diff --git a/contrib/pg_stat_statements/pg_stat_statements.c b/contrib/pg_stat_statements/pg_stat_statements.c
index 9673fe0..0c8e4fb 100644
--- a/contrib/pg_stat_statements/pg_stat_statements.c
+++ b/contrib/pg_stat_statements/pg_stat_statements.c
@@ -495,7 +495,7 @@ pgss_shmem_startup(void)
 	info.hash = pgss_hash_fn;
 	info.match = pgss_match_fn;
 	pgss_hash = ShmemInitHash("pg_stat_statements hash",
-							  pgss_max, pgss_max,
+							  pgss_max,
 							  &info,
 							  HASH_ELEM | HASH_FUNCTION | HASH_COMPARE);
 
diff --git a/src/backend/access/nbtree/nbtinsert.c b/src/backend/access/nbtree/nbtinsert.c
index e3c55eb..3908cc1 100644
--- a/src/backend/access/nbtree/nbtinsert.c
+++ b/src/backend/access/nbtree/nbtinsert.c
@@ -24,6 +24,7 @@
 #include "storage/predicate.h"
 #include "utils/tqual.h"
 
+#include "catalog/catalog.h"
 
 typedef struct
 {
@@ -60,7 +61,8 @@ static void _bt_findinsertloc(Relation rel,
 				  ScanKey scankey,
 				  IndexTuple newtup,
 				  BTStack stack,
-				  Relation heapRel);
+				  Relation heapRel,
+				  bool *updposing);
 static void _bt_insertonpg(Relation rel, Buffer buf, Buffer cbuf,
 			   BTStack stack,
 			   IndexTuple itup,
@@ -113,6 +115,7 @@ _bt_doinsert(Relation rel, IndexTuple itup,
 	BTStack		stack;
 	Buffer		buf;
 	OffsetNumber offset;
+	bool updposting = false;
 
 	/* we need an insertion scan key to do our search, so build one */
 	itup_scankey = _bt_mkscankey(rel, itup);
@@ -162,8 +165,9 @@ top:
 	{
 		TransactionId xwait;
 		uint32		speculativeToken;
+		bool fakeupdposting = false; /* Never update posting in unique index */
 
-		offset = _bt_binsrch(rel, buf, natts, itup_scankey, false);
+		offset = _bt_binsrch(rel, buf, natts, itup_scankey, false, &fakeupdposting);
 		xwait = _bt_check_unique(rel, itup, heapRel, buf, offset, itup_scankey,
 								 checkUnique, &is_unique, &speculativeToken);
 
@@ -200,8 +204,54 @@ top:
 		CheckForSerializableConflictIn(rel, NULL, buf);
 		/* do the insertion */
 		_bt_findinsertloc(rel, &buf, &offset, natts, itup_scankey, itup,
-						  stack, heapRel);
-		_bt_insertonpg(rel, buf, InvalidBuffer, stack, itup, offset, false);
+						  stack, heapRel, &updposting);
+
+		if (IsSystemRelation(rel))
+			updposting = false;
+
+		/*
+		 * New tuple has the same key with tuple at the page.
+		 * Unite them into one posting.
+		 */
+		if (updposting)
+		{
+			Page		page;
+			IndexTuple olditup, newitup;
+			ItemPointerData *ipd;
+			int nipd;
+
+			page = BufferGetPage(buf);
+			olditup = (IndexTuple) PageGetItem(page, PageGetItemId(page, offset));
+
+			if (BtreeTupleIsPosting(olditup))
+				nipd = BtreeGetNPosting(olditup);
+			else
+				nipd = 1;
+
+			ipd = palloc0(sizeof(ItemPointerData)*(nipd + 1));
+			/* copy item pointers from old tuple into ipd */
+			if (BtreeTupleIsPosting(olditup))
+				memcpy(ipd, BtreeGetPosting(olditup), sizeof(ItemPointerData)*nipd);
+			else
+				memcpy(ipd, olditup, sizeof(ItemPointerData));
+
+			/* add item pointer of the new tuple into ipd */
+			memcpy(ipd+nipd, itup, sizeof(ItemPointerData));
+
+			/*
+			 * Form posting tuple, then delete old tuple and insert posting tuple.
+			 */
+			newitup = BtreeReformPackedTuple(itup, ipd, nipd+1);
+			PageIndexTupleDelete(page, offset);
+			_bt_insertonpg(rel, buf, InvalidBuffer, stack, newitup, offset, false);
+
+			pfree(ipd);
+			pfree(newitup);
+		}
+		else
+		{
+			_bt_insertonpg(rel, buf, InvalidBuffer, stack, itup, offset, false);
+		}
 	}
 	else
 	{
@@ -306,6 +356,8 @@ _bt_check_unique(Relation rel, IndexTuple itup, Relation heapRel,
 
 				/* okay, we gotta fetch the heap tuple ... */
 				curitup = (IndexTuple) PageGetItem(page, curitemid);
+
+				Assert (!BtreeTupleIsPosting(curitup));
 				htid = curitup->t_tid;
 
 				/*
@@ -535,7 +587,8 @@ _bt_findinsertloc(Relation rel,
 				  ScanKey scankey,
 				  IndexTuple newtup,
 				  BTStack stack,
-				  Relation heapRel)
+				  Relation heapRel,
+				  bool *updposting)
 {
 	Buffer		buf = *bufptr;
 	Page		page = BufferGetPage(buf);
@@ -681,7 +734,7 @@ _bt_findinsertloc(Relation rel,
 	else if (firstlegaloff != InvalidOffsetNumber && !vacuumed)
 		newitemoff = firstlegaloff;
 	else
-		newitemoff = _bt_binsrch(rel, buf, keysz, scankey, false);
+		newitemoff = _bt_binsrch(rel, buf, keysz, scankey, false, updposting);
 
 	*bufptr = buf;
 	*offsetptr = newitemoff;
@@ -1042,6 +1095,9 @@ _bt_split(Relation rel, Buffer buf, Buffer cbuf, OffsetNumber firstright,
 		itemid = PageGetItemId(origpage, P_HIKEY);
 		itemsz = ItemIdGetLength(itemid);
 		item = (IndexTuple) PageGetItem(origpage, itemid);
+
+		Assert(!BtreeTupleIsPosting(item));
+
 		if (PageAddItem(rightpage, (Item) item, itemsz, rightoff,
 						false, false) == InvalidOffsetNumber)
 		{
@@ -1072,13 +1128,40 @@ _bt_split(Relation rel, Buffer buf, Buffer cbuf, OffsetNumber firstright,
 		itemsz = ItemIdGetLength(itemid);
 		item = (IndexTuple) PageGetItem(origpage, itemid);
 	}
-	if (PageAddItem(leftpage, (Item) item, itemsz, leftoff,
+
+	if (BtreeTupleIsPosting(item))
+	{
+		Size hikeysize =  BtreeGetPostingOffset(item);
+		IndexTuple hikey = palloc0(hikeysize);
+		/*
+		 * Truncate posting before insert it as a hikey.
+		 */
+		memcpy (hikey, item, hikeysize);
+		hikey->t_info &= ~INDEX_SIZE_MASK;
+		hikey->t_info |= hikeysize;
+		ItemPointerSet(&(hikey->t_tid), origpagenumber, P_HIKEY);
+
+		if (PageAddItem(leftpage, (Item) hikey, hikeysize, leftoff,
 					false, false) == InvalidOffsetNumber)
+		{
+			memset(rightpage, 0, BufferGetPageSize(rbuf));
+			elog(ERROR, "failed to add hikey to the left sibling"
+				" while splitting block %u of index \"%s\"",
+				origpagenumber, RelationGetRelationName(rel));
+		}
+
+		pfree(hikey);
+	}
+	else
 	{
-		memset(rightpage, 0, BufferGetPageSize(rbuf));
-		elog(ERROR, "failed to add hikey to the left sibling"
-			 " while splitting block %u of index \"%s\"",
-			 origpagenumber, RelationGetRelationName(rel));
+		if (PageAddItem(leftpage, (Item) item, itemsz, leftoff,
+						false, false) == InvalidOffsetNumber)
+		{
+			memset(rightpage, 0, BufferGetPageSize(rbuf));
+			elog(ERROR, "failed to add hikey to the left sibling"
+				" while splitting block %u of index \"%s\"",
+				origpagenumber, RelationGetRelationName(rel));
+		}
 	}
 	leftoff = OffsetNumberNext(leftoff);
 
diff --git a/src/backend/access/nbtree/nbtree.c b/src/backend/access/nbtree/nbtree.c
index f2905cb..f56c90f 100644
--- a/src/backend/access/nbtree/nbtree.c
+++ b/src/backend/access/nbtree/nbtree.c
@@ -75,6 +75,9 @@ static void btvacuumscan(IndexVacuumInfo *info, IndexBulkDeleteResult *stats,
 static void btvacuumpage(BTVacState *vstate, BlockNumber blkno,
 			 BlockNumber orig_blkno);
 
+static ItemPointer
+btreevacuumPosting(BTVacState *vstate, ItemPointerData *items,
+					  int nitem, int *nremaining);
 
