postgres/src/backend/access/nbtree/nbtree.c

/*-------------------------------------------------------------------------
 *
 * 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) 1996-2018, 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/nbtxlog.h"
#include "access/relscan.h"
#include "access/xlog.h"
#include "commands/vacuum.h"
#include "miscadmin.h"
#include "nodes/execnodes.h"
#include "pgstat.h"
#include "postmaster/autovacuum.h"
#include "storage/condition_variable.h"
#include "storage/indexfsm.h"
#include "storage/ipc.h"
#include "storage/lmgr.h"
#include "storage/smgr.h"
#include "utils/builtins.h"
#include "utils/index_selfuncs.h"
#include "utils/memutils.h"


/* 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 */
	TransactionId oldestBtpoXact;
	MemoryContext pagedelcontext;
} BTVacState;

/*
 * BTPARALLEL_NOT_INITIALIZED indicates that the scan has not started.
 *
 * BTPARALLEL_ADVANCING indicates that some process is advancing the scan to
 * a new page; others must wait.
 *
 * BTPARALLEL_IDLE indicates that no backend is currently advancing the scan
 * to a new page; some process can start doing that.
 *
 * BTPARALLEL_DONE indicates that the scan is complete (including error exit).
 * We reach this state once for every distinct combination of array keys.
 */
typedef enum
{
	BTPARALLEL_NOT_INITIALIZED,
	BTPARALLEL_ADVANCING,
	BTPARALLEL_IDLE,
	BTPARALLEL_DONE
} BTPS_State;

/*
 * BTParallelScanDescData contains btree specific shared information required
 * for parallel scan.
 */
typedef struct BTParallelScanDescData
{
	BlockNumber btps_scanPage;	/* latest or next page to be scanned */
	BTPS_State	btps_pageStatus;	/* indicates whether next page is
									 * available for scan. see above for
									 * possible states of parallel scan. */
	int			btps_arrayKeyCount; /* count indicating number of array scan
									 * keys processed by parallel scan */
	slock_t		btps_mutex;		/* protects above variables */
	ConditionVariable btps_cv;	/* used to synchronize parallel scan */
}			BTParallelScanDescData;

typedef struct BTParallelScanDescData *BTParallelScanDesc;


static void btvacuumscan(IndexVacuumInfo *info, IndexBulkDeleteResult *stats,
			 IndexBulkDeleteCallback callback, void *callback_state,
			 BTCycleId cycleid);
static void btvacuumpage(BTVacState *vstate, BlockNumber blkno,
			 BlockNumber orig_blkno);


/*
 * Btree handler function: return IndexAmRoutine with access method parameters
 * and callbacks.
 */
Datum
bthandler(PG_FUNCTION_ARGS)
{
	IndexAmRoutine *amroutine = makeNode(IndexAmRoutine);

	amroutine->amstrategies = BTMaxStrategyNumber;
	amroutine->amsupport = BTNProcs;
	amroutine->amcanorder = true;
	amroutine->amcanorderbyop = false;
	amroutine->amcanbackward = true;
	amroutine->amcanunique = true;
	amroutine->amcanmulticol = true;
	amroutine->amoptionalkey = true;
	amroutine->amsearcharray = true;
	amroutine->amsearchnulls = true;
	amroutine->amstorage = false;
	amroutine->amclusterable = true;
	amroutine->ampredlocks = true;
	amroutine->amcanparallel = true;
	amroutine->amcaninclude = true;
	amroutine->amkeytype = InvalidOid;

	amroutine->ambuild = btbuild;
	amroutine->ambuildempty = btbuildempty;
	amroutine->aminsert = btinsert;
	amroutine->ambulkdelete = btbulkdelete;
	amroutine->amvacuumcleanup = btvacuumcleanup;
	amroutine->amcanreturn = btcanreturn;
	amroutine->amcostestimate = btcostestimate;
	amroutine->amoptions = btoptions;
	amroutine->amproperty = btproperty;
	amroutine->amvalidate = btvalidate;
	amroutine->ambeginscan = btbeginscan;
	amroutine->amrescan = btrescan;
	amroutine->amgettuple = btgettuple;
	amroutine->amgetbitmap = btgetbitmap;
	amroutine->amendscan = btendscan;
	amroutine->ammarkpos = btmarkpos;
	amroutine->amrestrpos = btrestrpos;
	amroutine->amestimateparallelscan = btestimateparallelscan;
	amroutine->aminitparallelscan = btinitparallelscan;
	amroutine->amparallelrescan = btparallelrescan;

