C++ LockBuffer函数代码示例

/*
 * Try to find parent for current stack position. Returns correct parent and
 * child's offset in stack->parent. The root page is never released, to
 * to prevent conflict with vacuum process.
 */
static void
ginFindParents(GinBtree btree, GinBtreeStack *stack)
{
	Page		page;
	Buffer		buffer;
	BlockNumber blkno,
				leftmostBlkno;
	OffsetNumber offset;
	GinBtreeStack *root;
	GinBtreeStack *ptr;

	/*
	 * Unwind the stack all the way up to the root, leaving only the root
	 * item.
	 *
	 * Be careful not to release the pin on the root page! The pin on root
	 * page is required to lock out concurrent vacuums on the tree.
	 */
	root = stack->parent;
	while (root->parent)
	{
		ReleaseBuffer(root->buffer);
		root = root->parent;
	}

	Assert(root->blkno == btree->rootBlkno);
	Assert(BufferGetBlockNumber(root->buffer) == btree->rootBlkno);
	root->off = InvalidOffsetNumber;

	blkno = root->blkno;
	buffer = root->buffer;
	offset = InvalidOffsetNumber;

	ptr = (GinBtreeStack *) palloc(sizeof(GinBtreeStack));

	for (;;)
	{
		LockBuffer(buffer, GIN_EXCLUSIVE);
		page = BufferGetPage(buffer);
		if (GinPageIsLeaf(page))
			elog(ERROR, "Lost path");

		if (GinPageIsIncompleteSplit(page))
		{
			Assert(blkno != btree->rootBlkno);
			ptr->blkno = blkno;
			ptr->buffer = buffer;
			/*
			 * parent may be wrong, but if so, the ginFinishSplit call will
			 * recurse to call ginFindParents again to fix it.
			 */
			ptr->parent = root;
			ptr->off = InvalidOffsetNumber;

			ginFinishSplit(btree, ptr, false, NULL);
		}

		leftmostBlkno = btree->getLeftMostChild(btree, page);

		while ((offset = btree->findChildPtr(btree, page, stack->blkno, InvalidOffsetNumber)) == InvalidOffsetNumber)
		{
			blkno = GinPageGetOpaque(page)->rightlink;
			if (blkno == InvalidBlockNumber)
			{
				UnlockReleaseBuffer(buffer);
				break;
			}
			buffer = ginStepRight(buffer, btree->index, GIN_EXCLUSIVE);
			page = BufferGetPage(buffer);

			/* finish any incomplete splits, as above */
			if (GinPageIsIncompleteSplit(page))
			{
				Assert(blkno != btree->rootBlkno);
				ptr->blkno = blkno;
				ptr->buffer = buffer;
				ptr->parent = root;
				ptr->off = InvalidOffsetNumber;

				ginFinishSplit(btree, ptr, false, NULL);
			}
		}

		if (blkno != InvalidBlockNumber)
		{
			ptr->blkno = blkno;
			ptr->buffer = buffer;
			ptr->parent = root; /* it may be wrong, but in next call we will
								 * correct */
			ptr->off = offset;
			stack->parent = ptr;
			return;
		}

		/* Descend down to next level */
//.........这里部分代码省略.........

/*
 * Recursive guts of FreeSpaceMapVacuum
 *
 * Examine the FSM page indicated by addr, as well as its children, updating
 * upper-level nodes that cover the heap block range from start to end-1.
 * (It's okay if end is beyond the actual end of the map.)
 * Return the maximum freespace value on this page.
 *
 * If addr is past the end of the FSM, set *eof_p to true and return 0.
 *
 * This traverses the tree in depth-first order.  The tree is stored
 * physically in depth-first order, so this should be pretty I/O efficient.
 */
static uint8
fsm_vacuum_page(Relation rel, FSMAddress addr,
				BlockNumber start, BlockNumber end,
				bool *eof_p)
{
	Buffer		buf;
	Page		page;
	uint8		max_avail;

	/* Read the page if it exists, or return EOF */
	buf = fsm_readbuf(rel, addr, false);
	if (!BufferIsValid(buf))
	{
		*eof_p = true;
		return 0;
	}
	else
		*eof_p = false;

	page = BufferGetPage(buf);

	/*
	 * If we're above the bottom level, recurse into children, and fix the
	 * information stored about them at this level.
	 */
	if (addr.level > FSM_BOTTOM_LEVEL)
	{
		FSMAddress	fsm_start,
					fsm_end;
		uint16		fsm_start_slot,
					fsm_end_slot;
		int			slot,
					start_slot,
					end_slot;
		bool		eof = false;

		/*
		 * Compute the range of slots we need to update on this page, given
		 * the requested range of heap blocks to consider.  The first slot to
		 * update is the one covering the "start" block, and the last slot is
		 * the one covering "end - 1".  (Some of this work will be duplicated
		 * in each recursive call, but it's cheap enough to not worry about.)
		 */
		fsm_start = fsm_get_location(start, &fsm_start_slot);
		fsm_end = fsm_get_location(end - 1, &fsm_end_slot);

		while (fsm_start.level < addr.level)
		{
			fsm_start = fsm_get_parent(fsm_start, &fsm_start_slot);
			fsm_end = fsm_get_parent(fsm_end, &fsm_end_slot);
		}
		Assert(fsm_start.level == addr.level);

		if (fsm_start.logpageno == addr.logpageno)
			start_slot = fsm_start_slot;
		else if (fsm_start.logpageno > addr.logpageno)
			start_slot = SlotsPerFSMPage;	/* shouldn't get here... */
		else
			start_slot = 0;

		if (fsm_end.logpageno == addr.logpageno)
			end_slot = fsm_end_slot;
		else if (fsm_end.logpageno > addr.logpageno)
			end_slot = SlotsPerFSMPage - 1;
		else
			end_slot = -1;		/* shouldn't get here... */

		for (slot = start_slot; slot <= end_slot; slot++)
		{
			int			child_avail;

			CHECK_FOR_INTERRUPTS();

			/* After we hit end-of-file, just clear the rest of the slots */
			if (!eof)
				child_avail = fsm_vacuum_page(rel, fsm_get_child(addr, slot),
											  start, end,
											  &eof);
			else
				child_avail = 0;

			/* Update information about the child */
			if (fsm_get_avail(page, slot) != child_avail)
			{
				LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);
				fsm_set_avail(page, slot, child_avail);
				MarkBufferDirtyHint(buf, false);
//.........这里部分代码省略.........