 /*
  * Btree handler function: return IndexAmRoutine with access method parameters
@@ -962,6 +965,7 @@ restart:
 		OffsetNumber offnum,
 					minoff,
 					maxoff;
+		IndexTupleData *remaining;
 
 		/*
 		 * Trade in the initial read lock for a super-exclusive write lock on
@@ -1011,31 +1015,62 @@ restart:
 
 				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;
+				if(BtreeTupleIsPosting(itup))
+				{
+					int nipd, nnewipd;
+					ItemPointer newipd;
+
+					nipd = BtreeGetNPosting(itup);
+					newipd = btreevacuumPosting(vstate, BtreeGetPosting(itup), nipd, &nnewipd);
+
+					if (newipd != NULL)
+					{
+						if (nnewipd > 0)
+						{
+							/* There are still some live tuples in the posting.
+							 * 1) form new posting tuple, that contains remaining ipds
+							 * 2) delete "old" posting
+							 * 3) insert new posting back to the page
+							 */
+							remaining = BtreeReformPackedTuple(itup, newipd, nnewipd);
+							PageIndexTupleDelete(page, offnum);
+
+							if (PageAddItem(page, (Item) remaining, IndexTupleSize(remaining), offnum, false, false) != offnum)
+								elog(ERROR, "failed to add vacuumed posting tuple to index page in \"%s\"",
+										RelationGetRelationName(info->index));
+						}
+						else
+							deletable[ndeletable++] = offnum;
+					}
+				}
+				else
+				{
+					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;
+				}
 			}
 		}
 
@@ -1160,3 +1195,51 @@ btcanreturn(Relation index, int attno)
 {
 	return true;
 }
+
+
+/*
+ * Vacuums a posting list. The size of the list must be specified
+ * via number of items (nitems).
+ *
+ * If none of the items need to be removed, returns NULL. Otherwise returns
+ * a new palloc'd array with the remaining items. The number of remaining
+ * items is returned via nremaining.
+ */
+ItemPointer
+btreevacuumPosting(BTVacState *vstate, ItemPointerData *items,
+					  int nitem, int *nremaining)
+{
+	int			i,
+				remaining = 0;
+	ItemPointer tmpitems = NULL;
+	IndexBulkDeleteCallback callback = vstate->callback;
+	void	   *callback_state = vstate->callback_state;
+
+	/*
+	 * Iterate over TIDs array
+	 */
+	for (i = 0; i < nitem; i++)
+	{
+		if (callback(items + i, callback_state))
+		{
+			if (!tmpitems)
+			{
+				/*
+				 * First TID to be deleted: allocate memory to hold the
+				 * remaining items.
+				 */
+				tmpitems = palloc(sizeof(ItemPointerData) * nitem);
+				memcpy(tmpitems, items, sizeof(ItemPointerData) * i);
+			}
+		}
+		else
+		{
+			if (tmpitems)
+				tmpitems[remaining] = items[i];
+			remaining++;
+		}
+	}
+
+	*nremaining = remaining;
+	return tmpitems;
+}
diff --git a/src/backend/access/nbtree/nbtsearch.c b/src/backend/access/nbtree/nbtsearch.c
index 3db32e8..0428f04 100644
--- a/src/backend/access/nbtree/nbtsearch.c
+++ b/src/backend/access/nbtree/nbtsearch.c
@@ -29,6 +29,8 @@ static bool _bt_readpage(IndexScanDesc scan, ScanDirection dir,
 			 OffsetNumber offnum);
 static void _bt_saveitem(BTScanOpaque so, int itemIndex,
 			 OffsetNumber offnum, IndexTuple itup);
+static void _bt_savePostingitem(BTScanOpaque so, int itemIndex,
+			 OffsetNumber offnum, ItemPointer iptr, IndexTuple itup, int i);
 static bool _bt_steppage(IndexScanDesc scan, ScanDirection dir);
 static Buffer _bt_walk_left(Relation rel, Buffer buf);
 static bool _bt_endpoint(IndexScanDesc scan, ScanDirection dir);
@@ -90,6 +92,7 @@ _bt_search(Relation rel, int keysz, ScanKey scankey, bool nextkey,
 		   Buffer *bufP, int access)
 {
 	BTStack		stack_in = NULL;
+	bool fakeupdposting = false; /* fake variable for _bt_binsrch */
 
 	/* Get the root page to start with */
 	*bufP = _bt_getroot(rel, access);
@@ -136,7 +139,7 @@ _bt_search(Relation rel, int keysz, ScanKey scankey, bool nextkey,
 		 * Find the appropriate item on the internal page, and get the child
 		 * page that it points to.
 		 */
-		offnum = _bt_binsrch(rel, *bufP, keysz, scankey, nextkey);
+		offnum = _bt_binsrch(rel, *bufP, keysz, scankey, nextkey, &fakeupdposting);
 		itemid = PageGetItemId(page, offnum);
 		itup = (IndexTuple) PageGetItem(page, itemid);
 		blkno = ItemPointerGetBlockNumber(&(itup->t_tid));
@@ -310,7 +313,8 @@ _bt_binsrch(Relation rel,
 			Buffer buf,
 			int keysz,
 			ScanKey scankey,
-			bool nextkey)
+			bool nextkey,
+			bool *updposing)
 {
 	Page		page;
 	BTPageOpaque opaque;
@@ -373,7 +377,17 @@ _bt_binsrch(Relation rel,
 	 * scan key), which could be the last slot + 1.
 	 */
 	if (P_ISLEAF(opaque))
+	{
+		if (low <= PageGetMaxOffsetNumber(page))
+		{
+			IndexTuple oitup = (IndexTuple) PageGetItem(page, PageGetItemId(page, low));
+			/* one excessive check of equality. for possible posting tuple update or creation */
+			if ((_bt_compare(rel, keysz, scankey, page, low) == 0)
+				&& (IndexTupleSize(oitup) + sizeof(ItemPointerData) < BTMaxItemSize(page)))
+				*updposing = true;
+		}
 		return low;
+	}
 
 	/*
 	 * On a non-leaf page, return the last key < scan key (resp. <= scan key).
@@ -536,6 +550,7 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
 	int			i;
 	StrategyNumber strat_total;
 	BTScanPosItem *currItem;
+	bool fakeupdposing = false; /* fake variable for _bt_binsrch */
 
 	Assert(!BTScanPosIsValid(so->currPos));
 
@@ -1003,7 +1018,7 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
 	so->markItemIndex = -1;		/* ditto */
 
 	/* position to the precise item on the page */
-	offnum = _bt_binsrch(rel, buf, keysCount, scankeys, nextkey);
+	offnum = _bt_binsrch(rel, buf, keysCount, scankeys, nextkey, &fakeupdposing);
 
 	/*
 	 * If nextkey = false, we are positioned at the first item >= scan key, or
@@ -1161,6 +1176,7 @@ _bt_readpage(IndexScanDesc scan, ScanDirection dir, OffsetNumber offnum)
 	int			itemIndex;
 	IndexTuple	itup;
 	bool		continuescan;
+	int i;
 
 	/*
 	 * We must have the buffer pinned and locked, but the usual macro can't be
@@ -1195,6 +1211,7 @@ _bt_readpage(IndexScanDesc scan, ScanDirection dir, OffsetNumber offnum)
 
 	/* initialize tuple workspace to empty */
 	so->currPos.nextTupleOffset = 0;
+	so->currPos.prevTupleOffset = 0;
 
 	/*
 	 * Now that the current page has been made consistent, the macro should be
@@ -1215,8 +1232,19 @@ _bt_readpage(IndexScanDesc scan, ScanDirection dir, OffsetNumber offnum)
 			if (itup != NULL)
 			{
 				/* tuple passes all scan key conditions, so remember it */
-				_bt_saveitem(so, itemIndex, offnum, itup);
-				itemIndex++;
+				if (BtreeTupleIsPosting(itup))
+				{
+					for (i = 0; i < BtreeGetNPosting(itup); i++)
+					{
+						_bt_savePostingitem(so, itemIndex, offnum, BtreeGetPostingN(itup, i), itup, i);
+						itemIndex++;
+					}
+				}
+				else
+				{
+					_bt_saveitem(so, itemIndex, offnum, itup);
+					itemIndex++;
+				}
 			}
 			if (!continuescan)
 			{
@@ -1228,7 +1256,7 @@ _bt_readpage(IndexScanDesc scan, ScanDirection dir, OffsetNumber offnum)
 			offnum = OffsetNumberNext(offnum);
 		}
 
-		Assert(itemIndex <= MaxIndexTuplesPerPage);
+		Assert(itemIndex <= MaxPackedIndexTuplesPerPage);
 		so->currPos.firstItem = 0;
 		so->currPos.lastItem = itemIndex - 1;
 		so->currPos.itemIndex = 0;
@@ -1236,7 +1264,7 @@ _bt_readpage(IndexScanDesc scan, ScanDirection dir, OffsetNumber offnum)
 	else
 	{
 		/* load items[] in descending order */
-		itemIndex = MaxIndexTuplesPerPage;
+		itemIndex = MaxPackedIndexTuplesPerPage;
 
 		offnum = Min(offnum, maxoff);
 
