text: /*-------------------------------------------------------------------------
   *
   * nbtree.h
   *	  header file for postgres btree access method implementation.
   *
   *
   * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
   * Portions Copyright (c) 1994, Regents of the University of California
   *
   * src/include/access/nbtree.h
   *
   *-------------------------------------------------------------------------
   */
  #ifndef NBTREE_H
  #define NBTREE_H
  
  #include "access/amapi.h"
  #include "access/itup.h"
  #include "access/sdir.h"
  #include "access/xlogreader.h"
  #include "catalog/pg_am_d.h"
  #include "catalog/pg_index.h"
  #include "lib/stringinfo.h"
  #include "storage/bufmgr.h"
  #include "storage/shm_toc.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 MAX_BT_CYCLE_ID 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_DEAD tuples */
  #define BTP_INCOMPLETE_SPLIT (1 << 7)	/* right sibling's downlink is missing */
  
  /*
   * The max allowed value of a cycle ID is a bit less than 64K.  This is
   * for convenience of pg_filedump and similar utilities: we want to use
   * the last 2 bytes of special space as an index type indicator, and
   * restricting cycle ID lets btree use that space for vacuum cycle IDs
   * while still allowing index type to be identified.
   */
  #define MAX_BT_CYCLE_ID		0xFF7F
  
  
  /*
   * 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;	/* nbtree version (always <= 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 */
  	/* remaining fields only valid when btm_version >= BTREE_NOVAC_VERSION */
  	TransactionId btm_oldest_btpo_xact; /* oldest btpo_xact among all deleted
  										 * pages */
  	float8		btm_last_cleanup_num_heap_tuples;	/* number of heap tuples
  													 * during last cleanup */
  } BTMetaPageData;
  
  #define BTPageGetMeta(p) \
  	((BTMetaPageData *) PageGetContents(p))
  
  /*
   * The current Btree version is 4.  That's what you'll get when you create
   * a new index.
   *
   * Btree version 3 was used in PostgreSQL v11.  It is mostly the same as
   * version 4, but heap TIDs were not part of the keyspace.  Index tuples
   * with duplicate keys could be stored in any order.  We continue to
   * support reading and writing Btree versions 2 and 3, so that they don't
   * need to be immediately re-indexed at pg_upgrade.  In order to get the
   * new heapkeyspace semantics, however, a REINDEX is needed.
   *
   * Btree version 2 is mostly the same as version 3.  There are two new
   * fields in the metapage that were introduced in version 3.  A version 2
   * metapage will be automatically upgraded to version 3 on the first
   * insert to it.  INCLUDE indexes cannot use version 2.
   */
  #define BTREE_METAPAGE	0		/* first page is meta */
  #define BTREE_MAGIC		0x053162	/* magic number in metapage */
  #define BTREE_VERSION	4		/* current version number */
  #define BTREE_MIN_VERSION	2	/* minimal supported version number */
  #define BTREE_NOVAC_VERSION	3	/* minimal version with all meta fields */
  
  /*
   * Maximum size of a btree index entry, including its tuple header.
   *
   * 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.
   *
   * There are rare cases where _bt_truncate() will need to enlarge
   * a heap index tuple to make space for a tiebreaker heap TID
   * attribute, which we account for here.
   */
  #define BTMaxItemSize(page) \
  	MAXALIGN_DOWN((PageGetPageSize(page) - \
  				   MAXALIGN(SizeOfPageHeaderData + \
  							3*sizeof(ItemIdData)  + \
  							3*sizeof(ItemPointerData)) - \
  				   MAXALIGN(sizeof(BTPageOpaqueData))) / 3)
  #define BTMaxItemSizeNoHeapTid(page) \
  	MAXALIGN_DOWN((PageGetPageSize(page) - \
  				   MAXALIGN(SizeOfPageHeaderData + 3*sizeof(ItemIdData)) - \
  				   MAXALIGN(sizeof(BTPageOpaqueData))) / 3)
  
  /*
   * 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.  When splitting a page that's entirely
   * filled with a single value (duplicates), the effective leaf-page
   * fillfactor is 96%, regardless of whether the page is a rightmost
   * page.
   */
  #define BTREE_MIN_FILLFACTOR		10
  #define BTREE_DEFAULT_FILLFACTOR	90
  #define BTREE_NONLEAF_FILLFACTOR	70
  #define BTREE_SINGLEVAL_FILLFACTOR	96
  
