wal_update_changes_hot_update.patch

diff --git a/src/backend/access/common/heaptuple.c b/src/backend/access/common/heaptuple.c
index 034dfe5..371ef21 100644
--- a/src/backend/access/common/heaptuple.c
+++ b/src/backend/access/common/heaptuple.c
@@ -618,6 +618,428 @@ heap_copytuple_with_tuple(HeapTuple src, HeapTuple dest)
 }
 
 /*
+ * get_tuple_info - Gets the tuple offset and value.
+ *
+ * calculates the attribute value and offset, where the attribute ends in the
+ * tuple based on the attribute number and previous fetched attribute info.
+ *
+ * offset (I/P and O/P variable) - Input as end of previous attribute offset
+ *		and incase if it is a first attribute then it's value is zero.
+ *		Output as end of the current attribute in the tuple.
+ * usecacheoff (I/P and O/P variable) - Attribute cacheoff can be used or not.
+ */
+static void
+get_tuple_info(Form_pg_attribute *att, HeapTuple tuple, bits8 *bp,
+			   bool hasnulls, int attnum, Datum *value, uint16 *offset,
+			   bool *usecacheoff)
+{
+	Form_pg_attribute thisatt = att[attnum];
+	uint16		off = *offset;
+	bool		slow = *usecacheoff;
+	char	   *tp;
+	HeapTupleHeader tup = tuple->t_data;
+
+	tp = (char *) tup + tup->t_hoff;
+
+	if (hasnulls && att_isnull(attnum, bp))
+	{
+		slow = true;			/* can't use attcacheoff anymore */
+		*offset = off;
+		*usecacheoff = slow;
+		return;
+	}
+
+	if (!slow && thisatt->attcacheoff >= 0)
+		off = thisatt->attcacheoff;
+	else if (thisatt->attlen == -1)
+	{
+		/*
+		 * We can only cache the offset for a varlena attribute if the offset
+		 * is already suitably aligned, so that there would be no pad bytes in
+		 * any case: then the offset will be valid for either an aligned or
+		 * unaligned value.
+		 */
+		if (!slow &&
+			off == att_align_nominal(off, thisatt->attalign))
+			thisatt->attcacheoff = off;
+		else
+		{
+			off = att_align_pointer(off, thisatt->attalign, -1,
+									tp + off);
+			slow = true;
+		}
+	}
+	else
+	{
+		/* not varlena, so safe to use att_align_nominal */
+		off = att_align_nominal(off, thisatt->attalign);
+
+		if (!slow)
+			thisatt->attcacheoff = off;
+	}
+
+	*value = fetchatt(thisatt, tp + off);
+
+	off = att_addlength_pointer(off, thisatt->attlen, tp + off);
+
+	if (thisatt->attlen <= 0)
+		slow = true;			/* can't use attcacheoff anymore */
+
+	*offset = off;
+	*usecacheoff = slow;
+}
+
+
+/*
+ * encode_xlog_update
+ *		Forms a diff tuple from old and new tuple with the modified columns.
+ *
+ *		att - attribute list.
+ *		oldtup - pointer to the old tuple.
+ *		heaptup - pointer to the modified tuple.
+ *		wal_tup - pointer to the wal record which needs to be formed from old
+				  and new tuples by using the modified columns list.
+ *		modifiedCols - modified columns list by the update command.
+ */
+void
+encode_xlog_update(Form_pg_attribute *att, HeapTuple oldtup,
+				   HeapTuple heaptup, HeapTuple wal_tup,
+				   Bitmapset *modifiedCols)
+{
+	int			numberOfAttributes;
+	uint16		cur_offset = 0,
+				prev_offset = 0,
+				offset = 0;
+	int			attnum;
+	HeapTupleHeader newtuphdr = heaptup->t_data;
+	bits8	   *new_bp = newtuphdr->t_bits,
+			   *old_bp = oldtup->t_data->t_bits;
+	bool		old_hasnulls = HeapTupleHasNulls(oldtup);
+	bool		new_hasnulls = HeapTupleHasNulls(heaptup);
+	bool		cur_usecacheoff = false,
+				prev_usecacheoff = false;
+	Datum		cur_value,
+				prev_value;
+	uint16		data_length;
+	bool		check_for_padding = false;
+	char	   *data;
+	uint16		wal_offset = 0;
+
+	numberOfAttributes = HeapTupleHeaderGetNatts(newtuphdr);
+
+	data = (char *) wal_tup->t_data;
+	wal_offset = newtuphdr->t_hoff;
+
+	/* Copy the tuple header to the WAL tuple */
+	memcpy(data, heaptup->t_data, wal_offset);
+
+	for (attnum = 0; attnum < numberOfAttributes; attnum++)
+	{
+		/*
+		 * If the attribute is modified by the update operation, store the
+		 * appropiate offsets in the WAL record, otherwise skip to the next
+		 * attribute.
+		 */
+		if (bms_is_member((attnum + 1) - FirstLowInvalidHeapAttributeNumber,
+						  modifiedCols))
+		{
+			check_for_padding = true;
+
+			/*
+			 * calculate the offset where the modified attribute starts in the
+			 * old tuple used to store in the WAL record, this will be used to
+			 * traverse the old tuple during recovery.
+			 */
+			if (prev_offset)
+			{