@@ -1246,8 +1274,20 @@ _bt_readpage(IndexScanDesc scan, ScanDirection dir, OffsetNumber offnum)
 			if (itup != NULL)
 			{
 				/* tuple passes all scan key conditions, so remember it */
-				itemIndex--;
-				_bt_saveitem(so, itemIndex, offnum, itup);
+				if (BtreeTupleIsPosting(itup))
+				{
+					for (i = 0; i < BtreeGetNPosting(itup); i++)
+					{
+						itemIndex--;
+						_bt_savePostingitem(so, itemIndex, offnum, BtreeGetPostingN(itup, i), itup, i);
+					}
+				}
+				else
+				{
+					itemIndex--;
+					_bt_saveitem(so, itemIndex, offnum, itup);
+				}
+
 			}
 			if (!continuescan)
 			{
@@ -1261,8 +1301,8 @@ _bt_readpage(IndexScanDesc scan, ScanDirection dir, OffsetNumber offnum)
 
 		Assert(itemIndex >= 0);
 		so->currPos.firstItem = itemIndex;
-		so->currPos.lastItem = MaxIndexTuplesPerPage - 1;
-		so->currPos.itemIndex = MaxIndexTuplesPerPage - 1;
+		so->currPos.lastItem = MaxPackedIndexTuplesPerPage - 1;
+		so->currPos.itemIndex = MaxPackedIndexTuplesPerPage - 1;
 	}
 
 	return (so->currPos.firstItem <= so->currPos.lastItem);
@@ -1275,6 +1315,8 @@ _bt_saveitem(BTScanOpaque so, int itemIndex,
 {
 	BTScanPosItem *currItem = &so->currPos.items[itemIndex];
 
+	Assert (!BtreeTupleIsPosting(itup));
+
 	currItem->heapTid = itup->t_tid;
 	currItem->indexOffset = offnum;
 	if (so->currTuples)
@@ -1288,6 +1330,37 @@ _bt_saveitem(BTScanOpaque so, int itemIndex,
 }
 
 /*
+ * Save an index item into so->currPos.items[itemIndex]
+ * Performing index-only scan, handle the first elem separately.
+ * Save the key once, and connect it with posting tids using tupleOffset.
+ */
+static void
+_bt_savePostingitem(BTScanOpaque so, int itemIndex,
+			 OffsetNumber offnum, ItemPointer iptr, IndexTuple itup, int i)
+{
+	BTScanPosItem *currItem = &so->currPos.items[itemIndex];
+
+	currItem->heapTid = *iptr;
+	currItem->indexOffset = offnum;
+
+	if (so->currTuples)
+	{
+		if (i == 0)
+		{
+			/* save key. the same for all tuples in the posting */
+			Size		itupsz = BtreeGetPostingOffset(itup);
+			currItem->tupleOffset = so->currPos.nextTupleOffset;
+			memcpy(so->currTuples + so->currPos.nextTupleOffset, itup, itupsz);
+			so->currPos.nextTupleOffset += MAXALIGN(itupsz);
+			so->currPos.prevTupleOffset = currItem->tupleOffset;
+		}
+		else
+			currItem->tupleOffset = so->currPos.prevTupleOffset;
+	}
+}
+
+
+/*
  *	_bt_steppage() -- Step to next page containing valid data for scan
  *
  * On entry, if so->currPos.buf is valid the buffer is pinned but not locked;
diff --git a/src/backend/access/nbtree/nbtsort.c b/src/backend/access/nbtree/nbtsort.c
index 99a014e..e29d63f 100644
--- a/src/backend/access/nbtree/nbtsort.c
+++ b/src/backend/access/nbtree/nbtsort.c
@@ -75,6 +75,7 @@
 #include "utils/rel.h"
 #include "utils/sortsupport.h"
 #include "utils/tuplesort.h"
+#include "catalog/catalog.h"
 
 
 /*
@@ -527,15 +528,120 @@ _bt_buildadd(BTWriteState *wstate, BTPageState *state, IndexTuple itup)
 		Assert(last_off > P_FIRSTKEY);
 		ii = PageGetItemId(opage, last_off);
 		oitup = (IndexTuple) PageGetItem(opage, ii);
-		_bt_sortaddtup(npage, ItemIdGetLength(ii), oitup, P_FIRSTKEY);
 
 		/*
-		 * Move 'last' into the high key position on opage
+		 * If the item is PostingTuple, we can cut it.
+		 * Because HIKEY is not considered as real data, and it needn't to keep any ItemPointerData at all.
+		 * And of course it needn't to keep a list of ipd.
+		 * But, if it had a big posting list, there will be plenty of free space on the opage.
+		 * So we must split Posting tuple into 2 pieces.
 		 */
-		hii = PageGetItemId(opage, P_HIKEY);
-		*hii = *ii;
-		ItemIdSetUnused(ii);	/* redundant */
-		((PageHeader) opage)->pd_lower -= sizeof(ItemIdData);
+		 if (BtreeTupleIsPosting(oitup))
+		 {
+			int nipd, ntocut, ntoleave;
+			Size keytupsz;
+			IndexTuple keytup;
+			nipd = BtreeGetNPosting(oitup);
+			ntocut = (sizeof(ItemIdData) + BtreeGetPostingOffset(oitup))/sizeof(ItemPointerData);
+			ntocut++; /* round up to be sure that we cut enough */
+			ntoleave = nipd - ntocut;
+
+			/*
+			 * 0) Form key tuple, that doesn't contain any ipd.
+			 * NOTE: key tuple will have blkno & offset suitable for P_HIKEY.
+			 * any function that uses keytup should handle them itself.
+			 */
+			keytupsz =  BtreeGetPostingOffset(oitup);
+			keytup = palloc0(keytupsz);
+			memcpy (keytup, oitup, keytupsz);
+			keytup->t_info &= ~INDEX_SIZE_MASK;
+			keytup->t_info |= keytupsz;
+			ItemPointerSet(&(keytup->t_tid), oblkno, P_HIKEY);
+
+			if (ntocut < nipd)
+			{
+				ItemPointerData *newipd;
+				IndexTuple newitup, newlasttup;
+				/*
+				 * 1) Cut part of old tuple to shift to npage.
+				 * And insert it as P_FIRSTKEY.
+				 * This tuple is based on keytup.
+				 * Blkno & offnum are reset in BtreeFormPackedTuple.
+				 */
+				newipd = palloc0(sizeof(ItemPointerData)*ntocut);
+				/* Note, that we cut last 'ntocut' items */
+				memcpy(newipd, BtreeGetPosting(oitup)+ntoleave, sizeof(ItemPointerData)*ntocut);
+				newitup = BtreeFormPackedTuple(keytup, newipd, ntocut);
+
+				_bt_sortaddtup(npage, IndexTupleSize(newitup), newitup, P_FIRSTKEY);
+				pfree(newipd);
+				pfree(newitup);
+
+				/*
+				 * 2) set last item to the P_HIKEY linp
+				 * Move 'last' into the high key position on opage
+				 * NOTE: Do this because of indextuple deletion algorithm, which
+				 * doesn't allow to delete an item while we have unused one before it.
+				 */
+				hii = PageGetItemId(opage, P_HIKEY);
+				*hii = *ii;
+				ItemIdSetUnused(ii);	/* redundant */
+				((PageHeader) opage)->pd_lower -= sizeof(ItemIdData);
+
+				/* 3) delete "wrong" high key */
+				PageIndexTupleDelete(opage, P_HIKEY);
+
+				/* 4)Insert keytup as P_HIKEY. */
+				_bt_sortaddtup(opage, IndexTupleSize(keytup), keytup,  P_HIKEY);
+
+				/* 5) form the part of old tuple with ntoleave ipds. And insert it as last tuple. */
+				newlasttup = BtreeFormPackedTuple(keytup, BtreeGetPosting(oitup), ntoleave);
+
+				_bt_sortaddtup(opage, IndexTupleSize(newlasttup), newlasttup, PageGetMaxOffsetNumber(opage)+1);
+
+				pfree(newlasttup);
+			}
+			else
+			{
+				/* The tuple isn't big enough to split it. Handle it as a normal tuple. */
+
+				/*
+				 * 1) Shift the last tuple to npage.
+				 * Insert it as P_FIRSTKEY.
+				 */
+				_bt_sortaddtup(npage, ItemIdGetLength(ii), oitup, P_FIRSTKEY);
+
+				/* 2) set last item to the P_HIKEY linp */
+				/* Move 'last' into the high key position on opage */
+				hii = PageGetItemId(opage, P_HIKEY);
+				*hii = *ii;
+				ItemIdSetUnused(ii);	/* redundant */
+				((PageHeader) opage)->pd_lower -= sizeof(ItemIdData);
+
+				/* 3) delete "wrong" high key */
+				PageIndexTupleDelete(opage, P_HIKEY);
+
+				/* 4)Insert keytup as P_HIKEY. */
+				_bt_sortaddtup(opage, IndexTupleSize(keytup), keytup,  P_HIKEY);
+
+			}
+			pfree(keytup);
+		 }
+		 else
+		 {
+			/*
+			 * 1) Shift the last tuple to npage.
+			 * Insert it as P_FIRSTKEY.
+			 */
+			_bt_sortaddtup(npage, ItemIdGetLength(ii), oitup, P_FIRSTKEY);
+
+			/* 2) set last item to the P_HIKEY linp */
+			/* Move 'last' into the high key position on opage */
+			hii = PageGetItemId(opage, P_HIKEY);
+			*hii = *ii;
+			ItemIdSetUnused(ii);	/* redundant */
+			((PageHeader) opage)->pd_lower -= sizeof(ItemIdData);
+		}
 
