postgres/src/backend/access/gin/ginfast.c

/*-------------------------------------------------------------------------
 *
 * ginfast.c
 *	  Fast insert routines for the Postgres inverted index access method.
 *	  Pending entries are stored in linear list of pages.  Later on
 *	  (typically during VACUUM), ginInsertCleanup() will be invoked to
 *	  transfer pending entries into the regular index structure.  This
 *	  wins because bulk insertion is much more efficient than retail.
 *
 * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *			$PostgreSQL: pgsql/src/backend/access/gin/ginfast.c,v 1.2 2009/03/24 22:06:03 tgl Exp $
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "access/genam.h"
#include "access/gin.h"
#include "access/tuptoaster.h"
#include "catalog/index.h"
#include "commands/vacuum.h"
#include "miscadmin.h"
#include "storage/bufmgr.h"
#include "utils/memutils.h"


#define GIN_PAGE_FREESIZE \
	( BLCKSZ - MAXALIGN(SizeOfPageHeaderData) - MAXALIGN(sizeof(GinPageOpaqueData)) )

typedef struct DatumArray
{
	Datum	*values;			/* expansible array */
	int32	 nvalues;			/* current number of valid entries */
	int32	 maxvalues;			/* allocated size of array */
} DatumArray;


/*
 * Build a pending-list page from the given array of tuples, and write it out.
 */
static int32
writeListPage(Relation index, Buffer buffer,
			  IndexTuple *tuples, int32 ntuples, BlockNumber rightlink)
{
	Page			page = BufferGetPage(buffer);
	int 			i, freesize, size=0;
	OffsetNumber	l, off;
	char		   *workspace;
	char		   *ptr;

	/* workspace could be a local array; we use palloc for alignment */
	workspace = palloc(BLCKSZ);

	START_CRIT_SECTION();

	GinInitBuffer(buffer, GIN_LIST);

	off = FirstOffsetNumber;
	ptr = workspace;

	for(i=0; i<ntuples; i++)
	{
		int		this_size = IndexTupleSize(tuples[i]);

		memcpy(ptr, tuples[i], this_size);
		ptr += this_size;
		size += this_size;

		l = PageAddItem(page, (Item)tuples[i], this_size, off, false, false);

		if (l == InvalidOffsetNumber)
			elog(ERROR, "failed to add item to index page in \"%s\"",
				 RelationGetRelationName(index));

		off++;
	}

	Assert(size <= BLCKSZ);		/* else we overran workspace */

	GinPageGetOpaque(page)->rightlink = rightlink;

	/*
	 * tail page may contain only the whole row(s) or final
	 * part of row placed on previous pages
	 */
	if ( rightlink == InvalidBlockNumber )
	{
		GinPageSetFullRow(page);
		GinPageGetOpaque(page)->maxoff = 1;
	}
	else
	{
		GinPageGetOpaque(page)->maxoff = 0;
	}

	freesize = PageGetFreeSpace(page);

	MarkBufferDirty(buffer);

	if (!index->rd_istemp)
	{
		XLogRecData				rdata[2];
		ginxlogInsertListPage	data;
		XLogRecPtr  			recptr;

		rdata[0].buffer = buffer;
		rdata[0].buffer_std = true;
		rdata[0].data = (char*)&data;
		rdata[0].len = sizeof(ginxlogInsertListPage);
		rdata[0].next = rdata+1;

		rdata[1].buffer = InvalidBuffer;
		rdata[1].data = workspace;
		rdata[1].len = size;
		rdata[1].next = NULL;

		data.blkno = BufferGetBlockNumber(buffer);
		data.rightlink = rightlink;
		data.ntuples = ntuples;

		recptr = XLogInsert(RM_GIN_ID, XLOG_GIN_INSERT_LISTPAGE, rdata);
		PageSetLSN(page, recptr);
		PageSetTLI(page, ThisTimeLineID);
	}

	UnlockReleaseBuffer(buffer);

