endif   /* HTUP_DETAILS_H */