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/*------------------------------------------------------------------------- * * block.h * POSTGRES disk block definitions. * * * Portions Copyright (c) 1996-2016, 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 buf.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 macros * ---------------- */ /* * BlockNumberIsValid * True iff blockNumber is valid. */ #define BlockNumberIsValid(blockNumber) \ ((bool) ((BlockNumber) (blockNumber) != InvalidBlockNumber)) /* * BlockIdIsValid * True iff the block identifier is valid. */ #define BlockIdIsValid(blockId) \ ((bool) PointerIsValid(blockId)) /* * BlockIdSet * Sets a block identifier to the specified value. */ #define BlockIdSet(blockId, blockNumber) \ ( \ AssertMacro(PointerIsValid(blockId)), \ (blockId)->bi_hi = (blockNumber) >> 16, \ (blockId)->bi_lo = (blockNumber) & 0xffff \ ) /* * BlockIdCopy * Copy a block identifier. */ #define BlockIdCopy(toBlockId, fromBlockId) \ ( \ AssertMacro(PointerIsValid(toBlockId)), \ AssertMacro(PointerIsValid(fromBlockId)), \ (toBlockId)->bi_hi = (fromBlockId)->bi_hi, \ (toBlockId)->bi_lo = (fromBlockId)->bi_lo \ ) /* * BlockIdEquals * Check for block number equality. */ #define BlockIdEquals(blockId1, blockId2) \ ((blockId1)->bi_hi == (blockId2)->bi_hi && \ (blockId1)->bi_lo == (blockId2)->bi_lo) /* * BlockIdGetBlockNumber * Retrieve the block number from a block identifier. */ #define BlockIdGetBlockNumber(blockId) \ ( \ AssertMacro(BlockIdIsValid(blockId)), \ (BlockNumber) (((blockId)->bi_hi << 16) | ((uint16) (blockId)->bi_lo)) \ ) #endif /* BLOCK_H */