0001-btree_compression_pg12_v2.patch

diff --git a/contrib/amcheck/verify_nbtree.c b/contrib/amcheck/verify_nbtree.c
index 9126c18..2b05b1e 100644
--- a/contrib/amcheck/verify_nbtree.c
+++ b/contrib/amcheck/verify_nbtree.c
@@ -1033,12 +1033,34 @@ bt_target_page_check(BtreeCheckState *state)
 		{
 			IndexTuple	norm;
 
-			norm = bt_normalize_tuple(state, itup);
-			bloom_add_element(state->filter, (unsigned char *) norm,
-							  IndexTupleSize(norm));
-			/* Be tidy */
-			if (norm != itup)
-				pfree(norm);
+			if (BTreeTupleIsPosting(itup))
+			{
+				IndexTuple	onetup;
+				int i;
+
+				/* Fingerprint all elements of posting tuple one by one */
+				for (i = 0; i < BTreeTupleGetNPosting(itup); i++)
+				{
+					onetup = BTreeGetNthTupleOfPosting(itup, i);
+
+					norm = bt_normalize_tuple(state, onetup);
+					bloom_add_element(state->filter, (unsigned char *) norm,
+									  IndexTupleSize(norm));
+					/* Be tidy */
+					if (norm != onetup)
+						pfree(norm);
+					pfree(onetup);
+				}
+			}
+			else
+			{
+				norm = bt_normalize_tuple(state, itup);
+				bloom_add_element(state->filter, (unsigned char *) norm,
+								  IndexTupleSize(norm));
+				/* Be tidy */
+				if (norm != itup)
+					pfree(norm);
+			}
 		}
 
 		/*
diff --git a/src/backend/access/nbtree/nbtinsert.c b/src/backend/access/nbtree/nbtinsert.c
index 602f884..26ddf32 100644
--- a/src/backend/access/nbtree/nbtinsert.c
+++ b/src/backend/access/nbtree/nbtinsert.c
@@ -20,6 +20,7 @@
 #include "access/tableam.h"
 #include "access/transam.h"
 #include "access/xloginsert.h"
+#include "catalog/catalog.h"
 #include "miscadmin.h"
 #include "storage/lmgr.h"
 #include "storage/predicate.h"
@@ -56,6 +57,8 @@ static void _bt_insert_parent(Relation rel, Buffer buf, Buffer rbuf,
 static bool _bt_pgaddtup(Page page, Size itemsize, IndexTuple itup,
 						 OffsetNumber itup_off);
 static void _bt_vacuum_one_page(Relation rel, Buffer buffer, Relation heapRel);
+static bool insert_itupprev_to_page(Page page, BTCompressState *compressState);
+static void _bt_compress_one_page(Relation rel, Buffer buffer, Relation heapRel);
 
 /*
  *	_bt_doinsert() -- Handle insertion of a single index tuple in the tree.
@@ -759,6 +762,12 @@ _bt_findinsertloc(Relation rel,
 			_bt_vacuum_one_page(rel, insertstate->buf, heapRel);
 			insertstate->bounds_valid = false;
 		}
+
+		/*
+		 * If the target page is full, try to compress the page
+		 */
+		if (PageGetFreeSpace(page) < insertstate->itemsz)
+			_bt_compress_one_page(rel, insertstate->buf, heapRel);
 	}
 	else
 	{
@@ -806,6 +815,11 @@ _bt_findinsertloc(Relation rel,
 			}
 
