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db_include/access/htup.h

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+/*-------------------------------------------------------------------------
+ *
+ * htup.h
+ *	  POSTGRES heap tuple definitions.
+ *
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/access/htup.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef HTUP_H
+#define HTUP_H
+
+#include "storage/itemptr.h"
+
+/* typedefs and forward declarations for structs defined in htup_details.h */
+
+typedef struct HeapTupleHeaderData HeapTupleHeaderData;
+
+typedef HeapTupleHeaderData *HeapTupleHeader;
+
+typedef struct MinimalTupleData 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 */
+#define FIELDNO_HEAPTUPLEDATA_DATA 3
+	HeapTupleHeader t_data;		/* -> tuple header and data */
+} HeapTupleData;
+
+typedef HeapTupleData *HeapTuple;
+
+#define HEAPTUPLESIZE	MAXALIGN(sizeof(HeapTupleData))
+
+/*
+ * Accessor macros to be used with HeapTuple pointers.
+ */
+#define HeapTupleIsValid(tuple) PointerIsValid(tuple)
+
+/* HeapTupleHeader functions implemented in utils/time/combocid.c */
+extern CommandId HeapTupleHeaderGetCmin(HeapTupleHeader tup);
+extern CommandId HeapTupleHeaderGetCmax(HeapTupleHeader tup);
+extern void HeapTupleHeaderAdjustCmax(HeapTupleHeader tup,
+									  CommandId *cmax, bool *iscombo);
+
+/* Prototype for HeapTupleHeader accessors in heapam.c */
+extern TransactionId HeapTupleGetUpdateXid(HeapTupleHeader tuple);
+
+#endif							/* HTUP_H */