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1667148a4d
Previously a tuple that has been moved to a different partition (see
f16241bef7), set the block number on the old tuple to an invalid
value to indicate that fact. But the tuple offset was left
untouched. That turned out to trigger a wal_consistency_checking
failure as reported by Peter Geoghegan, as the offset wasn't
always overwritten during WAL replay.
Heikki observed that we're wasting valuable data by not putting
information also in the offset. Thus set that to
MovedPartitionsOffsetNumber when a tuple indicates it has moved.
We continue to set the block number to MovedPartitionsBlockNumber, as
that seems more likely to cause problems for code not updated to know
about moved tuples.
As t_ctid's offset number is now always set, this refinement also
fixes the wal_consistency_checking issue.
This technically is a minor disk format break, with previously created
moved tuples not being recognized anymore. But since there not even
has been a beta release since f16241bef7c...
Reported-By: Peter Geoghegan
Author: Heikki Linnakangas, Amul Sul
Discussion: https://postgr.es/m/CAH2-Wzm9ty+1BX7-GMNJ=xPRg67oJTVeDNdA9LSyJJtMgRiCMA@mail.gmail.com
206 lines
5.5 KiB
C
206 lines
5.5 KiB
C
/*-------------------------------------------------------------------------
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*
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* itemptr.h
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* POSTGRES disk item pointer definitions.
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*
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*
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* Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* src/include/storage/itemptr.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef ITEMPTR_H
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#define ITEMPTR_H
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#include "storage/block.h"
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#include "storage/off.h"
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/*
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* ItemPointer:
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*
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* This is a pointer to an item within a disk page of a known file
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* (for example, a cross-link from an index to its parent table).
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* blkid tells us which block, posid tells us which entry in the linp
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* (ItemIdData) array we want.
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*
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* Note: because there is an item pointer in each tuple header and index
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* tuple header on disk, it's very important not to waste space with
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* structure padding bytes. The struct is designed to be six bytes long
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* (it contains three int16 fields) but a few compilers will pad it to
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* eight bytes unless coerced. We apply appropriate persuasion where
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* possible. If your compiler can't be made to play along, you'll waste
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* lots of space.
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*/
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typedef struct ItemPointerData
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{
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BlockIdData ip_blkid;
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OffsetNumber ip_posid;
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}
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/* If compiler understands packed and aligned pragmas, use those */
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#if defined(pg_attribute_packed) && defined(pg_attribute_aligned)
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pg_attribute_packed()
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pg_attribute_aligned(2)
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#endif
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ItemPointerData;
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typedef ItemPointerData *ItemPointer;
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/* ----------------
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* special values used in heap tuples (t_ctid)
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* ----------------
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*/
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/*
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* If a heap tuple holds a speculative insertion token rather than a real
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* TID, ip_posid is set to SpecTokenOffsetNumber, and the token is stored in
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* ip_blkid. SpecTokenOffsetNumber must be higher than MaxOffsetNumber, so
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* that it can be distinguished from a valid offset number in a regular item
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* pointer.
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*/
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#define SpecTokenOffsetNumber 0xfffe
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/*
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* When a tuple is moved to a different partition by UPDATE, the t_ctid of
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* the old tuple version is set to this magic value.
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*/
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#define MovedPartitionsOffsetNumber 0xfffd
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#define MovedPartitionsBlockNumber InvalidBlockNumber
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/* ----------------
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* support macros
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* ----------------
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*/
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/*
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* ItemPointerIsValid
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* True iff the disk item pointer is not NULL.
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*/
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#define ItemPointerIsValid(pointer) \
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((bool) (PointerIsValid(pointer) && ((pointer)->ip_posid != 0)))
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/*
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* ItemPointerGetBlockNumberNoCheck
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* Returns the block number of a disk item pointer.