	END_CRIT_SECTION();

	pfree(workspace);

	return freesize;
}

static void
makeSublist(Relation index, IndexTuple *tuples, int32 ntuples,
			GinMetaPageData *res)
{
	Buffer			curBuffer = InvalidBuffer;
	Buffer			prevBuffer = InvalidBuffer;
	int 			i, size = 0, tupsize;
	int 			startTuple = 0;

	Assert(ntuples > 0);

	/*
	 * Split tuples into pages
	 */
	for(i=0;i<ntuples;i++)
	{
		if ( curBuffer == InvalidBuffer )
		{
			curBuffer = GinNewBuffer(index);

			if ( prevBuffer != InvalidBuffer )
			{
				res->nPendingPages++;
				writeListPage(index, prevBuffer,
							  tuples+startTuple, i-startTuple,
							  BufferGetBlockNumber(curBuffer));
			}
			else
			{
				res->head = BufferGetBlockNumber(curBuffer);
			}

			prevBuffer = curBuffer;
			startTuple = i;
			size = 0;
		}

		tupsize = MAXALIGN(IndexTupleSize(tuples[i])) + sizeof(ItemIdData);

		if ( size + tupsize >= GinListPageSize )
		{
			/* won't fit, force a new page and reprocess */
			i--;
			curBuffer = InvalidBuffer;
		}
		else
		{
			size += tupsize;
		}
	}

	/*
	 * Write last page
	 */
	res->tail = BufferGetBlockNumber(curBuffer);
	res->tailFreeSize = writeListPage(index, curBuffer,
									  tuples+startTuple, ntuples-startTuple,
									  InvalidBlockNumber);
	res->nPendingPages++;
	/* that was only one heap tuple */
	res->nPendingHeapTuples = 1;
}

/*
 * Inserts collected values during normal insertion. Function guarantees
 * that all values of heap will be stored sequentially, preserving order
 */
void
ginHeapTupleFastInsert(Relation index, GinState *ginstate,
					   GinTupleCollector *collector)
{
	Buffer				metabuffer;
	Page				metapage;
	GinMetaPageData    *metadata = NULL;
	XLogRecData			rdata[2];
	Buffer				buffer = InvalidBuffer;
	Page				page = NULL;
	ginxlogUpdateMeta	data;
	bool				separateList = false;
	bool				needCleanup = false;

	if ( collector->ntuples == 0 )
		return;

	data.node = index->rd_node;
	data.ntuples = 0;
	data.newRightlink = data.prevTail = InvalidBlockNumber;

	rdata[0].buffer = InvalidBuffer;
	rdata[0].data = (char *) &data;
	rdata[0].len = sizeof(ginxlogUpdateMeta);
	rdata[0].next = NULL;

	metabuffer = ReadBuffer(index, GIN_METAPAGE_BLKNO);
	metapage = BufferGetPage(metabuffer);

	if ( collector->sumsize + collector->ntuples * sizeof(ItemIdData) > GIN_PAGE_FREESIZE )
	{
		/*
		 * Total size is greater than one page => make sublist
		 */
		separateList = true;
	}
	else
	{
		LockBuffer(metabuffer, GIN_EXCLUSIVE);
		metadata = GinPageGetMeta(metapage);

		if ( metadata->head == InvalidBlockNumber ||
			collector->sumsize + collector->ntuples * sizeof(ItemIdData) > metadata->tailFreeSize )
		{
			/*
			 * Pending list is empty or total size is greater than freespace
			 * on tail page => make sublist
			 *
			 * We unlock metabuffer to keep high concurrency
			 */
			separateList = true;
			LockBuffer(metabuffer, GIN_UNLOCK);
		}
	}

	if ( separateList )
	{
		GinMetaPageData		sublist;

		/*
		 * We should make sublist separately and append it to the tail
		 */
		memset( &sublist, 0, sizeof(GinMetaPageData) );

		makeSublist(index, collector->tuples, collector->ntuples, &sublist);