+				*(uint8 *) (data + wal_offset) = HEAP_UPDATE_WAL_OPT_COPY;
+				wal_offset += sizeof(uint8);
+
+				wal_offset = SHORTALIGN(wal_offset);
+
+				*(uint16 *) (data + wal_offset) = prev_offset;
+				wal_offset += sizeof(uint16);
+			}
+
+			/* calculate the old tuple field length which needs to ignored */
+			offset = prev_offset;
+			get_tuple_info(att, oldtup, old_bp, old_hasnulls, attnum,
+						   &prev_value, &prev_offset, &prev_usecacheoff);
+
+			data_length = prev_offset - offset;
+
+			if (data_length)
+			{
+				*(uint8 *) (data + wal_offset) = HEAP_UPDATE_WAL_OPT_IGN;
+				wal_offset += sizeof(uint8);
+
+				wal_offset = SHORTALIGN(wal_offset);
+
+				*(uint16 *) (data + wal_offset) = data_length;
+				wal_offset += sizeof(uint16);
+			}
+
+			/*
+			 * calculate the new tuple field start position to check whether
+			 * any padding is required or not.
+			 */
+			offset = cur_offset;
+			cur_offset = att_align_pointer(cur_offset,
+								  att[attnum]->attalign, att[attnum]->attlen,
+						(char *) newtuphdr + newtuphdr->t_hoff + cur_offset);
+
+			data_length = cur_offset - offset;
+
+			/*
+			 * The above calculation is required to identify, that any
+			 * alignment is required or not. And the padding command is added
+			 * only incase of that the data is not NULL. which is done at
+			 * below.
+			 */
+
+			offset = cur_offset;
+			get_tuple_info(att, heaptup, new_bp, new_hasnulls, attnum,
+						   &cur_value, &cur_offset, &cur_usecacheoff);
+
+			/* if the new tuple data is null then nothing is required to add */
+			if (new_hasnulls && att_isnull(attnum, new_bp))
+			{
+				continue;
+			}
+
+			/* Add the padding if requires as the data is not NULL */
+			if (data_length)
+			{
+				*(uint8 *) (data + wal_offset) = HEAP_UPDATE_WAL_OPT_PAD;
+				wal_offset += sizeof(uint8);
+
+				*(uint8 *) (data + wal_offset) = data_length;
+				wal_offset += sizeof(uint8);
+			}
+
+			/* get the attribute value and end offset for same */
+			*(uint8 *) (data + wal_offset) = HEAP_UPDATE_WAL_OPT_ADD;
+			wal_offset += sizeof(uint8);
+
+			wal_offset = SHORTALIGN(wal_offset);
+
+			data_length = cur_offset - offset;
+			*(uint16 *) (data + wal_offset) = data_length;
+			wal_offset += sizeof(uint16);
+
+			if (att[attnum]->attbyval)
+			{
+				/* pass-by-value */
+				char		tempdata[sizeof(Datum)];
+
+				/*
+				 * Here we are not storing the data as aligned in the WAL
+				 * record as we don't have the tuple descriptor while
+				 * replaying the xlog.
+				 *
+				 * But this alignment is of the data is taken care while
+				 * framing the tuple during heap_xlog_update.
+				 */
+				store_att_byval(tempdata,
+								cur_value,
+								att[attnum]->attlen);
+				memcpy((data + wal_offset), tempdata, att[attnum]->attlen);
+			}
+			else
+			{
+				memcpy((data + wal_offset),
+					   DatumGetPointer(cur_value),
+					   data_length);
+			}
+
+			wal_offset += data_length;
+		}
+		else
+		{
+			/*
+			 * padding is required if the previous field is modified, so check
+			 * whether padding is required or not.
+			 *
+			 * The attnum is not modified so if the data in the old tuple is
+			 * NULL then in the new tuple also the field data is NULL.
+			 */
+			if (check_for_padding && !att_isnull(attnum, old_bp))
+			{
+				check_for_padding = false;
+
+				/*
+				 * calculate the old tuple field start position, required to
+				 * ignore if any alignmet is present.
+				 */
+				offset = prev_offset;
+				prev_offset = att_align_pointer(prev_offset,
+								  att[attnum]->attalign, att[attnum]->attlen,
+												(char *) oldtup->t_data + oldtup->t_data->t_hoff + prev_offset);
+
+				data_length = prev_offset - offset;
+
+				if (data_length)
+				{
+					*(uint8 *) (data + wal_offset) = HEAP_UPDATE_WAL_OPT_IGN;
+					wal_offset += sizeof(uint8);
+
+					wal_offset = SHORTALIGN(wal_offset);
+
+					*(uint16 *) (data + wal_offset) = data_length;
+					wal_offset += sizeof(uint16);
+				}
+
+				/*
+				 * calculate the new tuple field start position to check
+				 * whether any padding is required or not because field
+				 * alignment.
+				 */
+				offset = cur_offset;
+				cur_offset = att_align_pointer(cur_offset,
+								  att[attnum]->attalign, att[attnum]->attlen,
+						(char *) newtuphdr + newtuphdr->t_hoff + cur_offset);
+