  /*
   *	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) != 0)
  #define P_ISROOT(opaque)		(((opaque)->btpo_flags & BTP_ROOT) != 0)
  #define P_ISDELETED(opaque)		(((opaque)->btpo_flags & BTP_DELETED) != 0)
  #define P_ISMETA(opaque)		(((opaque)->btpo_flags & BTP_META) != 0)
  #define P_ISHALFDEAD(opaque)	(((opaque)->btpo_flags & BTP_HALF_DEAD) != 0)
  #define P_IGNORE(opaque)		(((opaque)->btpo_flags & (BTP_DELETED|BTP_HALF_DEAD)) != 0)
  #define P_HAS_GARBAGE(opaque)	(((opaque)->btpo_flags & BTP_HAS_GARBAGE) != 0)
  #define P_INCOMPLETE_SPLIT(opaque)	(((opaque)->btpo_flags & BTP_INCOMPLETE_SPLIT) != 0)
  
  /*
   *	Lehman and Yao's algorithm requires a ``high key'' on every non-rightmost
   *	page.  The high key is not a tuple that is used to visit the heap.  It is
   *	a pivot tuple (see "Notes on B-Tree tuple format" below for definition).
   *	The high key on a page is required to be greater than or equal to any
   *	other key that appears on the page.  If we find ourselves trying to
   *	insert a key that is strictly > 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)
  
  /*
   * Notes on B-Tree tuple format, and key and non-key attributes:
   *
   * INCLUDE B-Tree indexes have non-key attributes.  These are extra
   * attributes that may be returned by index-only scans, but do not influence
   * the order of items in the index (formally, non-key attributes are not
   * considered to be part of the key space).  Non-key attributes are only
   * present in leaf index tuples whose item pointers actually point to heap
   * tuples (non-pivot tuples).  _bt_check_natts() enforces the rules
   * described here.
   *
   * Non-pivot tuple format:
   *
   *  t_tid | t_info | key values | INCLUDE columns, if any
   *
   * t_tid points to the heap TID, which is a tiebreaker key column as of
   * BTREE_VERSION 4.  Currently, the INDEX_ALT_TID_MASK status bit is never
   * set for non-pivot tuples.
   *
   * All other types of index tuples ("pivot" tuples) only have key columns,
   * since pivot tuples only exist to represent how the key space is
   * separated.  In general, any B-Tree index that has more than one level
   * (i.e. any index that does not just consist of a metapage and a single
   * leaf root page) must have some number of pivot tuples, since pivot
   * tuples are used for traversing the tree.  Suffix truncation can omit
   * trailing key columns when a new pivot is formed, which makes minus
   * infinity their logical value.  Since BTREE_VERSION 4 indexes treat heap
   * TID as a trailing key column that ensures that all index tuples are
   * physically unique, it is necessary to represent heap TID as a trailing
   * key column in pivot tuples, though very often this can be truncated
   * away, just like any other key column. (Actually, the heap TID is
   * omitted rather than truncated, since its representation is different to
   * the non-pivot representation.)
   *
   * Pivot tuple format:
   *
   *  t_tid | t_info | key values | [heap TID]
   *
   * We store the number of columns present inside pivot tuples by abusing
   * their t_tid offset field, since pivot tuples never need to store a real
   * offset (downlinks only need to store a block number in t_tid).  The
   * offset field only stores the number of columns/attributes when the
   * INDEX_ALT_TID_MASK bit is set, which doesn't count the trailing heap
   * TID column sometimes stored in pivot tuples -- that's represented by
   * the presence of BT_HEAP_TID_ATTR.  The INDEX_ALT_TID_MASK bit in t_info
   * is always set on BTREE_VERSION 4.  BT_HEAP_TID_ATTR can only be set on
   * BTREE_VERSION 4.
   *
   * In version 3 indexes, the INDEX_ALT_TID_MASK flag might not be set in
   * pivot tuples.  In that case, the number of key columns is implicitly
   * the same as the number of key columns in the index.  It is not usually
   * set on version 2 indexes, which predate the introduction of INCLUDE
   * indexes.  (Only explicitly truncated pivot tuples explicitly represent
   * the number of key columns on versions 2 and 3, whereas all pivot tuples
   * are formed using truncation on version 4.  A version 2 index will have
   * it set for an internal page negative infinity item iff internal page
   * split occurred after upgrade to Postgres 11+.)
   *
   * The 12 least significant offset bits from t_tid are used to represent
   * the number of columns in INDEX_ALT_TID_MASK tuples, leaving 4 status
   * bits (BT_RESERVED_OFFSET_MASK bits), 3 of which that are reserved for
   * future use.  BT_N_KEYS_OFFSET_MASK should be large enough to store any
   * number of columns/attributes <= INDEX_MAX_KEYS.
   *
   * Note well: The macros that deal with the number of attributes in tuples
   * assume that a tuple with INDEX_ALT_TID_MASK set must be a pivot tuple,
   * and that a tuple without INDEX_ALT_TID_MASK set must be a non-pivot
   * tuple (or must have the same number of attributes as the index has
   * generally in the case of !heapkeyspace indexes).  They will need to be
   * updated if non-pivot tuples ever get taught to use INDEX_ALT_TID_MASK
   * for something else.
   */
  #define INDEX_ALT_TID_MASK			INDEX_AM_RESERVED_BIT
  