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*/
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#define ItemPointerGetBlockNumberNoCheck(pointer) \
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( \
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BlockIdGetBlockNumber(&(pointer)->ip_blkid) \
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)
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/*
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* ItemPointerGetBlockNumber
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* As above, but verifies that the item pointer looks valid.
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*/
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#define ItemPointerGetBlockNumber(pointer) \
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( \
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AssertMacro(ItemPointerIsValid(pointer)), \
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ItemPointerGetBlockNumberNoCheck(pointer) \
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)
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/*
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* ItemPointerGetOffsetNumberNoCheck
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* Returns the offset number of a disk item pointer.
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*/
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#define ItemPointerGetOffsetNumberNoCheck(pointer) \
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( \
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(pointer)->ip_posid \
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)
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/*
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* ItemPointerGetOffsetNumber
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* As above, but verifies that the item pointer looks valid.
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*/
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#define ItemPointerGetOffsetNumber(pointer) \
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( \
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AssertMacro(ItemPointerIsValid(pointer)), \
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ItemPointerGetOffsetNumberNoCheck(pointer) \
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)
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/*
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* ItemPointerSet
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* Sets a disk item pointer to the specified block and offset.
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*/
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#define ItemPointerSet(pointer, blockNumber, offNum) \
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( \
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AssertMacro(PointerIsValid(pointer)), \
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BlockIdSet(&((pointer)->ip_blkid), blockNumber), \
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(pointer)->ip_posid = offNum \
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)
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/*
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* ItemPointerSetBlockNumber
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* Sets a disk item pointer to the specified block.
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*/
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#define ItemPointerSetBlockNumber(pointer, blockNumber) \
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( \
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AssertMacro(PointerIsValid(pointer)), \
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BlockIdSet(&((pointer)->ip_blkid), blockNumber) \
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)
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/*
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* ItemPointerSetOffsetNumber
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* Sets a disk item pointer to the specified offset.
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*/
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#define ItemPointerSetOffsetNumber(pointer, offsetNumber) \
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( \
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AssertMacro(PointerIsValid(pointer)), \
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(pointer)->ip_posid = (offsetNumber) \
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)
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/*
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* ItemPointerCopy
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* Copies the contents of one disk item pointer to another.
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*
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* Should there ever be padding in an ItemPointer this would need to be handled
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* differently as it's used as hash key.
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*/
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#define ItemPointerCopy(fromPointer, toPointer) \
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( \
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AssertMacro(PointerIsValid(toPointer)), \
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AssertMacro(PointerIsValid(fromPointer)), \
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*(toPointer) = *(fromPointer) \
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)
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/*
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* ItemPointerSetInvalid
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* Sets a disk item pointer to be invalid.
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*/
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#define ItemPointerSetInvalid(pointer) \
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( \
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AssertMacro(PointerIsValid(pointer)), \
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BlockIdSet(&((pointer)->ip_blkid), InvalidBlockNumber), \
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(pointer)->ip_posid = InvalidOffsetNumber \
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)
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/*
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* ItemPointerIndicatesMovedPartitions
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* True iff the block number indicates the tuple has moved to another
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* partition.
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*/
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#define ItemPointerIndicatesMovedPartitions(pointer) \
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( \
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ItemPointerGetOffsetNumber(pointer) == MovedPartitionsOffsetNumber && \
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ItemPointerGetBlockNumberNoCheck(pointer) == MovedPartitionsBlockNumber \
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)
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/*
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* ItemPointerSetMovedPartitions
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* Indicate that the item referenced by the itempointer has moved into a
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* different partition.
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*/
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#define ItemPointerSetMovedPartitions(pointer) \
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ItemPointerSet((pointer), MovedPartitionsBlockNumber, MovedPartitionsOffsetNumber)
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/* ----------------
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* externs
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* ----------------
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*/
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extern bool ItemPointerEquals(ItemPointer pointer1, ItemPointer pointer2);
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extern int32 ItemPointerCompare(ItemPointer arg1, ItemPointer arg2);
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#endif /* ITEMPTR_H */
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