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The term "item pointer" should not be used to refer to ItemIdData variables, since that is needlessly ambiguous. Only ItemPointerData/ItemPointer variables should be called item pointers. To fix, establish the convention that ItemIdData variables should always be referred to either as "item identifiers" or "line pointers". The term "item identifier" already predominates in docs and translatable messages, and so should be the preferred alternative there. Discussion: https://postgr.es/m/CAH2-Wz=c=MZQjUzde3o9+2PLAPuHTpVZPPdYxN=E4ndQ2--8ew@mail.gmail.com
185 lines
4.3 KiB
C
185 lines
4.3 KiB
C
/*-------------------------------------------------------------------------
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*
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* itemid.h
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* Standard POSTGRES buffer page item identifier/line pointer definitions.
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*
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*
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* Portions Copyright (c) 1996-2019, 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/itemid.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef ITEMID_H
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#define ITEMID_H
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/*
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* A line pointer on a buffer page. See buffer page definitions and comments
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* for an explanation of how line pointers are used.
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*
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* In some cases a line pointer is "in use" but does not have any associated
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* storage on the page. By convention, lp_len == 0 in every line pointer
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* that does not have storage, independently of its lp_flags state.
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*/
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typedef struct ItemIdData
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{
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unsigned lp_off:15, /* offset to tuple (from start of page) */
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lp_flags:2, /* state of line pointer, see below */
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lp_len:15; /* byte length of tuple */
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} ItemIdData;
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typedef ItemIdData *ItemId;
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/*
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* lp_flags has these possible states. An UNUSED line pointer is available
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* for immediate re-use, the other states are not.
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*/
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#define LP_UNUSED 0 /* unused (should always have lp_len=0) */
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#define LP_NORMAL 1 /* used (should always have lp_len>0) */
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#define LP_REDIRECT 2 /* HOT redirect (should have lp_len=0) */
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#define LP_DEAD 3 /* dead, may or may not have storage */
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/*
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* Item offsets and lengths are represented by these types when
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* they're not actually stored in an ItemIdData.
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*/
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typedef uint16 ItemOffset;
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typedef uint16 ItemLength;
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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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* ItemIdGetLength
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*/
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#define ItemIdGetLength(itemId) \
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((itemId)->lp_len)
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/*
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* ItemIdGetOffset
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*/
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#define ItemIdGetOffset(itemId) \
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((itemId)->lp_off)
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/*
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* ItemIdGetFlags
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*/
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#define ItemIdGetFlags(itemId) \
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((itemId)->lp_flags)
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/*
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* ItemIdGetRedirect
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* In a REDIRECT pointer, lp_off holds offset number for next line pointer
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*/
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#define ItemIdGetRedirect(itemId) \
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((itemId)->lp_off)
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/*
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* ItemIdIsValid
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* True iff item identifier is valid.
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* This is a pretty weak test, probably useful only in Asserts.
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*/
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#define ItemIdIsValid(itemId) PointerIsValid(itemId)
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/*
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* ItemIdIsUsed
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* True iff item identifier is in use.
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*/
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#define ItemIdIsUsed(itemId) \
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((itemId)->lp_flags != LP_UNUSED)
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/*
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* ItemIdIsNormal
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* True iff item identifier is in state NORMAL.
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*/
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#define ItemIdIsNormal(itemId) \
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((itemId)->lp_flags == LP_NORMAL)
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/*
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* ItemIdIsRedirected
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* True iff item identifier is in state REDIRECT.
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*/
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#define ItemIdIsRedirected(itemId) \
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((itemId)->lp_flags == LP_REDIRECT)
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/*
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* ItemIdIsDead
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* True iff item identifier is in state DEAD.
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*/
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#define ItemIdIsDead(itemId) \
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((itemId)->lp_flags == LP_DEAD)
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/*
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* ItemIdHasStorage
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* True iff item identifier has associated storage.
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*/
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#define ItemIdHasStorage(itemId) \
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((itemId)->lp_len != 0)
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/*
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* ItemIdSetUnused
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* Set the item identifier to be UNUSED, with no storage.
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* Beware of multiple evaluations of itemId!
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*/
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#define ItemIdSetUnused(itemId) \
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( \
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(itemId)->lp_flags = LP_UNUSED, \
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(itemId)->lp_off = 0, \
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(itemId)->lp_len = 0 \
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)
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/*
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* ItemIdSetNormal
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* Set the item identifier to be NORMAL, with the specified storage.
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* Beware of multiple evaluations of itemId!
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*/
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#define ItemIdSetNormal(itemId, off, len) \
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( \
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(itemId)->lp_flags = LP_NORMAL, \
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(itemId)->lp_off = (off), \
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(itemId)->lp_len = (len) \
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)
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/*
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* ItemIdSetRedirect
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* Set the item identifier to be REDIRECT, with the specified link.
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* Beware of multiple evaluations of itemId!
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*/
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#define ItemIdSetRedirect(itemId, link) \
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( \
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(itemId)->lp_flags = LP_REDIRECT, \
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(itemId)->lp_off = (link), \
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(itemId)->lp_len = 0 \
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)
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/*
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* ItemIdSetDead
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* Set the item identifier to be DEAD, with no storage.
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* Beware of multiple evaluations of itemId!
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*/
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#define ItemIdSetDead(itemId) \
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( \
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(itemId)->lp_flags = LP_DEAD, \
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(itemId)->lp_off = 0, \
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(itemId)->lp_len = 0 \
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)
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/*
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* ItemIdMarkDead
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* Set the item identifier to be DEAD, keeping its existing storage.
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*
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* Note: in indexes, this is used as if it were a hint-bit mechanism;
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* we trust that multiple processors can do this in parallel and get
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* the same result.
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*/
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#define ItemIdMarkDead(itemId) \
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( \
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(itemId)->lp_flags = LP_DEAD \
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)
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#endif /* ITEMID_H */
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