+				data_length = cur_offset - offset;
+
+				if (data_length)
+				{
+					*(uint8 *) (data + wal_offset) = HEAP_UPDATE_WAL_OPT_PAD;
+					wal_offset += sizeof(uint8);
+
+					*(uint8 *) (data + wal_offset) = data_length;
+					wal_offset += sizeof(uint8);
+				}
+			}
+
+			get_tuple_info(att, oldtup, old_bp, old_hasnulls, attnum,
+						   &prev_value, &prev_offset, &prev_usecacheoff);
+
+			get_tuple_info(att, heaptup, new_bp, new_hasnulls, attnum,
+						   &cur_value, &cur_offset, &cur_usecacheoff);
+		}
+	}
+
+	wal_tup->t_len = wal_offset;
+	wal_tup->t_self = heaptup->t_self;
+	wal_tup->t_tableOid = heaptup->t_tableOid;
+}
+
+/*
+ * decode_xlog_update
+ *		deforms a diff tuple and forms the new tuple with the help of old tuple.
+ *
+ * The WAL record data is in the format as below
+ *
+ *	COPY + offset until copy required
+ *	IGN + length needs to be ignored from the old tuple.
+ *	PAD + length needs to padded with zero in new tuple.
+ *	ADD + length of data + data which is modified.
+ *
+ * For the COPY command, copy the specified length from old tuple.
+ *
+ * Once the old tuple data copied, then increase the offset by the
+ * copied length.
+ *
+ * For the IGN command, ignore the specified length in the old tuple.
+ *
+ * For the PAD command, fill with zeros of the specified length in
+ * the new tuple.
+ *
+ * For the ADD command, copy the corresponding length of data from WAL
+ * record to the new tuple.
+ *
+ * Repeat this procedure until the WAL record reaches the end.
+ *
+ * If any remaining left out old tuple data will be copied at last.
+ *
+ *	htup - old tuple data pointer from which new tuple needs to be formed.
+ *	old_tup_len - old tuple length.
+ *	data - pointer to the new tuple which needs to be framed.
+ *	new_tup_len - output of new tuple data length.
+ *	waldata - wal record pointer from which the new tuple needs to formed.
+ *	wal_len - wal record length.
+ */
+void
+decode_xlog_update(HeapTupleHeader htup, uint32 old_tup_len, char *data,
+				   uint32 *new_tup_len, char *waldata, uint32 wal_len)
+{
+	uint8		command;
+	uint16		len = 0,
+				data_length,
+				prev_offset = 0,
+				cur_offset = 0;
+	char	   *olddata = (char *) htup + htup->t_hoff;
+
+	/*
+	 * Frame the new tuple from old tuple and WAL record
+	 */
+	len = 0;
+
+	/* Frame the new tuple from the old and WAL tuples */
+	while (len < wal_len)
+	{
+		command = *(uint8 *) (waldata + len);
+		len += sizeof(uint8);
+
+		switch (command)
+		{
+			case HEAP_UPDATE_WAL_OPT_COPY:
+				len = SHORTALIGN(len);
+				data_length = *(uint16 *) (waldata + len) - prev_offset;
+
+				/* Copy the old tuple data */
+				memcpy((data + cur_offset),
+					   (olddata + prev_offset),
+					   data_length);
+				cur_offset += data_length;
+				prev_offset += data_length;
+
+				len += sizeof(uint16);
+				break;
+			case HEAP_UPDATE_WAL_OPT_ADD:
+				len = SHORTALIGN(len);
+				data_length = *(uint16 *) (waldata + len);
+				len += sizeof(uint16);
+
+				/* Copy the modified attribute data from WAL record */
+				memcpy((data + cur_offset), (waldata + len), data_length);
+				cur_offset += data_length;
+				len += data_length;
+				break;
+			case HEAP_UPDATE_WAL_OPT_IGN:
+				len = SHORTALIGN(len);
+				data_length = *(uint16 *) (waldata + len);
+
+				/* Skip the oldtuple with data length in the WAL record */
+				prev_offset += data_length;
+				len += sizeof(uint16);
+				break;
+			case HEAP_UPDATE_WAL_OPT_PAD:
+				data_length = *(uint8 *) (waldata + len);
+				cur_offset += data_length;
+				len += sizeof(uint8);
+				break;
+			default:
+				Assert(0);
+				break;
+		}
+	}
+
+	/* Copy the remaining old tuple data to the new tuple */
+	if (prev_offset < old_tup_len)
+	{
+		memcpy((data + cur_offset),
+			   (olddata + prev_offset),
+			   (old_tup_len - prev_offset));
+		cur_offset += (old_tup_len - prev_offset);
+	}
+
+	*new_tup_len = cur_offset
+		+ (htup->t_hoff - offsetof(HeapTupleHeaderData, t_bits));
+}
+
+
+/*
  * heap_form_tuple
  *		construct a tuple from the given values[] and isnull[] arrays,
  *		which are of the length indicated by tupleDescriptor->natts
diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index f28026b..bcf830e 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -70,7 +70,6 @@
 #include "utils/syscache.h"
 #include "utils/tqual.h"
 
