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/*------------------------------------------------------------------------- * * itemptr.h * POSTGRES disk item pointer definitions. * * * Portions Copyright (c) 1996-2016, 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). * blkid tells us which block, 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, and to cope with unpersuadable compilers, we try to use * "SizeOfIptrData" rather than "sizeof(ItemPointerData)" when computing * on-disk sizes. */ 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; #define SizeOfIptrData \ (offsetof(ItemPointerData, ip_posid) + sizeof(OffsetNumber)) typedef ItemPointerData *ItemPointer; /* ---------------- * support macros * ---------------- */ /* * ItemPointerIsValid * True iff the disk item pointer is not NULL. */ #define ItemPointerIsValid(pointer) \ ((bool) (PointerIsValid(pointer) && ((pointer)->ip_posid != 0))) /* * ItemPointerGetBlockNumber * Returns the block number of a disk item pointer. */ #define ItemPointerGetBlockNumber(pointer) \ ( \ AssertMacro(ItemPointerIsValid(pointer)), \ BlockIdGetBlockNumber(&(pointer)->ip_blkid) \ ) /* * ItemPointerGetOffsetNumber * Returns the offset number of a disk item pointer. */ #define ItemPointerGetOffsetNumber(pointer) \ ( \ AssertMacro(ItemPointerIsValid(pointer)), \ (pointer)->ip_posid \ ) /* * ItemPointerSet * Sets a disk item pointer to the specified block and offset. */ #define ItemPointerSet(pointer, blockNumber, offNum) \ ( \ AssertMacro(PointerIsValid(pointer)), \ BlockIdSet(&((pointer)->ip_blkid), blockNumber), \ (pointer)->ip_posid = offNum \ ) /* * ItemPointerSetBlockNumber * Sets a disk item pointer to the specified block. */ #define ItemPointerSetBlockNumber(pointer, blockNumber) \ ( \ AssertMacro(PointerIsValid(pointer)), \ BlockIdSet(&((pointer)->ip_blkid), blockNumber) \ ) /* * ItemPointerSetOffsetNumber * Sets a disk item pointer to the specified offset. */ #define ItemPointerSetOffsetNumber(pointer, offsetNumber) \ ( \ AssertMacro(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. */ #define ItemPointerCopy(fromPointer, toPointer) \ ( \ AssertMacro(PointerIsValid(toPointer)), \ AssertMacro(PointerIsValid(fromPointer)), \ *(toPointer) = *(fromPointer) \ ) /* * ItemPointerSetInvalid * Sets a disk item pointer to be invalid. */ #define ItemPointerSetInvalid(pointer) \ ( \ AssertMacro(PointerIsValid(pointer)), \ BlockIdSet(&((pointer)->ip_blkid), InvalidBlockNumber), \ (pointer)->ip_posid = InvalidOffsetNumber \ ) /* ---------------- * externs * ---------------- */ extern bool ItemPointerEquals(ItemPointer pointer1, ItemPointer pointer2); extern int32 ItemPointerCompare(ItemPointer arg1, ItemPointer arg2); #endif /* ITEMPTR_H */