nbtree.h

PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统

/*-------------------------------------------------------------------------
 *
 * nbtree.h
 *	  header file for postgres btree access method implementation.
 *
 *
 * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * $PostgreSQL: pgsql/src/include/access/nbtree.h,v 1.87 2005/10/15 02:49:42 momjian Exp $
 *
 *-------------------------------------------------------------------------
 */
#ifndef NBTREE_H
#define NBTREE_H

#include "access/itup.h"
#include "access/relscan.h"
#include "access/sdir.h"
#include "access/xlogutils.h"

/*
 *	BTPageOpaqueData -- At the end of every page, we store a pointer
 *	to both siblings in the tree.  This is used to do forward/backward
 *	index scans.  The next-page link is also critical for recovery when
 *	a search has navigated to the wrong page due to concurrent page splits
 *	or deletions; see src/backend/access/nbtree/README for more info.
 *
 *	In addition, we store the page's btree level (counting upwards from
 *	zero at a leaf page) as well as some flag bits indicating the page type
 *	and status.  If the page is deleted, we replace the level with the
 *	next-transaction-ID value indicating when it is safe to reclaim the page.
 *
 *	NOTE: the BTP_LEAF flag bit is redundant since level==0 could be tested
 *	instead.
 */

typedef struct BTPageOpaqueData
{
	BlockNumber btpo_prev;		/* left sibling, or P_NONE if leftmost */
	BlockNumber btpo_next;		/* right sibling, or P_NONE if rightmost */
	union
	{
		uint32		level;		/* tree level --- zero for leaf pages */
		TransactionId xact;		/* next transaction ID, if deleted */
	}			btpo;
	uint16		btpo_flags;		/* flag bits, see below */
} BTPageOpaqueData;

typedef BTPageOpaqueData *BTPageOpaque;

/* Bits defined in btpo_flags */
#define BTP_LEAF		(1 << 0)	/* leaf page, i.e. not internal page */
#define BTP_ROOT		(1 << 1)	/* root page (has no parent) */
#define BTP_DELETED		(1 << 2)	/* page has been deleted from tree */
#define BTP_META		(1 << 3)	/* meta-page */
#define BTP_HALF_DEAD	(1 << 4)	/* empty, but still in tree */


/*
 * The Meta page is always the first page in the btree index.
 * Its primary purpose is to point to the location of the btree root page.
 * We also point to the "fast" root, which is the current effective root;
 * see README for discussion.
 */

typedef struct BTMetaPageData
{
	uint32		btm_magic;		/* should contain BTREE_MAGIC */
	uint32		btm_version;	/* should contain BTREE_VERSION */
	BlockNumber btm_root;		/* current root location */
	uint32		btm_level;		/* tree level of the root page */
	BlockNumber btm_fastroot;	/* current "fast" root location */
	uint32		btm_fastlevel;	/* tree level of the "fast" root page */
} BTMetaPageData;

#define BTPageGetMeta(p) \
	((BTMetaPageData *) PageGetContents(p))

#define BTREE_METAPAGE	0		/* first page is meta */
#define BTREE_MAGIC		0x053162	/* magic number of btree pages */
#define BTREE_VERSION	2		/* current version number */

/*
 * We actually need to be able to fit three items on every page,
 * so restrict any one item to 1/3 the per-page available space.
 */
#define BTMaxItemSize(page) \
	((PageGetPageSize(page) - \
	  sizeof(PageHeaderData) - \
	  MAXALIGN(sizeof(BTPageOpaqueData))) / 3 - sizeof(ItemIdData))

/*
 *	BTItems are what we store in the btree.  Each item is an index tuple,
 *	including key and pointer values.  (In some cases either the key or the
 *	pointer may go unused, see backend/access/nbtree/README for details.)
 *
 *	Old comments:
 *	In addition, we must guarantee that all tuples in the index are unique,
 *	in order to satisfy some assumptions in Lehman and Yao.  The way that we
 *	do this is by generating a new OID for every insertion that we do in the
 *	tree.  This adds eight bytes to the size of btree index tuples.  Note
 *	that we do not use the OID as part of a composite key; the OID only
 *	serves as a unique identifier for a given index tuple (logical position
 *	within a page).
 *
 *	New comments:
 *	actually, we must guarantee that all tuples in A LEVEL
 *	are unique, not in ALL INDEX. So, we can use bti_itup->t_tid
 *	as unique identifier for a given index tuple (logical position
 *	within a level). - vadim 04/09/97
 */

typedef struct BTItemData
{
	IndexTupleData bti_itup;
} BTItemData;

typedef BTItemData *BTItem;

#define CopyBTItem(btitem) ((BTItem) CopyIndexTuple((IndexTuple) (btitem)))

/*
 * For XLOG: size without alignment. Sizeof works as long as
 * IndexTupleData has exactly 8 bytes.
 */
#define SizeOfBTItem	sizeof(BTItemData)

/* Test whether items are the "same" per the above notes */
#define BTTidSame(i1, i2)	\
	( (i1).ip_blkid.bi_hi == (i2).ip_blkid.bi_hi && \
	  (i1).ip_blkid.bi_lo == (i2).ip_blkid.bi_lo && \
	  (i1).ip_posid == (i2).ip_posid )
#define BTItemSame(i1, i2)	\
	BTTidSame((i1)->bti_itup.t_tid, (i2)->bti_itup.t_tid)