  /* Item pointer offset bits */
  #define BT_RESERVED_OFFSET_MASK		0xF000
  #define BT_N_KEYS_OFFSET_MASK		0x0FFF
  #define BT_HEAP_TID_ATTR			0x1000
  
  /* Get/set downlink block number in pivot tuple */
  #define BTreeTupleGetDownLink(itup) \
  	ItemPointerGetBlockNumberNoCheck(&((itup)->t_tid))
  #define BTreeTupleSetDownLink(itup, blkno) \
  	ItemPointerSetBlockNumber(&((itup)->t_tid), (blkno))
  
  /*
   * Get/set leaf page highkey's link. During the second phase of deletion, the
   * target leaf page's high key may point to an ancestor page (at all other
   * times, the leaf level high key's link is not used).  See the nbtree README
   * for full details.
   */
  #define BTreeTupleGetTopParent(itup) \
  	ItemPointerGetBlockNumberNoCheck(&((itup)->t_tid))
  #define BTreeTupleSetTopParent(itup, blkno)	\
  	do { \
  		ItemPointerSetBlockNumber(&((itup)->t_tid), (blkno)); \
  		BTreeTupleSetNAtts((itup), 0); \
  	} while(0)
  
  /*
   * Get/set number of attributes within B-tree index tuple.
   *
   * Note that this does not include an implicit tiebreaker heap TID
   * attribute, if any.  Note also that the number of key attributes must be
   * explicitly represented in all heapkeyspace pivot tuples.
   */
  #define BTreeTupleGetNAtts(itup, rel)	\
  	( \
  		(itup)->t_info & INDEX_ALT_TID_MASK ? \
  		( \
  			ItemPointerGetOffsetNumberNoCheck(&(itup)->t_tid) & BT_N_KEYS_OFFSET_MASK \
  		) \
  		: \
  		IndexRelationGetNumberOfAttributes(rel) \
  	)
  #define BTreeTupleSetNAtts(itup, n) \
  	do { \
  		(itup)->t_info |= INDEX_ALT_TID_MASK; \
  		ItemPointerSetOffsetNumber(&(itup)->t_tid, (n) & BT_N_KEYS_OFFSET_MASK); \
  	} while(0)
  
  /*
   * Get tiebreaker heap TID attribute, if any.  Macro works with both pivot
   * and non-pivot tuples, despite differences in how heap TID is represented.
   */
  #define BTreeTupleGetHeapTID(itup) \
  	( \
  	  (itup)->t_info & INDEX_ALT_TID_MASK && \
  	  (ItemPointerGetOffsetNumberNoCheck(&(itup)->t_tid) & BT_HEAP_TID_ATTR) != 0 ? \
  	  ( \
  		(ItemPointer) (((char *) (itup) + IndexTupleSize(itup)) - \
  					   sizeof(ItemPointerData)) \
  	  ) \
  	  : (itup)->t_info & INDEX_ALT_TID_MASK ? NULL : (ItemPointer) &((itup)->t_tid) \
  	)
  /*
   * Set the heap TID attribute for a tuple that uses the INDEX_ALT_TID_MASK
   * representation (currently limited to pivot tuples)
   */
  #define BTreeTupleSetAltHeapTID(itup) \
  	do { \
  		Assert((itup)->t_info & INDEX_ALT_TID_MASK); \
  		ItemPointerSetOffsetNumber(&(itup)->t_tid, \
  								   ItemPointerGetOffsetNumberNoCheck(&(itup)->t_tid) | BT_HEAP_TID_ATTR); \
  	} while(0)
  
  /*
   *	Operator strategy numbers for B-tree have been moved to access/stratnum.h,
   *	because many places need to use them in ScanKeyInit() calls.
   *
   *	The strategy numbers are chosen so that we can commute them by
   *	subtraction, thus:
   */
  #define BTCommuteStrategyNumber(strat)	(BTMaxStrategyNumber + 1 - (strat))
  
