text: /*-------------------------------------------------------------------------
   *
   * nbtree.c
   *	  Implementation of Lehman and Yao's btree management algorithm for
   *	  Postgres.
   *
   * NOTES
   *	  This file contains only the public interface routines.
   *
   *
   * Portions Copyright (c) 1996-2012, PostgreSQL Global Development Group
   * Portions Copyright (c) 1994, Regents of the University of California
   *
   * IDENTIFICATION
   *	  src/backend/access/nbtree/nbtree.c
   *
   *-------------------------------------------------------------------------
   */
  #include "postgres.h"
  
  #include "access/nbtree.h"
  #include "access/relscan.h"
  #include "catalog/index.h"
  #include "commands/vacuum.h"
  #include "storage/indexfsm.h"
  #include "storage/ipc.h"
  #include "storage/lmgr.h"
  #include "storage/smgr.h"
  #include "tcop/tcopprot.h"
  #include "utils/memutils.h"
  
  
  /* Working state for btbuild and its callback */
  typedef struct
  {
  	bool		isUnique;
  	bool		haveDead;
  	Relation	heapRel;
  	BTSpool    *spool;
  
  	/*
  	 * spool2 is needed only when the index is an unique index. Dead tuples
  	 * are put into spool2 instead of spool in order to avoid uniqueness
  	 * check.
  	 */
  	BTSpool    *spool2;
  	double		indtuples;
  } BTBuildState;
  
  /* Working state needed by btvacuumpage */
  typedef struct
  {
  	IndexVacuumInfo *info;
  	IndexBulkDeleteResult *stats;
  	IndexBulkDeleteCallback callback;
  	void	   *callback_state;
  	BTCycleId	cycleid;
  	BlockNumber lastBlockVacuumed;		/* highest blkno actually vacuumed */
  	BlockNumber lastBlockLocked;	/* highest blkno we've cleanup-locked */
  	BlockNumber totFreePages;	/* true total # of free pages */
  	MemoryContext pagedelcontext;
  } BTVacState;
  
  
  static void btbuildCallback(Relation index,
  				HeapTuple htup,
  				Datum *values,
  				bool *isnull,
  				bool tupleIsAlive,
  				void *state);
  static void btvacuumscan(IndexVacuumInfo *info, IndexBulkDeleteResult *stats,
  			 IndexBulkDeleteCallback callback, void *callback_state,
  			 BTCycleId cycleid);
  static void btvacuumpage(BTVacState *vstate, BlockNumber blkno,
  			 BlockNumber orig_blkno);
  
  
  /*
   *	btbuild() -- build a new btree index.
   */
  Datum
  btbuild(PG_FUNCTION_ARGS)
  {
  	Relation	heap = (Relation) PG_GETARG_POINTER(0);
  	Relation	index = (Relation) PG_GETARG_POINTER(1);
  	IndexInfo  *indexInfo = (IndexInfo *) PG_GETARG_POINTER(2);
  	IndexBuildResult *result;
  	double		reltuples;
  	BTBuildState buildstate;
  
  	buildstate.isUnique = indexInfo->ii_Unique;
  	buildstate.haveDead = false;
  	buildstate.heapRel = heap;
  	buildstate.spool = NULL;
  	buildstate.spool2 = NULL;
  	buildstate.indtuples = 0;
  
  #ifdef BTREE_BUILD_STATS
  	if (log_btree_build_stats)
  		ResetUsage();
  #endif   /* BTREE_BUILD_STATS */
  
  	/*
  	 * We expect to be called exactly once for any index relation. If that's
  	 * not the case, big trouble's what we have.
  	 */
  	if (RelationGetNumberOfBlocks(index) != 0)
  		elog(ERROR, "index \"%s\" already contains data",
  			 RelationGetRelationName(index));
  
  	buildstate.spool = _bt_spoolinit(index, indexInfo->ii_Unique, false);
  
  	/*
  	 * If building a unique index, put dead tuples in a second spool to keep
  	 * them out of the uniqueness check.
  	 */
  	if (indexInfo->ii_Unique)
  		buildstate.spool2 = _bt_spoolinit(index, false, true);
  
  	/* do the heap scan */
  	reltuples = IndexBuildHeapScan(heap, index, indexInfo, true,
  								   btbuildCallback, (void *) &buildstate);
  
  	/* okay, all heap tuples are indexed */
  	if (buildstate.spool2 && !buildstate.haveDead)
  	{
  		/* spool2 turns out to be unnecessary */
  		_bt_spooldestroy(buildstate.spool2);
  		buildstate.spool2 = NULL;
  	}
  
  	/*
  	 * Finish the build by (1) completing the sort of the spool file, (2)
  	 * inserting the sorted tuples into btree pages and (3) building the upper
  	 * levels.
  	 */
  	_bt_leafbuild(buildstate.spool, buildstate.spool2);
  	_bt_spooldestroy(buildstate.spool);
  	if (buildstate.spool2)
  		_bt_spooldestroy(buildstate.spool2);
  
  #ifdef BTREE_BUILD_STATS
  	if (log_btree_build_stats)
  	{
  		ShowUsage("BTREE BUILD STATS");
  		ResetUsage();
  	}
  #endif   /* BTREE_BUILD_STATS */
  