 		/*
 		 * Link the old page into its parent, using its minimum key. If we
@@ -547,6 +653,7 @@ _bt_buildadd(BTWriteState *wstate, BTPageState *state, IndexTuple itup)
 
 		Assert(state->btps_minkey != NULL);
 		ItemPointerSet(&(state->btps_minkey->t_tid), oblkno, P_HIKEY);
+
 		_bt_buildadd(wstate, state->btps_next, state->btps_minkey);
 		pfree(state->btps_minkey);
 
@@ -555,7 +662,9 @@ _bt_buildadd(BTWriteState *wstate, BTPageState *state, IndexTuple itup)
 		 * it off the old page, not the new one, in case we are not at leaf
 		 * level.
 		 */
-		state->btps_minkey = CopyIndexTuple(oitup);
+		ItemId iihk = PageGetItemId(opage, P_HIKEY);
+		IndexTuple hikey = (IndexTuple) PageGetItem(opage, iihk);
+		state->btps_minkey = CopyIndexTuple(hikey);
 
 		/*
 		 * Set the sibling links for both pages.
@@ -590,7 +699,29 @@ _bt_buildadd(BTWriteState *wstate, BTPageState *state, IndexTuple itup)
 	if (last_off == P_HIKEY)
 	{
 		Assert(state->btps_minkey == NULL);
-		state->btps_minkey = CopyIndexTuple(itup);
+
+		if (BtreeTupleIsPosting(itup))
+		{
+			Size keytupsz;
+			IndexTuple keytup;
+
+			/*
+			 * 0) Form key tuple, that doesn't contain any ipd.
+			 * NOTE: key tuple will have blkno & offset suitable for P_HIKEY.
+			 * any function that uses keytup should handle them itself.
+			 */
+			keytupsz =  BtreeGetPostingOffset(itup);
+			keytup = palloc0(keytupsz);
+			memcpy (keytup, itup, keytupsz);
+
+			keytup->t_info &= ~INDEX_SIZE_MASK;
+			keytup->t_info |= keytupsz;
+			ItemPointerSet(&(keytup->t_tid), nblkno, P_HIKEY);
+
+			state->btps_minkey = CopyIndexTuple(keytup);
+		}
+		else
+			state->btps_minkey = CopyIndexTuple(itup);
 	}
 
 	/*
@@ -670,6 +801,67 @@ _bt_uppershutdown(BTWriteState *wstate, BTPageState *state)
 }
 
 /*
+ * Prepare SortSupport structure for indextuples comparison
+ */
+SortSupport
+_bt_prepare_SortSupport(BTWriteState *wstate, int keysz)
+{
+	/* Prepare SortSupport data for each column */
+	ScanKey		indexScanKey = _bt_mkscankey_nodata(wstate->index);
+	SortSupport sortKeys = (SortSupport) palloc0(keysz * sizeof(SortSupportData));
+	int i;
+
+	for (i = 0; i < keysz; i++)
+	{
+		SortSupport sortKey = sortKeys + i;
+		ScanKey		scanKey = indexScanKey + i;
+		int16		strategy;
+
+		sortKey->ssup_cxt = CurrentMemoryContext;
+		sortKey->ssup_collation = scanKey->sk_collation;
+		sortKey->ssup_nulls_first =
+			(scanKey->sk_flags & SK_BT_NULLS_FIRST) != 0;
+		sortKey->ssup_attno = scanKey->sk_attno;
+		/* Abbreviation is not supported here */
+		sortKey->abbreviate = false;
+
+		AssertState(sortKey->ssup_attno != 0);
+
+		strategy = (scanKey->sk_flags & SK_BT_DESC) != 0 ?
+			BTGreaterStrategyNumber : BTLessStrategyNumber;
+
+		PrepareSortSupportFromIndexRel(wstate->index, strategy, sortKey);
+	}
+
+	_bt_freeskey(indexScanKey);
+	return sortKeys;
+}
+
+/*
+ * Compare two tuples using sortKey i
+ */
+int _bt_call_comparator(SortSupport sortKeys, int i,
+						 IndexTuple itup, IndexTuple itup2, TupleDesc tupdes)
+{
+		SortSupport entry;
+		Datum		attrDatum1,
+					attrDatum2;
+		bool		isNull1,
+					isNull2;
+		int32		compare;
+
+		entry = sortKeys + i - 1;
+		attrDatum1 = index_getattr(itup, i, tupdes, &isNull1);
+		attrDatum2 = index_getattr(itup2, i, tupdes, &isNull2);
+
+		compare = ApplySortComparator(attrDatum1, isNull1,
+										attrDatum2, isNull2,
+										entry);
+
+		return compare;
+}
+
+/*
  * Read tuples in correct sort order from tuplesort, and load them into
  * btree leaves.
  */
@@ -679,16 +871,20 @@ _bt_load(BTWriteState *wstate, BTSpool *btspool, BTSpool *btspool2)
 	BTPageState *state = NULL;
 	bool		merge = (btspool2 != NULL);
 	IndexTuple	itup,
-				itup2 = NULL;
+				itup2 = NULL,
+				itupprev = NULL;
 	bool		should_free,
 				should_free2,
 				load1;
 	TupleDesc	tupdes = RelationGetDescr(wstate->index);
 	int			i,
 				keysz = RelationGetNumberOfAttributes(wstate->index);
-	ScanKey		indexScanKey = NULL;
+	int			ntuples = 0;
 	SortSupport sortKeys;
 
+	/* Prepare SortSupport data */
+	sortKeys = (SortSupport)_bt_prepare_SortSupport(wstate, keysz);
+
 	if (merge)
 	{
 		/*
@@ -701,34 +897,6 @@ _bt_load(BTWriteState *wstate, BTSpool *btspool, BTSpool *btspool2)
 									   true, &should_free);
 		itup2 = tuplesort_getindextuple(btspool2->sortstate,
 										true, &should_free2);
-		indexScanKey = _bt_mkscankey_nodata(wstate->index);
-
-		/* Prepare SortSupport data for each column */
-		sortKeys = (SortSupport) palloc0(keysz * sizeof(SortSupportData));
-
-		for (i = 0; i < keysz; i++)
-		{
-			SortSupport sortKey = sortKeys + i;
-			ScanKey		scanKey = indexScanKey + i;
-			int16		strategy;
-
-			sortKey->ssup_cxt = CurrentMemoryContext;
-			sortKey->ssup_collation = scanKey->sk_collation;
-			sortKey->ssup_nulls_first =
-				(scanKey->sk_flags & SK_BT_NULLS_FIRST) != 0;
-			sortKey->ssup_attno = scanKey->sk_attno;
-			/* Abbreviation is not supported here */
-			sortKey->abbreviate = false;
-
-			AssertState(sortKey->ssup_attno != 0);
-
-			strategy = (scanKey->sk_flags & SK_BT_DESC) != 0 ?
-				BTGreaterStrategyNumber : BTLessStrategyNumber;
-
-			PrepareSortSupportFromIndexRel(wstate->index, strategy, sortKey);
-		}
-
-		_bt_freeskey(indexScanKey);
 
 		for (;;)
 		{
@@ -742,20 +910,8 @@ _bt_load(BTWriteState *wstate, BTSpool *btspool, BTSpool *btspool2)
 			{
 				for (i = 1; i <= keysz; i++)
 				{
-					SortSupport entry;
-					Datum		attrDatum1,
-								attrDatum2;
-					bool		isNull1,
-								isNull2;
-					int32		compare;
-
-					entry = sortKeys + i - 1;
-					attrDatum1 = index_getattr(itup, i, tupdes, &isNull1);
-					attrDatum2 = index_getattr(itup2, i, tupdes, &isNull2);
-
-					compare = ApplySortComparator(attrDatum1, isNull1,
-												  attrDatum2, isNull2,
-												  entry);
+					int32 compare = _bt_call_comparator(sortKeys, i, itup, itup2, tupdes);
+
 					if (compare > 0)
 					{
 						load1 = false;
@@ -794,19 +950,137 @@ _bt_load(BTWriteState *wstate, BTSpool *btspool, BTSpool *btspool2)
 	else
 	{
 		/* merge is unnecessary */
-		while ((itup = tuplesort_getindextuple(btspool->sortstate,
+
+		Relation indexRelation = wstate->index;
+		Form_pg_index index = indexRelation->rd_index;
+
+		if (index->indisunique)
+		{
+			/* Do not use compression for unique indexes. */
+			while ((itup = tuplesort_getindextuple(btspool->sortstate,
 											   true, &should_free)) != NULL)
+			{
+				/* When we see first tuple, create first index page */
+				if (state == NULL)
+					state = _bt_pagestate(wstate, 0);
+
+				_bt_buildadd(wstate, state, itup);
+				if (should_free)
+					pfree(itup);
+			}
+		}
+		else
 		{
-			/* When we see first tuple, create first index page */
-			if (state == NULL)
-				state = _bt_pagestate(wstate, 0);
+			ItemPointerData *ipd = NULL;
+			IndexTuple 		postingtuple;
+			Size			maxitemsize = 0,
+							maxpostingsize = 0;
+			int32 			compare = 0;
 