	PG_RETURN_POINTER(amroutine);
}

/*
 *	btbuildempty() -- build an empty btree index in the initialization fork
 */
void
btbuildempty(Relation index)
{
	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.
	 */
	PageSetChecksumInplace(metapage, BTREE_METAPAGE);
	smgrwrite(index->rd_smgr, INIT_FORKNUM, BTREE_METAPAGE,
			  (char *) metapage, true);
	log_newpage(&index->rd_smgr->smgr_rnode.node, INIT_FORKNUM,
				BTREE_METAPAGE, metapage, true);

	/*
	 * 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);
}

/*
 *	btinsert() -- insert an index tuple into a btree.
 *
 *		Descend the tree recursively, find the appropriate location for our
 *		new tuple, and put it there.
 */
bool
btinsert(Relation rel, Datum *values, bool *isnull,
		 ItemPointer ht_ctid, Relation heapRel,
		 IndexUniqueCheck checkUnique,
		 IndexInfo *indexInfo)
{
	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);

	return result;
}

/*
 *	btgettuple() -- Get the next tuple in the scan.
 */
bool
btgettuple(IndexScanDesc scan, ScanDirection dir)
{
	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)
			return 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));

	return res;
}

/*
 * btgetbitmap() -- gets all matching tuples, and adds them to a bitmap
 */
int64
btgetbitmap(IndexScanDesc scan, TIDBitmap *tbm)
{
	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)
			return 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));

	return ntids;
}

/*
 *	btbeginscan() -- start a scan on a btree index
 */
IndexScanDesc
btbeginscan(Relation rel, int nkeys, int norderbys)
{
	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));
	BTScanPosInvalidate(so->currPos);
	BTScanPosInvalidate(so->markPos);
	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;

	scan->xs_itupdesc = RelationGetDescr(rel);

	scan->opaque = so;

	return scan;
}

/*
 *	btrescan() -- rescan an index relation
 */
void
btrescan(IndexScanDesc scan, ScanKey scankey, int nscankeys,
		 ScanKey orderbys, int norderbys)
{
	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);
		BTScanPosUnpinIfPinned(so->currPos);
		BTScanPosInvalidate(so->currPos);
	}

	so->markItemIndex = -1;
	so->arrayKeyCount = 0;
	BTScanPosUnpinIfPinned(so->markPos);
	BTScanPosInvalidate(so->markPos);

	/*
	 * 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);
}

/*
 *	btendscan() -- close down a scan
 */
void
btendscan(IndexScanDesc scan)
{
	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);
		BTScanPosUnpinIfPinned(so->currPos);
	}

	so->markItemIndex = -1;
	BTScanPosUnpinIfPinned(so->markPos);

	/* No need to invalidate positions, the RAM is about to be freed. */

	/* 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);
}

/*
 *	btmarkpos() -- save current scan position
 */
void
btmarkpos(IndexScanDesc scan)
{
	BTScanOpaque so = (BTScanOpaque) scan->opaque;

	/* There may be an old mark with a pin (but no lock). */
	BTScanPosUnpinIfPinned(so->markPos);

	/*
	 * 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
	{
		BTScanPosInvalidate(so->markPos);
		so->markItemIndex = -1;
	}

	/* Also record the current positions of any array keys */
	if (so->numArrayKeys)
		_bt_mark_array_keys(scan);
}