/*
 *	visibilitymap_truncate - truncate the visibility map
 *
 * The caller must hold AccessExclusiveLock on the relation, to ensure that
 * other backends receive the smgr invalidation event that this function sends
 * before they access the VM again.
 *
 * nheapblocks is the new size of the heap.
 */
void
visibilitymap_truncate(Relation rel, BlockNumber nheapblocks)
{
	BlockNumber newnblocks;

	/* last remaining block, byte, and bit */
	BlockNumber truncBlock = HEAPBLK_TO_MAPBLOCK(nheapblocks);
	uint32		truncByte = HEAPBLK_TO_MAPBYTE(nheapblocks);
	uint8		truncBit = HEAPBLK_TO_MAPBIT(nheapblocks);

#ifdef TRACE_VISIBILITYMAP
	elog(DEBUG1, "vm_truncate %s %d", RelationGetRelationName(rel), nheapblocks);
#endif

	RelationOpenSmgr(rel);

	/*
	 * If no visibility map has been created yet for this relation, there's
	 * nothing to truncate.
	 */
	if (!smgrexists(rel->rd_smgr, VISIBILITYMAP_FORKNUM))
		return;

	/*
	 * Unless the new size is exactly at a visibility map page boundary, the
	 * tail bits in the last remaining map page, representing truncated heap
	 * blocks, need to be cleared. This is not only tidy, but also necessary
	 * because we don't get a chance to clear the bits if the heap is extended
	 * again.
	 */
	if (truncByte != 0 || truncBit != 0)
	{
		Buffer		mapBuffer;
		Page		page;
		char	   *map;

		newnblocks = truncBlock + 1;

		mapBuffer = vm_readbuf(rel, truncBlock, false);
		if (!BufferIsValid(mapBuffer))
		{
			/* nothing to do, the file was already smaller */
			return;
		}

		page = BufferGetPage(mapBuffer);
		map = PageGetContents(page);

		LockBuffer(mapBuffer, BUFFER_LOCK_EXCLUSIVE);

		/* Clear out the unwanted bytes. */
		MemSet(&map[truncByte + 1], 0, MAPSIZE - (truncByte + 1));

		/*
		 * Mask out the unwanted bits of the last remaining byte.
		 *
		 * ((1 << 0) - 1) = 00000000 ((1 << 1) - 1) = 00000001 ... ((1 << 6) -
		 * 1) = 00111111 ((1 << 7) - 1) = 01111111
		 */
		map[truncByte] &= (1 << truncBit) - 1;

		MarkBufferDirty(mapBuffer);
		UnlockReleaseBuffer(mapBuffer);
	}
	else
		newnblocks = truncBlock;

	if (smgrnblocks(rel->rd_smgr, VISIBILITYMAP_FORKNUM) <= newnblocks)
	{
		/* nothing to do, the file was already smaller than requested size */
		return;
	}

	/* Truncate the unused VM pages, and send smgr inval message */
	smgrtruncate(rel->rd_smgr, VISIBILITYMAP_FORKNUM, newnblocks);

	/*
	 * We might as well update the local smgr_vm_nblocks setting. smgrtruncate
	 * sent an smgr cache inval message, which will cause other backends to
	 * invalidate their copy of smgr_vm_nblocks, and this one too at the next
	 * command boundary.  But this ensures it isn't outright wrong until then.
	 */
	if (rel->rd_smgr)
		rel->rd_smgr->smgr_vm_nblocks = newnblocks;
}

//.........这里部分代码省略.........
				xlrec.is_primary_bucket_page = (buf == bucket_buf) ? true : false;

				XLogBeginInsert();
				XLogRegisterData((char *) &xlrec, SizeOfHashDelete);

				/*
				 * bucket buffer needs to be registered to ensure that we can
				 * acquire a cleanup lock on it during replay.
				 */
				if (!xlrec.is_primary_bucket_page)
					XLogRegisterBuffer(0, bucket_buf, REGBUF_STANDARD | REGBUF_NO_IMAGE);

				XLogRegisterBuffer(1, buf, REGBUF_STANDARD);
				XLogRegisterBufData(1, (char *) deletable,
									ndeletable * sizeof(OffsetNumber));

				recptr = XLogInsert(RM_HASH_ID, XLOG_HASH_DELETE);
				PageSetLSN(BufferGetPage(buf), recptr);
			}

			END_CRIT_SECTION();
		}

		/* bail out if there are no more pages to scan. */
		if (!BlockNumberIsValid(blkno))
			break;

		next_buf = _hash_getbuf_with_strategy(rel, blkno, HASH_WRITE,
											  LH_OVERFLOW_PAGE,
											  bstrategy);

		/*
		 * release the lock on previous page after acquiring the lock on next
		 * page
		 */
		if (retain_pin)
			LockBuffer(buf, BUFFER_LOCK_UNLOCK);
		else
			_hash_relbuf(rel, buf);

		buf = next_buf;
	}

	/*
	 * lock the bucket page to clear the garbage flag and squeeze the bucket.
	 * if the current buffer is same as bucket buffer, then we already have
	 * lock on bucket page.
	 */
	if (buf != bucket_buf)
	{
		_hash_relbuf(rel, buf);
		LockBuffer(bucket_buf, BUFFER_LOCK_EXCLUSIVE);
	}

	/*
	 * Clear the garbage flag from bucket after deleting the tuples that are
	 * moved by split.  We purposefully clear the flag before squeeze bucket,
	 * so that after restart, vacuum shouldn't again try to delete the moved
	 * by split tuples.
	 */
	if (split_cleanup)
	{
		HashPageOpaque bucket_opaque;
		Page		page;

		page = BufferGetPage(bucket_buf);
		bucket_opaque = (HashPageOpaque) PageGetSpecialPointer(page);