 			/*
+			 * Before considering moving right, try to compress the page
+			 */
+			_bt_compress_one_page(rel, insertstate->buf, heapRel);
+
+			/*
 			 * Nope, so check conditions (b) and (c) enumerated above
 			 *
 			 * The earlier _bt_check_unique() call may well have established a
@@ -2286,3 +2300,241 @@ _bt_vacuum_one_page(Relation rel, Buffer buffer, Relation heapRel)
 	 * the page.
 	 */
 }
+
+/*
+ * Add new item (compressed or not) to the page, while compressing it.
+ * If insertion failed, return false.
+ * Caller should consider this as compression failure and
+ * leave page uncompressed.
+ */
+static bool
+insert_itupprev_to_page(Page page, BTCompressState *compressState)
+{
+	IndexTuple	to_insert;
+	OffsetNumber offnum = PageGetMaxOffsetNumber(page);
+
+	if (compressState->ntuples == 0)
+		to_insert = compressState->itupprev;
+	else
+	{
+		IndexTuple	postingtuple;
+
+		/* form a tuple with a posting list */
+		postingtuple = BTreeFormPostingTuple(compressState->itupprev,
+											 compressState->ipd,
+											 compressState->ntuples);
+		to_insert = postingtuple;
+		pfree(compressState->ipd);
+	}
+
+	/* Add the new item into the page */
+	offnum = OffsetNumberNext(offnum);
+
+	elog(DEBUG4, "insert_itupprev_to_page. compressState->ntuples %d IndexTupleSize %zu free %zu",
+		 compressState->ntuples, IndexTupleSize(to_insert), PageGetFreeSpace(page));
+
+	if (PageAddItem(page, (Item) to_insert, IndexTupleSize(to_insert),
+					offnum, false, false) == InvalidOffsetNumber)
+	{
+		elog(DEBUG4, "insert_itupprev_to_page. failed");
+
+		/*
+		 * this may happen if tuple is bigger than freespace fallback to
+		 * uncompressed page case
+		 */
+		if (compressState->ntuples > 0)
+			pfree(to_insert);
+		return false;
+	}
+
+	if (compressState->ntuples > 0)
+		pfree(to_insert);
+	compressState->ntuples = 0;
+	return true;
+}
+
+/*
+ * Before splitting the page, try to compress items to free some space.
+ * If compression didn't succeed, buffer will contain old state of the page.
+ * This function should be called after lp_dead items
+ * were removed by _bt_vacuum_one_page().
+ */
+static void
+_bt_compress_one_page(Relation rel, Buffer buffer, Relation heapRel)
+{
+	OffsetNumber offnum,
+				minoff,
+				maxoff;
+	Page		page = BufferGetPage(buffer);
+	Page		newpage;
+	BTPageOpaque opaque = (BTPageOpaque) PageGetSpecialPointer(page);
+	bool		use_compression = false;
+	BTCompressState *compressState = NULL;
+	int			n_posting_on_page = 0;
+	int			natts = IndexRelationGetNumberOfAttributes(rel);
+
+	/*
+	 * Don't use compression for indexes with INCLUDEd columns, system indexes
+	 * and unique indexes.
+	 */
+	use_compression = ((IndexRelationGetNumberOfKeyAttributes(rel) ==
+						IndexRelationGetNumberOfAttributes(rel))
+					   && (!IsSystemRelation(rel))
+					   && (!rel->rd_index->indisunique));
+	if (!use_compression)
+		return;
+
+	/* init compress state needed to build posting tuples */
+	compressState = (BTCompressState *) palloc0(sizeof(BTCompressState));
+	compressState->ipd = NULL;
+	compressState->ntuples = 0;
+	compressState->itupprev = NULL;
+	compressState->maxitemsize = BTMaxItemSize(page);
+	compressState->maxpostingsize = 0;
+
+	/*
+	 * Scan over all items to see which ones can be compressed
+	 */
+	minoff = P_FIRSTDATAKEY(opaque);
+	maxoff = PageGetMaxOffsetNumber(page);
+
+	/*
+	 * Heuristic to avoid trying to compress page that has already contain
+	 * mostly compressed items
+	 */
+	for (offnum = minoff;
+		 offnum <= maxoff;
+		 offnum = OffsetNumberNext(offnum))
+	{
+		ItemId		itemid = PageGetItemId(page, P_HIKEY);
+		IndexTuple	item = (IndexTuple) PageGetItem(page, itemid);
+
+		if (BTreeTupleIsPosting(item))
+			n_posting_on_page++;
+	}
+
+	/*
+	 * If we have only a few uncompressed items on the full page,
+	 * it isn't worth to compress them
+	 */
+	if (maxoff - n_posting_on_page < BT_COMPRESS_THRESHOLD)
+		return;
+
+	newpage = PageGetTempPageCopySpecial(page);
+	elog(DEBUG4, "_bt_compress_one_page rel: %s,blkno: %u",
+		 RelationGetRelationName(rel), BufferGetBlockNumber(buffer));
+
+	/* Copy High Key if any */
+	if (!P_RIGHTMOST(opaque))
+	{
+		ItemId		itemid = PageGetItemId(page, P_HIKEY);
+		Size		itemsz = ItemIdGetLength(itemid);
+		IndexTuple	item = (IndexTuple) PageGetItem(page, itemid);
+
+		if (PageAddItem(newpage, (Item) item, itemsz, P_HIKEY,
+						false, false) == InvalidOffsetNumber)
+		{
+			/*
+			 * Should never happen. Anyway, fallback gently to scenario of
+			 * incompressible page and just return from function.
+			 */
+			elog(DEBUG4, "_bt_compress_one_page. failed to insert highkey to newpage");
+			return;
+		}
+	}
+
+	/*
+	 * Iterate over tuples on the page, try to compress them into posting
+	 * lists and insert into new page.
+	 */
+	for (offnum = minoff;
+		 offnum <= maxoff;
+		 offnum = OffsetNumberNext(offnum))
+	{
+		ItemId		itemId = PageGetItemId(page, offnum);
+		IndexTuple	itup = (IndexTuple) PageGetItem(page, itemId);
+
+		/*
+		 * We do not expect to meet any DEAD items, since this function is
+		 * called right after _bt_vacuum_one_page(). If for some reason we
+		 * found dead item, don't compress it, to allow upcoming microvacuum
+		 * or vacuum clean it up.
+		 */
+		if (ItemIdIsDead(itemId))
+			continue;
+
+		if (compressState->itupprev != NULL)
+		{
+			int			n_equal_atts =
+			_bt_keep_natts_fast(rel, compressState->itupprev, itup);
+			int			itup_ntuples = BTreeTupleIsPosting(itup) ?
+			BTreeTupleGetNPosting(itup) : 1;
+
+			if (n_equal_atts > natts)
+			{
+				/*
+				 * When tuples are equal, create or update posting.
+				 *
+				 * If posting is too big, insert it on page and continue.
+				 */
+				if (compressState->maxitemsize >
+					MAXALIGN(((IndexTupleSize(compressState->itupprev)
+							   + (compressState->ntuples + itup_ntuples + 1) * sizeof(ItemPointerData)))))
+				{
+					add_item_to_posting(compressState, itup);
+				}
+				else if (!insert_itupprev_to_page(newpage, compressState))
+				{
+					elog(DEBUG4, "_bt_compress_one_page. failed to insert posting");
+					return;
+				}
+			}
+			else
+			{
+				/*
+				 * Tuples are not equal. Insert itupprev into index. Save
+				 * current tuple for the next iteration.
+				 */
+				if (!insert_itupprev_to_page(newpage, compressState))
+				{
+					elog(DEBUG4, "_bt_compress_one_page. failed to insert posting");
+					return;
+				}
+			}
+		}
+
+		/*
+		 * Copy the tuple into temp variable itupprev to compare it with the
+		 * following tuple and maybe unite them into a posting tuple
+		 */
+		if (compressState->itupprev)
+			pfree(compressState->itupprev);
+		compressState->itupprev = CopyIndexTuple(itup);
+
+		Assert(IndexTupleSize(compressState->itupprev) <= compressState->maxitemsize);
+	}
+
+	/* Handle the last item. */
+	if (!insert_itupprev_to_page(newpage, compressState))
+	{
+		elog(DEBUG4, "_bt_compress_one_page. failed to insert posting for last item");
+		return;
+	}
+
+	START_CRIT_SECTION();
+	PageRestoreTempPage(newpage, page);
+	MarkBufferDirty(buffer);
+
+	/* Log full page write */
+	if (RelationNeedsWAL(rel))
+	{
+		XLogRecPtr	recptr;
+
+		recptr = log_newpage_buffer(buffer, true);
+		PageSetLSN(page, recptr);
+	}
+	END_CRIT_SECTION();
+
+	elog(DEBUG4, "_bt_compress_one_page. success");
+	return;
+}
diff --git a/src/backend/access/nbtree/nbtpage.c b/src/backend/access/nbtree/nbtpage.c
index 50455db..dff506d 100644
--- a/src/backend/access/nbtree/nbtpage.c
+++ b/src/backend/access/nbtree/nbtpage.c
@@ -1022,14 +1022,53 @@ _bt_page_recyclable(Page page)
 void
 _bt_delitems_vacuum(Relation rel, Buffer buf,
 					OffsetNumber *itemnos, int nitems,
+					OffsetNumber *remainingoffset,
+					IndexTuple *remaining, int nremaining,
 					BlockNumber lastBlockVacuumed)
 {
 	Page		page = BufferGetPage(buf);
 	BTPageOpaque opaque;
+	int			i;
+	Size		itemsz;
+	Size		remaining_sz = 0;
+	char	   *remaining_buf = NULL;
+
+	/* XLOG stuff, buffer for remainings */
+	if (nremaining && RelationNeedsWAL(rel))
+	{
+		Size		offset = 0;
+
+		for (i = 0; i < nremaining; i++)
+			remaining_sz += MAXALIGN(IndexTupleSize(remaining[i]));
+
+		remaining_buf = palloc0(remaining_sz);
+		for (i = 0; i < nremaining; i++)
+		{
+			itemsz = IndexTupleSize(remaining[i]);
+			memcpy(remaining_buf + offset, (char *) remaining[i], itemsz);
+			offset += MAXALIGN(itemsz);
+		}
+		Assert(offset == remaining_sz);
+	}
 
 	/* No ereport(ERROR) until changes are logged */
 	START_CRIT_SECTION();
 
+	/* Handle posting tuples here */
+	for (i = 0; i < nremaining; i++)
+	{
+		/* At first, delete the old tuple. */
+		PageIndexTupleDelete(page, remainingoffset[i]);
+
+		itemsz = IndexTupleSize(remaining[i]);
+		itemsz = MAXALIGN(itemsz);
+
+		/* Add tuple with remaining ItemPointers to the page. */
+		if (PageAddItem(page, (Item) remaining[i], itemsz, remainingoffset[i],
+						false, false) == InvalidOffsetNumber)
+			elog(ERROR, "failed to rewrite compressed item in index while doing vacuum");
+	}
+
 	/* Fix the page */
 	if (nitems > 0)
 		PageIndexMultiDelete(page, itemnos, nitems);
@@ -1059,6 +1098,8 @@ _bt_delitems_vacuum(Relation rel, Buffer buf,
 		xl_btree_vacuum xlrec_vacuum;
 
 		xlrec_vacuum.lastBlockVacuumed = lastBlockVacuumed;
+		xlrec_vacuum.nremaining = nremaining;
+		xlrec_vacuum.ndeleted = nitems;
 
 		XLogBeginInsert();
 		XLogRegisterBuffer(0, buf, REGBUF_STANDARD);
@@ -1072,6 +1113,19 @@ _bt_delitems_vacuum(Relation rel, Buffer buf,
 		if (nitems > 0)
 			XLogRegisterBufData(0, (char *) itemnos, nitems * sizeof(OffsetNumber));
 
+		/*
+		 * Here we should save offnums and remaining tuples themselves. It's
+		 * important to restore them in correct order. At first, we must
+		 * handle remaining tuples and only after that other deleted items.
+		 */
+		if (nremaining > 0)
+		{
+			Assert(remaining_buf != NULL);
+			XLogRegisterBufData(0, (char *) remainingoffset,
+								nremaining * sizeof(OffsetNumber));
+			XLogRegisterBufData(0, remaining_buf, remaining_sz);
+		}
+
 		recptr = XLogInsert(RM_BTREE_ID, XLOG_BTREE_VACUUM);
 
 		PageSetLSN(page, recptr);
diff --git a/src/backend/access/nbtree/nbtree.c b/src/backend/access/nbtree/nbtree.c
index 4cfd528..11e45c8 100644
--- a/src/backend/access/nbtree/nbtree.c
+++ b/src/backend/access/nbtree/nbtree.c
@@ -97,6 +97,8 @@ static void btvacuumscan(IndexVacuumInfo *info, IndexBulkDeleteResult *stats,
 						 BTCycleId cycleid, TransactionId *oldestBtpoXact);
 static void btvacuumpage(BTVacState *vstate, BlockNumber blkno,
 						 BlockNumber orig_blkno);
+static ItemPointer btreevacuumPosting(BTVacState *vstate, IndexTuple itup,
+									  int *nremaining);
 