-			_bt_buildadd(wstate, state, itup);
-			if (should_free)
-				pfree(itup);
+			while ((itup = tuplesort_getindextuple(btspool->sortstate,
+											   true, &should_free)) != NULL)
+			{
+				/* When we see first tuple, create first index page */
+				if (state == NULL)
+				{
+					state = _bt_pagestate(wstate, 0);
+					maxitemsize = BTMaxItemSize(state->btps_page);
+				}
+
+				/*
+				 * Compare current tuple with previous one.
+				 * If tuples are equal, we can unite them into a posting list.
+				 */
+				if (itupprev != NULL)
+				{
+					/* compare tuples */
+					compare = 0;
+					for (i = 1; i <= keysz; i++)
+					{
+						compare = _bt_call_comparator(sortKeys, i, itup, itupprev, tupdes);
+						if (compare != 0)
+							break;
+					}
+
+					if (compare == 0)
+					{
+						/* Tuples are equal. Create or update posting */
+						if (ntuples == 0)
+						{
+							/*
+							 * We haven't suitable posting list yet, so allocate
+							 * it and save both itupprev and current tuple.
+							 */
+
+							ipd = palloc0(maxitemsize);
+
+							memcpy(ipd, itupprev, sizeof(ItemPointerData));
+							ntuples++;
+							memcpy(ipd + ntuples, itup, sizeof(ItemPointerData));
+							ntuples++;
+						}
+						else
+						{
+							if ((ntuples+1)*sizeof(ItemPointerData) < maxpostingsize)
+							{
+								memcpy(ipd + ntuples, itup, sizeof(ItemPointerData));
+								ntuples++;
+							}
+							else
+							{
+								postingtuple = BtreeFormPackedTuple(itupprev, ipd, ntuples);
+								_bt_buildadd(wstate, state, postingtuple);
+								ntuples = 0;
+								pfree(ipd);
+							}
+						}
+
+					}
+					else
+					{
+						/* Tuples aren't equal. Insert itupprev into index. */
+						if (ntuples == 0)
+							_bt_buildadd(wstate, state, itupprev);
+						else
+						{
+							postingtuple = BtreeFormPackedTuple(itupprev, ipd, ntuples);
+							_bt_buildadd(wstate, state, postingtuple);
+							ntuples = 0;
+							pfree(ipd);
+						}
+					}
+				}
+
+				/*
+				 * Copy the tuple into temp variable itupprev
+				 * to compare it with the following tuple
+				 * and maybe unite them into a posting tuple
+				 */
+				itupprev = CopyIndexTuple(itup);
+				if (should_free)
+					pfree(itup);
+
+				/* compute max size of ipd list */
+				maxpostingsize = maxitemsize - IndexInfoFindDataOffset(itupprev->t_info) - MAXALIGN(IndexTupleSize(itupprev));
+			}
+
+			/* Handle the last item.*/
+			if (ntuples == 0)
+			{
+				if (itupprev != NULL)
+					_bt_buildadd(wstate, state, itupprev);
+			}
+			else
+			{
+				Assert(ipd!=NULL);
+				Assert(itupprev != NULL);
+				postingtuple = BtreeFormPackedTuple(itupprev, ipd, ntuples);
+				_bt_buildadd(wstate, state, postingtuple);
+				ntuples = 0;
+				pfree(ipd);
+			}
 		}
 	}
-
 	/* Close down final pages and write the metapage */
 	_bt_uppershutdown(wstate, state);
 
diff --git a/src/backend/access/nbtree/nbtutils.c b/src/backend/access/nbtree/nbtutils.c
index c850b48..0291342 100644
--- a/src/backend/access/nbtree/nbtutils.c
+++ b/src/backend/access/nbtree/nbtutils.c
@@ -1821,7 +1821,9 @@ _bt_killitems(IndexScanDesc scan)
 			ItemId		iid = PageGetItemId(page, offnum);
 			IndexTuple	ituple = (IndexTuple) PageGetItem(page, iid);
 
-			if (ItemPointerEquals(&ituple->t_tid, &kitem->heapTid))
+			/* No microvacuum for posting tuples */
+			if (!BtreeTupleIsPosting(ituple)
+				&& (ItemPointerEquals(&ituple->t_tid, &kitem->heapTid)))
 			{
 				/* found the item */
 				ItemIdMarkDead(iid);
@@ -2063,3 +2065,71 @@ btoptions(Datum reloptions, bool validate)
 {
 	return default_reloptions(reloptions, validate, RELOPT_KIND_BTREE);
 }
+
+
+/*
+ * Already have basic index tuple that contains key datum
+ */
+IndexTuple
+BtreeFormPackedTuple(IndexTuple tuple, ItemPointerData *data, int nipd)
+{
+	int i;
+	uint32		newsize;
+	IndexTuple itup = CopyIndexTuple(tuple);
+
+	/*
+	 * Determine and store offset to the posting list.
+	 */
+	newsize = IndexTupleSize(itup);
+	newsize = SHORTALIGN(newsize);
+
+	/*
+	 * Set meta info about the posting list.
+	 */
+	BtreeSetPostingOffset(itup, newsize);
+	BtreeSetNPosting(itup, nipd);
+	/*
+	 * Add space needed for posting list, if any.  Then check that the tuple
+	 * won't be too big to store.
+	 */
+	newsize += sizeof(ItemPointerData)*nipd;
+	newsize = MAXALIGN(newsize);
+
+	/*
+	 * Resize tuple if needed
+	 */
+	if (newsize != IndexTupleSize(itup))
+	{
+		itup = repalloc(itup, newsize);
+
+		/*
+		 * PostgreSQL 9.3 and earlier did not clear this new space, so we
+		 * might find uninitialized padding when reading tuples from disk.
+		 */
+		memset((char *) itup + IndexTupleSize(itup),
+			   0, newsize - IndexTupleSize(itup));
+		/* set new size in tuple header */
+		itup->t_info &= ~INDEX_SIZE_MASK;
+		itup->t_info |= newsize;
+	}
+
+	/*
+	 * Copy data into the posting tuple
+	 */
+	memcpy(BtreeGetPosting(itup), data, sizeof(ItemPointerData)*nipd);
+	return itup;
+}
+
+IndexTuple
+BtreeReformPackedTuple(IndexTuple tuple, ItemPointerData *data, int nipd)
+{
+	int size;
+	if (BtreeTupleIsPosting(tuple))
+	{
+		size = BtreeGetPostingOffset(tuple);
+		tuple->t_info &= ~INDEX_SIZE_MASK;
+		tuple->t_info |= size;
+	}
+
+	return BtreeFormPackedTuple(tuple, data, nipd);
+}
diff --git a/src/backend/storage/buffer/buf_table.c b/src/backend/storage/buffer/buf_table.c
index 39e8baf..dd5acb7 100644
--- a/src/backend/storage/buffer/buf_table.c
+++ b/src/backend/storage/buffer/buf_table.c
@@ -62,7 +62,7 @@ InitBufTable(int size)
 	info.num_partitions = NUM_BUFFER_PARTITIONS;
 
 	SharedBufHash = ShmemInitHash("Shared Buffer Lookup Table",
-								  size, size,
+								  size,
 								  &info,
 								  HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
 }
diff --git a/src/backend/storage/ipc/shmem.c b/src/backend/storage/ipc/shmem.c
index 81506ea..4c18701 100644
--- a/src/backend/storage/ipc/shmem.c
+++ b/src/backend/storage/ipc/shmem.c
@@ -237,7 +237,7 @@ InitShmemIndex(void)
 	hash_flags = HASH_ELEM;
 
 	ShmemIndex = ShmemInitHash("ShmemIndex",
-							   SHMEM_INDEX_SIZE, SHMEM_INDEX_SIZE,
+							   SHMEM_INDEX_SIZE,
 							   &info, hash_flags);
 }
 
@@ -255,17 +255,12 @@ InitShmemIndex(void)
  * exceeded substantially (since it's used to compute directory size and
  * the hash table buckets will get overfull).
  *
- * init_size is the number of hashtable entries to preallocate.  For a table
- * whose maximum size is certain, this should be equal to max_size; that
- * ensures that no run-time out-of-shared-memory failures can occur.
- *
  * Note: before Postgres 9.0, this function returned NULL for some failure
  * cases.  Now, it always throws error instead, so callers need not check
  * for NULL.
  */
 HTAB *
 ShmemInitHash(const char *name, /* table string name for shmem index */
-			  long init_size,	/* initial table size */
 			  long max_size,	/* max size of the table */
 			  HASHCTL *infoP,	/* info about key and bucket size */
 			  int hash_flags)	/* info about infoP */
@@ -299,7 +294,7 @@ ShmemInitHash(const char *name, /* table string name for shmem index */
 	/* Pass location of hashtable header to hash_create */
 	infoP->hctl = (HASHHDR *) location;
 