		/* No ereport(ERROR) until changes are logged */
		START_CRIT_SECTION();

		bucket_opaque->hasho_flag &= ~LH_BUCKET_NEEDS_SPLIT_CLEANUP;
		MarkBufferDirty(bucket_buf);

		/* XLOG stuff */
		if (RelationNeedsWAL(rel))
		{
			XLogRecPtr	recptr;

			XLogBeginInsert();
			XLogRegisterBuffer(0, bucket_buf, REGBUF_STANDARD);

			recptr = XLogInsert(RM_HASH_ID, XLOG_HASH_SPLIT_CLEANUP);
			PageSetLSN(page, recptr);
		}

		END_CRIT_SECTION();
	}

	/*
	 * If we have deleted anything, try to compact free space.  For squeezing
	 * the bucket, we must have a cleanup lock, else it can impact the
	 * ordering of tuples for a scan that has started before it.
	 */
	if (bucket_dirty && IsBufferCleanupOK(bucket_buf))
		_hash_squeezebucket(rel, cur_bucket, bucket_blkno, bucket_buf,
							bstrategy);
	else
		LockBuffer(bucket_buf, BUFFER_LOCK_UNLOCK);
}

/*
 * Read a FSM page.
 *
 * If the page doesn't exist, InvalidBuffer is returned, or if 'extend' is
 * true, the FSM file is extended.
 */
static Buffer
fsm_readbuf(Relation rel, FSMAddress addr, bool extend)
{
	BlockNumber blkno = fsm_logical_to_physical(addr);
	Buffer		buf;

	RelationOpenSmgr(rel);

	/*
	 * If we haven't cached the size of the FSM yet, check it first.  Also
	 * recheck if the requested block seems to be past end, since our cached
	 * value might be stale.  (We send smgr inval messages on truncation, but
	 * not on extension.)
	 */
	if (rel->rd_smgr->smgr_fsm_nblocks == InvalidBlockNumber ||
		blkno >= rel->rd_smgr->smgr_fsm_nblocks)
	{
		if (smgrexists(rel->rd_smgr, FSM_FORKNUM))
			rel->rd_smgr->smgr_fsm_nblocks = smgrnblocks(rel->rd_smgr,
														 FSM_FORKNUM);
		else
			rel->rd_smgr->smgr_fsm_nblocks = 0;
	}

	/* Handle requests beyond EOF */
	if (blkno >= rel->rd_smgr->smgr_fsm_nblocks)
	{
		if (extend)
			fsm_extend(rel, blkno + 1);
		else
			return InvalidBuffer;
	}

	/*
	 * Use ZERO_ON_ERROR mode, and initialize the page if necessary. The FSM
	 * information is not accurate anyway, so it's better to clear corrupt
	 * pages than error out. Since the FSM changes are not WAL-logged, the
	 * so-called torn page problem on crash can lead to pages with corrupt
	 * headers, for example.
	 *
	 * The initialize-the-page part is trickier than it looks, because of the
	 * possibility of multiple backends doing this concurrently, and our
	 * desire to not uselessly take the buffer lock in the normal path where
	 * the page is OK.  We must take the lock to initialize the page, so
	 * recheck page newness after we have the lock, in case someone else
	 * already did it.  Also, because we initially check PageIsNew with no
	 * lock, it's possible to fall through and return the buffer while someone
	 * else is still initializing the page (i.e., we might see pd_upper as set
	 * but other page header fields are still zeroes).  This is harmless for
	 * callers that will take a buffer lock themselves, but some callers
	 * inspect the page without any lock at all.  The latter is OK only so
	 * long as it doesn't depend on the page header having correct contents.
	 * Current usage is safe because PageGetContents() does not require that.
	 */
	buf = ReadBufferExtended(rel, FSM_FORKNUM, blkno, RBM_ZERO_ON_ERROR, NULL);
	if (PageIsNew(BufferGetPage(buf)))
	{
		LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);
		if (PageIsNew(BufferGetPage(buf)))
			PageInit(BufferGetPage(buf), BLCKSZ, 0);
		LockBuffer(buf, BUFFER_LOCK_UNLOCK);
	}
	return buf;
}

/*
 * Insert all matching tuples into a bitmap.
 */
int64
blgetbitmap(IndexScanDesc scan, TIDBitmap *tbm)
{
	int64		ntids = 0;
	BlockNumber blkno = BLOOM_HEAD_BLKNO,
				npages;
	int			i;
	BufferAccessStrategy bas;
	BloomScanOpaque so = (BloomScanOpaque) scan->opaque;

	if (so->sign == NULL)
	{
		/* New search: have to calculate search signature */
		ScanKey		skey = scan->keyData;

		so->sign = palloc0(sizeof(BloomSignatureWord) * so->state.opts.bloomLength);

		for (i = 0; i < scan->numberOfKeys; i++)
		{
			/*
			 * Assume bloom-indexable operators to be strict, so nothing could
			 * be found for NULL key.
			 */
			if (skey->sk_flags & SK_ISNULL)
			{
				pfree(so->sign);
				so->sign = NULL;
				return 0;
			}

			/* Add next value to the signature */
			signValue(&so->state, so->sign, skey->sk_argument,
					  skey->sk_attno - 1);

			skey++;
		}
	}

	/*
	 * We're going to read the whole index. This is why we use appropriate
	 * buffer access strategy.
	 */
	bas = GetAccessStrategy(BAS_BULKREAD);
	npages = RelationGetNumberOfBlocks(scan->indexRelation);

	for (blkno = BLOOM_HEAD_BLKNO; blkno < npages; blkno++)
	{
		Buffer		buffer;
		Page		page;

		buffer = ReadBufferExtended(scan->indexRelation, MAIN_FORKNUM,
									blkno, RBM_NORMAL, bas);