  	/*
  	 * If we are reindexing a pre-existing index, it is critical to send out a
  	 * relcache invalidation SI message to ensure all backends re-read the
  	 * index metapage.  We expect that the caller will ensure that happens
  	 * (typically as a side effect of updating index stats, but it must happen
  	 * even if the stats don't change!)
  	 */
  
  	/*
  	 * Return statistics
  	 */
  	result = (IndexBuildResult *) palloc(sizeof(IndexBuildResult));
  
  	result->heap_tuples = reltuples;
  	result->index_tuples = buildstate.indtuples;
  
  	PG_RETURN_POINTER(result);
  }
  
  /*
   * Per-tuple callback from IndexBuildHeapScan
   */
  static void
  btbuildCallback(Relation index,
  				HeapTuple htup,
  				Datum *values,
  				bool *isnull,
  				bool tupleIsAlive,
  				void *state)
  {
  	BTBuildState *buildstate = (BTBuildState *) state;
  	IndexTuple	itup;
  
  	/* form an index tuple and point it at the heap tuple */
  	itup = index_form_tuple(RelationGetDescr(index), values, isnull);
  	itup->t_tid = htup->t_self;
  
  	/*
  	 * insert the index tuple into the appropriate spool file for subsequent
  	 * processing
  	 */
  	if (tupleIsAlive || buildstate->spool2 == NULL)
  		_bt_spool(itup, buildstate->spool);
  	else
  	{
  		/* dead tuples are put into spool2 */
  		buildstate->haveDead = true;
  		_bt_spool(itup, buildstate->spool2);
  	}
  
  	buildstate->indtuples += 1;
  
  	pfree(itup);
  }
  
  /*
   *	btbuildempty() -- build an empty btree index in the initialization fork
   */
  Datum
  btbuildempty(PG_FUNCTION_ARGS)
  {
  	Relation	index = (Relation) PG_GETARG_POINTER(0);
  	Page		metapage;
  
  	/* Construct metapage. */
  	metapage = (Page) palloc(BLCKSZ);
  	_bt_initmetapage(metapage, P_NONE, 0);
  
  	/*
  	 * Write the page and log it.  It might seem that an immediate sync
  	 * would be sufficient to guarantee that the file exists on disk, but
  	 * recovery itself might remove it while replaying, for example, an
  	 * XLOG_DBASE_CREATE or XLOG_TBLSPC_CREATE record.  Therefore, we
  	 * need this even when wal_level=minimal.
  	 */
  	smgrwrite(index->rd_smgr, INIT_FORKNUM, BTREE_METAPAGE,
  			  (char *) metapage, true);
  	log_newpage(&index->rd_smgr->smgr_rnode.node, INIT_FORKNUM,
  				BTREE_METAPAGE, metapage);
  
  	/*
  	 * An immediate sync is required even if we xlog'd the page, because the
  	 * write did not go through shared_buffers and therefore a concurrent
  	 * checkpoint may have moved the redo pointer past our xlog record.
  	 */
  	smgrimmedsync(index->rd_smgr, INIT_FORKNUM);
  
  	PG_RETURN_VOID();
  }
  
  /*
   *	btinsert() -- insert an index tuple into a btree.
   *
   *		Descend the tree recursively, find the appropriate location for our
   *		new tuple, and put it there.
   */
  Datum
  btinsert(PG_FUNCTION_ARGS)
  {
  	Relation	rel = (Relation) PG_GETARG_POINTER(0);
  	Datum	   *values = (Datum *) PG_GETARG_POINTER(1);
  	bool	   *isnull = (bool *) PG_GETARG_POINTER(2);
  	ItemPointer ht_ctid = (ItemPointer) PG_GETARG_POINTER(3);
  	Relation	heapRel = (Relation) PG_GETARG_POINTER(4);
  	IndexUniqueCheck checkUnique = (IndexUniqueCheck) PG_GETARG_INT32(5);
  	bool		result;
  	IndexTuple	itup;
  
  	/* generate an index tuple */
  	itup = index_form_tuple(RelationGetDescr(rel), values, isnull);
  	itup->t_tid = *ht_ctid;
  
  	result = _bt_doinsert(rel, itup, checkUnique, heapRel);
  
  	pfree(itup);
  
  	PG_RETURN_BOOL(result);
  }
  
  /*
   *	btgettuple() -- Get the next tuple in the scan.
   */
  Datum
  btgettuple(PG_FUNCTION_ARGS)
  {
  	IndexScanDesc scan = (IndexScanDesc) PG_GETARG_POINTER(0);
  	ScanDirection dir = (ScanDirection) PG_GETARG_INT32(1);
  	BTScanOpaque so = (BTScanOpaque) scan->opaque;
  	bool		res;
  
  	/* btree indexes are never lossy */
  	scan->xs_recheck = false;
  
  	/*
  	 * If we have any array keys, initialize them during first call for a
  	 * scan.  We can't do this in btrescan because we don't know the scan
  	 * direction at that time.
  	 */
  	if (so->numArrayKeys && !BTScanPosIsValid(so->currPos))
  	{
  		/* punt if we have any unsatisfiable array keys */
  		if (so->numArrayKeys < 0)
  			PG_RETURN_BOOL(false);
  
