nbtree.h

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/*-------------------------------------------------------------------------
 *
 * nbtree.h
 *	  header file for postgres btree access method implementation.
 *
 *
 * Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * $PostgreSQL: pgsql/src/include/access/nbtree.h,v 1.106 2006/11/01 19:43:17 tgl Exp $
 *
 *-------------------------------------------------------------------------
 */
#ifndef NBTREE_H
#define NBTREE_H

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


/* There's room for a 16-bit vacuum cycle ID in BTPageOpaqueData */
typedef uint16 BTCycleId;

/*
 *	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.
 *
 *	We also store a "vacuum cycle ID".	When a page is split while VACUUM is
 *	processing the index, a nonzero value associated with the VACUUM run is
 *	stored into both halves of the split page.	(If VACUUM is not running,
 *	both pages receive zero cycleids.)	This allows VACUUM to detect whether
 *	a page was split since it started, with a small probability of false match
 *	if the page was last split some exact multiple of 65536 VACUUMs ago.
 *	Also, during a split, the BTP_SPLIT_END flag is cleared in the left
 *	(original) page, and set in the right page, but only if the next page
 *	to its right has a different cycleid.
 *
 *	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 */
	BTCycleId	btpo_cycleid;	/* vacuum cycle ID of latest split */
} 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 */
#define BTP_SPLIT_END	(1 << 5)	/* rightmost page of split group */
#define BTP_HAS_GARBAGE (1 << 6)	/* page has LP_DELETEd tuples */


/*
 * 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))

/*
 * The leaf-page fillfactor defaults to 90% but is user-adjustable.
 * For pages above the leaf level, we use a fixed 70% fillfactor.
 * The fillfactor is applied during index build and when splitting
 * a rightmost page; when splitting non-rightmost pages we try to
 * divide the data equally.
 */
#define BTREE_MIN_FILLFACTOR		10
#define BTREE_DEFAULT_FILLFACTOR	90
#define BTREE_NONLEAF_FILLFACTOR	70

/*
 *	Test whether two btree entries are "the same".
 *
 *	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 the t_tid
 *	as unique identifier for a given index tuple (logical position
 *	within a level). - vadim 04/09/97
 */
#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 BTEntrySame(i1, i2) \
	BTTidSame((i1)->t_tid, (i2)->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_ISHALFDEAD(opaque)	((opaque)->btpo_flags & BTP_HALF_DEAD)
#define P_IGNORE(opaque)		((opaque)->btpo_flags & (BTP_DELETED|BTP_HALF_DEAD))
#define P_HAS_GARBAGE(opaque)	((opaque)->btpo_flags & BTP_HAS_GARBAGE)

/*
 *	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 index tuple 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 index tuple with split */
#define XLOG_BTREE_SPLIT_R		0x40	/* as above, new item on right */
#define XLOG_BTREE_SPLIT_L_ROOT 0x50	/* add tuple with split of root */
#define XLOG_BTREE_SPLIT_R_ROOT 0x60	/* as above, new item on right */
#define XLOG_BTREE_DELETE		0x70	/* delete leaf index tuple */
#define XLOG_BTREE_DELETE_PAGE	0x80	/* delete an entire page */
#define XLOG_BTREE_DELETE_PAGE_META 0x90		/* same, and update metapage */
#define XLOG_BTREE_NEWROOT		0xA0	/* new root page */
#define XLOG_BTREE_DELETE_PAGE_HALF 0xB0		/* page deletion that makes
												 * parent half-dead */

/*
 * 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 */
	/* BlockNumber downlink field FOLLOWS IF NOT XLOG_BTREE_INSERT_LEAF */
	/* xl_btree_metadata FOLLOWS IF XLOG_BTREE_INSERT_META */
	/* INDEX TUPLE 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 tuple 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
 * split record should follow.	Note that a split record never carries a
 * metapage update --- we'll do that in the parent-level update.
 */
typedef struct xl_btree_split
{
	xl_btreetid target;			/* inserted tuple id */
	BlockNumber otherblk;		/* second block participated in split: */
	/* first one is stored in target' tid */
	BlockNumber leftblk;		/* prev/left block */
	BlockNumber rightblk;		/* next/right block */
	uint32		level;			/* tree level of page being split */
	uint16		leftlen;		/* len of left page items below */
	/* LEFT AND RIGHT PAGES TUPLES FOLLOW AT THE END */
} xl_btree_split;

#define SizeOfBtreeSplit	(offsetof(xl_btree_split, leftlen) + sizeof(uint16))

/*
 * This is what we need to know about delete of individual leaf index tuples.
 * The WAL record can represent deletion of any number of index tuples on a
 * single index page.
 */
typedef struct xl_btree_delete