-	return hash_create(name, init_size, infoP, hash_flags);
+	return hash_create(name, max_size, infoP, hash_flags);
 }
 
 /*
diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c
index 9c2e49c..8d9b36a 100644
--- a/src/backend/storage/lmgr/lock.c
+++ b/src/backend/storage/lmgr/lock.c
@@ -373,8 +373,7 @@ void
 InitLocks(void)
 {
 	HASHCTL		info;
-	long		init_table_size,
-				max_table_size;
+	long		max_table_size;
 	bool		found;
 
 	/*
@@ -382,7 +381,6 @@ InitLocks(void)
 	 * calculations must agree with LockShmemSize!
 	 */
 	max_table_size = NLOCKENTS();
-	init_table_size = max_table_size / 2;
 
 	/*
 	 * Allocate hash table for LOCK structs.  This stores per-locked-object
@@ -394,14 +392,12 @@ InitLocks(void)
 	info.num_partitions = NUM_LOCK_PARTITIONS;
 
 	LockMethodLockHash = ShmemInitHash("LOCK hash",
-									   init_table_size,
 									   max_table_size,
 									   &info,
 									HASH_ELEM | HASH_BLOBS | HASH_PARTITION);
 
 	/* Assume an average of 2 holders per lock */
 	max_table_size *= 2;
-	init_table_size *= 2;
 
 	/*
 	 * Allocate hash table for PROCLOCK structs.  This stores
@@ -413,7 +409,6 @@ InitLocks(void)
 	info.num_partitions = NUM_LOCK_PARTITIONS;
 
 	LockMethodProcLockHash = ShmemInitHash("PROCLOCK hash",
-										   init_table_size,
 										   max_table_size,
 										   &info,
 								 HASH_ELEM | HASH_FUNCTION | HASH_PARTITION);
diff --git a/src/backend/storage/lmgr/predicate.c b/src/backend/storage/lmgr/predicate.c
index d9d4e22..fc72d2d 100644
--- a/src/backend/storage/lmgr/predicate.c
+++ b/src/backend/storage/lmgr/predicate.c
@@ -1116,7 +1116,6 @@ InitPredicateLocks(void)
 
 	PredicateLockTargetHash = ShmemInitHash("PREDICATELOCKTARGET hash",
 											max_table_size,
-											max_table_size,
 											&info,
 											HASH_ELEM | HASH_BLOBS |
 											HASH_PARTITION | HASH_FIXED_SIZE);
@@ -1144,7 +1143,6 @@ InitPredicateLocks(void)
 
 	PredicateLockHash = ShmemInitHash("PREDICATELOCK hash",
 									  max_table_size,
-									  max_table_size,
 									  &info,
 									  HASH_ELEM | HASH_FUNCTION |
 									  HASH_PARTITION | HASH_FIXED_SIZE);
@@ -1225,7 +1223,6 @@ InitPredicateLocks(void)
 
 	SerializableXidHash = ShmemInitHash("SERIALIZABLEXID hash",
 										max_table_size,
-										max_table_size,
 										&info,
 										HASH_ELEM | HASH_BLOBS |
 										HASH_FIXED_SIZE);
diff --git a/src/backend/utils/hash/dynahash.c b/src/backend/utils/hash/dynahash.c
index 24a53da..ce9bb9c 100644
--- a/src/backend/utils/hash/dynahash.c
+++ b/src/backend/utils/hash/dynahash.c
@@ -15,7 +15,7 @@
  * to hash_create.  This prevents any attempt to split buckets on-the-fly.
  * Therefore, each hash bucket chain operates independently, and no fields
  * of the hash header change after init except nentries and freeList.
- * A partitioned table uses a spinlock to guard changes of those two fields.
+ * A partitioned table uses spinlocks to guard changes of those fields.
  * This lets any subset of the hash buckets be treated as a separately
  * lockable partition.  We expect callers to use the low-order bits of a
  * lookup key's hash value as a partition number --- this will work because
@@ -87,6 +87,7 @@
 #include "access/xact.h"
 #include "storage/shmem.h"
 #include "storage/spin.h"
+#include "storage/lock.h"
 #include "utils/dynahash.h"
 #include "utils/memutils.h"
 
@@ -128,12 +129,26 @@ typedef HASHBUCKET *HASHSEGMENT;
  */
 struct HASHHDR
 {
-	/* In a partitioned table, take this lock to touch nentries or freeList */
-	slock_t		mutex;			/* unused if not partitioned table */
-
-	/* These fields change during entry addition/deletion */
-	long		nentries;		/* number of entries in hash table */
-	HASHELEMENT *freeList;		/* linked list of free elements */
+	/*
+	 * There are two fields declared below: nentries and freeList. nentries
+	 * stores current number of entries in a hash table. freeList is a linked
+	 * list of free elements.
+	 *
+	 * To keep these fields consistent in a partitioned table we need to
+	 * synchronize access to them using a spinlock. But it turned out that a
+	 * single spinlock can create a bottleneck. To prevent lock contention an
+	 * array of NUM_LOCK_PARTITIONS spinlocks is used. Each spinlock
+	 * corresponds to a single table partition (see PARTITION_IDX definition)
+	 * and protects one element of nentries and freeList arrays. Since
+	 * partitions are locked on a calling side depending on lower bits of a
+	 * hash value this particular number of spinlocks prevents deadlocks.
+	 *
+	 * If hash table is not partitioned only nentries[0] and freeList[0] are
+	 * used and spinlocks are not used at all.
+	 */
+	slock_t		mutex[NUM_LOCK_PARTITIONS];		/* array of spinlocks */
+	long		nentries[NUM_LOCK_PARTITIONS];	/* number of entries */
+	HASHELEMENT *freeList[NUM_LOCK_PARTITIONS]; /* lists of free elements */
 
 	/* These fields can change, but not in a partitioned table */
 	/* Also, dsize can't change in a shared table, even if unpartitioned */
@@ -166,6 +181,8 @@ struct HASHHDR
 
 #define IS_PARTITIONED(hctl)  ((hctl)->num_partitions != 0)
 
+#define PARTITION_IDX(hctl, hashcode) (IS_PARTITIONED(hctl) ? LockHashPartition(hashcode) : 0)
+
 /*
  * Top control structure for a hashtable --- in a shared table, each backend
  * has its own copy (OK since no fields change at runtime)
@@ -219,10 +236,10 @@ static long hash_accesses,
  */
 static void *DynaHashAlloc(Size size);
 static HASHSEGMENT seg_alloc(HTAB *hashp);
-static bool element_alloc(HTAB *hashp, int nelem);
+static bool element_alloc(HTAB *hashp, int nelem, int partition_idx);
 static bool dir_realloc(HTAB *hashp);
 static bool expand_table(HTAB *hashp);
-static HASHBUCKET get_hash_entry(HTAB *hashp);
+static HASHBUCKET get_hash_entry(HTAB *hashp, int partition_idx);
 static void hdefault(HTAB *hashp);
 static int	choose_nelem_alloc(Size entrysize);
 static bool init_htab(HTAB *hashp, long nelem);
@@ -282,6 +299,9 @@ hash_create(const char *tabname, long nelem, HASHCTL *info, int flags)
 {
 	HTAB	   *hashp;
 	HASHHDR    *hctl;
+	int			i,
+				partitions_number,
+				nelem_alloc;
 
 	/*
 	 * For shared hash tables, we have a local hash header (HTAB struct) that
@@ -482,10 +502,24 @@ hash_create(const char *tabname, long nelem, HASHCTL *info, int flags)
 	if ((flags & HASH_SHARED_MEM) ||
 		nelem < hctl->nelem_alloc)
 	{
-		if (!element_alloc(hashp, (int) nelem))
-			ereport(ERROR,
-					(errcode(ERRCODE_OUT_OF_MEMORY),
-					 errmsg("out of memory")));
+		/*
+		 * If hash table is partitioned all freeLists have equal number of
+		 * elements. Otherwise only freeList[0] is used.
+		 */
+		if (IS_PARTITIONED(hashp->hctl))
+			partitions_number = NUM_LOCK_PARTITIONS;
+		else
+			partitions_number = 1;
+
+		nelem_alloc = ((int) nelem) / partitions_number;
+		if (nelem_alloc == 0)
+			nelem_alloc = 1;
+
+		for (i = 0; i < partitions_number; i++)
+			if (!element_alloc(hashp, nelem_alloc, i))
+				ereport(ERROR,
+						(errcode(ERRCODE_OUT_OF_MEMORY),
+						 errmsg("out of memory")));
 	}
 
 	if (flags & HASH_FIXED_SIZE)
@@ -503,9 +537,6 @@ hdefault(HTAB *hashp)
 