  		_bt_start_array_keys(scan, dir);
  	}
  
  	/* This loop handles advancing to the next array elements, if any */
  	do
  	{
  		/*
  		 * If we've already initialized this scan, we can just advance it in
  		 * the appropriate direction.  If we haven't done so yet, we call
  		 * _bt_first() to get the first item in the scan.
  		 */
  		if (!BTScanPosIsValid(so->currPos))
  			res = _bt_first(scan, dir);
  		else
  		{
  			/*
  			 * Check to see if we should kill the previously-fetched tuple.
  			 */
  			if (scan->kill_prior_tuple)
  			{
  				/*
  				 * Yes, remember it for later. (We'll deal with all such
  				 * tuples at once right before leaving the index page.)  The
  				 * test for numKilled overrun is not just paranoia: if the
  				 * caller reverses direction in the indexscan then the same
  				 * item might get entered multiple times. It's not worth
  				 * trying to optimize that, so we don't detect it, but instead
  				 * just forget any excess entries.
  				 */
  				if (so->killedItems == NULL)
  					so->killedItems = (int *)
  						palloc(MaxIndexTuplesPerPage * sizeof(int));
  				if (so->numKilled < MaxIndexTuplesPerPage)
  					so->killedItems[so->numKilled++] = so->currPos.itemIndex;
  			}
  
  			/*
  			 * Now continue the scan.
  			 */
  			res = _bt_next(scan, dir);
  		}
  
  		/* If we have a tuple, return it ... */
  		if (res)
  			break;
  		/* ... otherwise see if we have more array keys to deal with */
  	} while (so->numArrayKeys && _bt_advance_array_keys(scan, dir));
  
  	PG_RETURN_BOOL(res);
  }
  
  /*
   * btgetbitmap() -- gets all matching tuples, and adds them to a bitmap
   */
  Datum
  btgetbitmap(PG_FUNCTION_ARGS)
  {
  	IndexScanDesc scan = (IndexScanDesc) PG_GETARG_POINTER(0);
  	TIDBitmap  *tbm = (TIDBitmap *) PG_GETARG_POINTER(1);
  	BTScanOpaque so = (BTScanOpaque) scan->opaque;
  	int64		ntids = 0;
  	ItemPointer heapTid;
  
  	/*
  	 * If we have any array keys, initialize them.
  	 */
  	if (so->numArrayKeys)
  	{
  		/* punt if we have any unsatisfiable array keys */
  		if (so->numArrayKeys < 0)
  			PG_RETURN_INT64(ntids);
  
  		_bt_start_array_keys(scan, ForwardScanDirection);
  	}
  
  	/* This loop handles advancing to the next array elements, if any */
  	do
  	{
  		/* Fetch the first page & tuple */
  		if (_bt_first(scan, ForwardScanDirection))
  		{
  			/* Save tuple ID, and continue scanning */
  			heapTid = &scan->xs_ctup.t_self;
  			tbm_add_tuples(tbm, heapTid, 1, false);
  			ntids++;
  
  			for (;;)
  			{
  				/*
  				 * Advance to next tuple within page.  This is the same as the
  				 * easy case in _bt_next().
  				 */
  				if (++so->currPos.itemIndex > so->currPos.lastItem)
  				{
  					/* let _bt_next do the heavy lifting */
  					if (!_bt_next(scan, ForwardScanDirection))
  						break;
  				}
  
  				/* Save tuple ID, and continue scanning */
  				heapTid = &so->currPos.items[so->currPos.itemIndex].heapTid;
  				tbm_add_tuples(tbm, heapTid, 1, false);
  				ntids++;
  			}
  		}
  		/* Now see if we have more array keys to deal with */
  	} while (so->numArrayKeys && _bt_advance_array_keys(scan, ForwardScanDirection));
  
  	PG_RETURN_INT64(ntids);
  }
  
  /*
   *	btbeginscan() -- start a scan on a btree index
   */
  Datum
  btbeginscan(PG_FUNCTION_ARGS)
  {
  	Relation	rel = (Relation) PG_GETARG_POINTER(0);
  	int			nkeys = PG_GETARG_INT32(1);
  	int			norderbys = PG_GETARG_INT32(2);
  	IndexScanDesc scan;
  	BTScanOpaque so;
  
  	/* no order by operators allowed */
  	Assert(norderbys == 0);
  
  	/* get the scan */
  	scan = RelationGetIndexScan(rel, nkeys, norderbys);
  
  	/* allocate private workspace */
  	so = (BTScanOpaque) palloc(sizeof(BTScanOpaqueData));
  	so->currPos.buf = so->markPos.buf = InvalidBuffer;
  	if (scan->numberOfKeys > 0)
  		so->keyData = (ScanKey) palloc(scan->numberOfKeys * sizeof(ScanKeyData));
  	else
  		so->keyData = NULL;
  
  	so->arrayKeyData = NULL;	/* assume no array keys for now */
  	so->numArrayKeys = 0;
  	so->arrayKeys = NULL;
  	so->arrayContext = NULL;
  
  	so->killedItems = NULL;		/* until needed */
  	so->numKilled = 0;
  
  	/*
  	 * We don't know yet whether the scan will be index-only, so we do not
  	 * allocate the tuple workspace arrays until btrescan.  However, we set up
  	 * scan->xs_itupdesc whether we'll need it or not, since that's so cheap.
  	 */
  	so->currTuples = so->markTuples = NULL;
  	so->currPos.nextTupleOffset = 0;
  	so->markPos.nextTupleOffset = 0;
  
  	scan->xs_itupdesc = RelationGetDescr(rel);
  
  	scan->opaque = so;
  