		LockBuffer(buffer, BUFFER_LOCK_SHARE);
		page = BufferGetPage(buffer);
		TestForOldSnapshot(scan->xs_snapshot, scan->indexRelation, page);

		if (!PageIsNew(page) && !BloomPageIsDeleted(page))
		{
			OffsetNumber offset,
						maxOffset = BloomPageGetMaxOffset(page);

			for (offset = 1; offset <= maxOffset; offset++)
			{
				BloomTuple *itup = BloomPageGetTuple(&so->state, page, offset);
				bool		res = true;

				/* Check index signature with scan signature */
				for (i = 0; i < so->state.opts.bloomLength; i++)
				{
					if ((itup->sign[i] & so->sign[i]) != so->sign[i])
					{
						res = false;
						break;
					}
				}

				/* Add matching tuples to bitmap */
				if (res)
				{
					tbm_add_tuples(tbm, &itup->heapPtr, 1, true);
					ntids++;
				}
			}
		}

		UnlockReleaseBuffer(buffer);
		CHECK_FOR_INTERRUPTS();
	}
	FreeAccessStrategy(bas);

	return ntids;
}

/*
 *	hashgettuple() -- Get the next tuple in the scan.
 */
bool
hashgettuple(IndexScanDesc scan, ScanDirection dir)
{
	HashScanOpaque so = (HashScanOpaque) scan->opaque;
	Relation	rel = scan->indexRelation;
	Buffer		buf;
	Page		page;
	OffsetNumber offnum;
	ItemPointer current;
	bool		res;

	/* Hash indexes are always lossy since we store only the hash code */
	scan->xs_recheck = true;

	/*
	 * We hold pin but not lock on current buffer while outside the hash AM.
	 * Reacquire the read lock here.
	 */
	if (BufferIsValid(so->hashso_curbuf))
		LockBuffer(so->hashso_curbuf, BUFFER_LOCK_SHARE);

	/*
	 * 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 a routine to
	 * get the first item in the scan.
	 */
	current = &(so->hashso_curpos);
	if (ItemPointerIsValid(current))
	{
		/*
		 * An insertion into the current index page could have happened while
		 * we didn't have read lock on it.  Re-find our position by looking
		 * for the TID we previously returned.  (Because we hold a pin on the
		 * primary bucket page, no deletions or splits could have occurred;
		 * therefore we can expect that the TID still exists in the current
		 * index page, at an offset >= where we were.)
		 */
		OffsetNumber maxoffnum;

		buf = so->hashso_curbuf;
		Assert(BufferIsValid(buf));
		page = BufferGetPage(buf);

		/*
		 * We don't need test for old snapshot here as the current buffer is
		 * pinned, so vacuum can't clean the page.
		 */
		maxoffnum = PageGetMaxOffsetNumber(page);
		for (offnum = ItemPointerGetOffsetNumber(current);
			 offnum <= maxoffnum;
			 offnum = OffsetNumberNext(offnum))
		{
			IndexTuple	itup;

			itup = (IndexTuple) PageGetItem(page, PageGetItemId(page, offnum));
			if (ItemPointerEquals(&(so->hashso_heappos), &(itup->t_tid)))
				break;
		}
		if (offnum > maxoffnum)
			elog(ERROR, "failed to re-find scan position within index \"%s\"",
				 RelationGetRelationName(rel));
		ItemPointerSetOffsetNumber(current, offnum);

		/*
		 * Check to see if we should kill the previously-fetched tuple.
		 */
		if (scan->kill_prior_tuple)
		{
			/*
			 * Yes, so remember it for later. (We'll deal with all such
			 * tuples at once right after leaving the index page or at
			 * end of scan.) In case if caller reverses the indexscan
			 * direction it is quite possible that the same item might
			 * get entered multiple times. But, we don't detect that;
			 * instead, we just forget any excess entries.
			 */
			if (so->killedItems == NULL)
				so->killedItems = palloc(MaxIndexTuplesPerPage *
										 sizeof(HashScanPosItem));

			if (so->numKilled < MaxIndexTuplesPerPage)
			{
				so->killedItems[so->numKilled].heapTid = so->hashso_heappos;
				so->killedItems[so->numKilled].indexOffset =
							ItemPointerGetOffsetNumber(&(so->hashso_curpos));
				so->numKilled++;
			}
		}

		/*
		 * Now continue the scan.
		 */
		res = _hash_next(scan, dir);
	}
	else
		res = _hash_first(scan, dir);

//.........这里部分代码省略.........

/*
 *	_hash_init() -- Initialize the metadata page of a hash index,
 *				the initial buckets, and the initial bitmap page.
 *
 * The initial number of buckets is dependent on num_tuples, an estimate
 * of the number of tuples to be loaded into the index initially.  The
 * chosen number of buckets is returned.
 *
 * We are fairly cavalier about locking here, since we know that no one else
 * could be accessing this index.  In particular the rule about not holding
 * multiple buffer locks is ignored.
 */
uint32
_hash_init(Relation rel, double num_tuples, ForkNumber forkNum)
{
	Buffer		metabuf;
	Buffer		buf;
	Buffer		bitmapbuf;
	Page		pg;
	HashMetaPage metap;
	RegProcedure procid;
	int32		data_width;
	int32		item_width;
	int32		ffactor;
	uint32		num_buckets;
	uint32		i;
	bool		use_wal;

	/* safety check */
	if (RelationGetNumberOfBlocksInFork(rel, forkNum) != 0)
		elog(ERROR, "cannot initialize non-empty hash index \"%s\"",
			 RelationGetRelationName(rel));

	/*
	 * WAL log creation of pages if the relation is persistent, or this is the
	 * init fork.  Init forks for unlogged relations always need to be WAL
	 * logged.
	 */
	use_wal = RelationNeedsWAL(rel) || forkNum == INIT_FORKNUM;

	/*
	 * Determine the target fill factor (in tuples per bucket) for this index.
	 * The idea is to make the fill factor correspond to pages about as full
	 * as the user-settable fillfactor parameter says.  We can compute it
	 * exactly since the index datatype (i.e. uint32 hash key) is fixed-width.
	 */
	data_width = sizeof(uint32);
	item_width = MAXALIGN(sizeof(IndexTupleData)) + MAXALIGN(data_width) +
		sizeof(ItemIdData);		/* include the line pointer */
	ffactor = RelationGetTargetPageUsage(rel, HASH_DEFAULT_FILLFACTOR) / item_width;
	/* keep to a sane range */
	if (ffactor < 10)
		ffactor = 10;

	procid = index_getprocid(rel, 1, HASHSTANDARD_PROC);