  /*
   *	When a new operator class is declared, we require that the user
   *	supply us with an amproc procedure (BTORDER_PROC) for determining
   *	whether, for two keys a and b, a < b, a = b, or a > b.  This routine
   *	must return < 0, 0, > 0, respectively, in these three cases.
   *
   *	To facilitate accelerated sorting, an operator class may choose to
   *	offer a second procedure (BTSORTSUPPORT_PROC).  For full details, see
   *	src/include/utils/sortsupport.h.
   *
   *	To support window frames defined by "RANGE offset PRECEDING/FOLLOWING",
   *	an operator class may choose to offer a third amproc procedure
   *	(BTINRANGE_PROC), independently of whether it offers sortsupport.
   *	For full details, see doc/src/sgml/btree.sgml.
   */
  
  #define BTORDER_PROC		1
  #define BTSORTSUPPORT_PROC	2
  #define BTINRANGE_PROC		3
  #define BTNProcs			3
  
  /*
   *	We need to be able to tell the difference between read and write
   *	requests for pages, in order to do locking correctly.
   */
  
  #define BT_READ			BUFFER_LOCK_SHARE
  #define BT_WRITE		BUFFER_LOCK_EXCLUSIVE
  
  /*
   * BTStackData -- As we descend a tree, we push the location of pivot
   * tuples whose downlink we are about to follow onto a private stack.  If
   * we split a leaf, we use this stack to walk back up the tree and insert
   * data into its parent page at the correct location.  We also have to
   * recursively insert into the grandparent page if and when the parent page
   * splits.  Our private stack can become stale due to concurrent page
   * splits and page deletions, but it should never give us an irredeemably
   * bad picture.
   */
  typedef struct BTStackData
  {
  	BlockNumber bts_blkno;
  	OffsetNumber bts_offset;
  	struct BTStackData *bts_parent;
  } BTStackData;
  
  typedef BTStackData *BTStack;
  
  /*
   * BTScanInsertData is the btree-private state needed to find an initial
   * position for an indexscan, or to insert new tuples -- an "insertion
   * scankey" (not to be confused with a search scankey).  It's used to descend
   * a B-Tree using _bt_search.
   *
   * heapkeyspace indicates if we expect all keys in the index to be physically
   * unique because heap TID is used as a tiebreaker attribute, and if index may
   * have truncated key attributes in pivot tuples.  This is actually a property
   * of the index relation itself (not an indexscan).  heapkeyspace indexes are
   * indexes whose version is >= version 4.  It's convenient to keep this close
   * by, rather than accessing the metapage repeatedly.
   *
   * anynullkeys indicates if any of the keys had NULL value when scankey was
   * built from index tuple (note that already-truncated tuple key attributes
   * set NULL as a placeholder key value, which also affects value of
   * anynullkeys).  This is a convenience for unique index non-pivot tuple
   * insertion, which usually temporarily unsets scantid, but shouldn't iff
   * anynullkeys is true.  Value generally matches non-pivot tuple's HasNulls
   * bit, but may not when inserting into an INCLUDE index (tuple header value
   * is affected by the NULL-ness of both key and non-key attributes).
   *
   * When nextkey is false (the usual case), _bt_search and _bt_binsrch will
   * locate the first item >= scankey.  When nextkey is true, they will locate
   * the first item > scan key.
   *
   * pivotsearch is set to true by callers that want to re-find a leaf page
   * using a scankey built from a leaf page's high key.  Most callers set this
   * to false.
   *
   * scantid is the heap TID that is used as a final tiebreaker attribute.  It
   * is set to NULL when index scan doesn't need to find a position for a
   * specific physical tuple.  Must be set when inserting new tuples into
   * heapkeyspace indexes, since every tuple in the tree unambiguously belongs
   * in one exact position (it's never set with !heapkeyspace indexes, though).
   * Despite the representational difference, nbtree search code considers
   * scantid to be just another insertion scankey attribute.
   *
   * scankeys is an array of scan key entries for attributes that are compared
   * before scantid (user-visible attributes).  keysz is the size of the array.
   * During insertion, there must be a scan key for every attribute, but when
   * starting a regular index scan some can be omitted.  The array is used as a
   * flexible array member, though it's sized in a way that makes it possible to
   * use stack allocations.  See nbtree/README for full details.
   */
  typedef struct BTScanInsertData
  {
  	bool		heapkeyspace;
  	bool		anynullkeys;
  	bool		nextkey;
  	bool		pivotsearch;
  	ItemPointer scantid;		/* tiebreaker for scankeys */
  	int			keysz;			/* Size of scankeys array */
  	ScanKeyData scankeys[INDEX_MAX_KEYS];	/* Must appear last */
  } BTScanInsertData;
  
  typedef BTScanInsertData *BTScanInsert;
  