-
 /* GUC variable */
 bool		synchronize_seqscans = true;
 
@@ -84,7 +83,8 @@ static HeapTuple heap_prepare_insert(Relation relation, HeapTuple tup,
 					TransactionId xid, CommandId cid, int options);
 static XLogRecPtr log_heap_update(Relation reln, Buffer oldbuf,
 				ItemPointerData from, Buffer newbuf, HeapTuple newtup,
-				bool all_visible_cleared, bool new_all_visible_cleared);
+				bool all_visible_cleared, bool new_all_visible_cleared,
+				bool diff_update);
 static bool HeapSatisfiesHOTUpdate(Relation relation, Bitmapset *hot_attrs,
 					   HeapTuple oldtup, HeapTuple newtup);
 
@@ -2686,6 +2686,7 @@ simple_heap_delete(Relation relation, ItemPointer tid)
  *	cid - update command ID (used for visibility test, and stored into
  *		cmax/cmin if successful)
  *	crosscheck - if not InvalidSnapshot, also check old tuple against this
+ *	modifiedCols - the modified column list of the update command.
  *	wait - true if should wait for any conflicting update to commit/abort
  *
  * Normal, successful return value is HeapTupleMayBeUpdated, which
@@ -2707,7 +2708,8 @@ simple_heap_delete(Relation relation, ItemPointer tid)
 HTSU_Result
 heap_update(Relation relation, ItemPointer otid, HeapTuple newtup,
 			ItemPointer ctid, TransactionId *update_xmax,
-			CommandId cid, Snapshot crosscheck, bool wait)
+			CommandId cid, Snapshot crosscheck, Bitmapset *modifiedCols,
+			bool wait)
 {
 	HTSU_Result result;
 	TransactionId xid = GetCurrentTransactionId();
@@ -2715,6 +2717,7 @@ heap_update(Relation relation, ItemPointer otid, HeapTuple newtup,
 	ItemId		lp;
 	HeapTupleData oldtup;
 	HeapTuple	heaptup;
+	HeapTupleData wal_tup;
 	Page		page;
 	BlockNumber block;
 	Buffer		buffer,
@@ -2730,6 +2733,11 @@ heap_update(Relation relation, ItemPointer otid, HeapTuple newtup,
 	bool		use_hot_update = false;
 	bool		all_visible_cleared = false;
 	bool		all_visible_cleared_new = false;
+	struct
+	{
+		HeapTupleHeaderData hdr;
+		char		data[MaxHeapTupleSize];
+	}			tbuf;
 