 	MemSet(hctl, 0, sizeof(HASHHDR));
 
-	hctl->nentries = 0;
-	hctl->freeList = NULL;
-
 	hctl->dsize = DEF_DIRSIZE;
 	hctl->nsegs = 0;
 
@@ -572,12 +603,14 @@ init_htab(HTAB *hashp, long nelem)
 	HASHSEGMENT *segp;
 	int			nbuckets;
 	int			nsegs;
+	int			i;
 
 	/*
 	 * initialize mutex if it's a partitioned table
 	 */
 	if (IS_PARTITIONED(hctl))
-		SpinLockInit(&hctl->mutex);
+		for (i = 0; i < NUM_LOCK_PARTITIONS; i++)
+			SpinLockInit(&(hctl->mutex[i]));
 
 	/*
 	 * Divide number of elements by the fill factor to determine a desired
@@ -648,7 +681,7 @@ init_htab(HTAB *hashp, long nelem)
 			"HIGH MASK       ", hctl->high_mask,
 			"LOW  MASK       ", hctl->low_mask,
 			"NSEGS           ", hctl->nsegs,
-			"NENTRIES        ", hctl->nentries);
+			"NENTRIES        ", hash_get_num_entries(hctl));
 #endif
 	return true;
 }
@@ -769,7 +802,7 @@ hash_stats(const char *where, HTAB *hashp)
 			where, hashp->hctl->accesses, hashp->hctl->collisions);
 
 	fprintf(stderr, "hash_stats: entries %ld keysize %ld maxp %u segmentcount %ld\n",
-			hashp->hctl->nentries, (long) hashp->hctl->keysize,
+			hash_get_num_entries(hashp), (long) hashp->hctl->keysize,
 			hashp->hctl->max_bucket, hashp->hctl->nsegs);
 	fprintf(stderr, "%s: total accesses %ld total collisions %ld\n",
 			where, hash_accesses, hash_collisions);
@@ -863,6 +896,7 @@ hash_search_with_hash_value(HTAB *hashp,
 	HASHBUCKET	currBucket;
 	HASHBUCKET *prevBucketPtr;
 	HashCompareFunc match;
+	int			partition_idx = PARTITION_IDX(hctl, hashvalue);
 
 #if HASH_STATISTICS
 	hash_accesses++;
@@ -885,7 +919,7 @@ hash_search_with_hash_value(HTAB *hashp,
 		 * order of these tests is to try to check cheaper conditions first.
 		 */
 		if (!IS_PARTITIONED(hctl) && !hashp->frozen &&
-			hctl->nentries / (long) (hctl->max_bucket + 1) >= hctl->ffactor &&
+		hctl->nentries[0] / (long) (hctl->max_bucket + 1) >= hctl->ffactor &&
 			!has_seq_scans(hashp))
 			(void) expand_table(hashp);
 	}
@@ -943,20 +977,20 @@ hash_search_with_hash_value(HTAB *hashp,
 			{
 				/* if partitioned, must lock to touch nentries and freeList */
 				if (IS_PARTITIONED(hctl))
-					SpinLockAcquire(&hctl->mutex);
+					SpinLockAcquire(&(hctl->mutex[partition_idx]));
 
-				Assert(hctl->nentries > 0);
-				hctl->nentries--;
+				Assert(hctl->nentries[partition_idx] > 0);
+				hctl->nentries[partition_idx]--;
 
 				/* remove record from hash bucket's chain. */
 				*prevBucketPtr = currBucket->link;
 
 				/* add the record to the freelist for this table.  */
-				currBucket->link = hctl->freeList;
-				hctl->freeList = currBucket;
+				currBucket->link = hctl->freeList[partition_idx];
+				hctl->freeList[partition_idx] = currBucket;
 
 				if (IS_PARTITIONED(hctl))
-					SpinLockRelease(&hctl->mutex);
+					SpinLockRelease(&hctl->mutex[partition_idx]);
 
 				/*
 				 * better hope the caller is synchronizing access to this
@@ -982,7 +1016,7 @@ hash_search_with_hash_value(HTAB *hashp,
 				elog(ERROR, "cannot insert into frozen hashtable \"%s\"",
 					 hashp->tabname);
 
-			currBucket = get_hash_entry(hashp);
+			currBucket = get_hash_entry(hashp, partition_idx);
 			if (currBucket == NULL)
 			{
 				/* out of memory */
@@ -1175,41 +1209,71 @@ hash_update_hash_key(HTAB *hashp,
  * create a new entry if possible
  */
 static HASHBUCKET
-get_hash_entry(HTAB *hashp)
+get_hash_entry(HTAB *hashp, int partition_idx)
 {
-	HASHHDR *hctl = hashp->hctl;
+	HASHHDR    *hctl = hashp->hctl;
 	HASHBUCKET	newElement;
+	int			i,
+				borrow_from_idx;
 
 	for (;;)
 	{
 		/* if partitioned, must lock to touch nentries and freeList */
 		if (IS_PARTITIONED(hctl))
-			SpinLockAcquire(&hctl->mutex);
+			SpinLockAcquire(&hctl->mutex[partition_idx]);
 
 		/* try to get an entry from the freelist */
-		newElement = hctl->freeList;
+		newElement = hctl->freeList[partition_idx];
+
 		if (newElement != NULL)
-			break;
+		{
+			/* remove entry from freelist, bump nentries */
+			hctl->freeList[partition_idx] = newElement->link;
+			hctl->nentries[partition_idx]++;
+			if (IS_PARTITIONED(hctl))
+				SpinLockRelease(&hctl->mutex[partition_idx]);
+
+			return newElement;
+		}
 
-		/* no free elements.  allocate another chunk of buckets */
 		if (IS_PARTITIONED(hctl))
-			SpinLockRelease(&hctl->mutex);
+			SpinLockRelease(&hctl->mutex[partition_idx]);
 
-		if (!element_alloc(hashp, hctl->nelem_alloc))
+		/* no free elements.  allocate another chunk of buckets */
+		if (!element_alloc(hashp, hctl->nelem_alloc, partition_idx))
 		{
-			/* out of memory */
-			return NULL;
-		}
-	}
+			if (!IS_PARTITIONED(hctl))
+				return NULL;	/* out of memory */
 
-	/* remove entry from freelist, bump nentries */
-	hctl->freeList = newElement->link;
-	hctl->nentries++;
+			/* try to borrow element from another partition */
+			borrow_from_idx = partition_idx;
+			for (;;)
+			{
+				borrow_from_idx = (borrow_from_idx + 1) % NUM_LOCK_PARTITIONS;
+				if (borrow_from_idx == partition_idx)
+					break;
 
-	if (IS_PARTITIONED(hctl))
-		SpinLockRelease(&hctl->mutex);
+				SpinLockAcquire(&(hctl->mutex[borrow_from_idx]));
+				newElement = hctl->freeList[borrow_from_idx];
+
+				if (newElement != NULL)
+				{
+					hctl->freeList[borrow_from_idx] = newElement->link;
+					SpinLockRelease(&(hctl->mutex[borrow_from_idx]));
+
+					SpinLockAcquire(&hctl->mutex[partition_idx]);
+					hctl->nentries[partition_idx]++;
+					SpinLockRelease(&hctl->mutex[partition_idx]);
+
+					break;
+				}
 
-	return newElement;
+				SpinLockRelease(&(hctl->mutex[borrow_from_idx]));
+			}
+
+			return newElement;
+		}
+	}
 }
 
 /*
@@ -1218,11 +1282,21 @@ get_hash_entry(HTAB *hashp)
 long
 hash_get_num_entries(HTAB *hashp)
 {
+	int			i;
+	long		sum = hashp->hctl->nentries[0];
+
 	/*
 	 * We currently don't bother with the mutex; it's only sensible to call
 	 * this function if you've got lock on all partitions of the table.
 	 */
-	return hashp->hctl->nentries;
+
+	if (!IS_PARTITIONED(hashp->hctl))
+		return sum;
+
+	for (i = 1; i < NUM_LOCK_PARTITIONS; i++)
+		sum += hashp->hctl->nentries[i];
+
+	return sum;
 }
 
 /*
@@ -1530,9 +1604,9 @@ seg_alloc(HTAB *hashp)
  * allocate some new elements and link them into the free list
  */
 static bool
-element_alloc(HTAB *hashp, int nelem)
+element_alloc(HTAB *hashp, int nelem, int partition_idx)
 {
-	HASHHDR *hctl = hashp->hctl;
+	HASHHDR    *hctl = hashp->hctl;
 	Size		elementSize;
 	HASHELEMENT *firstElement;
 	HASHELEMENT *tmpElement;
@@ -1563,14 +1637,14 @@ element_alloc(HTAB *hashp, int nelem)
 
 	/* if partitioned, must lock to touch freeList */
 	if (IS_PARTITIONED(hctl))
-		SpinLockAcquire(&hctl->mutex);
+		SpinLockAcquire(&hctl->mutex[partition_idx]);
 