/*
 *	btrestrpos() -- restore scan to last saved position
 */
void
btrestrpos(IndexScanDesc scan)
{
	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 scan has never moved to a new page since the last mark.  Just
		 * restore the itemIndex.
		 *
		 * NB: In this case we can't count on anything in so->markPos to be
		 * accurate.
		 */
		so->currPos.itemIndex = so->markItemIndex;
	}
	else
	{
		/*
		 * The scan moved to a new page after last mark or restore, and we are
		 * now restoring to the marked page.  We aren't holding any read
		 * locks, but if we're still holding the pin for the current position,
		 * we must drop it.
		 */
		if (BTScanPosIsValid(so->currPos))
		{
			/* Before leaving current page, deal with any killed items */
			if (so->numKilled > 0)
				_bt_killitems(scan);
			BTScanPosUnpinIfPinned(so->currPos);
		}

		if (BTScanPosIsValid(so->markPos))
		{
			/* bump pin on mark buffer for assignment to current buffer */
			if (BTScanPosIsPinned(so->markPos))
				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);
		}
		else
			BTScanPosInvalidate(so->currPos);
	}
}

/*
 * btestimateparallelscan -- estimate storage for BTParallelScanDescData
 */
Size
btestimateparallelscan(void)
{
	return sizeof(BTParallelScanDescData);
}

/*
 * btinitparallelscan -- initialize BTParallelScanDesc for parallel btree scan
 */
void
btinitparallelscan(void *target)
{
	BTParallelScanDesc bt_target = (BTParallelScanDesc) target;

	SpinLockInit(&bt_target->btps_mutex);
	bt_target->btps_scanPage = InvalidBlockNumber;
	bt_target->btps_pageStatus = BTPARALLEL_NOT_INITIALIZED;
	bt_target->btps_arrayKeyCount = 0;
	ConditionVariableInit(&bt_target->btps_cv);
}

/*
 *	btparallelrescan() -- reset parallel scan
 */
void
btparallelrescan(IndexScanDesc scan)
{
	BTParallelScanDesc btscan;
	ParallelIndexScanDesc parallel_scan = scan->parallel_scan;

	Assert(parallel_scan);

	btscan = (BTParallelScanDesc) OffsetToPointer((void *) parallel_scan,
												  parallel_scan->ps_offset);

	/*
	 * In theory, we don't need to acquire the spinlock here, because there
	 * shouldn't be any other workers running at this point, but we do so for
	 * consistency.
	 */
	SpinLockAcquire(&btscan->btps_mutex);
	btscan->btps_scanPage = InvalidBlockNumber;
	btscan->btps_pageStatus = BTPARALLEL_NOT_INITIALIZED;
	btscan->btps_arrayKeyCount = 0;
	SpinLockRelease(&btscan->btps_mutex);
}

/*
 * _bt_parallel_seize() -- Begin the process of advancing the scan to a new
 *		page.  Other scans must wait until we call bt_parallel_release() or
 *		bt_parallel_done().
 *
 * The return value is true if we successfully seized the scan and false
 * if we did not.  The latter case occurs if no pages remain for the current
 * set of scankeys.
 *
 * If the return value is true, *pageno returns the next or current page
 * of the scan (depending on the scan direction).  An invalid block number
 * means the scan hasn't yet started, and P_NONE means we've reached the end.
 * The first time a participating process reaches the last page, it will return
 * true and set *pageno to P_NONE; after that, further attempts to seize the
 * scan will return false.
 *
 * Callers should ignore the value of pageno if the return value is false.
 */
bool
_bt_parallel_seize(IndexScanDesc scan, BlockNumber *pageno)
{
	BTScanOpaque so = (BTScanOpaque) scan->opaque;
	BTPS_State	pageStatus;
	bool		exit_loop = false;
	bool		status = true;
	ParallelIndexScanDesc parallel_scan = scan->parallel_scan;
	BTParallelScanDesc btscan;