 	Assert(ItemPointerIsValid(otid));
 
@@ -3173,10 +3181,31 @@ l2:
 	/* XLOG stuff */
 	if (RelationNeedsWAL(relation))
 	{
-		XLogRecPtr	recptr = log_heap_update(relation, buffer, oldtup.t_self,
-											 newbuf, heaptup,
-											 all_visible_cleared,
-											 all_visible_cleared_new);
+		XLogRecPtr	recptr;
+
+		/*
+		 * Apply the xlog diff update algorithm only for hot updates.
+		 */
+		if (modifiedCols && use_hot_update)
+		{
+			wal_tup.t_data = (HeapTupleHeader) &tbuf;
+			encode_xlog_update(relation->rd_att->attrs, &oldtup, heaptup,
+							   &wal_tup, modifiedCols);
+
+			recptr = log_heap_update(relation, buffer, oldtup.t_self,
+									 newbuf, &wal_tup,
+									 all_visible_cleared,
+									 all_visible_cleared_new,
+									 true);
+		}
+		else
+		{
+			recptr = log_heap_update(relation, buffer, oldtup.t_self,
+									 newbuf, heaptup,
+									 all_visible_cleared,
+									 all_visible_cleared_new,
+									 false);
+		}
 
 		if (newbuf != buffer)
 		{
@@ -3363,6 +3392,7 @@ simple_heap_update(Relation relation, ItemPointer otid, HeapTuple tup)
 	result = heap_update(relation, otid, tup,
 						 &update_ctid, &update_xmax,
 						 GetCurrentCommandId(true), InvalidSnapshot,
+						 NULL,
 						 true /* wait for commit */ );
 	switch (result)
 	{
@@ -4407,7 +4437,8 @@ log_heap_visible(RelFileNode rnode, BlockNumber block, Buffer vm_buffer,
 static XLogRecPtr
 log_heap_update(Relation reln, Buffer oldbuf, ItemPointerData from,
 				Buffer newbuf, HeapTuple newtup,
-				bool all_visible_cleared, bool new_all_visible_cleared)
+				bool all_visible_cleared, bool new_all_visible_cleared,
+				bool diff_update)
 {
 	xl_heap_update xlrec;
 	xl_heap_header xlhdr;
@@ -4426,9 +4457,15 @@ log_heap_update(Relation reln, Buffer oldbuf, ItemPointerData from,
 
 	xlrec.target.node = reln->rd_node;
 	xlrec.target.tid = from;
-	xlrec.all_visible_cleared = all_visible_cleared;
+	xlrec.diff_update = diff_update;
 	xlrec.newtid = newtup->t_self;
-	xlrec.new_all_visible_cleared = new_all_visible_cleared;
+
+	/*
+	 * MSB 4 bits tells PD_ALL_VISIBLE was cleared of new page and rest 4 bits
+	 * for the old page
+	 */
+	xlrec.new_all_visible_cleared |= all_visible_cleared;
+	xlrec.new_all_visible_cleared |= new_all_visible_cleared << 4;
 
 	rdata[0].data = (char *) &xlrec;
 	rdata[0].len = SizeOfHeapUpdate;
@@ -5217,14 +5254,18 @@ heap_xlog_update(XLogRecPtr lsn, XLogRecord *record, bool hot_update)
 	}			tbuf;
 	xl_heap_header xlhdr;
 	int			hsize;
-	uint32		newlen;
+	uint32		new_tup_len = 0;
 	Size		freespace;
 