  	PG_RETURN_POINTER(scan);
  }
  
  /*
   *	btrescan() -- rescan an index relation
   */
  Datum
  btrescan(PG_FUNCTION_ARGS)
  {
  	IndexScanDesc scan = (IndexScanDesc) PG_GETARG_POINTER(0);
  	ScanKey		scankey = (ScanKey) PG_GETARG_POINTER(1);
  
  	/* remaining arguments are ignored */
  	BTScanOpaque so = (BTScanOpaque) scan->opaque;
  
  	/* we aren't holding any read locks, but gotta drop the pins */
  	if (BTScanPosIsValid(so->currPos))
  	{
  		/* Before leaving current page, deal with any killed items */
  		if (so->numKilled > 0)
  			_bt_killitems(scan, false);
  		ReleaseBuffer(so->currPos.buf);
  		so->currPos.buf = InvalidBuffer;
  	}
  
  	if (BTScanPosIsValid(so->markPos))
  	{
  		ReleaseBuffer(so->markPos.buf);
  		so->markPos.buf = InvalidBuffer;
  	}
  	so->markItemIndex = -1;
  
  	/*
  	 * Allocate tuple workspace arrays, if needed for an index-only scan and
  	 * not already done in a previous rescan call.  To save on palloc
  	 * overhead, both workspaces are allocated as one palloc block; only this
  	 * function and btendscan know that.
  	 *
  	 * NOTE: this data structure also makes it safe to return data from a
  	 * "name" column, even though btree name_ops uses an underlying storage
  	 * datatype of cstring.  The risk there is that "name" is supposed to be
  	 * padded to NAMEDATALEN, but the actual index tuple is probably shorter.
  	 * However, since we only return data out of tuples sitting in the
  	 * currTuples array, a fetch of NAMEDATALEN bytes can at worst pull some
  	 * data out of the markTuples array --- running off the end of memory for
  	 * a SIGSEGV is not possible.  Yeah, this is ugly as sin, but it beats
  	 * adding special-case treatment for name_ops elsewhere.
  	 */
  	if (scan->xs_want_itup && so->currTuples == NULL)
  	{
  		so->currTuples = (char *) palloc(BLCKSZ * 2);
  		so->markTuples = so->currTuples + BLCKSZ;
  	}
  
  	/*
  	 * Reset the scan keys. Note that keys ordering stuff moved to _bt_first.
  	 * - vadim 05/05/97
  	 */
  	if (scankey && scan->numberOfKeys > 0)
  		memmove(scan->keyData,
  				scankey,
  				scan->numberOfKeys * sizeof(ScanKeyData));
  	so->numberOfKeys = 0;		/* until _bt_preprocess_keys sets it */
  
  	/* If any keys are SK_SEARCHARRAY type, set up array-key info */
  	_bt_preprocess_array_keys(scan);
  
  	PG_RETURN_VOID();
  }
  
  /*
   *	btendscan() -- close down a scan
   */
  Datum
  btendscan(PG_FUNCTION_ARGS)
  {
  	IndexScanDesc scan = (IndexScanDesc) PG_GETARG_POINTER(0);
  	BTScanOpaque so = (BTScanOpaque) scan->opaque;
  
  	/* we aren't holding any read locks, but gotta drop the pins */
  	if (BTScanPosIsValid(so->currPos))
  	{
  		/* Before leaving current page, deal with any killed items */
  		if (so->numKilled > 0)
  			_bt_killitems(scan, false);
  		ReleaseBuffer(so->currPos.buf);
  		so->currPos.buf = InvalidBuffer;
  	}
  
  	if (BTScanPosIsValid(so->markPos))
  	{
  		ReleaseBuffer(so->markPos.buf);
  		so->markPos.buf = InvalidBuffer;
  	}
  	so->markItemIndex = -1;
  
  	/* Release storage */
  	if (so->keyData != NULL)
  		pfree(so->keyData);
  	/* so->arrayKeyData and so->arrayKeys are in arrayContext */
  	if (so->arrayContext != NULL)
  		MemoryContextDelete(so->arrayContext);
  	if (so->killedItems != NULL)
  		pfree(so->killedItems);
  	if (so->currTuples != NULL)
  		pfree(so->currTuples);
  	/* so->markTuples should not be pfree'd, see btrescan */
  	pfree(so);
  
  	PG_RETURN_VOID();
  }
  
  /*
   *	btmarkpos() -- save current scan position
   */
  Datum
  btmarkpos(PG_FUNCTION_ARGS)
  {
  	IndexScanDesc scan = (IndexScanDesc) PG_GETARG_POINTER(0);
  	BTScanOpaque so = (BTScanOpaque) scan->opaque;
  
  	/* we aren't holding any read locks, but gotta drop the pin */
  	if (BTScanPosIsValid(so->markPos))
  	{
  		ReleaseBuffer(so->markPos.buf);
  		so->markPos.buf = InvalidBuffer;
  	}
  
  	/*
  	 * Just record the current itemIndex.  If we later step to next page
  	 * before releasing the marked position, _bt_steppage makes a full copy of
  	 * the currPos struct in markPos.  If (as often happens) the mark is moved
  	 * before we leave the page, we don't have to do that work.
  	 */
  	if (BTScanPosIsValid(so->currPos))
  		so->markItemIndex = so->currPos.itemIndex;
  	else
  		so->markItemIndex = -1;
  