	/*
	 * We initialize the metapage, the first N bucket pages, and the first
	 * bitmap page in sequence, using _hash_getnewbuf to cause smgrextend()
	 * calls to occur.  This ensures that the smgr level has the right idea of
	 * the physical index length.
	 *
	 * Critical section not required, because on error the creation of the
	 * whole relation will be rolled back.
	 */
	metabuf = _hash_getnewbuf(rel, HASH_METAPAGE, forkNum);
	_hash_init_metabuffer(metabuf, num_tuples, procid, ffactor, false);
	MarkBufferDirty(metabuf);

	pg = BufferGetPage(metabuf);
	metap = HashPageGetMeta(pg);

	/* XLOG stuff */
	if (use_wal)
	{
		xl_hash_init_meta_page xlrec;
		XLogRecPtr	recptr;

		xlrec.num_tuples = num_tuples;
		xlrec.procid = metap->hashm_procid;
		xlrec.ffactor = metap->hashm_ffactor;

		XLogBeginInsert();
		XLogRegisterData((char *) &xlrec, SizeOfHashInitMetaPage);
		XLogRegisterBuffer(0, metabuf, REGBUF_WILL_INIT);

		recptr = XLogInsert(RM_HASH_ID, XLOG_HASH_INIT_META_PAGE);

		PageSetLSN(BufferGetPage(metabuf), recptr);
	}

	num_buckets = metap->hashm_maxbucket + 1;

	/*
	 * Release buffer lock on the metapage while we initialize buckets.
	 * Otherwise, we'll be in interrupt holdoff and the CHECK_FOR_INTERRUPTS
	 * won't accomplish anything.  It's a bad idea to hold buffer locks for
	 * long intervals in any case, since that can block the bgwriter.
	 */
	LockBuffer(metabuf, BUFFER_LOCK_UNLOCK);
//.........这里部分代码省略.........

/*
 * Attempt to expand the hash table by creating one new bucket.
 *
 * This will silently do nothing if we don't get cleanup lock on old or
 * new bucket.
 *
 * Complete the pending splits and remove the tuples from old bucket,
 * if there are any left over from the previous split.
 *
 * The caller must hold a pin, but no lock, on the metapage buffer.
 * The buffer is returned in the same state.
 */
void
_hash_expandtable(Relation rel, Buffer metabuf)
{
	HashMetaPage metap;
	Bucket		old_bucket;
	Bucket		new_bucket;
	uint32		spare_ndx;
	BlockNumber start_oblkno;
	BlockNumber start_nblkno;
	Buffer		buf_nblkno;
	Buffer		buf_oblkno;
	Page		opage;
	Page		npage;
	HashPageOpaque oopaque;
	HashPageOpaque nopaque;
	uint32		maxbucket;
	uint32		highmask;
	uint32		lowmask;
	bool		metap_update_masks = false;
	bool		metap_update_splitpoint = false;

restart_expand:

	/*
	 * Write-lock the meta page.  It used to be necessary to acquire a
	 * heavyweight lock to begin a split, but that is no longer required.
	 */
	LockBuffer(metabuf, BUFFER_LOCK_EXCLUSIVE);

	_hash_checkpage(rel, metabuf, LH_META_PAGE);
	metap = HashPageGetMeta(BufferGetPage(metabuf));

	/*
	 * Check to see if split is still needed; someone else might have already
	 * done one while we waited for the lock.
	 *
	 * Make sure this stays in sync with _hash_doinsert()
	 */
	if (metap->hashm_ntuples <=
		(double) metap->hashm_ffactor * (metap->hashm_maxbucket + 1))
		goto fail;

	/*
	 * Can't split anymore if maxbucket has reached its maximum possible
	 * value.
	 *
	 * Ideally we'd allow bucket numbers up to UINT_MAX-1 (no higher because
	 * the calculation maxbucket+1 mustn't overflow).  Currently we restrict
	 * to half that because of overflow looping in _hash_log2() and
	 * insufficient space in hashm_spares[].  It's moot anyway because an
	 * index with 2^32 buckets would certainly overflow BlockNumber and hence
	 * _hash_alloc_buckets() would fail, but if we supported buckets smaller
	 * than a disk block then this would be an independent constraint.
	 *
	 * If you change this, see also the maximum initial number of buckets in
	 * _hash_init().
	 */
	if (metap->hashm_maxbucket >= (uint32) 0x7FFFFFFE)
		goto fail;

	/*
	 * Determine which bucket is to be split, and attempt to take cleanup lock
	 * on the old bucket.  If we can't get the lock, give up.
	 *
	 * The cleanup lock protects us not only against other backends, but
	 * against our own backend as well.
	 *
	 * The cleanup lock is mainly to protect the split from concurrent
	 * inserts. See src/backend/access/hash/README, Lock Definitions for
	 * further details.  Due to this locking restriction, if there is any
	 * pending scan, the split will give up which is not good, but harmless.
	 */
	new_bucket = metap->hashm_maxbucket + 1;

	old_bucket = (new_bucket & metap->hashm_lowmask);

	start_oblkno = BUCKET_TO_BLKNO(metap, old_bucket);

	buf_oblkno = _hash_getbuf_with_condlock_cleanup(rel, start_oblkno, LH_BUCKET_PAGE);
	if (!buf_oblkno)
		goto fail;

	opage = BufferGetPage(buf_oblkno);
	oopaque = (HashPageOpaque) PageGetSpecialPointer(opage);

	/*
	 * We want to finish the split from a bucket as there is no apparent
	 * benefit by not doing so and it will make the code complicated to finish
//.........这里部分代码省略.........