+	/* Initialize the buffer, used to frame the new tuple */
+	MemSet((char *) &tbuf.hdr, 0, sizeof(HeapTupleHeaderData));
+	hsize = SizeOfHeapUpdate + SizeOfHeapHeader;
+
 	/*
 	 * The visibility map may need to be fixed even if the heap page is
 	 * already up-to-date.
 	 */
-	if (xlrec->all_visible_cleared)
+	if (xlrec->new_all_visible_cleared & 0x0F)
 	{
 		Relation	reln = CreateFakeRelcacheEntry(xlrec->target.node);
 		BlockNumber block = ItemPointerGetBlockNumber(&xlrec->target.tid);
@@ -5244,12 +5285,14 @@ heap_xlog_update(XLogRecPtr lsn, XLogRecord *record, bool hot_update)
 	}
 
 	/* Deal with old tuple version */
-
 	buffer = XLogReadBuffer(xlrec->target.node,
 							ItemPointerGetBlockNumber(&(xlrec->target.tid)),
 							false);
 	if (!BufferIsValid(buffer))
+	{
 		goto newt;
+	}
+
 	page = (Page) BufferGetPage(buffer);
 
 	if (XLByteLE(lsn, PageGetLSN(page)))		/* changes are applied */
@@ -5269,6 +5312,29 @@ heap_xlog_update(XLogRecPtr lsn, XLogRecord *record, bool hot_update)
 
 	htup = (HeapTupleHeader) PageGetItem(page, lp);
 
+	if (xlrec->diff_update)
+	{
+		char	   *data = (char *) &tbuf.hdr + htup->t_hoff;
+		uint32		old_tup_len;
+		uint32		wal_len;
+		char	   *waldata = (char *) xlrec + hsize + htup->t_hoff
+		- offsetof(HeapTupleHeaderData, t_bits);
+
+		wal_len = record->xl_len - hsize;
+		Assert(wal_len <= MaxHeapTupleSize);
+
+		wal_len -= (htup->t_hoff - offsetof(HeapTupleHeaderData, t_bits));
+
+		old_tup_len = ItemIdGetLength(lp) - htup->t_hoff;
+
+		/* copy exactly the tuple header present in the WAL to new tuple */
+		memcpy((char *) &tbuf.hdr + offsetof(HeapTupleHeaderData, t_bits),
+			   (char *) xlrec + hsize,
+			   (htup->t_hoff - offsetof(HeapTupleHeaderData, t_bits)));
+
+		decode_xlog_update(htup, old_tup_len, data, &new_tup_len, waldata, wal_len);
+	}
+
 	htup->t_infomask &= ~(HEAP_XMAX_COMMITTED |
 						  HEAP_XMAX_INVALID |
 						  HEAP_XMAX_IS_MULTI |
@@ -5286,7 +5352,7 @@ heap_xlog_update(XLogRecPtr lsn, XLogRecord *record, bool hot_update)
 	/* Mark the page as a candidate for pruning */
 	PageSetPrunable(page, record->xl_xid);
 
-	if (xlrec->all_visible_cleared)
+	if (xlrec->new_all_visible_cleared & 0x0F)
 		PageClearAllVisible(page);
 
 	/*
@@ -5295,6 +5361,7 @@ heap_xlog_update(XLogRecPtr lsn, XLogRecord *record, bool hot_update)
 	 */
 	if (samepage)
 		goto newsame;
+
 	PageSetLSN(page, lsn);
 	PageSetTLI(page, ThisTimeLineID);
 	MarkBufferDirty(buffer);
@@ -5308,7 +5375,7 @@ newt:;
 	 * The visibility map may need to be fixed even if the heap page is
 	 * already up-to-date.
 	 */
-	if (xlrec->new_all_visible_cleared)
+	if ((xlrec->new_all_visible_cleared >> 4) & 0x0F)
 	{
 		Relation	reln = CreateFakeRelcacheEntry(xlrec->target.node);
 		BlockNumber block = ItemPointerGetBlockNumber(&xlrec->newtid);
@@ -5355,20 +5422,24 @@ newsame:;
 	if (PageGetMaxOffsetNumber(page) + 1 < offnum)
 		elog(PANIC, "heap_update_redo: invalid max offset number");
 