	*pageno = P_NONE;

	btscan = (BTParallelScanDesc) OffsetToPointer((void *) parallel_scan,
												  parallel_scan->ps_offset);

	while (1)
	{
		SpinLockAcquire(&btscan->btps_mutex);
		pageStatus = btscan->btps_pageStatus;

		if (so->arrayKeyCount < btscan->btps_arrayKeyCount)
		{
			/* Parallel scan has already advanced to a new set of scankeys. */
			status = false;
		}
		else if (pageStatus == BTPARALLEL_DONE)
		{
			/*
			 * We're done with this set of scankeys.  This may be the end, or
			 * there could be more sets to try.
			 */
			status = false;
		}
		else if (pageStatus != BTPARALLEL_ADVANCING)
		{
			/*
			 * We have successfully seized control of the scan for the purpose
			 * of advancing it to a new page!
			 */
			btscan->btps_pageStatus = BTPARALLEL_ADVANCING;
			*pageno = btscan->btps_scanPage;
			exit_loop = true;
		}
		SpinLockRelease(&btscan->btps_mutex);
		if (exit_loop || !status)
			break;
		ConditionVariableSleep(&btscan->btps_cv, WAIT_EVENT_BTREE_PAGE);
	}
	ConditionVariableCancelSleep();

	return status;
}

/*
 * _bt_parallel_release() -- Complete the process of advancing the scan to a
 *		new page.  We now have the new value btps_scanPage; some other backend
 *		can now begin advancing the scan.
 */
void
_bt_parallel_release(IndexScanDesc scan, BlockNumber scan_page)
{
	ParallelIndexScanDesc parallel_scan = scan->parallel_scan;
	BTParallelScanDesc btscan;

	btscan = (BTParallelScanDesc) OffsetToPointer((void *) parallel_scan,
												  parallel_scan->ps_offset);

	SpinLockAcquire(&btscan->btps_mutex);
	btscan->btps_scanPage = scan_page;
	btscan->btps_pageStatus = BTPARALLEL_IDLE;
	SpinLockRelease(&btscan->btps_mutex);
	ConditionVariableSignal(&btscan->btps_cv);
}

/*
 * _bt_parallel_done() -- Mark the parallel scan as complete.
 *
 * When there are no pages left to scan, this function should be called to
 * notify other workers.  Otherwise, they might wait forever for the scan to
 * advance to the next page.
 */
void
_bt_parallel_done(IndexScanDesc scan)
{
	BTScanOpaque so = (BTScanOpaque) scan->opaque;
	ParallelIndexScanDesc parallel_scan = scan->parallel_scan;
	BTParallelScanDesc btscan;
	bool		status_changed = false;

	/* Do nothing, for non-parallel scans */
	if (parallel_scan == NULL)
		return;

	btscan = (BTParallelScanDesc) OffsetToPointer((void *) parallel_scan,
												  parallel_scan->ps_offset);

	/*
	 * Mark the parallel scan as done for this combination of scan keys,
	 * unless some other process already did so.  See also
	 * _bt_advance_array_keys.
	 */
	SpinLockAcquire(&btscan->btps_mutex);
	if (so->arrayKeyCount >= btscan->btps_arrayKeyCount &&
		btscan->btps_pageStatus != BTPARALLEL_DONE)
	{
		btscan->btps_pageStatus = BTPARALLEL_DONE;
		status_changed = true;
	}
	SpinLockRelease(&btscan->btps_mutex);

	/* wake up all the workers associated with this parallel scan */
	if (status_changed)
		ConditionVariableBroadcast(&btscan->btps_cv);
}

/*
 * _bt_parallel_advance_array_keys() -- Advances the parallel scan for array
 *			keys.
 *
 * Updates the count of array keys processed for both local and parallel
 * scans.
 */
void
_bt_parallel_advance_array_keys(IndexScanDesc scan)
{
	BTScanOpaque so = (BTScanOpaque) scan->opaque;
	ParallelIndexScanDesc parallel_scan = scan->parallel_scan;
	BTParallelScanDesc btscan;

	btscan = (BTParallelScanDesc) OffsetToPointer((void *) parallel_scan,
												  parallel_scan->ps_offset);

	so->arrayKeyCount++;
	SpinLockAcquire(&btscan->btps_mutex);
	if (btscan->btps_pageStatus == BTPARALLEL_DONE)
	{
		btscan->btps_scanPage = InvalidBlockNumber;
		btscan->btps_pageStatus = BTPARALLEL_NOT_INITIALIZED;
		btscan->btps_arrayKeyCount++;
	}
	SpinLockRelease(&btscan->btps_mutex);
}