 
 /*
@@ -1069,7 +1071,8 @@ btvacuumscan(IndexVacuumInfo *info, IndexBulkDeleteResult *stats,
 								 RBM_NORMAL, info->strategy);
 		LockBufferForCleanup(buf);
 		_bt_checkpage(rel, buf);
-		_bt_delitems_vacuum(rel, buf, NULL, 0, vstate.lastBlockVacuumed);
+		_bt_delitems_vacuum(rel, buf, NULL, 0, NULL, NULL, 0,
+							vstate.lastBlockVacuumed);
 		_bt_relbuf(rel, buf);
 	}
 
@@ -1193,6 +1196,9 @@ restart:
 		OffsetNumber offnum,
 					minoff,
 					maxoff;
+		IndexTuple	remaining[MaxOffsetNumber];
+		OffsetNumber remainingoffset[MaxOffsetNumber];
+		int			nremaining;
 
 		/*
 		 * Trade in the initial read lock for a super-exclusive write lock on
@@ -1229,6 +1235,7 @@ restart:
 		 * callback function.
 		 */
 		ndeletable = 0;
+		nremaining = 0;
 		minoff = P_FIRSTDATAKEY(opaque);
 		maxoff = PageGetMaxOffsetNumber(page);
 		if (callback)
@@ -1242,31 +1249,78 @@ 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			nnewipd = 0;
+					ItemPointer newipd = NULL;
+
+					newipd = btreevacuumPosting(vstate, itup, &nnewipd);
+
+					if (nnewipd == 0)
+					{
+						/*
+						 * All TIDs from posting list must be deleted, we can
+						 * delete whole tuple in a regular way.
+						 */
+						deletable[ndeletable++] = offnum;
+					}
+					else if (nnewipd == BTreeTupleGetNPosting(itup))
+					{
+						/*
+						 * All TIDs from posting tuple must remain. Do
+						 * nothing, just cleanup.
+						 */
+						pfree(newipd);
+					}
+					else if (nnewipd < BTreeTupleGetNPosting(itup))
+					{
+						/* Some TIDs from posting tuple must remain. */
+						Assert(nnewipd > 0);
+						Assert(newipd != NULL);
+
+						/*
+						 * Form new tuple that contains only remaining TIDs.
+						 * Remember this tuple and the offset of the old tuple
+						 * to update it in place.
+						 */
+						remainingoffset[nremaining] = offnum;
+						remaining[nremaining] = BTreeFormPostingTuple(itup, newipd, nnewipd);
+						nremaining++;
+						pfree(newipd);
+
+						Assert(IndexTupleSize(itup) <= BTMaxItemSize(page));
+					}
+				}
+				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;
+				}
 			}
 		}
 
@@ -1274,7 +1328,7 @@ restart:
 		 * Apply any needed deletes.  We issue just one _bt_delitems_vacuum()
 		 * call per page, so as to minimize WAL traffic.
 		 */
-		if (ndeletable > 0)
+		if (ndeletable > 0 || nremaining > 0)
 		{
 			/*
 			 * Notice that the issued XLOG_BTREE_VACUUM WAL record includes
@@ -1291,6 +1345,7 @@ restart:
 			 * that.
 			 */
 			_bt_delitems_vacuum(rel, buf, deletable, ndeletable,
+								remainingoffset, remaining, nremaining,
 								vstate->lastBlockVacuumed);
 
 			/*
@@ -1376,6 +1431,42 @@ restart:
 }
 
 /*
+ * btreevacuumPosting() -- vacuums a posting tuple.
+ *
+ * Returns new palloc'd posting list with remaining items.
+ * Posting list size is returned via nremaining.
+ *
+ * If all items are dead,
+ * nremaining is 0 and resulting posting list is NULL.
+ */
+static ItemPointer
+btreevacuumPosting(BTVacState *vstate, IndexTuple itup, int *nremaining)
+{
+	int			i,
+				remaining = 0;
+	int			nitem = BTreeTupleGetNPosting(itup);
+	ItemPointer tmpitems = NULL,
+				items = BTreeTupleGetPosting(itup);
+
+	/*
+	 * Check each tuple in the posting list, save alive tuples into tmpitems
+	 */
+	for (i = 0; i < nitem; i++)
+	{
+		if (vstate->callback(items + i, vstate->callback_state))
+			continue;
+
+		if (tmpitems == NULL)
+			tmpitems = palloc(sizeof(ItemPointerData) * nitem);
+
+		tmpitems[remaining++] = items[i];
+	}
+
+	*nremaining = remaining;
+	return tmpitems;
+}
+
+/*
  *	btcanreturn() -- Check whether btree indexes support index-only scans.
  *
  * btrees always do, so this is trivial.
diff --git a/src/backend/access/nbtree/nbtsearch.c b/src/backend/access/nbtree/nbtsearch.c
index c655dad..49a1aae 100644
--- a/src/backend/access/nbtree/nbtsearch.c
+++ b/src/backend/access/nbtree/nbtsearch.c
@@ -30,6 +30,9 @@ 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 bool _bt_readnextpage(IndexScanDesc scan, BlockNumber blkno, ScanDirection dir);
 static bool _bt_parallel_readpage(IndexScanDesc scan, BlockNumber blkno,
@@ -665,6 +668,9 @@ _bt_compare(Relation rel,
 	 * Use the heap TID attribute and scantid to try to break the tie.  The
 	 * rules are the same as any other key attribute -- only the
 	 * representation differs.
+	 * TODO when itup is a posting tuple, the check becomes more complex.
+	 * we have an option that key nor smaller, nor larger than the tuple,
+	 * but exactly in between of BTreeTupleGetMinTID to BTreeTupleGetMaxTID.
 	 */
 	heapTid = BTreeTupleGetHeapTID(itup);
 	if (key->scantid == NULL)
@@ -1410,6 +1416,7 @@ _bt_readpage(IndexScanDesc scan, ScanDirection dir, OffsetNumber offnum)
 	int			itemIndex;
 	bool		continuescan;
 	int			indnatts;
+	int			i;
 
 	/*
 	 * We must have the buffer pinned and locked, but the usual macro can't be
@@ -1456,6 +1463,7 @@ _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
@@ -1490,8 +1498,22 @@ _bt_readpage(IndexScanDesc scan, ScanDirection dir, OffsetNumber offnum)
 			if (_bt_checkkeys(scan, itup, indnatts, dir, &continuescan))
 			{
 				/* tuple passes all scan key conditions, so remember it */
-				_bt_saveitem(so, itemIndex, offnum, itup);
-				itemIndex++;
+				if (BTreeTupleIsPosting(itup))
+				{
+					for (i = 0; i < BTreeTupleGetNPosting(itup); i++)
+					{
+						_bt_savePostingitem(so, itemIndex, offnum,
+											BTreeTupleGetPostingN(itup, i),
+											itup, i);
+						itemIndex++;
+					}
+				}
+				else
+				{
+					_bt_saveitem(so, itemIndex, offnum, itup);
+					itemIndex++;
+				}
+
 			}
 			/* When !continuescan, there can't be any more matches, so stop */
 			if (!continuescan)
@@ -1524,7 +1546,7 @@ _bt_readpage(IndexScanDesc scan, ScanDirection dir, OffsetNumber offnum)
 		if (!continuescan)
 			so->currPos.moreRight = false;
 
-		Assert(itemIndex <= MaxIndexTuplesPerPage);
+		Assert(itemIndex <= MaxPostingIndexTuplesPerPage);
 		so->currPos.firstItem = 0;
 		so->currPos.lastItem = itemIndex - 1;
 		so->currPos.itemIndex = 0;
@@ -1532,7 +1554,7 @@ _bt_readpage(IndexScanDesc scan, ScanDirection dir, OffsetNumber offnum)
 	else
 	{
 		/* load items[] in descending order */
-		itemIndex = MaxIndexTuplesPerPage;
+		itemIndex = MaxPostingIndexTuplesPerPage;
 
 		offnum = Min(offnum, maxoff);
 
@@ -1574,8 +1596,22 @@ _bt_readpage(IndexScanDesc scan, ScanDirection dir, OffsetNumber offnum)
 			if (passes_quals && tuple_alive)
 			{
 				/* tuple passes all scan key conditions, so remember it */
-				itemIndex--;
-				_bt_saveitem(so, itemIndex, offnum, itup);
+				if (BTreeTupleIsPosting(itup))
+				{
+					for (i = 0; i < BTreeTupleGetNPosting(itup); i++)
+					{
+						itemIndex--;
+						_bt_savePostingitem(so, itemIndex, offnum,
+											BTreeTupleGetPostingN(itup, i),
+											itup, i);
+					}
+				}
+				else
+				{
+					itemIndex--;
+					_bt_saveitem(so, itemIndex, offnum, itup);
+				}
+
 			}
 			if (!continuescan)
 			{
@@ -1589,8 +1625,8 @@ _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 = MaxPostingIndexTuplesPerPage - 1;
+		so->currPos.itemIndex = MaxPostingIndexTuplesPerPage - 1;
 	}
 
 	return (so->currPos.firstItem <= so->currPos.lastItem);
@@ -1603,6 +1639,8 @@ _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)
@@ -1615,6 +1653,33 @@ _bt_saveitem(BTScanOpaque so, int itemIndex,
 	}
 }
 