-	hsize = SizeOfHeapUpdate + SizeOfHeapHeader;
-
-	newlen = record->xl_len - hsize;
-	Assert(newlen <= MaxHeapTupleSize);
 	memcpy((char *) &xlhdr,
 		   (char *) xlrec + SizeOfHeapUpdate,
 		   SizeOfHeapHeader);
+
 	htup = &tbuf.hdr;
-	MemSet((char *) htup, 0, sizeof(HeapTupleHeaderData));
-	/* PG73FORMAT: get bitmap [+ padding] [+ oid] + data */
-	memcpy((char *) htup + offsetof(HeapTupleHeaderData, t_bits),
-		   (char *) xlrec + hsize,
-		   newlen);
-	newlen += offsetof(HeapTupleHeaderData, t_bits);
+
+	if (!xlrec->diff_update)
+	{
+		new_tup_len = record->xl_len - hsize;
+		Assert(new_tup_len <= MaxHeapTupleSize);
+
+		/* PG73FORMAT: get bitmap [+ padding] [+ oid] + data */
+		memcpy((char *) htup + offsetof(HeapTupleHeaderData, t_bits),
+			   (char *) xlrec + hsize,
+			   new_tup_len);
+	}
+
+	new_tup_len += offsetof(HeapTupleHeaderData, t_bits);
 	htup->t_infomask2 = xlhdr.t_infomask2;
 	htup->t_infomask = xlhdr.t_infomask;
 	htup->t_hoff = xlhdr.t_hoff;
@@ -5378,7 +5449,7 @@ newsame:;
 	/* Make sure there is no forward chain link in t_ctid */
 	htup->t_ctid = xlrec->newtid;
 
-	offnum = PageAddItem(page, (Item) htup, newlen, offnum, true, true);
+	offnum = PageAddItem(page, (Item) htup, new_tup_len, offnum, true, true);
 	if (offnum == InvalidOffsetNumber)
 		elog(PANIC, "heap_update_redo: failed to add tuple");
 
diff --git a/src/backend/executor/nodeModifyTable.c b/src/backend/executor/nodeModifyTable.c
index a7bce75..756fcf7 100644
--- a/src/backend/executor/nodeModifyTable.c
+++ b/src/backend/executor/nodeModifyTable.c
@@ -48,6 +48,7 @@
 #include "utils/memutils.h"
 #include "utils/rel.h"
 #include "utils/tqual.h"
+#include "parser/parsetree.h"
 
 
 /*
@@ -478,12 +479,14 @@ ExecUpdate(ItemPointer tupleid,
 		   bool canSetTag)
 {
 	HeapTuple	tuple;
+	HeapTuple	tuple_bf_trigger;
 	ResultRelInfo *resultRelInfo;
 	Relation	resultRelationDesc;
 	HTSU_Result result;
 	ItemPointerData update_ctid;
 	TransactionId update_xmax;
 	List	   *recheckIndexes = NIL;
+	Bitmapset  *modifiedCols = NULL;
 
 	/*
 	 * abort the operation if not running transactions
@@ -495,7 +498,7 @@ ExecUpdate(ItemPointer tupleid,
 	 * get the heap tuple out of the tuple table slot, making sure we have a
 	 * writable copy
 	 */
-	tuple = ExecMaterializeSlot(slot);
+	tuple = tuple_bf_trigger = ExecMaterializeSlot(slot);
 
 	/*
 	 * get information on the (current) result relation
@@ -553,6 +556,15 @@ lreplace:;
 		if (resultRelationDesc->rd_att->constr)
 			ExecConstraints(resultRelInfo, slot, estate);
 
+		/* check whether the xlog diff update can be applied or not? */
+		if ((resultRelationDesc->rd_toastoid == InvalidOid)
+			&& (tuple_bf_trigger == tuple)
+			&& (tuple->t_len > MinHeapTupleSizeForDiffUpdate))
+		{
+			modifiedCols = (rt_fetch(resultRelInfo->ri_RangeTableIndex,
+									 estate->es_range_table)->modifiedCols);
+		}
+
 		/*
 		 * replace the heap tuple
 		 *
@@ -566,6 +578,7 @@ lreplace:;
 							 &update_ctid, &update_xmax,
 							 estate->es_output_cid,
 							 estate->es_crosscheck_snapshot,
+							 modifiedCols,
 							 true /* wait for commit */ );
 		switch (result)
 		{
@@ -596,6 +609,14 @@ lreplace:;
 						*tupleid = update_ctid;
 						slot = ExecFilterJunk(resultRelInfo->ri_junkFilter, epqslot);
 						tuple = ExecMaterializeSlot(slot);
+
+						/*
+						 * Incase of revalidation reinitialize the values
+						 * which are used for the xlog diff update algorithm.
+						 */
+						tuple_bf_trigger = tuple;
+						modifiedCols = NULL;
+
 						goto lreplace;
 					}
 				}
diff --git a/src/include/access/heapam.h b/src/include/access/heapam.h
index 660a854..5e91ba8 100644
--- a/src/include/access/heapam.h
+++ b/src/include/access/heapam.h
@@ -105,7 +105,8 @@ extern HTSU_Result heap_delete(Relation relation, ItemPointer tid,
 extern HTSU_Result heap_update(Relation relation, ItemPointer otid,
 			HeapTuple newtup,
 			ItemPointer ctid, TransactionId *update_xmax,
-			CommandId cid, Snapshot crosscheck, bool wait);
+			CommandId cid, Snapshot crosscheck, Bitmapset  *modifiedCols,
+			bool wait);
 extern HTSU_Result heap_lock_tuple(Relation relation, HeapTuple tuple,
 				Buffer *buffer, ItemPointer ctid,
 				TransactionId *update_xmax, CommandId cid,
diff --git a/src/include/access/htup.h b/src/include/access/htup.h
index b289e14..9ab9713 100644
--- a/src/include/access/htup.h
+++ b/src/include/access/htup.h
@@ -16,6 +16,7 @@
 