/*
 * _bt_vacuum_needs_cleanup() -- Checks if index needs cleanup
 *
 * Called by btvacuumcleanup when btbulkdelete was never called because no
 * tuples need to be deleted.
 *
 * When we return false, VACUUM can even skip the cleanup-only call to
 * btvacuumscan (i.e. there will be no btvacuumscan call for this index at
 * all).  Otherwise, a cleanup-only btvacuumscan call is required.
 */
static bool
_bt_vacuum_needs_cleanup(IndexVacuumInfo *info)
{
	Buffer		metabuf;
	Page		metapg;
	BTMetaPageData *metad;
	bool		result = false;

	metabuf = _bt_getbuf(info->index, BTREE_METAPAGE, BT_READ);
	metapg = BufferGetPage(metabuf);
	metad = BTPageGetMeta(metapg);

	if (metad->btm_version < BTREE_VERSION)
	{
		/*
		 * Do cleanup if metapage needs upgrade, because we don't have
		 * cleanup-related meta-information yet.
		 */
		result = true;
	}
	else if (TransactionIdIsValid(metad->btm_oldest_btpo_xact) &&
			 TransactionIdPrecedes(metad->btm_oldest_btpo_xact,
								   RecentGlobalXmin))
	{
		/*
		 * If any oldest btpo.xact from a previously deleted page in the index
		 * is older than RecentGlobalXmin, then at least one deleted page can
		 * be recycled -- don't skip cleanup.
		 *
		 * Note that btvacuumpage currently doesn't make any effort to
		 * recognize when a recycled page is already in the FSM (i.e. put
		 * there by a previous VACUUM operation).  We have to be conservative
		 * because the FSM isn't crash safe.  Hopefully recycled pages get
		 * reused before too long.
		 */
		result = true;
	}
	else
	{
		StdRdOptions *relopts;
		float8		cleanup_scale_factor;
		float8		prev_num_heap_tuples;

		/*
		 * If table receives enough insertions and no cleanup was performed,
		 * then index would appear have stale statistics.  If scale factor is
		 * set, we avoid that by performing cleanup if the number of inserted
		 * tuples exceeds vacuum_cleanup_index_scale_factor fraction of
		 * original tuples count.
		 */
		relopts = (StdRdOptions *) info->index->rd_options;
		cleanup_scale_factor = (relopts &&
								relopts->vacuum_cleanup_index_scale_factor >= 0)
			? relopts->vacuum_cleanup_index_scale_factor
			: vacuum_cleanup_index_scale_factor;
		prev_num_heap_tuples = metad->btm_last_cleanup_num_heap_tuples;

		if (cleanup_scale_factor <= 0 ||
			prev_num_heap_tuples <= 0 ||
			(info->num_heap_tuples - prev_num_heap_tuples) /
			prev_num_heap_tuples >= cleanup_scale_factor)
			result = true;
	}

	_bt_relbuf(info->index, metabuf);
	return result;
}

/*
 * 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.
 */
IndexBulkDeleteResult *
btbulkdelete(IndexVacuumInfo *info, IndexBulkDeleteResult *stats,
			 IndexBulkDeleteCallback callback, void *callback_state)
{
	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);

	return stats;
}

/*
 * Post-VACUUM cleanup.
 *
 * Result: a palloc'd struct containing statistical info for VACUUM displays.
 */
IndexBulkDeleteResult *
btvacuumcleanup(IndexVacuumInfo *info, IndexBulkDeleteResult *stats)
{
	/* No-op in ANALYZE ONLY mode */
	if (info->analyze_only)
		return 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 might
	 * still need to do a pass over the index, to recycle any newly-recyclable
	 * pages or to obtain index statistics.  _bt_vacuum_needs_cleanup
	 * determines if either are needed.
	 *
	 * 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)
	{
		/* Check if we need a cleanup */
		if (!_bt_vacuum_needs_cleanup(info))
			return NULL;

		stats = (IndexBulkDeleteResult *) palloc0(sizeof(IndexBulkDeleteResult));
		btvacuumscan(info, stats, NULL, NULL, 0);
	}