  	/* Also record the current positions of any array keys */
  	if (so->numArrayKeys)
  		_bt_mark_array_keys(scan);
  
  	PG_RETURN_VOID();
  }
  
  /*
   *	btrestrpos() -- restore scan to last saved position
   */
  Datum
  btrestrpos(PG_FUNCTION_ARGS)
  {
  	IndexScanDesc scan = (IndexScanDesc) PG_GETARG_POINTER(0);
  	BTScanOpaque so = (BTScanOpaque) scan->opaque;
  
  	/* Restore the marked positions of any array keys */
  	if (so->numArrayKeys)
  		_bt_restore_array_keys(scan);
  
  	if (so->markItemIndex >= 0)
  	{
  		/*
  		 * The mark position is on the same page we are currently on. Just
  		 * restore the itemIndex.
  		 */
  		so->currPos.itemIndex = so->markItemIndex;
  	}
  	else
  	{
  		/* we aren't holding any read locks, but gotta drop the pin */
  		if (BTScanPosIsValid(so->currPos))
  		{
  			/* Before leaving current page, deal with any killed items */
  			if (so->numKilled > 0 &&
  				so->currPos.buf != so->markPos.buf)
  				_bt_killitems(scan, false);
  			ReleaseBuffer(so->currPos.buf);
  			so->currPos.buf = InvalidBuffer;
  		}
  
  		if (BTScanPosIsValid(so->markPos))
  		{
  			/* bump pin on mark buffer for assignment to current buffer */
  			IncrBufferRefCount(so->markPos.buf);
  			memcpy(&so->currPos, &so->markPos,
  				   offsetof(BTScanPosData, items[1]) +
  				   so->markPos.lastItem * sizeof(BTScanPosItem));
  			if (so->currTuples)
  				memcpy(so->currTuples, so->markTuples,
  					   so->markPos.nextTupleOffset);
  		}
  	}
  
  	PG_RETURN_VOID();
  }
  
  /*
   * Bulk deletion of all index entries pointing to a set of heap tuples.
   * The set of target tuples is specified via a callback routine that tells
   * whether any given heap tuple (identified by ItemPointer) is being deleted.
   *
   * Result: a palloc'd struct containing statistical info for VACUUM displays.
   */
  Datum
  btbulkdelete(PG_FUNCTION_ARGS)
  {
  	IndexVacuumInfo *info = (IndexVacuumInfo *) PG_GETARG_POINTER(0);
  	IndexBulkDeleteResult *volatile stats = (IndexBulkDeleteResult *) PG_GETARG_POINTER(1);
  	IndexBulkDeleteCallback callback = (IndexBulkDeleteCallback) PG_GETARG_POINTER(2);
  	void	   *callback_state = (void *) PG_GETARG_POINTER(3);
  	Relation	rel = info->index;
  	BTCycleId	cycleid;
  
  	/* allocate stats if first time through, else re-use existing struct */
  	if (stats == NULL)
  		stats = (IndexBulkDeleteResult *) palloc0(sizeof(IndexBulkDeleteResult));
  
  	/* Establish the vacuum cycle ID to use for this scan */
  	/* The ENSURE stuff ensures we clean up shared memory on failure */
  	PG_ENSURE_ERROR_CLEANUP(_bt_end_vacuum_callback, PointerGetDatum(rel));
  	{
  		cycleid = _bt_start_vacuum(rel);
  
  		btvacuumscan(info, stats, callback, callback_state, cycleid);
  	}
  	PG_END_ENSURE_ERROR_CLEANUP(_bt_end_vacuum_callback, PointerGetDatum(rel));
  	_bt_end_vacuum(rel);
  
  	PG_RETURN_POINTER(stats);
  }
  
  /*
   * Post-VACUUM cleanup.
   *
   * Result: a palloc'd struct containing statistical info for VACUUM displays.
   */
  Datum
  btvacuumcleanup(PG_FUNCTION_ARGS)
  {
  	IndexVacuumInfo *info = (IndexVacuumInfo *) PG_GETARG_POINTER(0);
  	IndexBulkDeleteResult *stats = (IndexBulkDeleteResult *) PG_GETARG_POINTER(1);
  
  	/* No-op in ANALYZE ONLY mode */
  	if (info->analyze_only)
  		PG_RETURN_POINTER(stats);
  
  	/*
  	 * If btbulkdelete was called, we need not do anything, just return the
  	 * stats from the latest btbulkdelete call.  If it wasn't called, we must
  	 * still do a pass over the index, to recycle any newly-recyclable pages
  	 * and to obtain index statistics.
  	 *
  	 * Since we aren't going to actually delete any leaf items, there's no
  	 * need to go through all the vacuum-cycle-ID pushups.
  	 */
  	if (stats == NULL)
  	{
  		stats = (IndexBulkDeleteResult *) palloc0(sizeof(IndexBulkDeleteResult));
  		btvacuumscan(info, stats, NULL, NULL, 0);
  	}
  
  	/* Finally, vacuum the FSM */
  	IndexFreeSpaceMapVacuum(info->index);
  
  	/*
  	 * It's quite possible for us to be fooled by concurrent page splits into
  	 * double-counting some index tuples, so disbelieve any total that exceeds
  	 * the underlying heap's count ... if we know that accurately.  Otherwise
  	 * this might just make matters worse.
  	 */
  	if (!info->estimated_count)
  	{
  		if (stats->num_index_tuples > info->num_heap_tuples)
  			stats->num_index_tuples = info->num_heap_tuples;
  	}
  