 	/* freelist could be nonempty if two backends did this concurrently */
-	firstElement->link = hctl->freeList;
-	hctl->freeList = prevElement;
+	firstElement->link = hctl->freeList[partition_idx];
+	hctl->freeList[partition_idx] = prevElement;
 
 	if (IS_PARTITIONED(hctl))
-		SpinLockRelease(&hctl->mutex);
+		SpinLockRelease(&hctl->mutex[partition_idx]);
 
 	return true;
 }
diff --git a/src/include/access/itup.h b/src/include/access/itup.h
index 8350fa0..eb4467a 100644
--- a/src/include/access/itup.h
+++ b/src/include/access/itup.h
@@ -137,7 +137,12 @@ typedef IndexAttributeBitMapData *IndexAttributeBitMap;
 #define MaxIndexTuplesPerPage	\
 	((int) ((BLCKSZ - SizeOfPageHeaderData) / \
 			(MAXALIGN(sizeof(IndexTupleData) + 1) + sizeof(ItemIdData))))
-
+#define MaxPackedIndexTuplesPerPage	\
+	((int) ((BLCKSZ - SizeOfPageHeaderData) / \
+			(sizeof(ItemPointerData))))
+// #define MaxIndexTuplesPerPage	\
+// 	((int) ((BLCKSZ - SizeOfPageHeaderData) / \
+// 			(sizeof(ItemPointerData))))
 
 /* routines in indextuple.c */
 extern IndexTuple index_form_tuple(TupleDesc tupleDescriptor,
diff --git a/src/include/access/nbtree.h b/src/include/access/nbtree.h
index 06822fa..41e407d 100644
--- a/src/include/access/nbtree.h
+++ b/src/include/access/nbtree.h
@@ -75,6 +75,7 @@ typedef BTPageOpaqueData *BTPageOpaque;
 #define BTP_SPLIT_END	(1 << 5)	/* rightmost page of split group */
 #define BTP_HAS_GARBAGE (1 << 6)	/* page has LP_DEAD tuples */
 #define BTP_INCOMPLETE_SPLIT (1 << 7)	/* right sibling's downlink is missing */
+#define BTP_HAS_POSTING (1 << 8)		/* page contains compressed duplicates (only for leaf pages) */
 
 /*
  * The max allowed value of a cycle ID is a bit less than 64K.  This is
@@ -181,6 +182,8 @@ typedef struct BTMetaPageData
 #define P_IGNORE(opaque)		((opaque)->btpo_flags & (BTP_DELETED|BTP_HALF_DEAD))
 #define P_HAS_GARBAGE(opaque)	((opaque)->btpo_flags & BTP_HAS_GARBAGE)
 #define P_INCOMPLETE_SPLIT(opaque)	((opaque)->btpo_flags & BTP_INCOMPLETE_SPLIT)
+#define P_HAS_POSTING(opaque)		((opaque)->btpo_flags & BTP_HAS_POSTING)
+
 
 /*
  *	Lehman and Yao's algorithm requires a ``high key'' on every non-rightmost
@@ -538,6 +541,8 @@ typedef struct BTScanPosData
 	 * location in the associated tuple storage workspace.
 	 */
 	int			nextTupleOffset;
+	/* prevTupleOffset is for Posting list handling*/
+	int			prevTupleOffset;
 
 	/*
 	 * The items array is always ordered in index order (ie, increasing
@@ -550,7 +555,7 @@ typedef struct BTScanPosData
 	int			lastItem;		/* last valid index in items[] */
 	int			itemIndex;		/* current index in items[] */
 
-	BTScanPosItem items[MaxIndexTuplesPerPage]; /* MUST BE LAST */
+	BTScanPosItem items[MaxPackedIndexTuplesPerPage]; /* MUST BE LAST */
 } BTScanPosData;
 
 typedef BTScanPosData *BTScanPos;
@@ -651,6 +656,28 @@ typedef BTScanOpaqueData *BTScanOpaque;
 #define SK_BT_DESC			(INDOPTION_DESC << SK_BT_INDOPTION_SHIFT)
 #define SK_BT_NULLS_FIRST	(INDOPTION_NULLS_FIRST << SK_BT_INDOPTION_SHIFT)
 
+
+/*
+ * We use our own ItemPointerGet(BlockNumber|OffsetNumber)
+ * to avoid Asserts, since sometimes the ip_posid isn't "valid"
+ */
+#define BtreeItemPointerGetBlockNumber(pointer) \
+	BlockIdGetBlockNumber(&(pointer)->ip_blkid)
+
+#define BtreeItemPointerGetOffsetNumber(pointer) \
+	((pointer)->ip_posid)
+
+#define BT_POSTING (1<<31)
+#define BtreeGetNPosting(itup)			BtreeItemPointerGetOffsetNumber(&(itup)->t_tid)
+#define BtreeSetNPosting(itup,n)		ItemPointerSetOffsetNumber(&(itup)->t_tid,n)
+
+#define BtreeGetPostingOffset(itup)		(BtreeItemPointerGetBlockNumber(&(itup)->t_tid) & (~BT_POSTING))
+#define BtreeSetPostingOffset(itup,n)	ItemPointerSetBlockNumber(&(itup)->t_tid,(n)|BT_POSTING)
+#define BtreeTupleIsPosting(itup)    	(BtreeItemPointerGetBlockNumber(&(itup)->t_tid) & BT_POSTING)
+#define BtreeGetPosting(itup)			(ItemPointerData*) ((char*)(itup) + BtreeGetPostingOffset(itup))
+#define BtreeGetPostingN(itup,n)		(ItemPointerData*) (BtreeGetPosting(itup) + n)
+
+
 /*
  * prototypes for functions in nbtree.c (external entry points for btree)
  */
@@ -715,8 +742,8 @@ extern BTStack _bt_search(Relation rel,
 extern Buffer _bt_moveright(Relation rel, Buffer buf, int keysz,
 			  ScanKey scankey, bool nextkey, bool forupdate, BTStack stack,
 			  int access);
-extern OffsetNumber _bt_binsrch(Relation rel, Buffer buf, int keysz,
-			ScanKey scankey, bool nextkey);
+extern OffsetNumber _bt_binsrch( Relation rel, Buffer buf, int keysz,
+								ScanKey scankey, bool nextkey, bool* updposting);
 extern int32 _bt_compare(Relation rel, int keysz, ScanKey scankey,
 			Page page, OffsetNumber offnum);
 extern bool _bt_first(IndexScanDesc scan, ScanDirection dir);
@@ -747,6 +774,8 @@ extern void _bt_end_vacuum_callback(int code, Datum arg);
 extern Size BTreeShmemSize(void);
 extern void BTreeShmemInit(void);
 extern bytea *btoptions(Datum reloptions, bool validate);
+extern IndexTuple BtreeFormPackedTuple(IndexTuple tuple, ItemPointerData *data, int nipd);
+extern IndexTuple BtreeReformPackedTuple(IndexTuple tuple, ItemPointerData *data, int nipd);
 
 /*
  * prototypes for functions in nbtvalidate.c
diff --git a/src/include/storage/lwlock.h b/src/include/storage/lwlock.h
index 5e8825e..177371b 100644
--- a/src/include/storage/lwlock.h
+++ b/src/include/storage/lwlock.h
@@ -128,13 +128,19 @@ extern char *MainLWLockNames[];
  * having this file include lock.h or bufmgr.h would be backwards.
  */
 
-/* Number of partitions of the shared buffer mapping hashtable */
-#define NUM_BUFFER_PARTITIONS  128
-
-/* Number of partitions the shared lock tables are divided into */
-#define LOG2_NUM_LOCK_PARTITIONS  4
+/*
+ * Number of partitions the shared lock tables are divided into.
+ *
+ * This particular number of partitions significantly reduces lock contention
+ * in partitioned hash tables, almost if partitioned tables didn't use any
+ * locking at all.
+ */
+#define LOG2_NUM_LOCK_PARTITIONS  7
 #define NUM_LOCK_PARTITIONS  (1 << LOG2_NUM_LOCK_PARTITIONS)
 
+/* Number of partitions of the shared buffer mapping hashtable */
+#define NUM_BUFFER_PARTITIONS NUM_LOCK_PARTITIONS
+
 /* Number of partitions the shared predicate lock tables are divided into */
 #define LOG2_NUM_PREDICATELOCK_PARTITIONS  4
 #define NUM_PREDICATELOCK_PARTITIONS  (1 << LOG2_NUM_PREDICATELOCK_PARTITIONS)
diff --git a/src/include/storage/shmem.h b/src/include/storage/shmem.h
index 6468e66..50cf928 100644
--- a/src/include/storage/shmem.h
+++ b/src/include/storage/shmem.h
@@ -37,7 +37,7 @@ extern void InitShmemAllocation(void);
 extern void *ShmemAlloc(Size size);
 extern bool ShmemAddrIsValid(const void *addr);
 extern void InitShmemIndex(void);
-extern HTAB *ShmemInitHash(const char *name, long init_size, long max_size,
+extern HTAB *ShmemInitHash(const char *name, long max_size,
 			  HASHCTL *infoP, int hash_flags);
 extern void *ShmemInitStruct(const char *name, Size size, bool *foundPtr);
 extern Size add_size(Size s1, Size s2);