	/*
	 * 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;
	}

	return 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 and _bt_vacuum_needs_cleanup returned true).
 * Note that this is also where the metadata used by _bt_vacuum_needs_cleanup
 * is maintained.
 *
 * 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;
	vstate.oldestBtpoXact = InvalidTransactionId;

	/* Create a temporary memory context to run _bt_pagedel in */
	vstate.pagedelcontext = AllocSetContextCreate(CurrentMemoryContext,
												  "_bt_pagedel",
												  ALLOCSET_DEFAULT_SIZES);

	/*
	 * 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);
		}
	}

	/*
	 * Check to see if we need to issue one final WAL record for this index,
	 * which may be needed for correctness on a hot standby node when non-MVCC
	 * index scans could take place.
	 *
	 * 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);

	/*
	 * Maintain a count of the oldest btpo.xact and current number of heap
	 * tuples in the metapage (for the benefit of _bt_vacuum_needs_cleanup).
	 * The oldest page is typically a page deleted by a previous VACUUM
	 * operation.
	 */
	_bt_update_meta_cleanup_info(rel, vstate.oldestBtpoXact,
								 info->num_heap_tuples);

	/*
	 * If we found any recyclable pages (and recorded them in the FSM), then
	 * forcibly update the upper-level FSM pages to ensure that searchers can
	 * find them.  It's possible that the pages were also found during
	 * previous scans and so this is a waste of time, but it's cheap enough
	 * relative to scanning the index that it shouldn't matter much, and
	 * making sure that free pages are available sooner not later seems
	 * worthwhile.
	 *
	 * Note that if no recyclable pages exist, we don't bother vacuuming the
	 * FSM at all.
	 */
	if (vstate.totFreePages > 0)
		IndexFreeSpaceMapVacuum(rel);

	/* 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 = NULL;

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);
	if (!PageIsNew(page))
	{
		_bt_checkpage(rel, buf);
		opaque = (BTPageOpaque) PageGetSpecialPointer(page);
	}

	/*
	 * 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 (which could be leaf or internal) */
		RecordFreeIndexPage(rel, blkno);
		vstate->totFreePages++;
		stats->pages_deleted++;
	}
	else if (P_ISDELETED(opaque))
	{
		/*
		 * Already deleted page (which could be leaf or internal).  Can't
		 * recycle yet.
		 */
		stats->pages_deleted++;

		/* Maintain the oldest btpo.xact */
		if (!TransactionIdIsValid(vstate->oldestBtpoXact) ||
			TransactionIdPrecedes(opaque->btpo.xact, vstate->oldestBtpoXact))
			vstate->oldestBtpoXact = opaque->btpo.xact;
	}
	else if (P_ISHALFDEAD(opaque))
	{
		/*
		 * Half-dead leaf page.  Try to delete now.  Might update
		 * oldestBtpoXact and pages_deleted below.
		 */
		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
			 * all information to the replay code to allow it to get a cleanup
			 * lock on all pages between the previous lastBlockVacuumed and
			 * this page. This ensures that WAL replay locks all leaf pages at
			 * some point, which is important should non-MVCC scans be
			 * requested. This is currently unused on standby, but we record
			 * it anyway, so that the WAL contains the required information.
			 *
			 * 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 leaf 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;
				MarkBufferDirtyHint(buf, true);
			}
		}

		/*
		 * If the leaf page is now empty, try to delete it; 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, &vstate->oldestBtpoXact);

		/* 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.
 */
bool
btcanreturn(Relation index, int attno)
{
	return true;
}