  	PG_RETURN_POINTER(stats);
  }
  
  /*
   * btvacuumscan --- scan the index for VACUUMing purposes
   *
   * This combines the functions of looking for leaf tuples that are deletable
   * according to the vacuum callback, looking for empty pages that can be
   * deleted, and looking for old deleted pages that can be recycled.  Both
   * btbulkdelete and btvacuumcleanup invoke this (the latter only if no
   * btbulkdelete call occurred).
   *
   * The caller is responsible for initially allocating/zeroing a stats struct
   * and for obtaining a vacuum cycle ID if necessary.
   */
  static void
  btvacuumscan(IndexVacuumInfo *info, IndexBulkDeleteResult *stats,
  			 IndexBulkDeleteCallback callback, void *callback_state,
  			 BTCycleId cycleid)
  {
  	Relation	rel = info->index;
  	BTVacState	vstate;
  	BlockNumber num_pages;
  	BlockNumber blkno;
  	bool		needLock;
  
  	/*
  	 * Reset counts that will be incremented during the scan; needed in case
  	 * of multiple scans during a single VACUUM command
  	 */
  	stats->estimated_count = false;
  	stats->num_index_tuples = 0;
  	stats->pages_deleted = 0;
  
  	/* Set up info to pass down to btvacuumpage */
  	vstate.info = info;
  	vstate.stats = stats;
  	vstate.callback = callback;
  	vstate.callback_state = callback_state;
  	vstate.cycleid = cycleid;
  	vstate.lastBlockVacuumed = BTREE_METAPAGE;	/* Initialise at first block */
  	vstate.lastBlockLocked = BTREE_METAPAGE;
  	vstate.totFreePages = 0;
  
  	/* Create a temporary memory context to run _bt_pagedel in */
  	vstate.pagedelcontext = AllocSetContextCreate(CurrentMemoryContext,
  												  "_bt_pagedel",
  												  ALLOCSET_DEFAULT_MINSIZE,
  												  ALLOCSET_DEFAULT_INITSIZE,
  												  ALLOCSET_DEFAULT_MAXSIZE);
  
  	/*
  	 * The outer loop iterates over all index pages except the metapage, in
  	 * physical order (we hope the kernel will cooperate in providing
  	 * read-ahead for speed).  It is critical that we visit all leaf pages,
  	 * including ones added after we start the scan, else we might fail to
  	 * delete some deletable tuples.  Hence, we must repeatedly check the
  	 * relation length.  We must acquire the relation-extension lock while
  	 * doing so to avoid a race condition: if someone else is extending the
  	 * relation, there is a window where bufmgr/smgr have created a new
  	 * all-zero page but it hasn't yet been write-locked by _bt_getbuf(). If
  	 * we manage to scan such a page here, we'll improperly assume it can be
  	 * recycled.  Taking the lock synchronizes things enough to prevent a
  	 * problem: either num_pages won't include the new page, or _bt_getbuf
  	 * already has write lock on the buffer and it will be fully initialized
  	 * before we can examine it.  (See also vacuumlazy.c, which has the same
  	 * issue.)	Also, we need not worry if a page is added immediately after
  	 * we look; the page splitting code already has write-lock on the left
  	 * page before it adds a right page, so we must already have processed any
  	 * tuples due to be moved into such a page.
  	 *
  	 * We can skip locking for new or temp relations, however, since no one
  	 * else could be accessing them.
  	 */
  	needLock = !RELATION_IS_LOCAL(rel);
  
  	blkno = BTREE_METAPAGE + 1;
  	for (;;)
  	{
  		/* Get the current relation length */
  		if (needLock)
  			LockRelationForExtension(rel, ExclusiveLock);
  		num_pages = RelationGetNumberOfBlocks(rel);
  		if (needLock)
  			UnlockRelationForExtension(rel, ExclusiveLock);
  
  		/* Quit if we've scanned the whole relation */
  		if (blkno >= num_pages)
  			break;
  		/* Iterate over pages, then loop back to recheck length */
  		for (; blkno < num_pages; blkno++)
  		{
  			btvacuumpage(&vstate, blkno, blkno);
  		}
  	}
  
  	/*
  	 * If the WAL is replayed in hot standby, the replay process needs to get
  	 * cleanup locks on all index leaf pages, just as we've been doing here.
  	 * However, we won't issue any WAL records about pages that have no items
  	 * to be deleted.  For pages between pages we've vacuumed, the replay code
  	 * will take locks under the direction of the lastBlockVacuumed fields in
  	 * the XLOG_BTREE_VACUUM WAL records.  To cover pages after the last one
  	 * we vacuum, we need to issue a dummy XLOG_BTREE_VACUUM WAL record
  	 * against the last leaf page in the index, if that one wasn't vacuumed.
  	 */
  	if (XLogStandbyInfoActive() &&
  		vstate.lastBlockVacuumed < vstate.lastBlockLocked)
  	{
  		Buffer		buf;
  