		/*
		 * metapage was unlocked, see above
		 */
		LockBuffer(metabuffer, GIN_EXCLUSIVE);
		metadata = GinPageGetMeta(metapage);

		if ( metadata->head == InvalidBlockNumber )
		{
			/*
			 * Sublist becomes main list
			 */
			START_CRIT_SECTION();
			memcpy(metadata, &sublist, sizeof(GinMetaPageData) );
			memcpy(&data.metadata, &sublist, sizeof(GinMetaPageData) );
		}
		else
		{
			/*
			 * merge lists
			 */

			data.prevTail = metadata->tail;
			buffer = ReadBuffer(index, metadata->tail);
			LockBuffer(buffer, GIN_EXCLUSIVE);
			page = BufferGetPage(buffer);
			Assert(GinPageGetOpaque(page)->rightlink == InvalidBlockNumber);

			START_CRIT_SECTION();

			GinPageGetOpaque(page)->rightlink = sublist.head;
			metadata->tail = sublist.tail;
			metadata->tailFreeSize = sublist.tailFreeSize;

			metadata->nPendingPages += sublist.nPendingPages;
			metadata->nPendingHeapTuples += sublist.nPendingHeapTuples;

			memcpy(&data.metadata, metadata, sizeof(GinMetaPageData) );
			data.newRightlink = sublist.head;

			MarkBufferDirty(buffer);
		}
	}
	else
	{
		/*
		 * Insert into tail page, metapage is already locked
		 */

		OffsetNumber	l, off;
		int				i, tupsize;
		char			*ptr;

		buffer = ReadBuffer(index, metadata->tail);
		LockBuffer(buffer, GIN_EXCLUSIVE);
		page = BufferGetPage(buffer);
		off = (PageIsEmpty(page)) ? FirstOffsetNumber :
				OffsetNumberNext(PageGetMaxOffsetNumber(page));

		rdata[0].next = rdata + 1;

		rdata[1].buffer = buffer;
		rdata[1].buffer_std = true;
		ptr = rdata[1].data = (char *) palloc( collector->sumsize );
		rdata[1].len = collector->sumsize;
		rdata[1].next = NULL;

		data.ntuples = collector->ntuples;

		START_CRIT_SECTION();

		/*
		 * Increase counter of heap tuples
		 */
		Assert( GinPageGetOpaque(page)->maxoff <= metadata->nPendingHeapTuples );
		GinPageGetOpaque(page)->maxoff++;
		metadata->nPendingHeapTuples++;

		for(i=0; i<collector->ntuples; i++)
		{
			tupsize = IndexTupleSize(collector->tuples[i]);
			l = PageAddItem(page, (Item)collector->tuples[i], tupsize, off, false, false);

			if (l == InvalidOffsetNumber)
				elog(ERROR, "failed to add item to index page in \"%s\"",
						 RelationGetRelationName(index));

			memcpy(ptr, collector->tuples[i], tupsize);
			ptr+=tupsize;

			off++;
		}

		metadata->tailFreeSize -= collector->sumsize + collector->ntuples * sizeof(ItemIdData);
		memcpy(&data.metadata, metadata, sizeof(GinMetaPageData) );
		MarkBufferDirty(buffer);
	}

	/*
	 *  Make real write
	 */

	MarkBufferDirty(metabuffer);
	if ( !index->rd_istemp )
	{
		XLogRecPtr  recptr;

		recptr = XLogInsert(RM_GIN_ID, XLOG_GIN_UPDATE_META_PAGE, rdata);
		PageSetLSN(metapage, recptr);
		PageSetTLI(metapage, ThisTimeLineID);

		if ( buffer != InvalidBuffer )
		{
			PageSetLSN(page, recptr);
			PageSetTLI(page, ThisTimeLineID);
		}
	}

	if (buffer != InvalidBuffer)
		UnlockReleaseBuffer(buffer);

