text: /*-------------------------------------------------------------------------
   *
   * htup_details.h
   *	  POSTGRES heap tuple header definitions.
   *
   *
   * Portions Copyright (c) 1996-2019, 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_OLD is set in t_infomask, not created
   *          anymore)
   *			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.  Or
   * if the tuple is moved from one partition to another, due to an update of
   * the partition key, t_ctid is set to a special value to indicate that
   * (see ItemPointerSetMovedPartitions).  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, unless it was moved to a different
   * partition.  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 */
  
  	/*
  	 * datum_typeid cannot be a domain over composite, only plain composite,
  	 * even if the datum is meant as a value of a domain-over-composite type.
  	 * This is in line with the general principle that CoerceToDomain does not
  	 * change the physical representation of the base type value.
  	 *
  	 * 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! */
  
  #define FIELDNO_HEAPTUPLEHEADERDATA_INFOMASK2 2
  	uint16		t_infomask2;	/* number of attributes + various flags */
  
  #define FIELDNO_HEAPTUPLEHEADERDATA_INFOMASK 3
  	uint16		t_infomask;		/* various flag bits, see below */
  
  #define FIELDNO_HEAPTUPLEHEADERDATA_HOFF 4
  	uint8		t_hoff;			/* sizeof header incl. bitmap, padding */
  
  	/* ^ - 23 bytes - ^ */
  
  #define FIELDNO_HEAPTUPLEHEADERDATA_BITS 5
  	bits8		t_bits[FLEXIBLE_ARRAY_MEMBER];	/* bitmap of NULLs */
  
  	/* MORE DATA FOLLOWS AT END OF STRUCT */
  };
  
  /* typedef appears in htup.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_OLD			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))
  
  /*
   * A tuple that has HEAP_XMAX_IS_MULTI and HEAP_XMAX_LOCK_ONLY but neither of
   * HEAP_XMAX_EXCL_LOCK and HEAP_XMAX_KEYSHR_LOCK must come from a tuple that was
   * share-locked in 9.2 or earlier and then pg_upgrade'd.
   *
   * In 9.2 and prior, HEAP_XMAX_IS_MULTI was only set when there were multiple
   * FOR SHARE lockers of that tuple.  That set HEAP_XMAX_LOCK_ONLY (with a
   * different name back then) but neither of HEAP_XMAX_EXCL_LOCK and
   * HEAP_XMAX_KEYSHR_LOCK.  That combination is no longer possible in 9.3 and
   * up, so if we see that combination we know for certain that the tuple was
   * locked in an earlier release; since all such lockers are gone (they cannot
   * survive through pg_upgrade), such tuples can safely be considered not
   * locked.
   *
   * We must not resolve such multixacts locally, because the result would be
   * bogus, regardless of where they stand with respect to the current valid
   * multixact range.
   */
  #define HEAP_LOCKED_UPGRADED(infomask) \
  ( \
  	 ((infomask) & HEAP_XMAX_IS_MULTI) != 0 && \
  	 ((infomask) & HEAP_XMAX_LOCK_ONLY) != 0 && \
  	 (((infomask) & (HEAP_XMAX_EXCL_LOCK | HEAP_XMAX_KEYSHR_LOCK)) == 0) \
  )
  
  /*
   * 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 */
  
  /*
   * 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) != 0 \
  )
  
  #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) \
  ( \
  	(ItemPointerGetOffsetNumberNoCheck(&(tup)->t_ctid) == SpecTokenOffsetNumber) \
  )
  
  #define HeapTupleHeaderGetSpeculativeToken(tup) \
  ( \
  	AssertMacro(HeapTupleHeaderIsSpeculative(tup)), \
  	ItemPointerGetBlockNumber(&(tup)->t_ctid) \
  )
  
  #define HeapTupleHeaderSetSpeculativeToken(tup, token)	\
  ( \
  	ItemPointerSet(&(tup)->t_ctid, token, SpecTokenOffsetNumber) \
  )
  
  #define HeapTupleHeaderIndicatesMovedPartitions(tup) \
  	(ItemPointerGetOffsetNumber(&(tup)->t_ctid) == MovedPartitionsOffsetNumber && \
  	 ItemPointerGetBlockNumberNoCheck(&(tup)->t_ctid) == MovedPartitionsBlockNumber)
  
  #define HeapTupleHeaderSetMovedPartitions(tup) \
  	ItemPointerSet(&(tup)->t_ctid, MovedPartitionsBlockNumber, MovedPartitionsOffsetNumber)
  
  #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) \
  )
  
  /*
   * 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) != 0 \
  )
  
  #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) != 0 \
  )
  
  #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 line 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)
  
  
  /* ----------------
   *		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) ?											\
  	(																\
  		TupleDescAttr((tupleDesc), (attnum)-1)->attcacheoff >= 0 ?	\
  		(															\
  			fetchatt(TupleDescAttr((tupleDesc), (attnum)-1),		\
  				(char *) (tup)->t_data + (tup)->t_data->t_hoff +	\
  				TupleDescAttr((tupleDesc), (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)) ? \
  				getmissingattr((tupleDesc), (attnum), (isnull)) \
  			: \
  				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, TupleDesc tupleDesc);
  extern Datum nocachegetattr(HeapTuple tup, int attnum,
  							TupleDesc att);
  extern Datum heap_getsysattr(HeapTuple tup, int attnum, TupleDesc tupleDesc,
  							 bool *isnull);
  extern Datum getmissingattr(TupleDesc tupleDesc,
  							int attnum, 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 HeapTuple heap_modify_tuple_by_cols(HeapTuple tuple,
  										   TupleDesc tupleDesc,
  										   int nCols,
  										   int *replCols,
  										   Datum *replValues,
  										   bool *replIsnull);
  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);
  extern size_t varsize_any(void *p);
  extern HeapTuple heap_expand_tuple(HeapTuple sourceTuple, TupleDesc tupleDesc);
  extern MinimalTuple minimal_expand_tuple(HeapTuple sourceTuple, TupleDesc tupleDesc);
  
  #endif							/* HTUP_DETAILS_H */
  