//.........这里部分代码省略.........
				 */
				new_itup = CopyIndexTuple(itup);

				/*
				 * mark the index tuple as moved by split, such tuples are
				 * skipped by scan if there is split in progress for a bucket.
				 */
				new_itup->t_info |= INDEX_MOVED_BY_SPLIT_MASK;

				/*
				 * insert the tuple into the new bucket.  if it doesn't fit on
				 * the current page in the new bucket, we must allocate a new
				 * overflow page and place the tuple on that page instead.
				 */
				itemsz = IndexTupleDSize(*new_itup);
				itemsz = MAXALIGN(itemsz);

				if (PageGetFreeSpaceForMultipleTuples(npage, nitups + 1) < (all_tups_size + itemsz))
				{
					/*
					 * Change the shared buffer state in critical section,
					 * otherwise any error could make it unrecoverable.
					 */
					START_CRIT_SECTION();

					_hash_pgaddmultitup(rel, nbuf, itups, itup_offsets, nitups);
					MarkBufferDirty(nbuf);
					/* log the split operation before releasing the lock */
					log_split_page(rel, nbuf);

					END_CRIT_SECTION();

					/* drop lock, but keep pin */
					LockBuffer(nbuf, BUFFER_LOCK_UNLOCK);

					/* be tidy */
					for (i = 0; i < nitups; i++)
						pfree(itups[i]);
					nitups = 0;
					all_tups_size = 0;

					/* chain to a new overflow page */
					nbuf = _hash_addovflpage(rel, metabuf, nbuf, (nbuf == bucket_nbuf) ? true : false);
					npage = BufferGetPage(nbuf);
					nopaque = (HashPageOpaque) PageGetSpecialPointer(npage);
				}

				itups[nitups++] = new_itup;
				all_tups_size += itemsz;
			}
			else
			{
				/*
				 * the tuple stays on this page, so nothing to do.
				 */
				Assert(bucket == obucket);
			}
		}

		oblkno = oopaque->hasho_nextblkno;

		/* retain the pin on the old primary bucket */
		if (obuf == bucket_obuf)
			LockBuffer(obuf, BUFFER_LOCK_UNLOCK);
		else
			_hash_relbuf(rel, obuf);

/*
 *	_hash_finish_split() -- Finish the previously interrupted split operation
 *
 * To complete the split operation, we form the hash table of TIDs in new
 * bucket which is then used by split operation to skip tuples that are
 * already moved before the split operation was previously interrupted.
 *
 * The caller must hold a pin, but no lock, on the metapage and old bucket's
 * primary page buffer.  The buffers are returned in the same state.  (The
 * metapage is only touched if it becomes necessary to add or remove overflow
 * pages.)
 */
void
_hash_finish_split(Relation rel, Buffer metabuf, Buffer obuf, Bucket obucket,
				   uint32 maxbucket, uint32 highmask, uint32 lowmask)
{
	HASHCTL		hash_ctl;
	HTAB	   *tidhtab;
	Buffer		bucket_nbuf = InvalidBuffer;
	Buffer		nbuf;
	Page		npage;
	BlockNumber nblkno;
	BlockNumber bucket_nblkno;
	HashPageOpaque npageopaque;
	Bucket		nbucket;
	bool		found;

	/* Initialize hash tables used to track TIDs */
	memset(&hash_ctl, 0, sizeof(hash_ctl));
	hash_ctl.keysize = sizeof(ItemPointerData);
	hash_ctl.entrysize = sizeof(ItemPointerData);
	hash_ctl.hcxt = CurrentMemoryContext;

	tidhtab =
		hash_create("bucket ctids",
					256,		/* arbitrary initial size */
					&hash_ctl,
					HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);

	bucket_nblkno = nblkno = _hash_get_newblock_from_oldbucket(rel, obucket);

	/*
	 * Scan the new bucket and build hash table of TIDs
	 */
	for (;;)
	{
		OffsetNumber noffnum;
		OffsetNumber nmaxoffnum;

		nbuf = _hash_getbuf(rel, nblkno, HASH_READ,
							LH_BUCKET_PAGE | LH_OVERFLOW_PAGE);

		/* remember the primary bucket buffer to acquire cleanup lock on it. */
		if (nblkno == bucket_nblkno)
			bucket_nbuf = nbuf;

		npage = BufferGetPage(nbuf);
		npageopaque = (HashPageOpaque) PageGetSpecialPointer(npage);

		/* Scan each tuple in new page */
		nmaxoffnum = PageGetMaxOffsetNumber(npage);
		for (noffnum = FirstOffsetNumber;
			 noffnum <= nmaxoffnum;
			 noffnum = OffsetNumberNext(noffnum))
		{
			IndexTuple	itup;

			/* Fetch the item's TID and insert it in hash table. */
			itup = (IndexTuple) PageGetItem(npage,
											PageGetItemId(npage, noffnum));

			(void) hash_search(tidhtab, &itup->t_tid, HASH_ENTER, &found);

			Assert(!found);
		}

		nblkno = npageopaque->hasho_nextblkno;

		/*
		 * release our write lock without modifying buffer and ensure to
		 * retain the pin on primary bucket.
		 */
		if (nbuf == bucket_nbuf)
			LockBuffer(nbuf, BUFFER_LOCK_UNLOCK);
		else
			_hash_relbuf(rel, nbuf);

		/* Exit loop if no more overflow pages in new bucket */
		if (!BlockNumberIsValid(nblkno))
			break;
	}

	/*
	 * Conditionally get the cleanup lock on old and new buckets to perform
	 * the split operation.  If we don't get the cleanup locks, silently give
	 * up and next insertion on old bucket will try again to complete the
	 * split.
	 */
	if (!ConditionalLockBufferForCleanup(obuf))
	{
//.........这里部分代码省略.........