	/*
	 * Force pending list cleanup when it becomes too long.
	 * And, ginInsertCleanup could take significant amount of
	 * time, so we prefer to call it when it can do all the work in a
	 * single collection cycle. In non-vacuum mode, it shouldn't
	 * require maintenance_work_mem, so fire it while pending list is
	 * still small enough to fit into work_mem.
	 *
	 * ginInsertCleanup() should not be called inside our CRIT_SECTION.
	 */
	if ( metadata->nPendingPages * GIN_PAGE_FREESIZE > work_mem * 1024L )
		needCleanup = true;

	UnlockReleaseBuffer(metabuffer);

	END_CRIT_SECTION();

	if ( needCleanup )
		ginInsertCleanup(index, ginstate, false, NULL);
}

/*
 * Collect values from one tuples to be indexed. All values for
 * one tuples should be written at once - to guarantee consistent state
 */
uint32
ginHeapTupleFastCollect(Relation index, GinState *ginstate,
						GinTupleCollector *collector,
						OffsetNumber attnum, Datum value, ItemPointer item)
{
	Datum	   *entries;
	int32		i,
				nentries;

	entries = extractEntriesSU(ginstate, attnum, value, &nentries);

	if (nentries == 0)
		/* nothing to insert */
		return 0;

	/*
	 * Allocate/reallocate memory for storing collected tuples
	 */
	if ( collector->tuples == NULL )
	{
		collector->lentuples = nentries * index->rd_att->natts;
		collector->tuples = (IndexTuple*)palloc(sizeof(IndexTuple) * collector->lentuples);
	}

	while ( collector->ntuples + nentries > collector->lentuples )
	{
		collector->lentuples *= 2;
		collector->tuples = (IndexTuple*)repalloc( collector->tuples,
													sizeof(IndexTuple) * collector->lentuples);
	}

	/*
	 * Creates tuple's array
	 */
	for (i = 0; i < nentries; i++)
	{
		int32 tupsize;

		collector->tuples[collector->ntuples + i] = GinFormTuple(ginstate, attnum, entries[i], NULL, 0);
		collector->tuples[collector->ntuples + i]->t_tid = *item;
		tupsize = IndexTupleSize(collector->tuples[collector->ntuples + i]);

		if ( tupsize > TOAST_INDEX_TARGET || tupsize >= GinMaxItemSize)
			elog(ERROR, "huge tuple");

		collector->sumsize += tupsize;
	}

	collector->ntuples += nentries;

	return nentries;
}

/*
 * Deletes pending list pages up to (not including) newHead page.
 * If newHead == InvalidBlockNumber then function drops the whole list.
 *
 * metapage is pinned and exclusive-locked throughout this function.
 *
 * Returns true if another cleanup process is running concurrently
 * (if so, we can just abandon our own efforts)
 */
static bool
shiftList(Relation index, Buffer metabuffer, BlockNumber newHead,
		  IndexBulkDeleteResult *stats)
{
	Page					metapage;
	GinMetaPageData 	   *metadata;
	BlockNumber				blknoToDelete;

	metapage = BufferGetPage(metabuffer);
	metadata = GinPageGetMeta(metapage);
	blknoToDelete = metadata->head;

	do
	{
		Page					page;
		int						i;
		int64					nDeletedHeapTuples = 0;
		ginxlogDeleteListPages	data;
		XLogRecData				rdata[1];
		Buffer					buffers[GIN_NDELETE_AT_ONCE];

		data.node = index->rd_node;

		rdata[0].buffer = InvalidBuffer;
		rdata[0].data = (char *) &data;
		rdata[0].len = sizeof(ginxlogDeleteListPages);
		rdata[0].next = NULL;

		data.ndeleted = 0;
		while (data.ndeleted < GIN_NDELETE_AT_ONCE && blknoToDelete != newHead)
		{
			data.toDelete[ data.ndeleted ] = blknoToDelete;
			buffers[ data.ndeleted ] = ReadBuffer(index, blknoToDelete);
			LockBuffer( buffers[ data.ndeleted ], GIN_EXCLUSIVE );
			page = BufferGetPage( buffers[ data.ndeleted ] );

			data.ndeleted++;

			if ( GinPageIsDeleted(page) )
			{
				/* concurrent cleanup process is detected */
				for(i=0;i<data.ndeleted;i++)
					UnlockReleaseBuffer( buffers[i] );

				return true;
			}

			nDeletedHeapTuples += GinPageGetOpaque(page)->maxoff;
			blknoToDelete = GinPageGetOpaque( page )->rightlink;
		}

		if (stats)
			stats->pages_deleted += data.ndeleted;

