postgresql-11.1\src\include\access\htup_details.h里的HeapTupleHeaderData结构体

typedef HeapTupleHeaderData *HeapTupleHeader;

//这个定义在postgresql-11.1\src\include\access\htup.h
//里的HeapTuple指针和HeapTupleData结构体文章里面

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 */
};