  /*
   * BTInsertStateData is a working area used during insertion.
   *
   * This is filled in after descending the tree to the first leaf page the new
   * tuple might belong on.  Tracks the current position while performing
   * uniqueness check, before we have determined which exact page to insert
   * to.
   *
   * (This should be private to nbtinsert.c, but it's also used by
   * _bt_binsrch_insert)
   */
  typedef struct BTInsertStateData
  {
  	IndexTuple	itup;			/* Item we're inserting */
  	Size		itemsz;			/* Size of itup -- should be MAXALIGN()'d */
  	BTScanInsert itup_key;		/* Insertion scankey */
  
  	/* Buffer containing leaf page we're likely to insert itup on */
  	Buffer		buf;
  
  	/*
  	 * Cache of bounds within the current buffer.  Only used for insertions
  	 * where _bt_check_unique is called.  See _bt_binsrch_insert and
  	 * _bt_findinsertloc for details.
  	 */
  	bool		bounds_valid;
  	OffsetNumber low;
  	OffsetNumber stricthigh;
  } BTInsertStateData;
  
  typedef BTInsertStateData *BTInsertState;
  
  /*
   * BTScanOpaqueData is the btree-private state needed for an indexscan.
   * This consists of preprocessed scan keys (see _bt_preprocess_keys() for
   * details of the preprocessing), information about the current location
   * of the scan, and information about the marked location, if any.  (We use
   * BTScanPosData to represent the data needed for each of current and marked
   * locations.)	In addition we can remember some known-killed index entries
   * that must be marked before we can move off the current page.
   *
   * Index scans work a page at a time: we pin and read-lock the page, identify
   * all the matching items on the page and save them in BTScanPosData, then
   * release the read-lock while returning the items to the caller for
   * processing.  This approach minimizes lock/unlock traffic.  Note that we
   * keep the pin on the index page until the caller is done with all the items
   * (this is needed for VACUUM synchronization, see nbtree/README).  When we
   * are ready to step to the next page, if the caller has told us any of the
   * items were killed, we re-lock the page to mark them killed, then unlock.
   * Finally we drop the pin and step to the next page in the appropriate
   * direction.
   *
   * If we are doing an index-only scan, we save the entire IndexTuple for each
   * matched item, otherwise only its heap TID and offset.  The IndexTuples go
   * into a separate workspace array; each BTScanPosItem stores its tuple's
   * offset within that array.
   */
  
  typedef struct BTScanPosItem	/* what we remember about each match */
  {
  	ItemPointerData heapTid;	/* TID of referenced heap item */
  	OffsetNumber indexOffset;	/* index item's location within page */
  	LocationIndex tupleOffset;	/* IndexTuple's offset in workspace, if any */
  } BTScanPosItem;
  
  typedef struct BTScanPosData
  {
  	Buffer		buf;			/* if valid, the buffer is pinned */
  
  	XLogRecPtr	lsn;			/* pos in the WAL stream when page was read */
  	BlockNumber currPage;		/* page referenced by items array */
  	BlockNumber nextPage;		/* page's right link when we scanned it */
  
  	/*
  	 * moreLeft and moreRight track whether we think there may be matching
  	 * index entries to the left and right of the current page, respectively.
  	 * We can clear the appropriate one of these flags when _bt_checkkeys()
  	 * returns continuescan = false.
  	 */
  	bool		moreLeft;
  	bool		moreRight;
  
  	/*
  	 * If we are doing an index-only scan, nextTupleOffset is the first free
  	 * location in the associated tuple storage workspace.
  	 */
  	int			nextTupleOffset;
  
  	/*
  	 * The items array is always ordered in index order (ie, increasing
  	 * indexoffset).  When scanning backwards it is convenient to fill the
  	 * array back-to-front, so we start at the last slot and fill downwards.
  	 * Hence we need both a first-valid-entry and a last-valid-entry counter.
  	 * itemIndex is a cursor showing which entry was last returned to caller.
  	 */
  	int			firstItem;		/* first valid index in items[] */
  	int			lastItem;		/* last valid index in items[] */
  	int			itemIndex;		/* current index in items[] */
  
  	BTScanPosItem items[MaxIndexTuplesPerPage]; /* MUST BE LAST */
  } BTScanPosData;
  
  typedef BTScanPosData *BTScanPos;
  