		START_CRIT_SECTION();

		metadata->head = blknoToDelete;

		Assert( metadata->nPendingPages >= data.ndeleted );
		metadata->nPendingPages -= data.ndeleted;
		Assert( metadata->nPendingHeapTuples >= nDeletedHeapTuples );
		metadata->nPendingHeapTuples -= nDeletedHeapTuples;

		if ( blknoToDelete == InvalidBlockNumber )
		{
			metadata->tail = InvalidBlockNumber;
			metadata->tailFreeSize = 0;
			metadata->nPendingPages = 0;
			metadata->nPendingHeapTuples = 0;
		}
		memcpy( &data.metadata, metadata, sizeof(GinMetaPageData));

		MarkBufferDirty( metabuffer );

		for(i=0; i<data.ndeleted; i++)
		{
			page = BufferGetPage( buffers[ i ] );
			GinPageGetOpaque( page )->flags = GIN_DELETED;
			MarkBufferDirty( buffers[ i ] );
		}

		if ( !index->rd_istemp )
		{
			XLogRecPtr  recptr;

			recptr = XLogInsert(RM_GIN_ID, XLOG_GIN_DELETE_LISTPAGE, rdata);
			PageSetLSN(metapage, recptr);
			PageSetTLI(metapage, ThisTimeLineID);

			for(i=0; i<data.ndeleted; i++)
			{
				page = BufferGetPage( buffers[ i ] );
				PageSetLSN(page, recptr);
				PageSetTLI(page, ThisTimeLineID);
			}
		}

		for(i=0; i<data.ndeleted; i++)
			UnlockReleaseBuffer( buffers[ i ] );

		END_CRIT_SECTION();
	} while( blknoToDelete != newHead );

	return false;
}

/* Add datum to DatumArray, resizing if needed */
static void
addDatum(DatumArray *datums, Datum datum)
{
	if ( datums->nvalues >= datums->maxvalues)
	{
		datums->maxvalues *= 2;
		datums->values = (Datum*)repalloc(datums->values,
										  sizeof(Datum)*datums->maxvalues);
	}

	datums->values[ datums->nvalues++ ] = datum;
}

/*
 * Go through all tuples >= startoff on page and collect values in memory
 *
 * Note that da is just workspace --- it does not carry any state across
 * calls.
 */
static void
processPendingPage(BuildAccumulator *accum, DatumArray *da,
				   Page page, OffsetNumber startoff)
{
	ItemPointerData	heapptr;
	OffsetNumber 	i,maxoff;
	OffsetNumber	attrnum, curattnum;

	/* reset *da to empty */
	da->nvalues = 0;

	maxoff = PageGetMaxOffsetNumber(page);
	Assert( maxoff >= FirstOffsetNumber );
	ItemPointerSetInvalid(&heapptr);
	attrnum = 0;

	for (i = startoff; i <= maxoff; i = OffsetNumberNext(i))
	{
		IndexTuple  itup = (IndexTuple) PageGetItem(page, PageGetItemId(page, i));

		curattnum = gintuple_get_attrnum(accum->ginstate, itup);

