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) 1996-2023, 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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