/*
 * Initialize a sequence's relation with the specified tuple as content
 */
static void
fill_seq_with_data(Relation rel, HeapTuple tuple)
{
	Buffer		buf;
	Page		page;
	sequence_magic *sm;
	OffsetNumber offnum;

	/* Initialize first page of relation with special magic number */

	buf = ReadBuffer(rel, P_NEW);
	Assert(BufferGetBlockNumber(buf) == 0);

	page = BufferGetPage(buf);

	PageInit(page, BufferGetPageSize(buf), sizeof(sequence_magic));
	sm = (sequence_magic *) PageGetSpecialPointer(page);
	sm->magic = SEQ_MAGIC;

	/* Now insert sequence tuple */

	LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);

	/*
	 * Since VACUUM does not process sequences, we have to force the tuple to
	 * have xmin = FrozenTransactionId now.  Otherwise it would become
	 * invisible to SELECTs after 2G transactions.  It is okay to do this
	 * because if the current transaction aborts, no other xact will ever
	 * examine the sequence tuple anyway.
	 */
	HeapTupleHeaderSetXmin(tuple->t_data, FrozenTransactionId);
	HeapTupleHeaderSetXminFrozen(tuple->t_data);
	HeapTupleHeaderSetCmin(tuple->t_data, FirstCommandId);
	HeapTupleHeaderSetXmax(tuple->t_data, InvalidTransactionId);
	tuple->t_data->t_infomask |= HEAP_XMAX_INVALID;
	ItemPointerSet(&tuple->t_data->t_ctid, 0, FirstOffsetNumber);

	/* check the comment above nextval_internal()'s equivalent call. */
	if (RelationNeedsWAL(rel))
		GetTopTransactionId();

	START_CRIT_SECTION();

	MarkBufferDirty(buf);

	offnum = PageAddItem(page, (Item) tuple->t_data, tuple->t_len,
						 InvalidOffsetNumber, false, false);
	if (offnum != FirstOffsetNumber)
		elog(ERROR, "failed to add sequence tuple to page");

	/* XLOG stuff */
	if (RelationNeedsWAL(rel))
	{
		xl_seq_rec	xlrec;
		XLogRecPtr	recptr;

		XLogBeginInsert();
		XLogRegisterBuffer(0, buf, REGBUF_WILL_INIT);

		xlrec.node = rel->rd_node;

		XLogRegisterData((char *) &xlrec, sizeof(xl_seq_rec));
		XLogRegisterData((char *) tuple->t_data, tuple->t_len);

		recptr = XLogInsert(RM_SEQ_ID, XLOG_SEQ_LOG);

		PageSetLSN(page, recptr);
	}

	END_CRIT_SECTION();

	UnlockReleaseBuffer(buf);
}

/*
 * Descend the tree to the leaf page that contains or would contain the key
 * we're searching for. The key should already be filled in 'btree', in
 * tree-type specific manner. If btree->fullScan is true, descends to the
 * leftmost leaf page.
 *
 * If 'searchmode' is false, on return stack->buffer is exclusively locked,
 * and the stack represents the full path to the root. Otherwise stack->buffer
 * is share-locked, and stack->parent is NULL.
 */
GinBtreeStack *
ginFindLeafPage(GinBtree btree, bool searchMode)
{
	GinBtreeStack *stack;

	stack = (GinBtreeStack *) palloc(sizeof(GinBtreeStack));
	stack->blkno = btree->rootBlkno;
	stack->buffer = ReadBuffer(btree->index, btree->rootBlkno);
	stack->parent = NULL;
	stack->predictNumber = 1;

	for (;;)
	{
		Page		page;
		BlockNumber child;
		int			access;

		stack->off = InvalidOffsetNumber;

		page = BufferGetPage(stack->buffer);

		access = ginTraverseLock(stack->buffer, searchMode);

		/*
		 * If we're going to modify the tree, finish any incomplete splits we
		 * encounter on the way.
		 */
		if (!searchMode && GinPageIsIncompleteSplit(page))
			ginFinishSplit(btree, stack, false, NULL);

		/*
		 * ok, page is correctly locked, we should check to move right ..,
		 * root never has a right link, so small optimization
		 */
		while (btree->fullScan == FALSE && stack->blkno != btree->rootBlkno &&
			   btree->isMoveRight(btree, page))
		{
			BlockNumber rightlink = GinPageGetOpaque(page)->rightlink;

			if (rightlink == InvalidBlockNumber)
				/* rightmost page */
				break;

			stack->buffer = ginStepRight(stack->buffer, btree->index, access);
			stack->blkno = rightlink;
			page = BufferGetPage(stack->buffer);

			if (!searchMode && GinPageIsIncompleteSplit(page))
				ginFinishSplit(btree, stack, false, NULL);
		}

		if (GinPageIsLeaf(page))	/* we found, return locked page */
			return stack;

		/* now we have correct buffer, try to find child */
		child = btree->findChildPage(btree, stack);

		LockBuffer(stack->buffer, GIN_UNLOCK);
		Assert(child != InvalidBlockNumber);
		Assert(stack->blkno != child);

		if (searchMode)
		{
			/* in search mode we may forget path to leaf */
			stack->blkno = child;
			stack->buffer = ReleaseAndReadBuffer(stack->buffer, btree->index, stack->blkno);
		}
		else
		{
			GinBtreeStack *ptr = (GinBtreeStack *) palloc(sizeof(GinBtreeStack));

			ptr->parent = stack;
			stack = ptr;
			stack->blkno = child;
			stack->buffer = ReadBuffer(btree->index, stack->blkno);
			stack->predictNumber = 1;
		}
	}
}

/*
 * Finish a split by inserting the downlink for the new page to parent.
 *
 * On entry, stack->buffer is exclusively locked.
 *
 * If freestack is true, all the buffers are released and unlocked as we
 * crawl up the tree, and 'stack' is freed. Otherwise stack->buffer is kept
 * locked, and stack is unmodified, except for possibly moving right to find
 * the correct parent of page.
 */
static void
ginFinishSplit(GinBtree btree, GinBtreeStack *stack, bool freestack,
			   GinStatsData *buildStats)
{
	Page		page;
	bool		done;
	bool		first = true;

	/*
	 * freestack == false when we encounter an incompletely split page during a
	 * scan, while freestack == true is used in the normal scenario that a
	 * split is finished right after the initial insert.
	 */
	if (!freestack)
		elog(DEBUG1, "finishing incomplete split of block %u in gin index \"%s\"",
			 stack->blkno, RelationGetRelationName(btree->index));