 #include "access/tupdesc.h"
 #include "access/tupmacs.h"
+#include "nodes/bitmapset.h"
 #include "storage/bufpage.h"
 #include "storage/itemptr.h"
 #include "storage/relfilenode.h"
@@ -575,6 +576,11 @@ typedef HeapTupleData *HeapTuple;
 #define HeapTupleSetOid(tuple, oid) \
 		HeapTupleHeaderSetOid((tuple)->t_data, (oid))
 
+/*
+ * Minimum tuple length required by the tuple during update operation for doing
+ * WAL optimization of update operation.
+ */
+#define MinHeapTupleSizeForDiffUpdate 128
 
 /*
  * WAL record definitions for heapam.c's WAL operations
@@ -692,18 +698,29 @@ typedef struct xl_multi_insert_tuple
 
 #define SizeOfMultiInsertTuple	(offsetof(xl_multi_insert_tuple, t_hoff) + sizeof(uint8))
 
-/* This is what we need to know about update|hot_update */
+/* This is what we need to know about update|hot_update|optimized_update */
 typedef struct xl_heap_update
 {
 	xl_heaptid	target;			/* deleted tuple id */
 	ItemPointerData newtid;		/* new inserted tuple id */
-	bool		all_visible_cleared;	/* PD_ALL_VISIBLE was cleared */
-	bool		new_all_visible_cleared;		/* same for the page of newtid */
+	bool	diff_update;		/* optimized update or not */
+	/*
+	 * To keep the structure size same all_visible_cleared is merged with
+	 * new_all_visible_cleared.
+	 */
+	bool	new_all_visible_cleared; /* MSB 4 bits tells PD_ALL_VISIBLE	was
+										cleared of new page and rest 4 bits
+										for the old page */
 	/* NEW TUPLE xl_heap_header AND TUPLE DATA FOLLOWS AT END OF STRUCT */
 } xl_heap_update;
 
 #define SizeOfHeapUpdate	(offsetof(xl_heap_update, new_all_visible_cleared) + sizeof(bool))
 
+#define HEAP_UPDATE_WAL_OPT_COPY 0
+#define HEAP_UPDATE_WAL_OPT_ADD  1
+#define HEAP_UPDATE_WAL_OPT_IGN  2
+#define HEAP_UPDATE_WAL_OPT_PAD  3
+
 /*
  * This is what we need to know about vacuum page cleanup/redirect
  *
@@ -900,6 +917,11 @@ extern Datum heap_getsysattr(HeapTuple tup, int attnum, TupleDesc tupleDesc,
 				bool *isnull);
 extern HeapTuple heap_copytuple(HeapTuple tuple);
 extern void heap_copytuple_with_tuple(HeapTuple src, HeapTuple dest);
+extern void encode_xlog_update(Form_pg_attribute *att, HeapTuple oldtup,
+					 HeapTuple heaptup, HeapTuple wal_tup,
+					 Bitmapset *modifiedCols);
+extern void decode_xlog_update(HeapTupleHeader htup, uint32 old_tup_len,
+			char *data, uint32* new_tup_len, char *waldata, uint32 wal_len);
 extern HeapTuple heap_form_tuple(TupleDesc tupleDescriptor,
 				Datum *values, bool *isnull);
 extern HeapTuple heap_modify_tuple(HeapTuple tuple,