		if ( !ItemPointerIsValid(&heapptr) )
		{
			heapptr = itup->t_tid;
			attrnum = curattnum;
		}
		else if ( !(ItemPointerEquals(&heapptr, &itup->t_tid) &&
					curattnum == attrnum) )
		{
			/*
			 * We can insert several datums per call, but only for one heap
			 * tuple and one column.
			 */
			ginInsertRecordBA(accum, &heapptr, attrnum, da->values, da->nvalues);
			da->nvalues = 0;
			heapptr = itup->t_tid;
			attrnum = curattnum;
		}
		addDatum(da, gin_index_getattr(accum->ginstate, itup));
	}

	ginInsertRecordBA(accum, &heapptr, attrnum, da->values, da->nvalues);
}

/*
 * Move tuples from pending pages into regular GIN structure.
 *
 * This can be called concurrently by multiple backends, so it must cope.
 * On first glance it looks completely not concurrent-safe and not crash-safe
 * either.  The reason it's okay is that multiple insertion of the same entry
 * is detected and treated as a no-op by gininsert.c.  If we crash after
 * posting entries to the main index and before removing them from the
 * pending list, it's okay because when we redo the posting later on, nothing
 * bad will happen.  Likewise, if two backends simultaneously try to post
 * a pending entry into the main index, one will succeed and one will do
 * nothing.  We try to notice when someone else is a little bit ahead of
 * us in the process, but that's just to avoid wasting cycles.  Only the
 * action of removing a page from the pending list really needs exclusive
 * lock.
 *
 * vac_delay indicates that ginInsertCleanup is called from vacuum process,
 * so call vacuum_delay_point() periodically.
 * If stats isn't null, we count deleted pending pages into the counts.
 */
void
ginInsertCleanup(Relation index, GinState *ginstate,
				 bool vac_delay, IndexBulkDeleteResult *stats)
{
	Buffer				metabuffer, buffer;
	Page				metapage, page;
	GinMetaPageData    *metadata;
	MemoryContext		opCtx, oldCtx;
	BuildAccumulator	accum;
	DatumArray			datums;
	BlockNumber			blkno;

	metabuffer = ReadBuffer(index, GIN_METAPAGE_BLKNO);
	LockBuffer(metabuffer, GIN_SHARE);
	metapage = BufferGetPage(metabuffer);
	metadata = GinPageGetMeta(metapage);

	if ( metadata->head == InvalidBlockNumber )
	{
		/* Nothing to do */
		UnlockReleaseBuffer(metabuffer);
		return;
	}

	/*
	 * Read and lock head of pending list
	 */
	blkno = metadata->head;
	buffer = ReadBuffer(index, blkno);
	LockBuffer(buffer, GIN_SHARE);
	page = BufferGetPage(buffer);

	LockBuffer(metabuffer, GIN_UNLOCK);

	/*
	 * Initialize.  All temporary space will be in opCtx
	 */
	opCtx = AllocSetContextCreate(CurrentMemoryContext,
								  "GIN insert cleanup temporary context",
								  ALLOCSET_DEFAULT_MINSIZE,
								  ALLOCSET_DEFAULT_INITSIZE,
								  ALLOCSET_DEFAULT_MAXSIZE);

	oldCtx = MemoryContextSwitchTo(opCtx);

	datums.maxvalues=128;
	datums.nvalues = 0;
	datums.values = (Datum*)palloc(sizeof(Datum)*datums.maxvalues);

	ginInitBA(&accum);
	accum.ginstate = ginstate;

	/*
	 * At the top of this loop, we have pin and lock on the current page
	 * of the pending list.  However, we'll release that before exiting
	 * the loop.  Note we also have pin but not lock on the metapage.
	 */
	for(;;)
	{
		if ( GinPageIsDeleted(page) )
		{
			/* another cleanup process is running concurrently */
			UnlockReleaseBuffer( buffer );
			break;
		}

		/*
		 * read page's datums into memory
		 */
		processPendingPage(&accum, &datums, page, FirstOffsetNumber);

		if (vac_delay)
			vacuum_delay_point();