  #define BTScanPosIsPinned(scanpos) \
  ( \
  	AssertMacro(BlockNumberIsValid((scanpos).currPage) || \
  				!BufferIsValid((scanpos).buf)), \
  	BufferIsValid((scanpos).buf) \
  )
  #define BTScanPosUnpin(scanpos) \
  	do { \
  		ReleaseBuffer((scanpos).buf); \
  		(scanpos).buf = InvalidBuffer; \
  	} while (0)
  #define BTScanPosUnpinIfPinned(scanpos) \
  	do { \
  		if (BTScanPosIsPinned(scanpos)) \
  			BTScanPosUnpin(scanpos); \
  	} while (0)
  
  #define BTScanPosIsValid(scanpos) \
  ( \
  	AssertMacro(BlockNumberIsValid((scanpos).currPage) || \
  				!BufferIsValid((scanpos).buf)), \
  	BlockNumberIsValid((scanpos).currPage) \
  )
  #define BTScanPosInvalidate(scanpos) \
  	do { \
  		(scanpos).currPage = InvalidBlockNumber; \
  		(scanpos).nextPage = InvalidBlockNumber; \
  		(scanpos).buf = InvalidBuffer; \
  		(scanpos).lsn = InvalidXLogRecPtr; \
  		(scanpos).nextTupleOffset = 0; \
  	} while (0);
  
  /* We need one of these for each equality-type SK_SEARCHARRAY scan key */
  typedef struct BTArrayKeyInfo
  {
  	int			scan_key;		/* index of associated key in arrayKeyData */
  	int			cur_elem;		/* index of current element in elem_values */
  	int			mark_elem;		/* index of marked element in elem_values */
  	int			num_elems;		/* number of elems in current array value */
  	Datum	   *elem_values;	/* array of num_elems Datums */
  } BTArrayKeyInfo;
  
  typedef struct BTScanOpaqueData
  {
  	/* these fields are set by _bt_preprocess_keys(): */
  	bool		qual_ok;		/* false if qual can never be satisfied */
  	int			numberOfKeys;	/* number of preprocessed scan keys */
  	ScanKey		keyData;		/* array of preprocessed scan keys */
  
  	/* workspace for SK_SEARCHARRAY support */
  	ScanKey		arrayKeyData;	/* modified copy of scan->keyData */
  	int			numArrayKeys;	/* number of equality-type array keys (-1 if
  								 * there are any unsatisfiable array keys) */
  	int			arrayKeyCount;	/* count indicating number of array scan keys
  								 * processed */
  	BTArrayKeyInfo *arrayKeys;	/* info about each equality-type array key */
  	MemoryContext arrayContext; /* scan-lifespan context for array data */
  
  	/* info about killed items if any (killedItems is NULL if never used) */
  	int		   *killedItems;	/* currPos.items indexes of killed items */
  	int			numKilled;		/* number of currently stored items */
  
  	/*
  	 * If we are doing an index-only scan, these are the tuple storage
  	 * workspaces for the currPos and markPos respectively.  Each is of size
  	 * BLCKSZ, so it can hold as much as a full page's worth of tuples.
  	 */
  	char	   *currTuples;		/* tuple storage for currPos */
  	char	   *markTuples;		/* tuple storage for markPos */
  
  	/*
  	 * If the marked position is on the same page as current position, we
  	 * don't use markPos, but just keep the marked itemIndex in markItemIndex
  	 * (all the rest of currPos is valid for the mark position). Hence, to
  	 * determine if there is a mark, first look at markItemIndex, then at
  	 * markPos.
  	 */
  	int			markItemIndex;	/* itemIndex, or -1 if not valid */
  
  	/* keep these last in struct for efficiency */
  	BTScanPosData currPos;		/* current position data */
  	BTScanPosData markPos;		/* marked position, if any */
  } BTScanOpaqueData;
  
  typedef BTScanOpaqueData *BTScanOpaque;
  
  /*
   * We use some private sk_flags bits in preprocessed scan keys.  We're allowed
   * to use bits 16-31 (see skey.h).  The uppermost bits are copied from the
   * index's indoption[] array entry for the index attribute.
   */
  #define SK_BT_REQFWD	0x00010000	/* required to continue forward scan */
  #define SK_BT_REQBKWD	0x00020000	/* required to continue backward scan */
  #define SK_BT_INDOPTION_SHIFT  24	/* must clear the above bits */
  #define SK_BT_DESC			(INDOPTION_DESC << SK_BT_INDOPTION_SHIFT)
  #define SK_BT_NULLS_FIRST	(INDOPTION_NULLS_FIRST << SK_BT_INDOPTION_SHIFT)
  
  typedef struct BTOptions
  {
  	int32		varlena_header_;	/* varlena header (do not touch directly!) */
  	int			fillfactor;		/* page fill factor in percent (0..100) */
  	/* fraction of newly inserted tuples prior to trigger index cleanup */
  	float8		vacuum_cleanup_index_scale_factor;
  } BTOptions;
  