  		/*
  		 * The page should be valid, but we can't use _bt_getbuf() because we
  		 * want to use a nondefault buffer access strategy.  Since we aren't
  		 * going to delete any items, getting cleanup lock again is probably
  		 * overkill, but for consistency do that anyway.
  		 */
  		buf = ReadBufferExtended(rel, MAIN_FORKNUM, vstate.lastBlockLocked,
  								 RBM_NORMAL, info->strategy);
  		LockBufferForCleanup(buf);
  		_bt_checkpage(rel, buf);
  		_bt_delitems_vacuum(rel, buf, NULL, 0, vstate.lastBlockVacuumed);
  		_bt_relbuf(rel, buf);
  	}
  
  	MemoryContextDelete(vstate.pagedelcontext);
  
  	/* update statistics */
  	stats->num_pages = num_pages;
  	stats->pages_free = vstate.totFreePages;
  }
  
  /*
   * btvacuumpage --- VACUUM one page
   *
   * This processes a single page for btvacuumscan().  In some cases we
   * must go back and re-examine previously-scanned pages; this routine
   * recurses when necessary to handle that case.
   *
   * blkno is the page to process.  orig_blkno is the highest block number
   * reached by the outer btvacuumscan loop (the same as blkno, unless we
   * are recursing to re-examine a previous page).
   */
  static void
  btvacuumpage(BTVacState *vstate, BlockNumber blkno, BlockNumber orig_blkno)
  {
  	IndexVacuumInfo *info = vstate->info;
  	IndexBulkDeleteResult *stats = vstate->stats;
  	IndexBulkDeleteCallback callback = vstate->callback;
  	void	   *callback_state = vstate->callback_state;
  	Relation	rel = info->index;
  	bool		delete_now;
  	BlockNumber recurse_to;
  	Buffer		buf;
  	Page		page;
  	BTPageOpaque opaque;
  
  restart:
  	delete_now = false;
  	recurse_to = P_NONE;
  
  	/* call vacuum_delay_point while not holding any buffer lock */
  	vacuum_delay_point();
  
  	/*
  	 * We can't use _bt_getbuf() here because it always applies
  	 * _bt_checkpage(), which will barf on an all-zero page. We want to
  	 * recycle all-zero pages, not fail.  Also, we want to use a nondefault
  	 * buffer access strategy.
  	 */
  	buf = ReadBufferExtended(rel, MAIN_FORKNUM, blkno, RBM_NORMAL,
  							 info->strategy);
  	LockBuffer(buf, BT_READ);
  	page = BufferGetPage(buf);
  	opaque = (BTPageOpaque) PageGetSpecialPointer(page);
  	if (!PageIsNew(page))
  		_bt_checkpage(rel, buf);
  
  	/*
  	 * If we are recursing, the only case we want to do anything with is a
  	 * live leaf page having the current vacuum cycle ID.  Any other state
  	 * implies we already saw the page (eg, deleted it as being empty).
  	 */
  	if (blkno != orig_blkno)
  	{
  		if (_bt_page_recyclable(page) ||
  			P_IGNORE(opaque) ||
  			!P_ISLEAF(opaque) ||
  			opaque->btpo_cycleid != vstate->cycleid)
  		{
  			_bt_relbuf(rel, buf);
  			return;
  		}
  	}
  
  	/* Page is valid, see what to do with it */
  	if (_bt_page_recyclable(page))
  	{
  		/* Okay to recycle this page */
  		RecordFreeIndexPage(rel, blkno);
  		vstate->totFreePages++;
  		stats->pages_deleted++;
  	}
  	else if (P_ISDELETED(opaque))
  	{
  		/* Already deleted, but can't recycle yet */
  		stats->pages_deleted++;
  	}
  	else if (P_ISHALFDEAD(opaque))
  	{
  		/* Half-dead, try to delete */
  		delete_now = true;
  	}
  	else if (P_ISLEAF(opaque))
  	{
  		OffsetNumber deletable[MaxOffsetNumber];
  		int			ndeletable;
  		OffsetNumber offnum,
  					minoff,
  					maxoff;
  
  		/*
  		 * Trade in the initial read lock for a super-exclusive write lock on
  		 * this page.  We must get such a lock on every leaf page over the
  		 * course of the vacuum scan, whether or not it actually contains any
  		 * deletable tuples --- see nbtree/README.
  		 */
  		LockBuffer(buf, BUFFER_LOCK_UNLOCK);
  		LockBufferForCleanup(buf);
  
  		/*
  		 * Remember highest leaf page number we've taken cleanup lock on; see
  		 * notes in btvacuumscan
  		 */
  		if (blkno > vstate->lastBlockLocked)
  			vstate->lastBlockLocked = blkno;
  
  		/*
  		 * Check whether we need to recurse back to earlier pages.  What we
  		 * are concerned about is a page split that happened since we started
  		 * the vacuum scan.  If the split moved some tuples to a lower page
  		 * then we might have missed 'em.  If so, set up for tail recursion.
  		 * (Must do this before possibly clearing btpo_cycleid below!)
  		 */
  		if (vstate->cycleid != 0 &&
  			opaque->btpo_cycleid == vstate->cycleid &&
  			!(opaque->btpo_flags & BTP_SPLIT_END) &&
  			!P_RIGHTMOST(opaque) &&
  			opaque->btpo_next < orig_blkno)
  			recurse_to = opaque->btpo_next;
  