+/* Save an index item into so->currPos.items[itemIndex] for posting tuples. */
+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 = BTreeTupleGetPostingOffset(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
  *
diff --git a/src/backend/access/nbtree/nbtsort.c b/src/backend/access/nbtree/nbtsort.c
index d0b9013..955a628 100644
--- a/src/backend/access/nbtree/nbtsort.c
+++ b/src/backend/access/nbtree/nbtsort.c
@@ -65,6 +65,7 @@
 #include "access/xact.h"
 #include "access/xlog.h"
 #include "access/xloginsert.h"
+#include "catalog/catalog.h"
 #include "catalog/index.h"
 #include "commands/progress.h"
 #include "miscadmin.h"
@@ -288,6 +289,9 @@ static void _bt_sortaddtup(Page page, Size itemsize,
 static void _bt_buildadd(BTWriteState *wstate, BTPageState *state,
 						 IndexTuple itup);
 static void _bt_uppershutdown(BTWriteState *wstate, BTPageState *state);
+static void insert_itupprev_to_page_buildadd(BTWriteState *wstate,
+											 BTPageState *state,
+											 BTCompressState *compressState);
 static void _bt_load(BTWriteState *wstate,
 					 BTSpool *btspool, BTSpool *btspool2);
 static void _bt_begin_parallel(BTBuildState *buildstate, bool isconcurrent,
@@ -972,6 +976,11 @@ _bt_buildadd(BTWriteState *wstate, BTPageState *state, IndexTuple itup)
 			 * only shift the line pointer array back and forth, and overwrite
 			 * the tuple space previously occupied by oitup.  This is fairly
 			 * cheap.
+			 *
+			 * If lastleft tuple was a posting tuple, we'll truncate its
+			 * posting list in _bt_truncate as well. Note that it is also
+			 * applicable only to leaf pages, since internal pages never
+			 * contain posting tuples.
 			 */
 			ii = PageGetItemId(opage, OffsetNumberPrev(last_off));
 			lastleft = (IndexTuple) PageGetItem(opage, ii);
@@ -1011,6 +1020,7 @@ _bt_buildadd(BTWriteState *wstate, BTPageState *state, IndexTuple itup)
 		 * the minimum key for the new page.
 		 */
 		state->btps_minkey = CopyIndexTuple(oitup);
+		Assert(!BTreeTupleIsPosting(state->btps_minkey));
 
 		/*
 		 * Set the sibling links for both pages.
@@ -1050,8 +1060,36 @@ _bt_buildadd(BTWriteState *wstate, BTPageState *state, IndexTuple itup)
 	if (last_off == P_HIKEY)
 	{
 		Assert(state->btps_minkey == NULL);
-		state->btps_minkey = CopyIndexTuple(itup);
-		/* _bt_sortaddtup() will perform full truncation later */
+
+		/*
+		 * Stashed copy must be a non-posting tuple, with truncated posting
+		 * list and correct t_tid since we're going to use it to build
+		 * downlink.
+		 */
+		if (BTreeTupleIsPosting(itup))
+		{
+			Size		keytupsz;
+			IndexTuple	keytup;
+
+			/*
+			 * Form key tuple, that doesn't contain any ipd. NOTE: since we'll
+			 * need TID later, set t_tid to the first t_tid from posting list.
+			 */
+			keytupsz = BTreeTupleGetPostingOffset(itup);
+			keytup = palloc0(keytupsz);
+			memcpy(keytup, itup, keytupsz);
+
+			keytup->t_info &= ~INDEX_SIZE_MASK;
+			keytup->t_info |= keytupsz;
+			ItemPointerCopy(BTreeTupleGetPosting(itup), &keytup->t_tid);
+			state->btps_minkey = CopyIndexTuple(keytup);
+			pfree(keytup);
+		}
+		else
+			state->btps_minkey = CopyIndexTuple(itup);	/* _bt_sortaddtup() will
+														 * perform full
+														 * truncation later */
+
 		BTreeTupleSetNAtts(state->btps_minkey, 0);
 	}
 
@@ -1137,6 +1175,89 @@ _bt_uppershutdown(BTWriteState *wstate, BTPageState *state)
 }
 
 /*
+ * Add new tuple (posting or non-posting) to the page, while building index.
+ */
+void
+insert_itupprev_to_page_buildadd(BTWriteState *wstate, BTPageState *state,
+								 BTCompressState *compressState)
+{
+	IndexTuple	to_insert;
+
+	/* Return, if there is no tuple to insert */
+	if (state == NULL)
+		return;
+
+	if (compressState->ntuples == 0)
+		to_insert = compressState->itupprev;
+	else
+	{
+		IndexTuple	postingtuple;
+
+		/* form a tuple with a posting list */
+		postingtuple = BTreeFormPostingTuple(compressState->itupprev,
+											 compressState->ipd,
+											 compressState->ntuples);
+		to_insert = postingtuple;
+		pfree(compressState->ipd);
+	}
+
+	_bt_buildadd(wstate, state, to_insert);
+
+	if (compressState->ntuples > 0)
+		pfree(to_insert);
+	compressState->ntuples = 0;
+}
+
+/*
+ * Save item pointer(s) of itup to the posting list in compressState.
+ * Helper function for bt_load() and _bt_compress_one_page().
+ *
+ * Note: caller is responsible for size check to ensure that
+ * resulting tuple won't exceed BTMaxItemSize.
+ */
+void
+add_item_to_posting(BTCompressState *compressState, IndexTuple itup)
+{
+	int			nposting = 0;
+
+	if (compressState->ntuples == 0)
+	{
+		compressState->ipd = palloc0(compressState->maxitemsize);
+
+		if (BTreeTupleIsPosting(compressState->itupprev))
+		{
+			/* if itupprev is posting, add all its TIDs to the posting list */
+			nposting = BTreeTupleGetNPosting(compressState->itupprev);
+			memcpy(compressState->ipd, BTreeTupleGetPosting(compressState->itupprev),
+				   sizeof(ItemPointerData) * nposting);
+			compressState->ntuples += nposting;
+		}
+		else
+		{
+			memcpy(compressState->ipd, compressState->itupprev,
+				   sizeof(ItemPointerData));
+			compressState->ntuples++;
+		}
+	}
+
+	if (BTreeTupleIsPosting(itup))
+	{
+		/* if tuple is posting, add all its TIDs to the posting list */
+		nposting = BTreeTupleGetNPosting(itup);
+		memcpy(compressState->ipd + compressState->ntuples,
+			   BTreeTupleGetPosting(itup),
+			   sizeof(ItemPointerData) * nposting);
+		compressState->ntuples += nposting;
+	}
+	else
+	{
+		memcpy(compressState->ipd + compressState->ntuples, itup,
+			   sizeof(ItemPointerData));
+		compressState->ntuples++;
+	}
+}
+
+/*
  * Read tuples in correct sort order from tuplesort, and load them into
  * btree leaves.
  */
@@ -1150,9 +1271,21 @@ _bt_load(BTWriteState *wstate, BTSpool *btspool, BTSpool *btspool2)
 	bool		load1;
 	TupleDesc	tupdes = RelationGetDescr(wstate->index);
 	int			i,
-				keysz = IndexRelationGetNumberOfKeyAttributes(wstate->index);
+				keysz = IndexRelationGetNumberOfKeyAttributes(wstate->index),
+				natts = IndexRelationGetNumberOfAttributes(wstate->index);
 	SortSupport sortKeys;
 	int64		tuples_done = 0;
+	bool		use_compression = false;
+	BTCompressState *compressState = NULL;
+
+	/*
+	 * Don't use compression for indexes with INCLUDEd columns, system indexes
+	 * and unique indexes.
+	 */
+	use_compression = ((IndexRelationGetNumberOfKeyAttributes(wstate->index) ==
+						IndexRelationGetNumberOfAttributes(wstate->index))
+					   && (!IsSystemRelation(wstate->index))
+					   && (!wstate->index->rd_index->indisunique));
 
 	if (merge)
 	{
@@ -1266,19 +1399,88 @@ _bt_load(BTWriteState *wstate, BTSpool *btspool, BTSpool *btspool2)
 	}
 	else
 	{
-		/* merge is unnecessary */
-		while ((itup = tuplesort_getindextuple(btspool->sortstate,
-											   true)) != NULL)
+		if (!use_compression)
 		{
-			/* When we see first tuple, create first index page */
-			if (state == NULL)
-				state = _bt_pagestate(wstate, 0);
+			/* merge is unnecessary */
+			while ((itup = tuplesort_getindextuple(btspool->sortstate,
+												   true)) != NULL)
+			{
+				/* When we see first tuple, create first index page */
+				if (state == NULL)
+					state = _bt_pagestate(wstate, 0);
 