  #define BTGetFillFactor(relation) \
  	(AssertMacro(relation->rd_rel->relkind == RELKIND_INDEX && \
  				 relation->rd_rel->relam == BTREE_AM_OID), \
  	 (relation)->rd_options ? \
  	 ((BTOptions *) (relation)->rd_options)->fillfactor : \
  	 BTREE_DEFAULT_FILLFACTOR)
  #define BTGetTargetPageFreeSpace(relation) \
  	(BLCKSZ * (100 - BTGetFillFactor(relation)) / 100)
  
  /*
   * Constant definition for progress reporting.  Phase numbers must match
   * btbuildphasename.
   */
  /* PROGRESS_CREATEIDX_SUBPHASE_INITIALIZE is 1 (see progress.h) */
  #define PROGRESS_BTREE_PHASE_INDEXBUILD_TABLESCAN		2
  #define PROGRESS_BTREE_PHASE_PERFORMSORT_1				3
  #define PROGRESS_BTREE_PHASE_PERFORMSORT_2				4
  #define PROGRESS_BTREE_PHASE_LEAF_LOAD					5
  
  /*
   * external entry points for btree, in nbtree.c
   */
  extern void btbuildempty(Relation index);
  extern bool btinsert(Relation rel, Datum *values, bool *isnull,
  					 ItemPointer ht_ctid, Relation heapRel,
  					 IndexUniqueCheck checkUnique,
  					 struct IndexInfo *indexInfo);
  extern IndexScanDesc btbeginscan(Relation rel, int nkeys, int norderbys);
  extern Size btestimateparallelscan(void);
  extern void btinitparallelscan(void *target);
  extern bool btgettuple(IndexScanDesc scan, ScanDirection dir);
  extern int64 btgetbitmap(IndexScanDesc scan, TIDBitmap *tbm);
  extern void btrescan(IndexScanDesc scan, ScanKey scankey, int nscankeys,
  					 ScanKey orderbys, int norderbys);
  extern void btparallelrescan(IndexScanDesc scan);
  extern void btendscan(IndexScanDesc scan);
  extern void btmarkpos(IndexScanDesc scan);
  extern void btrestrpos(IndexScanDesc scan);
  extern IndexBulkDeleteResult *btbulkdelete(IndexVacuumInfo *info,
  										   IndexBulkDeleteResult *stats,
  										   IndexBulkDeleteCallback callback,
  										   void *callback_state);
  extern IndexBulkDeleteResult *btvacuumcleanup(IndexVacuumInfo *info,
  											  IndexBulkDeleteResult *stats);
  extern bool btcanreturn(Relation index, int attno);
  
  /*
   * prototypes for internal functions in nbtree.c
   */
  extern bool _bt_parallel_seize(IndexScanDesc scan, BlockNumber *pageno);
  extern void _bt_parallel_release(IndexScanDesc scan, BlockNumber scan_page);
  extern void _bt_parallel_done(IndexScanDesc scan);
  extern void _bt_parallel_advance_array_keys(IndexScanDesc scan);
  
  /*
   * prototypes for functions in nbtinsert.c
   */
  extern bool _bt_doinsert(Relation rel, IndexTuple itup,
  						 IndexUniqueCheck checkUnique, Relation heapRel);
  extern void _bt_finish_split(Relation rel, Buffer bbuf, BTStack stack);
  extern Buffer _bt_getstackbuf(Relation rel, BTStack stack, BlockNumber child);
  
  /*
   * prototypes for functions in nbtsplitloc.c
   */
  extern OffsetNumber _bt_findsplitloc(Relation rel, Page page,
  									 OffsetNumber newitemoff, Size newitemsz, IndexTuple newitem,
  									 bool *newitemonleft);
  
