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/*-------------------------------------------------------------------------
*
* itemptr.h
* POSTGRES disk item pointer definitions.
*
*
* Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* src/include/storage/itemptr.h
*
*-------------------------------------------------------------------------
*/
#ifndef ITEMPTR_H
#define ITEMPTR_H
#include "storage/block.h"
#include "storage/off.h"
/*
* ItemPointer:
*
* This is a pointer to an item within a disk page of a known file
* (for example, a cross-link from an index to its parent table).
* ip_blkid tells us which block, ip_posid tells us which entry in
* the linp (ItemIdData) array we want.
*
* Note: because there is an item pointer in each tuple header and index
* tuple header on disk, it's very important not to waste space with
* structure padding bytes. The struct is designed to be six bytes long
* (it contains three int16 fields) but a few compilers will pad it to
* eight bytes unless coerced. We apply appropriate persuasion where
* possible. If your compiler can't be made to play along, you'll waste
* lots of space.
*/
typedef struct ItemPointerData
{
BlockIdData ip_blkid;
OffsetNumber ip_posid;
}
/* If compiler understands packed and aligned pragmas, use those */
#if defined(pg_attribute_packed) && defined(pg_attribute_aligned)
pg_attribute_packed()
pg_attribute_aligned(2)
#endif
ItemPointerData;
typedef ItemPointerData *ItemPointer;
/* ----------------
* special values used in heap tuples (t_ctid)
* ----------------
*/
/*
* If a heap tuple holds a speculative insertion token rather than a real
* TID, ip_posid is set to SpecTokenOffsetNumber, and the token is stored in
* ip_blkid. SpecTokenOffsetNumber must be higher than MaxOffsetNumber, so
* that it can be distinguished from a valid offset number in a regular item
* pointer.
*/
#define SpecTokenOffsetNumber 0xfffe
/*
* When a tuple is moved to a different partition by UPDATE, the t_ctid of
* the old tuple version is set to this magic value.
*/
#define MovedPartitionsOffsetNumber 0xfffd
#define MovedPartitionsBlockNumber InvalidBlockNumber
/* ----------------
* support functions
* ----------------
*/
/*
* ItemPointerIsValid
* True iff the disk item pointer is not NULL.
*/
static inline bool
ItemPointerIsValid(const ItemPointerData *pointer)
{
return PointerIsValid(pointer) && pointer->ip_posid != 0;
}
/*
* ItemPointerGetBlockNumberNoCheck
* Returns the block number of a disk item pointer.
*/
static inline BlockNumber
ItemPointerGetBlockNumberNoCheck(const ItemPointerData *pointer)
{
return BlockIdGetBlockNumber(&pointer->ip_blkid);
}
/*
* ItemPointerGetBlockNumber
* As above, but verifies that the item pointer looks valid.
*/
static inline BlockNumber
ItemPointerGetBlockNumber(const ItemPointerData *pointer)
{
Assert(ItemPointerIsValid(pointer));
return ItemPointerGetBlockNumberNoCheck(pointer);
}
/*
* ItemPointerGetOffsetNumberNoCheck
* Returns the offset number of a disk item pointer.
*/
static inline OffsetNumber
ItemPointerGetOffsetNumberNoCheck(const ItemPointerData *pointer)
{
return pointer->ip_posid;
}
/*
* ItemPointerGetOffsetNumber
* As above, but verifies that the item pointer looks valid.
*/
static inline OffsetNumber
ItemPointerGetOffsetNumber(const ItemPointerData *pointer)
{
Assert(ItemPointerIsValid(pointer));
return ItemPointerGetOffsetNumberNoCheck(pointer);
}
/*
* ItemPointerSet
* Sets a disk item pointer to the specified block and offset.
*/
static inline void
ItemPointerSet(ItemPointerData *pointer, BlockNumber blockNumber, OffsetNumber offNum)
{
Assert(PointerIsValid(pointer));
BlockIdSet(&pointer->ip_blkid, blockNumber);
pointer->ip_posid = offNum;
}
/*
* ItemPointerSetBlockNumber
* Sets a disk item pointer to the specified block.
*/
static inline void
ItemPointerSetBlockNumber(ItemPointerData *pointer, BlockNumber blockNumber)
{
Assert(PointerIsValid(pointer));
BlockIdSet(&pointer->ip_blkid, blockNumber);
}
/*
* ItemPointerSetOffsetNumber
* Sets a disk item pointer to the specified offset.
*/
static inline void
ItemPointerSetOffsetNumber(ItemPointerData *pointer, OffsetNumber offsetNumber)
{
Assert(PointerIsValid(pointer));
pointer->ip_posid = offsetNumber;
}
/*
* ItemPointerCopy
* Copies the contents of one disk item pointer to another.
*
* Should there ever be padding in an ItemPointer this would need to be handled
* differently as it's used as hash key.
*/
static inline void
ItemPointerCopy(const ItemPointerData *fromPointer, ItemPointerData *toPointer)
{
Assert(PointerIsValid(toPointer));
Assert(PointerIsValid(fromPointer));
*toPointer = *fromPointer;
}
/*
* ItemPointerSetInvalid
* Sets a disk item pointer to be invalid.
*/
static inline void
ItemPointerSetInvalid(ItemPointerData *pointer)
{
Assert(PointerIsValid(pointer));
BlockIdSet(&pointer->ip_blkid, InvalidBlockNumber);
pointer->ip_posid = InvalidOffsetNumber;
}
/*
* ItemPointerIndicatesMovedPartitions
* True iff the block number indicates the tuple has moved to another
* partition.
*/
static inline bool
ItemPointerIndicatesMovedPartitions(const ItemPointerData *pointer)
{
return
ItemPointerGetOffsetNumber(pointer) == MovedPartitionsOffsetNumber &&
ItemPointerGetBlockNumberNoCheck(pointer) == MovedPartitionsBlockNumber;
}
/*
* ItemPointerSetMovedPartitions
* Indicate that the item referenced by the itempointer has moved into a
* different partition.
*/
static inline void
ItemPointerSetMovedPartitions(ItemPointerData *pointer)
{
ItemPointerSet(pointer, MovedPartitionsBlockNumber, MovedPartitionsOffsetNumber);
}
/* ----------------
* externs
* ----------------
*/
extern bool ItemPointerEquals(ItemPointer pointer1, ItemPointer pointer2);
extern int32 ItemPointerCompare(ItemPointer arg1, ItemPointer arg2);
extern void ItemPointerInc(ItemPointer pointer);
extern void ItemPointerDec(ItemPointer pointer);
/* ----------------
* Datum conversion functions
* ----------------
*/
static inline ItemPointer
DatumGetItemPointer(Datum X)
{
return (ItemPointer) DatumGetPointer(X);
}
static inline Datum
ItemPointerGetDatum(const ItemPointerData *X)
{
return PointerGetDatum(X);
}
#define PG_GETARG_ITEMPOINTER(n) DatumGetItemPointer(PG_GETARG_DATUM(n))
#define PG_RETURN_ITEMPOINTER(x) return ItemPointerGetDatum(x)
#endif /* ITEMPTR_H */
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