-			_bt_buildadd(wstate, state, itup);
+				_bt_buildadd(wstate, state, itup);
 
-			/* Report progress */
-			pgstat_progress_update_param(PROGRESS_CREATEIDX_TUPLES_DONE,
-										 ++tuples_done);
+				/* Report progress */
+				pgstat_progress_update_param(PROGRESS_CREATEIDX_TUPLES_DONE,
+											 ++tuples_done);
+			}
+		}
+		else
+		{
+			/* init compress state needed to build posting tuples */
+			compressState = (BTCompressState *) palloc0(sizeof(BTCompressState));
+			compressState->ipd = NULL;
+			compressState->ntuples = 0;
+			compressState->itupprev = NULL;
+			compressState->maxitemsize = 0;
+			compressState->maxpostingsize = 0;
+
+			while ((itup = tuplesort_getindextuple(btspool->sortstate,
+												   true)) != NULL)
+			{
+				/* When we see first tuple, create first index page */
+				if (state == NULL)
+				{
+					state = _bt_pagestate(wstate, 0);
+					compressState->maxitemsize = BTMaxItemSize(state->btps_page);
+				}
+
+				if (compressState->itupprev != NULL)
+				{
+					int			n_equal_atts = _bt_keep_natts_fast(wstate->index,
+																   compressState->itupprev, itup);
+
+					if (n_equal_atts > natts)
+					{
+						/*
+						 * Tuples are equal. Create or update posting.
+						 *
+						 * Else If posting is too big, insert it on page and
+						 * continue.
+						 */
+						if ((compressState->ntuples + 1) * sizeof(ItemPointerData) <
+							compressState->maxpostingsize)
+							add_item_to_posting(compressState, itup);
+						else
+							insert_itupprev_to_page_buildadd(wstate, state, compressState);
+					}
+					else
+					{
+						/*
+						 * Tuples are not equal. Insert itupprev into index.
+						 * Save current tuple for the next iteration.
+						 */
+						insert_itupprev_to_page_buildadd(wstate, state, compressState);
+					}
+				}
+
+				/*
+				 * Save the tuple to compare it with the next one and maybe
+				 * unite them into a posting tuple.
+				 */
+				if (compressState->itupprev)
+					pfree(compressState->itupprev);
+				compressState->itupprev = CopyIndexTuple(itup);
+
+				/* compute max size of posting list */
+				compressState->maxpostingsize = compressState->maxitemsize -
+					IndexInfoFindDataOffset(compressState->itupprev->t_info) -
+					MAXALIGN(IndexTupleSize(compressState->itupprev));
+			}
+
+			/* Handle the last item */
+			insert_itupprev_to_page_buildadd(wstate, state, compressState);
 		}
 	}
 
diff --git a/src/backend/access/nbtree/nbtutils.c b/src/backend/access/nbtree/nbtutils.c
index 93fab26..0da6fa8 100644
--- a/src/backend/access/nbtree/nbtutils.c
+++ b/src/backend/access/nbtree/nbtutils.c
@@ -1787,7 +1787,9 @@ _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);
@@ -2145,6 +2147,16 @@ _bt_truncate(Relation rel, IndexTuple lastleft, IndexTuple firstright,
 
 		pivot = index_truncate_tuple(itupdesc, firstright, keepnatts);
 
+		if (BTreeTupleIsPosting(firstright))
+		{
+			BTreeTupleClearBtIsPosting(pivot);
+			BTreeTupleSetNAtts(pivot, keepnatts);
+			pivot->t_info &= ~INDEX_SIZE_MASK;
+			pivot->t_info |= BTreeTupleGetPostingOffset(firstright);
+		}
+
+		Assert(!BTreeTupleIsPosting(pivot));
+
 		/*
 		 * If there is a distinguishing key attribute within new pivot tuple,
 		 * there is no need to add an explicit heap TID attribute
@@ -2168,6 +2180,27 @@ _bt_truncate(Relation rel, IndexTuple lastleft, IndexTuple firstright,
 		pfree(pivot);
 		pivot = tidpivot;
 	}
+	else if (BTreeTupleIsPosting(firstright))
+	{
+		/*
+		 * No truncation was possible, since key attributes are all equal. But
+		 * the tuple is a compressed tuple with a posting list, so we still
+		 * must truncate it.
+		 *
+		 * It's necessary to add a heap TID attribute to the new pivot tuple.
+		 */
+		newsize = BTreeTupleGetPostingOffset(firstright) +
+			MAXALIGN(sizeof(ItemPointerData));
+		pivot = palloc0(newsize);
+		memcpy(pivot, firstright, BTreeTupleGetPostingOffset(firstright));
+
+		pivot->t_info &= ~INDEX_SIZE_MASK;
+		pivot->t_info |= newsize;
+		BTreeTupleClearBtIsPosting(pivot);
+		BTreeTupleSetAltHeapTID(pivot);
+
+		Assert(!BTreeTupleIsPosting(pivot));
+	}
 	else
 	{
 		/*
@@ -2205,7 +2238,7 @@ _bt_truncate(Relation rel, IndexTuple lastleft, IndexTuple firstright,
 	 */
 	pivotheaptid = (ItemPointer) ((char *) pivot + newsize -
 								  sizeof(ItemPointerData));
-	ItemPointerCopy(&lastleft->t_tid, pivotheaptid);
+	ItemPointerCopy(BTreeTupleGetMaxTID(lastleft), pivotheaptid);
 
 	/*
 	 * Lehman and Yao require that the downlink to the right page, which is to
@@ -2216,9 +2249,12 @@ _bt_truncate(Relation rel, IndexTuple lastleft, IndexTuple firstright,
 	 * tiebreaker.
 	 */
 #ifndef DEBUG_NO_TRUNCATE
-	Assert(ItemPointerCompare(&lastleft->t_tid, &firstright->t_tid) < 0);
-	Assert(ItemPointerCompare(pivotheaptid, &lastleft->t_tid) >= 0);
-	Assert(ItemPointerCompare(pivotheaptid, &firstright->t_tid) < 0);
+	Assert(ItemPointerCompare(BTreeTupleGetMaxTID(lastleft),
+							  BTreeTupleGetMinTID(firstright)) < 0);
+	Assert(ItemPointerCompare(pivotheaptid,
+							  BTreeTupleGetMinTID(lastleft)) >= 0);
+	Assert(ItemPointerCompare(pivotheaptid,
+							  BTreeTupleGetMinTID(firstright)) < 0);
 #else
 
 	/*
@@ -2231,7 +2267,7 @@ _bt_truncate(Relation rel, IndexTuple lastleft, IndexTuple firstright,
 	 * attribute values along with lastleft's heap TID value when lastleft's
 	 * TID happens to be greater than firstright's TID.
 	 */
-	ItemPointerCopy(&firstright->t_tid, pivotheaptid);
+	ItemPointerCopy(BTreeTupleGetMinTID(firstright), pivotheaptid);
 
 	/*
 	 * Pivot heap TID should never be fully equal to firstright.  Note that
@@ -2240,7 +2276,8 @@ _bt_truncate(Relation rel, IndexTuple lastleft, IndexTuple firstright,
 	 */
 	ItemPointerSetOffsetNumber(pivotheaptid,
 							   OffsetNumberPrev(ItemPointerGetOffsetNumber(pivotheaptid)));
-	Assert(ItemPointerCompare(pivotheaptid, &firstright->t_tid) < 0);
+	Assert(ItemPointerCompare(pivotheaptid,
+							  BTreeTupleGetMinTID(firstright)) < 0);
 #endif
 