  /*
   * prototypes for functions in nbtpage.c
   */
  extern void _bt_initmetapage(Page page, BlockNumber rootbknum, uint32 level);
  extern void _bt_update_meta_cleanup_info(Relation rel,
  										 TransactionId oldestBtpoXact, float8 numHeapTuples);
  extern void _bt_upgrademetapage(Page page);
  extern Buffer _bt_getroot(Relation rel, int access);
  extern Buffer _bt_gettrueroot(Relation rel);
  extern int	_bt_getrootheight(Relation rel);
  extern bool _bt_heapkeyspace(Relation rel);
  extern void _bt_checkpage(Relation rel, Buffer buf);
  extern Buffer _bt_getbuf(Relation rel, BlockNumber blkno, int access);
  extern Buffer _bt_relandgetbuf(Relation rel, Buffer obuf,
  							   BlockNumber blkno, int access);
  extern void _bt_relbuf(Relation rel, Buffer buf);
  extern void _bt_pageinit(Page page, Size size);
  extern bool _bt_page_recyclable(Page page);
  extern void _bt_delitems_delete(Relation rel, Buffer buf,
  								OffsetNumber *itemnos, int nitems, Relation heapRel);
  extern void _bt_delitems_vacuum(Relation rel, Buffer buf,
  								OffsetNumber *itemnos, int nitems,
  								BlockNumber lastBlockVacuumed);
  extern int	_bt_pagedel(Relation rel, Buffer buf);
  
  /*
   * prototypes for functions in nbtsearch.c
   */
  extern BTStack _bt_search(Relation rel, BTScanInsert key, Buffer *bufP,
  						  int access, Snapshot snapshot);
  extern Buffer _bt_moveright(Relation rel, BTScanInsert key, Buffer buf,
  							bool forupdate, BTStack stack, int access, Snapshot snapshot);
  extern OffsetNumber _bt_binsrch_insert(Relation rel, BTInsertState insertstate);
  extern int32 _bt_compare(Relation rel, BTScanInsert key, Page page, OffsetNumber offnum);
  extern bool _bt_first(IndexScanDesc scan, ScanDirection dir);
  extern bool _bt_next(IndexScanDesc scan, ScanDirection dir);
  extern Buffer _bt_get_endpoint(Relation rel, uint32 level, bool rightmost,
  							   Snapshot snapshot);
  
  /*
   * prototypes for functions in nbtutils.c
   */
  extern BTScanInsert _bt_mkscankey(Relation rel, IndexTuple itup);
  extern void _bt_freestack(BTStack stack);
  extern void _bt_preprocess_array_keys(IndexScanDesc scan);
  extern void _bt_start_array_keys(IndexScanDesc scan, ScanDirection dir);
  extern bool _bt_advance_array_keys(IndexScanDesc scan, ScanDirection dir);
  extern void _bt_mark_array_keys(IndexScanDesc scan);
  extern void _bt_restore_array_keys(IndexScanDesc scan);
  extern void _bt_preprocess_keys(IndexScanDesc scan);
  extern bool _bt_checkkeys(IndexScanDesc scan, IndexTuple tuple,
  						  int tupnatts, ScanDirection dir, bool *continuescan);
  extern void _bt_killitems(IndexScanDesc scan);
  extern BTCycleId _bt_vacuum_cycleid(Relation rel);
  extern BTCycleId _bt_start_vacuum(Relation rel);
  extern void _bt_end_vacuum(Relation rel);
  extern void _bt_end_vacuum_callback(int code, Datum arg);
  extern Size BTreeShmemSize(void);
  extern void BTreeShmemInit(void);
  extern bytea *btoptions(Datum reloptions, bool validate);
  extern bool btproperty(Oid index_oid, int attno,
  					   IndexAMProperty prop, const char *propname,
  					   bool *res, bool *isnull);
  extern char *btbuildphasename(int64 phasenum);
  extern IndexTuple _bt_truncate(Relation rel, IndexTuple lastleft,
  							   IndexTuple firstright, BTScanInsert itup_key);
  extern int	_bt_keep_natts_fast(Relation rel, IndexTuple lastleft,
  								IndexTuple firstright);
  extern bool _bt_check_natts(Relation rel, bool heapkeyspace, Page page,
  							OffsetNumber offnum);
  extern void _bt_check_third_page(Relation rel, Relation heap,
  								 bool needheaptidspace, Page page, IndexTuple newtup);
  
  /*
   * prototypes for functions in nbtvalidate.c
   */
  extern bool btvalidate(Oid opclassoid);
  
  /*
   * prototypes for functions in nbtsort.c
   */
  extern IndexBuildResult *btbuild(Relation heap, Relation index,
  								 struct IndexInfo *indexInfo);
  extern void _bt_parallel_build_main(dsm_segment *seg, shm_toc *toc);
  
  #endif							/* NBTREE_H */
  