htup.h

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#define MaxTupleSize	\
	(BLCKSZ - MAXALIGN(sizeof(PageHeaderData) + MaxSpecialSpace))

/*
 * 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.
 */
#define MaxHeapTuplesPerPage	\
	((int) ((BLCKSZ - offsetof(PageHeaderData, pd_linp)) / \
			(MAXALIGN(offsetof(HeapTupleHeaderData, t_bits)) + 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 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)


/*
 * Attribute numbers for the system-defined attributes
 */
#define SelfItemPointerAttributeNumber			(-1)
#define ObjectIdAttributeNumber					(-2)
#define MinTransactionIdAttributeNumber			(-3)
#define MinCommandIdAttributeNumber				(-4)
#define MaxTransactionIdAttributeNumber			(-5)
#define MaxCommandIdAttributeNumber				(-6)
#define TableOidAttributeNumber					(-7)
#define FirstLowInvalidHeapAttributeNumber		(-8)


/*
 * MinimalTuple is an alternate 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_natts.	The padding is chosen so that
 * offsetof(t_natts) 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.
 */
#define MINIMAL_TUPLE_OFFSET \
	((offsetof(HeapTupleHeaderData, t_natts) - sizeof(uint32)) / MAXIMUM_ALIGNOF * MAXIMUM_ALIGNOF)
#define MINIMAL_TUPLE_PADDING \
	((offsetof(HeapTupleHeaderData, t_natts) - sizeof(uint32)) % MAXIMUM_ALIGNOF)

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

	char		mt_padding[MINIMAL_TUPLE_PADDING];

	/* Fields below here must match HeapTupleHeaderData! */

	int16		t_natts;		/* number of attributes */

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

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

	/* ^ - 27 bytes - ^ */

	bits8		t_bits[1];		/* bitmap of NULLs -- VARIABLE LENGTH */

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

typedef MinimalTupleData *MinimalTuple;


/*
 * HeapTupleData is an in-memory data structure that points to a tuple.
 *
 * There are several ways in which this data structure is used:
 *
 * * Pointer to a tuple in a disk buffer: t_data points directly into the
 *	 buffer (which the code had better be holding a pin on, but this is not
 *	 reflected in HeapTupleData itself).
 *
 * * Pointer to nothing: t_data is NULL.  This is used as a failure indication
 *	 in some functions.
 *
 * * Part of a palloc'd tuple: the HeapTupleData itself and the tuple
 *	 form a single palloc'd chunk.  t_data points to the memory location
 *	 immediately following the HeapTupleData struct (at offset HEAPTUPLESIZE).
 *	 This is the output format of heap_form_tuple and related routines.
 *
 * * Separately allocated tuple: t_data points to a palloc'd chunk that
 *	 is not adjacent to the HeapTupleData.	(This case is deprecated since
 *	 it's difficult to tell apart from case #1.  It should be used only in
 *	 limited contexts where the code knows that case #1 will never apply.)
 *
 * * Separately allocated minimal tuple: t_data points MINIMAL_TUPLE_OFFSET
 *	 bytes before the start of a MinimalTuple.	As with the previous case,
 *	 this can't be told apart from case #1 by inspection; code setting up
 *	 or destroying this representation has to know what it's doing.
 *
 * t_len should always be valid, except in the pointer-to-nothing case.
 * t_self and t_tableOid should be valid if the HeapTupleData points to
 * a disk buffer, or if it represents a copy of a tuple on disk.  They
 * should be explicitly set invalid in manufactured tuples.
 */
typedef struct HeapTupleData
{
	uint32		t_len;			/* length of *t_data */
	ItemPointerData t_self;		/* SelfItemPointer */
	Oid			t_tableOid;		/* table the tuple came from */
	HeapTupleHeader t_data;		/* -> tuple header and data */
} HeapTupleData;

typedef HeapTupleData *HeapTuple;

#define HEAPTUPLESIZE	MAXALIGN(sizeof(HeapTupleData))

/*
 * 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 HeapTupleIsValid(tuple) PointerIsValid(tuple)

#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 HeapTupleHasCompressed(tuple) \
		(((tuple)->t_data->t_infomask & HEAP_HASCOMPRESSED) != 0)

#define HeapTupleHasExtended(tuple) \
		(((tuple)->t_data->t_infomask & HEAP_HASEXTENDED) != 0)

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

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


/*
 * WAL record definitions for heapam.c's WAL operations
 *
 * XLOG allows to store some information in high 4 bits of log
 * record xl_info field.  We use 3 for opcode and one for init bit.
 */
#define XLOG_HEAP_INSERT	0x00
#define XLOG_HEAP_DELETE	0x10
#define XLOG_HEAP_UPDATE	0x20
#define XLOG_HEAP_MOVE		0x30
#define XLOG_HEAP_CLEAN		0x40
#define XLOG_HEAP_NEWPAGE	0x50
#define XLOG_HEAP_LOCK		0x60
#define XLOG_HEAP_INPLACE	0x70
#define XLOG_HEAP_OPMASK	0x70
/*
 * When we insert 1st item on new page in INSERT/UPDATE
 * we can (and we do) restore entire page in redo
 */
#define XLOG_HEAP_INIT_PAGE 0x80
/*
 * We ran out of opcodes, so heapam.c now has a second RmgrId.  These opcodes
 * are associated with RM_HEAP2_ID, but are not logically different from
 * the ones above associated with RM_HEAP_ID.  We apply XLOG_HEAP_OPMASK,
 * although currently XLOG_HEAP_INIT_PAGE is not used for any of these.
 */
#define XLOG_HEAP2_FREEZE	0x00

