nbtree.c

postgresql8.3.4源码,开源数据库

		 * 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));
		}
	}

	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);

	/*
	 * 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);
	}

	/*
	 * During a non-FULL vacuum 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. (We
	 * can't check this during btbulkdelete.)
	 */
	if (!info->vacuum_full)
	{
		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->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.freePages = NULL;	/* temporarily */
	vstate.nFreePages = 0;
	vstate.maxFreePages = 0;
	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);

		/* Allocate freePages after we read num_pages the first time */
		if (vstate.freePages == NULL)
		{
			/* No point in remembering more than MaxFSMPages pages */
			vstate.maxFreePages = MaxFSMPages;
			if ((BlockNumber) vstate.maxFreePages > num_pages)
				vstate.maxFreePages = (int) num_pages;
			vstate.freePages = (BlockNumber *)
				palloc(vstate.maxFreePages * sizeof(BlockNumber));
		}

		/* 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);
		}
	}

	/*
	 * During VACUUM FULL, we truncate off any recyclable pages at the end of
	 * the index.  In a normal vacuum it'd be unsafe to do this except by
	 * acquiring exclusive lock on the index and then rechecking all the
	 * pages; doesn't seem worth it.
	 */
	if (info->vacuum_full && vstate.nFreePages > 0)
	{
		BlockNumber new_pages = num_pages;

		while (vstate.nFreePages > 0 &&
			   vstate.freePages[vstate.nFreePages - 1] == new_pages - 1)
		{
			new_pages--;
			stats->pages_deleted--;
			vstate.nFreePages--;
			vstate.totFreePages = vstate.nFreePages;	/* can't be more */
		}
		if (new_pages != num_pages)
		{
			/*
			 * Okay to truncate.
			 */
			RelationTruncate(rel, new_pages);

			/* update statistics */
			stats->pages_removed += num_pages - new_pages;

			num_pages = new_pages;
		}
	}

	/*
	 * Update the shared Free Space Map with the info we now have about free
	 * pages in the index, discarding any old info the map may have. We do not
	 * need to sort the page numbers; they're in order already.
	 */
	RecordIndexFreeSpace(&rel->rd_node, vstate.totFreePages,
						 vstate.nFreePages, vstate.freePages);

	pfree(vstate.freePages);

	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 = ReadBufferWithStrategy(rel, blkno, 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). In
	 * particular, we don't want to risk adding it to freePages twice.
	 */
	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 */
		if (vstate->nFreePages < vstate->maxFreePages)
			vstate->freePages[vstate->nFreePages++] = 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);

		/*
		 * 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);
				if (callback(htup, callback_state))
					deletable[ndeletable++] = offnum;
			}
		}

		/*
		 * Apply any needed deletes.  We issue just one _bt_delitems() call
		 * per page, so as to minimize WAL traffic.
		 */
		if (ndeletable > 0)
		{
			_bt_delitems(rel, buf, deletable, ndeletable);
			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 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, info->vacuum_full);

		/* count only this page, else may double-count parent */
		if (ndel)
			stats->pages_deleted++;

		/*
		 * During VACUUM FULL it's okay to recycle deleted pages immediately,
		 * since there can be no other transactions scanning the index.  Note
		 * that we will only recycle the current page and not any parent pages
		 * that _bt_pagedel might have recursed to; this seems reasonable in
		 * the name of simplicity.	(Trying to do otherwise would mean we'd
		 * have to sort the list of recyclable pages we're building.)
		 */
		if (ndel && info->vacuum_full)
		{
			if (vstate->nFreePages < vstate->maxFreePages)
				vstate->freePages[vstate->nFreePages++] = blkno;
			vstate->totFreePages++;
		}

		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;
	}
}