	/* this loop crawls up the stack until the insertion is complete */
	do
	{
		GinBtreeStack *parent = stack->parent;
		void	   *insertdata;
		BlockNumber updateblkno;

		/* search parent to lock */
		LockBuffer(parent->buffer, GIN_EXCLUSIVE);

		/*
		 * If the parent page was incompletely split, finish that split first,
		 * then continue with the current one.
		 *
		 * Note: we have to finish *all* incomplete splits we encounter, even
		 * if we have to move right. Otherwise we might choose as the target
		 * a page that has no downlink in the parent, and splitting it further
		 * would fail.
		 */
		if (GinPageIsIncompleteSplit(BufferGetPage(parent->buffer)))
			ginFinishSplit(btree, parent, false, buildStats);

		/* move right if it's needed */
		page = BufferGetPage(parent->buffer);
		while ((parent->off = btree->findChildPtr(btree, page, stack->blkno, parent->off)) == InvalidOffsetNumber)
		{
			if (GinPageRightMost(page))
			{
				/*
				 * rightmost page, but we don't find parent, we should use
				 * plain search...
				 */
				LockBuffer(parent->buffer, GIN_UNLOCK);
				ginFindParents(btree, stack);
				parent = stack->parent;
				Assert(parent != NULL);
				break;
			}

			parent->buffer = ginStepRight(parent->buffer, btree->index, GIN_EXCLUSIVE);
			parent->blkno = BufferGetBlockNumber(parent->buffer);
			page = BufferGetPage(parent->buffer);

			if (GinPageIsIncompleteSplit(BufferGetPage(parent->buffer)))
				ginFinishSplit(btree, parent, false, buildStats);
		}

		/* insert the downlink */
		insertdata = btree->prepareDownlink(btree, stack->buffer);
		updateblkno = GinPageGetOpaque(BufferGetPage(stack->buffer))->rightlink;
		done = ginPlaceToPage(btree, parent,
							  insertdata, updateblkno,
							  stack->buffer, buildStats);
		pfree(insertdata);

		/*
		 * If the caller requested to free the stack, unlock and release the
		 * child buffer now. Otherwise keep it pinned and locked, but if we
		 * have to recurse up the tree, we can unlock the upper pages, only
		 * keeping the page at the bottom of the stack locked.
		 */
		if (!first || freestack)
			LockBuffer(stack->buffer, GIN_UNLOCK);
		if (freestack)
		{
			ReleaseBuffer(stack->buffer);
			pfree(stack);
		}
		stack = parent;

		first = false;
	} while (!done);

//.........这里部分代码省略.........

/* ----------------
 *		index_getnext - get the next heap tuple from a scan
 *
 * The result is the next heap tuple satisfying the scan keys and the
 * snapshot, or NULL if no more matching tuples exist.	On success,
 * the buffer containing the heap tuple is pinned (the pin will be dropped
 * at the next index_getnext or index_endscan).
 *
 * Note: caller must check scan->xs_recheck, and perform rechecking of the
 * scan keys if required.  We do not do that here because we don't have
 * enough information to do it efficiently in the general case.
 * ----------------
 */
HeapTuple
index_getnext(IndexScanDesc scan, ScanDirection direction)
{
	HeapTuple	heapTuple = &scan->xs_ctup;
	ItemPointer tid = &heapTuple->t_self;
	FmgrInfo   *procedure;
	bool		all_dead = false;

	SCAN_CHECKS;
	GET_SCAN_PROCEDURE(amgettuple);

	Assert(TransactionIdIsValid(RecentGlobalXmin));

	for (;;)
	{
		bool	got_heap_tuple;

		if (scan->xs_continue_hot)
		{
			/*
			 * We are resuming scan of a HOT chain after having returned an
			 * earlier member.	Must still hold pin on current heap page.
			 */
			Assert(BufferIsValid(scan->xs_cbuf));
			Assert(ItemPointerGetBlockNumber(tid) ==
				   BufferGetBlockNumber(scan->xs_cbuf));
		}
		else
		{
			bool		found;
			Buffer		prev_buf;

			/*
			 * If we scanned a whole HOT chain and found only dead tuples,
			 * tell index AM to kill its entry for that TID. We do not do this
			 * when in recovery because it may violate MVCC to do so. see
			 * comments in RelationGetIndexScan().
			 */
			if (!scan->xactStartedInRecovery)
				scan->kill_prior_tuple = all_dead;

			/*
			 * The AM's gettuple proc finds the next index entry matching the
			 * scan keys, and puts the TID in xs_ctup.t_self (ie, *tid). It
			 * should also set scan->xs_recheck, though we pay no attention to
			 * that here.
			 */
			found = DatumGetBool(FunctionCall2(procedure,
											   PointerGetDatum(scan),
											   Int32GetDatum(direction)));

			/* Reset kill flag immediately for safety */
			scan->kill_prior_tuple = false;

			/* If we're out of index entries, break out of outer loop */
			if (!found)
				break;

			pgstat_count_index_tuples(scan->indexRelation, 1);

			/* Switch to correct buffer if we don't have it already */
			prev_buf = scan->xs_cbuf;
			scan->xs_cbuf = ReleaseAndReadBuffer(scan->xs_cbuf,
												 scan->heapRelation,
											 ItemPointerGetBlockNumber(tid));

			/*
			 * Prune page, but only if we weren't already on this page
			 */
			if (prev_buf != scan->xs_cbuf)
				heap_page_prune_opt(scan->heapRelation, scan->xs_cbuf,
									RecentGlobalXmin);
		}

		/* Obtain share-lock on the buffer so we can examine visibility */
		LockBuffer(scan->xs_cbuf, BUFFER_LOCK_SHARE);
		got_heap_tuple = heap_hot_search_buffer(tid, scan->heapRelation,
												scan->xs_cbuf,
												scan->xs_snapshot,
												&scan->xs_ctup,
												&all_dead,
												!scan->xs_continue_hot);
		LockBuffer(scan->xs_cbuf, BUFFER_LOCK_UNLOCK);

		if (got_heap_tuple)
		{
			/*
//.........这里部分代码省略.........