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/*-------------------------------------------------------------------------
*
* block.h
* POSTGRES disk block definitions.
*
*
* Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* src/include/storage/block.h
*
*-------------------------------------------------------------------------
*/
#ifndef BLOCK_H
#define BLOCK_H
/*
* BlockNumber:
*
* each data file (heap or index) is divided into postgres disk blocks
* (which may be thought of as the unit of i/o -- a postgres buffer
* contains exactly one disk block). the blocks are numbered
* sequentially, 0 to 0xFFFFFFFE.
*
* InvalidBlockNumber is the same thing as P_NEW in bufmgr.h.
*
* the access methods, the buffer manager and the storage manager are
* more or less the only pieces of code that should be accessing disk
* blocks directly.
*/
typedef uint32 BlockNumber;
#define InvalidBlockNumber ((BlockNumber) 0xFFFFFFFF)
#define MaxBlockNumber ((BlockNumber) 0xFFFFFFFE)
/*
* BlockId:
*
* this is a storage type for BlockNumber. in other words, this type
* is used for on-disk structures (e.g., in HeapTupleData) whereas
* BlockNumber is the type on which calculations are performed (e.g.,
* in access method code).
*
* there doesn't appear to be any reason to have separate types except
* for the fact that BlockIds can be SHORTALIGN'd (and therefore any
* structures that contains them, such as ItemPointerData, can also be
* SHORTALIGN'd). this is an important consideration for reducing the
* space requirements of the line pointer (ItemIdData) array on each
* page and the header of each heap or index tuple, so it doesn't seem
* wise to change this without good reason.
*/
typedef struct BlockIdData
{
uint16 bi_hi;
uint16 bi_lo;
} BlockIdData;
typedef BlockIdData *BlockId; /* block identifier */
/* ----------------
* support functions
* ----------------
*/
/*
* BlockNumberIsValid
* True iff blockNumber is valid.
*/
static inline bool
BlockNumberIsValid(BlockNumber blockNumber)
{
return blockNumber != InvalidBlockNumber;
}
/*
* BlockIdSet
* Sets a block identifier to the specified value.
*/
static inline void
BlockIdSet(BlockIdData *blockId, BlockNumber blockNumber)
{
blockId->bi_hi = blockNumber >> 16;
blockId->bi_lo = blockNumber & 0xffff;
}
/*
* BlockIdEquals
* Check for block number equality.
*/
static inline bool
BlockIdEquals(const BlockIdData *blockId1, const BlockIdData *blockId2)
{
return (blockId1->bi_hi == blockId2->bi_hi &&
blockId1->bi_lo == blockId2->bi_lo);
}
/*
* BlockIdGetBlockNumber
* Retrieve the block number from a block identifier.
*/
static inline BlockNumber
BlockIdGetBlockNumber(const BlockIdData *blockId)
{
return (((BlockNumber) blockId->bi_hi) << 16) | ((BlockNumber) blockId->bi_lo);
}
#endif /* BLOCK_H */