  		/*
  		 * Scan over all items to see which ones need deleted according to the
  		 * callback function.
  		 */
  		ndeletable = 0;
  		minoff = P_FIRSTDATAKEY(opaque);
  		maxoff = PageGetMaxOffsetNumber(page);
  		if (callback)
  		{
  			for (offnum = minoff;
  				 offnum <= maxoff;
  				 offnum = OffsetNumberNext(offnum))
  			{
  				IndexTuple	itup;
  				ItemPointer htup;
  
  				itup = (IndexTuple) PageGetItem(page,
  												PageGetItemId(page, offnum));
  				htup = &(itup->t_tid);
  
  				/*
  				 * During Hot Standby we currently assume that
  				 * XLOG_BTREE_VACUUM records do not produce conflicts. That is
  				 * only true as long as the callback function depends only
  				 * upon whether the index tuple refers to heap tuples removed
  				 * in the initial heap scan. When vacuum starts it derives a
  				 * value of OldestXmin. Backends taking later snapshots could
  				 * have a RecentGlobalXmin with a later xid than the vacuum's
  				 * OldestXmin, so it is possible that row versions deleted
  				 * after OldestXmin could be marked as killed by other
  				 * backends. The callback function *could* look at the index
  				 * tuple state in isolation and decide to delete the index
  				 * tuple, though currently it does not. If it ever did, we
  				 * would need to reconsider whether XLOG_BTREE_VACUUM records
  				 * should cause conflicts. If they did cause conflicts they
  				 * would be fairly harsh conflicts, since we haven't yet
  				 * worked out a way to pass a useful value for
  				 * latestRemovedXid on the XLOG_BTREE_VACUUM records. This
  				 * applies to *any* type of index that marks index tuples as
  				 * killed.
  				 */
  				if (callback(htup, callback_state))
  					deletable[ndeletable++] = offnum;
  			}
  		}
  
  		/*
  		 * Apply any needed deletes.  We issue just one _bt_delitems_vacuum()
  		 * call per page, so as to minimize WAL traffic.
  		 */
  		if (ndeletable > 0)
  		{
  			/*
  			 * Notice that the issued XLOG_BTREE_VACUUM WAL record includes an
  			 * instruction to the replay code to get cleanup lock on all pages
  			 * between the previous lastBlockVacuumed and this page.  This
  			 * ensures that WAL replay locks all leaf pages at some point.
  			 *
  			 * Since we can visit leaf pages out-of-order when recursing,
  			 * replay might end up locking such pages an extra time, but it
  			 * doesn't seem worth the amount of bookkeeping it'd take to avoid
  			 * that.
  			 */
  			_bt_delitems_vacuum(rel, buf, deletable, ndeletable,
  								vstate->lastBlockVacuumed);
  
  			/*
  			 * Remember highest leaf page number we've issued a
  			 * XLOG_BTREE_VACUUM WAL record for.
  			 */
  			if (blkno > vstate->lastBlockVacuumed)
  				vstate->lastBlockVacuumed = blkno;
  
  			stats->tuples_removed += ndeletable;
  			/* must recompute maxoff */
  			maxoff = PageGetMaxOffsetNumber(page);
  		}
  		else
  		{
  			/*
  			 * If the page has been split during this vacuum cycle, it seems
  			 * worth expending a write to clear btpo_cycleid even if we don't
  			 * have any deletions to do.  (If we do, _bt_delitems_vacuum takes
  			 * care of this.)  This ensures we won't process the page again.
  			 *
  			 * We treat this like a hint-bit update because there's no need to
  			 * WAL-log it.
  			 */
  			if (vstate->cycleid != 0 &&
  				opaque->btpo_cycleid == vstate->cycleid)
  			{
  				opaque->btpo_cycleid = 0;
  				SetBufferCommitInfoNeedsSave(buf);
  			}
  		}
  
  		/*
  		 * If it's now empty, try to delete; else count the live tuples. We
  		 * don't delete when recursing, though, to avoid putting entries into
  		 * freePages out-of-order (doesn't seem worth any extra code to handle
  		 * the case).
  		 */
  		if (minoff > maxoff)
  			delete_now = (blkno == orig_blkno);
  		else
  			stats->num_index_tuples += maxoff - minoff + 1;
  	}
  
  	if (delete_now)
  	{
  		MemoryContext oldcontext;
  		int			ndel;
  
  		/* Run pagedel in a temp context to avoid memory leakage */
  		MemoryContextReset(vstate->pagedelcontext);
  		oldcontext = MemoryContextSwitchTo(vstate->pagedelcontext);
  
  		ndel = _bt_pagedel(rel, buf, NULL);
  
  		/* count only this page, else may double-count parent */
  		if (ndel)
  			stats->pages_deleted++;
  
  		MemoryContextSwitchTo(oldcontext);
  		/* pagedel released buffer, so we shouldn't */
  	}
  	else
  		_bt_relbuf(rel, buf);
  
  	/*
  	 * This is really tail recursion, but if the compiler is too stupid to
  	 * optimize it as such, we'd eat an uncomfortably large amount of stack
  	 * space per recursion level (due to the deletable[] array). A failure is
  	 * improbable since the number of levels isn't likely to be large ... but
  	 * just in case, let's hand-optimize into a loop.
  	 */
  	if (recurse_to != P_NONE)
  	{
  		blkno = recurse_to;
  		goto restart;
  	}
  }
  
  /*
   *	btcanreturn() -- Check whether btree indexes support index-only scans.
   *
   * btrees always do, so this is trivial.
   */
  Datum
  btcanreturn(PG_FUNCTION_ARGS)
  {
  	PG_RETURN_BOOL(true);
  }
  