/*
 * All what we need to find changed tuple
 *
 * NB: on most machines, sizeof(xl_heaptid) will include some trailing pad
 * bytes for alignment.  We don't want to store the pad space in the XLOG,
 * so use SizeOfHeapTid for space calculations.  Similar comments apply for
 * the other xl_FOO structs.
 */
typedef struct xl_heaptid
{
	RelFileNode node;
	ItemPointerData tid;		/* changed tuple id */
} xl_heaptid;

#define SizeOfHeapTid		(offsetof(xl_heaptid, tid) + SizeOfIptrData)

/* This is what we need to know about delete */
typedef struct xl_heap_delete
{
	xl_heaptid	target;			/* deleted tuple id */
} xl_heap_delete;

#define SizeOfHeapDelete	(offsetof(xl_heap_delete, target) + SizeOfHeapTid)

/*
 * We don't store the whole fixed part (HeapTupleHeaderData) of an inserted
 * or updated tuple in WAL; we can save a few bytes by reconstructing the
 * fields that are available elsewhere in the WAL record, or perhaps just
 * plain needn't be reconstructed.  These are the fields we must store.
 * NOTE: t_hoff could be recomputed, but we may as well store it because
 * it will come for free due to alignment considerations.
 */
typedef struct xl_heap_header
{
	int16		t_natts;
	uint16		t_infomask;
	uint8		t_hoff;
} xl_heap_header;

#define SizeOfHeapHeader	(offsetof(xl_heap_header, t_hoff) + sizeof(uint8))

/* This is what we need to know about insert */
typedef struct xl_heap_insert
{
	xl_heaptid	target;			/* inserted tuple id */
	/* xl_heap_header & TUPLE DATA FOLLOWS AT END OF STRUCT */
} xl_heap_insert;

#define SizeOfHeapInsert	(offsetof(xl_heap_insert, target) + SizeOfHeapTid)

/* This is what we need to know about update|move */
typedef struct xl_heap_update
{
	xl_heaptid	target;			/* deleted tuple id */
	ItemPointerData newtid;		/* new inserted tuple id */
	/* NEW TUPLE xl_heap_header (PLUS xmax & xmin IF MOVE OP) */
	/* and TUPLE DATA FOLLOWS AT END OF STRUCT */
} xl_heap_update;

#define SizeOfHeapUpdate	(offsetof(xl_heap_update, newtid) + SizeOfIptrData)

/* This is what we need to know about vacuum page cleanup */
typedef struct xl_heap_clean
{
	RelFileNode node;
	BlockNumber block;
	/* UNUSED OFFSET NUMBERS FOLLOW AT THE END */
} xl_heap_clean;

#define SizeOfHeapClean (offsetof(xl_heap_clean, block) + sizeof(BlockNumber))

/* This is for replacing a page's contents in toto */
/* NB: this is used for indexes as well as heaps */
typedef struct xl_heap_newpage
{
	RelFileNode node;
	BlockNumber blkno;			/* location of new page */
	/* entire page contents follow at end of record */
} xl_heap_newpage;

#define SizeOfHeapNewpage	(offsetof(xl_heap_newpage, blkno) + sizeof(BlockNumber))

/* This is what we need to know about lock */
typedef struct xl_heap_lock
{
	xl_heaptid	target;			/* locked tuple id */
	TransactionId locking_xid;	/* might be a MultiXactId not xid */
	bool		xid_is_mxact;	/* is it? */
	bool		shared_lock;	/* shared or exclusive row lock? */
} xl_heap_lock;

#define SizeOfHeapLock	(offsetof(xl_heap_lock, shared_lock) + sizeof(bool))

/* This is what we need to know about in-place update */
typedef struct xl_heap_inplace
{
	xl_heaptid	target;			/* updated tuple id */
	/* TUPLE DATA FOLLOWS AT END OF STRUCT */
} xl_heap_inplace;

#define SizeOfHeapInplace	(offsetof(xl_heap_inplace, target) + SizeOfHeapTid)

/* This is what we need to know about tuple freezing during vacuum */
typedef struct xl_heap_freeze
{
	RelFileNode node;
	BlockNumber block;
	TransactionId cutoff_xid;
	/* TUPLE OFFSET NUMBERS FOLLOW AT THE END */
} xl_heap_freeze;

#define SizeOfHeapFreeze (offsetof(xl_heap_freeze, cutoff_xid) + sizeof(TransactionId))

#endif   /* HTUP_H */