 	BTreeTupleSetNAtts(pivot, nkeyatts);
@@ -2330,6 +2367,10 @@ _bt_keep_natts(Relation rel, IndexTuple lastleft, IndexTuple firstright,
  * leaving excessive amounts of free space on either side of page split.
  * Callers can rely on the fact that attributes considered equal here are
  * definitely also equal according to _bt_keep_natts.
+ *
+ * To build a posting tuple we need to ensure that all attributes
+ * of both tuples are equal. Use this function to compare them.
+ * TODO: maybe it's worth to rename the function.
  */
 int
 _bt_keep_natts_fast(Relation rel, IndexTuple lastleft, IndexTuple firstright)
@@ -2415,7 +2456,7 @@ _bt_check_natts(Relation rel, bool heapkeyspace, Page page, OffsetNumber offnum)
 			 * Non-pivot tuples currently never use alternative heap TID
 			 * representation -- even those within heapkeyspace indexes
 			 */
-			if ((itup->t_info & INDEX_ALT_TID_MASK) != 0)
+			if (BTreeTupleIsPivot(itup))
 				return false;
 
 			/*
@@ -2470,7 +2511,7 @@ _bt_check_natts(Relation rel, bool heapkeyspace, Page page, OffsetNumber offnum)
 			 * that to decide if the tuple is a pre-v11 tuple.
 			 */
 			return tupnatts == 0 ||
-				((itup->t_info & INDEX_ALT_TID_MASK) == 0 &&
+				(!BTreeTupleIsPivot(itup) &&
 				 ItemPointerGetOffsetNumber(&(itup->t_tid)) == P_HIKEY);
 		}
 		else
@@ -2497,7 +2538,7 @@ _bt_check_natts(Relation rel, bool heapkeyspace, Page page, OffsetNumber offnum)
 	 * heapkeyspace index pivot tuples, regardless of whether or not there are
 	 * non-key attributes.
 	 */
-	if ((itup->t_info & INDEX_ALT_TID_MASK) == 0)
+	if (!BTreeTupleIsPivot(itup))
 		return false;
 
 	/*
@@ -2549,6 +2590,8 @@ _bt_check_third_page(Relation rel, Relation heap, bool needheaptidspace,
 	if (!needheaptidspace && itemsz <= BTMaxItemSizeNoHeapTid(page))
 		return;
 
+	/* TODO correct error messages for posting tuples */
+
 	/*
 	 * Internal page insertions cannot fail here, because that would mean that
 	 * an earlier leaf level insertion that should have failed didn't
@@ -2575,3 +2618,79 @@ _bt_check_third_page(Relation rel, Relation heap, bool needheaptidspace,
 					 "or use full text indexing."),
 			 errtableconstraint(heap, RelationGetRelationName(rel))));
 }
+
+/*
+ * Given a basic tuple that contains key datum and posting list,
+ * build a posting tuple.
+ *
+ * Basic tuple can be a posting tuple, but we only use key part of it,
+ * all ItemPointers must be passed via ipd.
+ *
+ * If nipd == 1 fallback to building a non-posting tuple.
+ * It is necessary to avoid storage overhead after posting tuple was vacuumed.
+ */
+IndexTuple
+BTreeFormPostingTuple(IndexTuple tuple, ItemPointerData *ipd, int nipd)
+{
+	uint32		keysize,
+				newsize = 0;
+	IndexTuple	itup;
+
+	/* We only need key part of the tuple */
+	if (BTreeTupleIsPosting(tuple))
+		keysize = BTreeTupleGetPostingOffset(tuple);
+	else
+		keysize = IndexTupleSize(tuple);
+
+	Assert(nipd > 0);
+
+	/* Add space needed for posting list */
+	if (nipd > 1)
+		newsize = SHORTALIGN(keysize) + sizeof(ItemPointerData) * nipd;
+	else
+		newsize = keysize;
+
+	newsize = MAXALIGN(newsize);
+	itup = palloc0(newsize);
+	memcpy(itup, tuple, keysize);
+	itup->t_info &= ~INDEX_SIZE_MASK;
+	itup->t_info |= newsize;
+
+	if (nipd > 1)
+	{
+		/* Form posting tuple, fill posting fields */
+
+		/* Set meta info about the posting list */
+		itup->t_info |= INDEX_ALT_TID_MASK;
+		BTreeSetPostingMeta(itup, nipd, SHORTALIGN(keysize));
+
+		/* sort the list to preserve TID order invariant */
+		qsort((void *) ipd, nipd, sizeof(ItemPointerData),
+		  (int (*) (const void *, const void *)) ItemPointerCompare);
+
+		/* Copy posting list into the posting tuple */
+		memcpy(BTreeTupleGetPosting(itup), ipd,
+			   sizeof(ItemPointerData) * nipd);
+	}
+	else
+	{
+		/* To finish building of a non-posting tuple, copy TID from ipd */
+		itup->t_info &= ~INDEX_ALT_TID_MASK;
+		ItemPointerCopy(ipd, &itup->t_tid);
+	}
+
+	return itup;
+}
+
+/*
+ * Opposite of BTreeFormPostingTuple.
+ * returns regular tuple that contains the key,
+ * the tid of the new tuple is the nth tid of original tuple's posting list
+ * result tuple palloc'd in a caller's context.
+ */
+IndexTuple
+BTreeGetNthTupleOfPosting(IndexTuple tuple, int n)
+{
+	Assert(BTreeTupleIsPosting(tuple));
+	return BTreeFormPostingTuple(tuple, BTreeTupleGetPostingN(tuple, n), 1);
+}
diff --git a/src/backend/access/nbtree/nbtxlog.c b/src/backend/access/nbtree/nbtxlog.c
index 3147ea4..7daadc9 100644
--- a/src/backend/access/nbtree/nbtxlog.c
+++ b/src/backend/access/nbtree/nbtxlog.c
@@ -384,8 +384,8 @@ btree_xlog_vacuum(XLogReaderState *record)
 	Buffer		buffer;
 	Page		page;
 	BTPageOpaque opaque;
-#ifdef UNUSED
 	xl_btree_vacuum *xlrec = (xl_btree_vacuum *) XLogRecGetData(record);
+#ifdef UNUSED
 
 	/*
 	 * This section of code is thought to be no longer needed, after analysis
@@ -476,14 +476,35 @@ btree_xlog_vacuum(XLogReaderState *record)
 
 		if (len > 0)
 		{
-			OffsetNumber *unused;
-			OffsetNumber *unend;
+			if (xlrec->nremaining)
+			{
+				int			i;
+				OffsetNumber *remainingoffset;
+				IndexTuple	remaining;
+				Size		itemsz;
+
+				remainingoffset = (OffsetNumber *)
+					(ptr + xlrec->ndeleted * sizeof(OffsetNumber));
+				remaining = (IndexTuple) ((char *) remainingoffset +
+										  xlrec->nremaining * sizeof(OffsetNumber));
 
-			unused = (OffsetNumber *) ptr;
-			unend = (OffsetNumber *) ((char *) ptr + len);
+				/* Handle posting tuples */
+				for (i = 0; i < xlrec->nremaining; i++)
+				{
+					PageIndexTupleDelete(page, remainingoffset[i]);
+
+					itemsz = MAXALIGN(IndexTupleSize(remaining));
+
+					if (PageAddItem(page, (Item) remaining, itemsz, remainingoffset[i],
+									false, false) == InvalidOffsetNumber)
+						elog(PANIC, "btree_xlog_vacuum: failed to add remaining item");
+
+					remaining = (IndexTuple) ((char *) remaining + itemsz);
+				}
+			}
 
-			if ((unend - unused) > 0)
-				PageIndexMultiDelete(page, unused, unend - unused);
+			if (xlrec->ndeleted)
+				PageIndexMultiDelete(page, (OffsetNumber *) ptr, xlrec->ndeleted);
 		}
 