/*
 *	In general, the btree code tries to localize its knowledge about
 *	page layout to a couple of routines.  However, we need a special
 *	value to indicate "no page number" in those places where we expect
 *	page numbers.  We can use zero for this because we never need to
 *	make a pointer to the metadata page.
 */

#define P_NONE			0

/*
 * Macros to test whether a page is leftmost or rightmost on its tree level,
 * as well as other state info kept in the opaque data.
 */
#define P_LEFTMOST(opaque)		((opaque)->btpo_prev == P_NONE)
#define P_RIGHTMOST(opaque)		((opaque)->btpo_next == P_NONE)
#define P_ISLEAF(opaque)		((opaque)->btpo_flags & BTP_LEAF)
#define P_ISROOT(opaque)		((opaque)->btpo_flags & BTP_ROOT)
#define P_ISDELETED(opaque)		((opaque)->btpo_flags & BTP_DELETED)
#define P_IGNORE(opaque)		((opaque)->btpo_flags & (BTP_DELETED|BTP_HALF_DEAD))

/*
 *	Lehman and Yao's algorithm requires a ``high key'' on every non-rightmost
 *	page.  The high key is not a data key, but gives info about what range of
 *	keys is supposed to be on this page.  The high key on a page is required
 *	to be greater than or equal to any data key that appears on the page.
 *	If we find ourselves trying to insert a key > high key, we know we need
 *	to move right (this should only happen if the page was split since we
 *	examined the parent page).
 *
 *	Our insertion algorithm guarantees that we can use the initial least key
 *	on our right sibling as the high key.  Once a page is created, its high
 *	key changes only if the page is split.
 *
 *	On a non-rightmost page, the high key lives in item 1 and data items
 *	start in item 2.  Rightmost pages have no high key, so we store data
 *	items beginning in item 1.
 */

#define P_HIKEY				((OffsetNumber) 1)
#define P_FIRSTKEY			((OffsetNumber) 2)
#define P_FIRSTDATAKEY(opaque)	(P_RIGHTMOST(opaque) ? P_HIKEY : P_FIRSTKEY)

/*
 * XLOG records for btree operations
 *
 * XLOG allows to store some information in high 4 bits of log
 * record xl_info field
 */
#define XLOG_BTREE_INSERT_LEAF	0x00	/* add btitem without split */
#define XLOG_BTREE_INSERT_UPPER 0x10	/* same, on a non-leaf page */
#define XLOG_BTREE_INSERT_META	0x20	/* same, plus update metapage */
#define XLOG_BTREE_SPLIT_L		0x30	/* add btitem with split */
#define XLOG_BTREE_SPLIT_R		0x40	/* as above, new item on right */
#define XLOG_BTREE_SPLIT_L_ROOT 0x50	/* add btitem with split of root */
#define XLOG_BTREE_SPLIT_R_ROOT 0x60	/* as above, new item on right */
#define XLOG_BTREE_DELETE		0x70	/* delete leaf btitem */
#define XLOG_BTREE_DELETE_PAGE	0x80	/* delete an entire page */
#define XLOG_BTREE_DELETE_PAGE_META 0x90		/* same, plus update metapage */
#define XLOG_BTREE_NEWROOT		0xA0	/* new root page */
#define XLOG_BTREE_NEWMETA		0xB0	/* update metadata page */

/*
 * All that we need to find changed index tuple
 */
typedef struct xl_btreetid
{
	RelFileNode node;
	ItemPointerData tid;		/* changed tuple id */
} xl_btreetid;

/*
 * All that we need to regenerate the meta-data page
 */
typedef struct xl_btree_metadata
{
	BlockNumber root;
	uint32		level;
	BlockNumber fastroot;
	uint32		fastlevel;
} xl_btree_metadata;

/*
 * This is what we need to know about simple (without split) insert.
 *
 * This data record is used for INSERT_LEAF, INSERT_UPPER, INSERT_META.
 * Note that INSERT_META implies it's not a leaf page.
 */
typedef struct xl_btree_insert
{
	xl_btreetid target;			/* inserted tuple id */
	/* xl_btree_metadata FOLLOWS IF XLOG_BTREE_INSERT_META */
	/* BTITEM FOLLOWS AT END OF STRUCT */
} xl_btree_insert;

#define SizeOfBtreeInsert	(offsetof(xl_btreetid, tid) + SizeOfIptrData)

/*
 * On insert with split we save items of both left and right siblings
 * and restore content of both pages from log record.  This way takes less
 * xlog space than the normal approach, because if we did it standardly,
 * XLogInsert would almost always think the right page is new and store its
 * whole page image.
 *
 * Note: the four XLOG_BTREE_SPLIT xl_info codes all use this data record.
 * The _L and _R variants indicate whether the inserted btitem went into the
 * left or right split page (and thus, whether otherblk is the right or left
 * page of the split pair).  The _ROOT variants indicate that we are splitting
 * the root page, and thus that a newroot record rather than an insert or