		/*
		 * Is it time to flush memory to disk?  Flush if we are at the end
		 * of the pending list, or if we have a full row and memory is
		 * getting full.
		 *
		 * XXX using up maintenance_work_mem here is probably unreasonably
		 * much, since vacuum might already be using that much.
		 */
		if (GinPageGetOpaque(page)->rightlink == InvalidBlockNumber ||
			(GinPageHasFullRow(page) &&
			 (accum.allocatedMemory >= maintenance_work_mem * 1024L ||
			  accum.maxdepth > GIN_MAX_TREE_DEPTH)))
		{
			ItemPointerData    *list;
			uint32      		nlist;
			Datum       		entry;
			OffsetNumber  		maxoff, attnum;

			/*
			 * Unlock current page to increase performance.
			 * Changes of page will be checked later by comparing
			 * maxoff after completion of memory flush.
			 */
			maxoff = PageGetMaxOffsetNumber(page);
			LockBuffer(buffer, GIN_UNLOCK);

			/*
			 * Moving collected data into regular structure can take
			 * significant amount of time - so, run it without locking pending
			 * list.
			 */
			while ((list = ginGetEntry(&accum, &attnum, &entry, &nlist)) != NULL)
			{
				ginEntryInsert(index, ginstate, attnum, entry, list, nlist, FALSE);
				if (vac_delay)
					vacuum_delay_point();
			}

			/*
			 * Lock the whole list to remove pages
			 */
			LockBuffer(metabuffer, GIN_EXCLUSIVE);
			LockBuffer(buffer, GIN_SHARE);

			if ( GinPageIsDeleted(page) )
			{
				/* another cleanup process is running concurrently */
				UnlockReleaseBuffer(buffer);
				LockBuffer(metabuffer, GIN_UNLOCK);
				break;
			}

			/*
			 * While we left the page unlocked, more stuff might have gotten
			 * added to it.  If so, process those entries immediately.  There
			 * shouldn't be very many, so we don't worry about the fact that
			 * we're doing this with exclusive lock. Insertion algorithm
			 * gurantees that inserted row(s) will not continue on next page.
			 * NOTE: intentionally no vacuum_delay_point in this loop.
			 */
			if ( PageGetMaxOffsetNumber(page) != maxoff )
			{
				ginInitBA(&accum);
				processPendingPage(&accum, &datums, page, maxoff+1);

				while ((list = ginGetEntry(&accum, &attnum, &entry, &nlist)) != NULL)
					ginEntryInsert(index, ginstate, attnum, entry, list, nlist, FALSE);
			}

			/*
			 * Remember next page - it will become the new list head
			 */
			blkno = GinPageGetOpaque(page)->rightlink;
			UnlockReleaseBuffer(buffer); /* shiftList will do exclusive locking */

			/*
			 * remove readed pages from pending list, at this point all
			 * content of readed pages is in regular structure
			 */
			if ( shiftList(index, metabuffer, blkno, stats) )
			{
				/* another cleanup process is running concurrently */
				LockBuffer(metabuffer, GIN_UNLOCK);
				break;
			}

			Assert( blkno == metadata->head );
			LockBuffer(metabuffer, GIN_UNLOCK);

			/*
			 * if we removed the whole pending list just exit
			 */
			if ( blkno == InvalidBlockNumber )
				break;

			/*
			 * release memory used so far and reinit state
			 */
			MemoryContextReset(opCtx);
			ginInitBA(&accum);
			datums.nvalues = 0;
			datums.values = (Datum*)palloc(sizeof(Datum)*datums.maxvalues);
		}
		else
		{
			blkno = GinPageGetOpaque(page)->rightlink;
			UnlockReleaseBuffer(buffer);
		}

		/*
		 * Read next page in pending list
		 */
		CHECK_FOR_INTERRUPTS();
		buffer = ReadBuffer(index, blkno);
		LockBuffer(buffer, GIN_SHARE);
		page = BufferGetPage(buffer);
	}

	ReleaseBuffer(metabuffer);

	/* Clean up temporary space */
	MemoryContextSwitchTo(oldCtx);
	MemoryContextDelete(opCtx);
}