 		/*
diff --git a/src/include/access/itup.h b/src/include/access/itup.h
index 744ffb6..85ee040 100644
--- a/src/include/access/itup.h
+++ b/src/include/access/itup.h
@@ -141,6 +141,11 @@ typedef IndexAttributeBitMapData * IndexAttributeBitMap;
  * On such a page, N tuples could take one MAXALIGN quantum less space than
  * estimated here, seemingly allowing one more tuple than estimated here.
  * But such a page always has at least MAXALIGN special space, so we're safe.
+ *
+ * Note: btree leaf pages may contain posting tuples, which store duplicates
+ * in a more effective way, so they may contain more tuples.
+ * Use MaxPostingIndexTuplesPerPage instead.
+
  */
 #define MaxIndexTuplesPerPage	\
 	((int) ((BLCKSZ - SizeOfPageHeaderData) / \
diff --git a/src/include/access/nbtree.h b/src/include/access/nbtree.h
index a3583f2..7d0d456 100644
--- a/src/include/access/nbtree.h
+++ b/src/include/access/nbtree.h
@@ -234,8 +234,7 @@ typedef struct BTMetaPageData
  *  t_tid | t_info | key values | INCLUDE columns, if any
  *
  * t_tid points to the heap TID, which is a tiebreaker key column as of
- * BTREE_VERSION 4.  Currently, the INDEX_ALT_TID_MASK status bit is never
- * set for non-pivot tuples.
+ * BTREE_VERSION 4.
  *
  * All other types of index tuples ("pivot" tuples) only have key columns,
  * since pivot tuples only exist to represent how the key space is
@@ -252,6 +251,39 @@ typedef struct BTMetaPageData
  * omitted rather than truncated, since its representation is different to
  * the non-pivot representation.)
  *
+ * Non-pivot posting tuple format:
+ *  t_tid | t_info | key values | INCLUDE columns, if any | posting_list[]
+ *
+ * In order to store duplicated keys more effectively,
+ * we use special format of tuples - posting tuples.
+ * posting_list is an array of ItemPointerData.
+ *
+ * This type of compression never applies to system indexes, unique indexes
+ * or indexes with INCLUDEd columns.
+ *
+ * To differ posting tuples we use INDEX_ALT_TID_MASK flag in t_info and
+ * BT_IS_POSTING flag in t_tid.
+ * These flags redefine the content of the posting tuple's tid:
+ * - t_tid.ip_blkid contains offset of the posting list.
+ * - t_tid offset field contains number of posting items this tuple contain
+ *
+ * The 12 least significant offset bits from t_tid are used to represent
+ * the number of posting items in posting tuples, leaving 4 status
+ * bits (BT_RESERVED_OFFSET_MASK bits), 3 of which that are reserved for
+ * future use.
+ * BT_N_POSTING_OFFSET_MASK is large enough to store any number of posting
+ * tuples, which is constrainted by BTMaxItemSize.
+
+ * If page contains so many duplicates, that they do not fit into one posting
+ * tuple (bounded by BTMaxItemSize and ), page may contain several posting
+ * tuples with the same key.
+ * Also page can contain both posting and non-posting tuples with the same key.
+ * Currently, posting tuples always contain at least two TIDs in the posting
+ * list.
+ *
+ * Posting tuples always have the same number of attributes as the index has
+ * generally.
+ *
  * Pivot tuple format:
  *
  *  t_tid | t_info | key values | [heap TID]
@@ -281,23 +313,157 @@ typedef struct BTMetaPageData
  * bits (BT_RESERVED_OFFSET_MASK bits), 3 of which that are reserved for
  * future use.  BT_N_KEYS_OFFSET_MASK should be large enough to store any
  * number of columns/attributes <= INDEX_MAX_KEYS.
+ * BT_IS_POSTING bit must be unset for pivot tuples, since we use it
+ * to distinct posting tuples from pivot tuples.
  *
  * Note well: The macros that deal with the number of attributes in tuples
- * assume that a tuple with INDEX_ALT_TID_MASK set must be a pivot tuple,
- * and that a tuple without INDEX_ALT_TID_MASK set must be a non-pivot
- * tuple (or must have the same number of attributes as the index has
- * generally in the case of !heapkeyspace indexes).  They will need to be
- * updated if non-pivot tuples ever get taught to use INDEX_ALT_TID_MASK
- * for something else.
+ * assume that a tuple with INDEX_ALT_TID_MASK set must be a pivot tuple or
+ * non-pivot posting tuple, and that a tuple without INDEX_ALT_TID_MASK set
+ * must be a non-pivot tuple (or must have the same number of attributes as
+ * the index has generally in the case of !heapkeyspace indexes).
  */
 #define INDEX_ALT_TID_MASK			INDEX_AM_RESERVED_BIT
 
 /* Item pointer offset bits */
 #define BT_RESERVED_OFFSET_MASK		0xF000
 #define BT_N_KEYS_OFFSET_MASK		0x0FFF
+#define BT_N_POSTING_OFFSET_MASK	0x0FFF
 #define BT_HEAP_TID_ATTR			0x1000
+#define BT_IS_POSTING				0x2000
+
+#define BTreeTupleIsPosting(itup)  \
+	( \
+		((itup)->t_info & INDEX_ALT_TID_MASK && \
+		((ItemPointerGetOffsetNumberNoCheck(&(itup)->t_tid) & BT_IS_POSTING) != 0))\
+	)
+
+#define BTreeTupleIsPivot(itup)  \
+	( \
+		((itup)->t_info & INDEX_ALT_TID_MASK && \
+		((ItemPointerGetOffsetNumberNoCheck(&(itup)->t_tid) & BT_IS_POSTING) == 0))\
+	)
+
+/*
+ * MaxPostingIndexTuplesPerPage is an upper bound on the number of tuples
+ * that can fit on one btree leaf page.
+ *
+ * Btree leaf pages may contain posting tuples, which store duplicates
+ * in a more effective way, so MaxPostingIndexTuplesPerPage is larger then
+ * MaxIndexTuplesPerPage.
+ *
+ * Each leaf page must contain at least three items, so estimate it as
+ * if we have three posting tuples with minimal size keys.
+ */
+#define MaxPostingIndexTuplesPerPage \
+	((int) ((BLCKSZ - SizeOfPageHeaderData - \
+			3*((MAXALIGN(sizeof(IndexTupleData) + 1) + sizeof(ItemIdData))) )) / \
+			(sizeof(ItemPointerData)))
 
-/* Get/set downlink block number */
+/*
+ * Btree-private state needed to build posting tuples.
+ * ipd is a posting list - an array of ItemPointerData.
+ *
+ * Iterating over tuples during index build or applying compression to a
+ * single page, we remember a tuple in itupprev, then compare the next one
+ * with it. If tuples are equal, save their TIDs in the posting list.
+ * ntuples contains the size of the posting list.
+ *
+ * Use maxitemsize and maxpostingsize to ensure that resulting posting tuple
+ * will satisfy BTMaxItemSize.
+ */
+typedef struct BTCompressState
+{
+	Size		maxitemsize;
+	Size		maxpostingsize;
+	IndexTuple	itupprev;
+	int			ntuples;
+	ItemPointerData *ipd;
+} BTCompressState;
+
+/*
+ * For use in _bt_compress_one_page().
+ * If there is only a few uncompressed items on a page,
+ * it isn't worth to apply compression.
+ * Currently it is just a magic number,
+ * proper benchmarking will probably help to choose better value.
+ */
+#define BT_COMPRESS_THRESHOLD 10
+
+/* macros to work with posting tuples *BEGIN* */
+#define BTreeTupleSetBtIsPosting(itup) \
+	do { \
+		Assert((itup)->t_info & INDEX_ALT_TID_MASK); \
+		Assert(!((ItemPointerGetOffsetNumberNoCheck(&(itup)->t_tid) & BT_IS_POSTING) != 0)); \
+		ItemPointerSetOffsetNumber(&(itup)->t_tid, \
+			ItemPointerGetOffsetNumberNoCheck(&(itup)->t_tid) | BT_IS_POSTING); \
+	} while(0)
+
+#define BTreeTupleClearBtIsPosting(itup) \
+	do { \
+		ItemPointerSetOffsetNumber(&(itup)->t_tid, \
+		ItemPointerGetOffsetNumberNoCheck(&(itup)->t_tid) & ~BT_IS_POSTING); \
+	} while(0)
+
+#define BTreeTupleGetNPosting(itup)	\
+	( \
+		ItemPointerGetOffsetNumberNoCheck(&(itup)->t_tid) & BT_N_POSTING_OFFSET_MASK \
+	)
+
+#define BTreeTupleSetNPosting(itup, n) \
+	do { \
+		ItemPointerSetOffsetNumber(&(itup)->t_tid, (n) & BT_N_POSTING_OFFSET_MASK); \
+		BTreeTupleSetBtIsPosting(itup); \
+	} while(0)
+
+/*
+ * If tuple is posting, t_tid.ip_blkid contains offset of the posting list.
+ * Caller is responsible for checking BTreeTupleIsPosting to ensure that
+ * it will get what he expects
+ */
+#define BTreeTupleGetPostingOffset(itup) \
+	ItemPointerGetBlockNumberNoCheck(&((itup)->t_tid))
+#define BTreeTupleSetPostingOffset(itup, offset) \
+	ItemPointerSetBlockNumber(&((itup)->t_tid), (offset))
+
+#define BTreeSetPostingMeta(itup, nposting, off) \
+	do { \
+		BTreeTupleSetNPosting(itup, nposting); \
+		BTreeTupleSetPostingOffset(itup, off); \
+	} while(0)
+
+#define BTreeTupleGetPosting(itup) \
+	(ItemPointerData*) ((char*)(itup) + BTreeTupleGetPostingOffset(itup))
+#define BTreeTupleGetPostingN(itup,n) \
+	(ItemPointerData*) (BTreeTupleGetPosting(itup) + (n))
+
+/*
+ * Posting tuples always contain several TIDs.
+ * Some functions that use TID as a tiebreaker,
+ * to ensure correct order of TID keys they can use two macros below:
+ */
+#define BTreeTupleGetMinTID(itup) \
+	( \
+		((itup)->t_info & INDEX_ALT_TID_MASK && \
+		((ItemPointerGetOffsetNumberNoCheck(&(itup)->t_tid) & BT_IS_POSTING))) ? \
+		( \
+			(ItemPointer) BTreeTupleGetPosting(itup) \
+		) \
+		: \
+		(ItemPointer) &((itup)->t_tid) \
+	)
+#define BTreeTupleGetMaxTID(itup) \
+	( \
+		((itup)->t_info & INDEX_ALT_TID_MASK && \
+		((ItemPointerGetOffsetNumberNoCheck(&(itup)->t_tid) & BT_IS_POSTING))) ? \
+		( \
+			(ItemPointer) (BTreeTupleGetPosting(itup) + (BTreeTupleGetNPosting(itup)-1)) \
+		) \
+		: \
+		(ItemPointer) &((itup)->t_tid) \
+	)
+/* macros to work with posting tuples *END* */
+
+/* Get/set downlink block number  */
 #define BTreeInnerTupleGetDownLink(itup) \
 	ItemPointerGetBlockNumberNoCheck(&((itup)->t_tid))
 #define BTreeInnerTupleSetDownLink(itup, blkno) \
@@ -326,7 +492,8 @@ typedef struct BTMetaPageData
  */
 #define BTreeTupleGetNAtts(itup, rel)	\
 	( \
-		(itup)->t_info & INDEX_ALT_TID_MASK ? \
+		((itup)->t_info & INDEX_ALT_TID_MASK && \
+		((ItemPointerGetOffsetNumberNoCheck(&(itup)->t_tid) & BT_IS_POSTING) == 0)) ? \
 		( \
 			ItemPointerGetOffsetNumberNoCheck(&(itup)->t_tid) & BT_N_KEYS_OFFSET_MASK \
 		) \
@@ -335,6 +502,7 @@ typedef struct BTMetaPageData
 	)
 #define BTreeTupleSetNAtts(itup, n) \
 	do { \
+		Assert(!BTreeTupleIsPosting(itup)); \
 		(itup)->t_info |= INDEX_ALT_TID_MASK; \
 		ItemPointerSetOffsetNumber(&(itup)->t_tid, (n) & BT_N_KEYS_OFFSET_MASK); \
 	} while(0)
@@ -342,6 +510,8 @@ typedef struct BTMetaPageData
 /*
  * Get tiebreaker heap TID attribute, if any.  Macro works with both pivot
  * and non-pivot tuples, despite differences in how heap TID is represented.
+ *
+ * For non-pivot posting tuple it returns the first tid from posting list.
  */
 #define BTreeTupleGetHeapTID(itup) \
 	( \
@@ -351,7 +521,10 @@ typedef struct BTMetaPageData
 		(ItemPointer) (((char *) (itup) + IndexTupleSize(itup)) - \
 					   sizeof(ItemPointerData)) \
 	  ) \
-	  : (itup)->t_info & INDEX_ALT_TID_MASK ? NULL : (ItemPointer) &((itup)->t_tid) \
+	  : (itup)->t_info & INDEX_ALT_TID_MASK ? \
+		(((ItemPointerGetOffsetNumberNoCheck(&(itup)->t_tid) & BT_IS_POSTING) != 0) ? \
+		(ItemPointer) BTreeTupleGetPosting(itup) : NULL) \
+		: (ItemPointer) &((itup)->t_tid) \
 	)
 /*
  * Set the heap TID attribute for a tuple that uses the INDEX_ALT_TID_MASK
@@ -360,6 +533,7 @@ typedef struct BTMetaPageData
 #define BTreeTupleSetAltHeapTID(itup) \
 	do { \
 		Assert((itup)->t_info & INDEX_ALT_TID_MASK); \
+		Assert(!((ItemPointerGetOffsetNumberNoCheck(&(itup)->t_tid) & BT_IS_POSTING) != 0)); \
 		ItemPointerSetOffsetNumber(&(itup)->t_tid, \
 								   ItemPointerGetOffsetNumberNoCheck(&(itup)->t_tid) | BT_HEAP_TID_ATTR); \
 	} while(0)
@@ -567,6 +741,8 @@ 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
@@ -579,7 +755,7 @@ typedef struct BTScanPosData
 	int			lastItem;		/* last valid index in items[] */
 	int			itemIndex;		/* current index in items[] */
 
-	BTScanPosItem items[MaxIndexTuplesPerPage]; /* MUST BE LAST */
+	BTScanPosItem items[MaxPostingIndexTuplesPerPage];	/* MUST BE LAST */
 } BTScanPosData;
 
 typedef BTScanPosData *BTScanPos;
@@ -763,6 +939,8 @@ extern void _bt_delitems_delete(Relation rel, Buffer buf,
 								OffsetNumber *itemnos, int nitems, Relation heapRel);
 extern void _bt_delitems_vacuum(Relation rel, Buffer buf,
 								OffsetNumber *itemnos, int nitems,
+								OffsetNumber *remainingoffset,
+								IndexTuple *remaining, int nremaining,
 								BlockNumber lastBlockVacuumed);
 extern int	_bt_pagedel(Relation rel, Buffer buf);
 
@@ -813,6 +991,9 @@ extern bool _bt_check_natts(Relation rel, bool heapkeyspace, Page page,
 							OffsetNumber offnum);
 extern void _bt_check_third_page(Relation rel, Relation heap,
 								 bool needheaptidspace, Page page, IndexTuple newtup);
+extern IndexTuple BTreeFormPostingTuple(IndexTuple tuple, ItemPointerData *ipd,
+										int nipd);
+extern IndexTuple BTreeGetNthTupleOfPosting(IndexTuple tuple, int n);
 
 /*
  * prototypes for functions in nbtvalidate.c
@@ -825,5 +1006,7 @@ extern bool btvalidate(Oid opclassoid);
 extern IndexBuildResult *btbuild(Relation heap, Relation index,
 								 struct IndexInfo *indexInfo);
 extern void _bt_parallel_build_main(dsm_segment *seg, shm_toc *toc);
+extern void add_item_to_posting(BTCompressState *compressState,
+								IndexTuple itup);
 
 #endif							/* NBTREE_H */
diff --git a/src/include/access/nbtxlog.h b/src/include/access/nbtxlog.h
index 9beccc8..6f60ca5 100644
--- a/src/include/access/nbtxlog.h
+++ b/src/include/access/nbtxlog.h
@@ -173,10 +173,19 @@ typedef struct xl_btree_vacuum
 {
 	BlockNumber lastBlockVacuumed;
 
-	/* TARGET OFFSET NUMBERS FOLLOW */
+	/*
+	 * This field helps us to find beginning of the remaining tuples from
+	 * postings which follow array of offset numbers.
+	 */
+	uint32		nremaining;
+	uint32		ndeleted;
+
+	/* REMAINING OFFSET NUMBERS FOLLOW (nremaining values) */
+	/* REMAINING TUPLES TO INSERT FOLLOW (if nremaining > 0) */
+	/* TARGET OFFSET NUMBERS FOLLOW (if any) */
 } xl_btree_vacuum;
 
-#define SizeOfBtreeVacuum	(offsetof(xl_btree_vacuum, lastBlockVacuumed) + sizeof(BlockNumber))
+#define SizeOfBtreeVacuum	(offsetof(xl_btree_vacuum, ndeleted) + sizeof(BlockNumber))
 
 /*
  * This is what we need to know about marking an empty branch for deletion.