wal_update_pglz_with_history-heikki.patch

diff --git a/src/backend/access/common/heaptuple.c b/src/backend/access/common/heaptuple.c
index e39b977..bbdee4f 100644
--- a/src/backend/access/common/heaptuple.c
+++ b/src/backend/access/common/heaptuple.c
@@ -60,7 +60,11 @@
 #include "access/sysattr.h"
 #include "access/tuptoaster.h"
 #include "executor/tuptable.h"
+#include "utils/datum.h"
+#include "utils/pg_lzcompress.h"
 
+/* guc variable for EWT compression ratio*/
+int			wal_update_compression_ratio = 25;
 
 /* Does att's datatype allow packing into the 1-byte-header varlena format? */
 #define ATT_IS_PACKABLE(att) \
@@ -617,6 +621,119 @@ heap_copytuple_with_tuple(HeapTuple src, HeapTuple dest)
 	memcpy((char *) dest->t_data, (char *) src->t_data, src->t_len);
 }
 
+
+/* ----------------
+ * heap_delta_encode
+ *
+ *		Calculate the delta between two tuples, using pglz. The result is
+ * stored in *encdata. *encdata must point to a PGLZ_header buffer, with at
+ * least PGLZ_MAX_OUTPUT(newtup->t_len) bytes.
+ * ----------------
+ */
+bool
+heap_delta_encode(TupleDesc tupleDesc, HeapTuple oldtup, HeapTuple newtup,
+				  char *encdata)
+{
+	HeapTupleHeader tup = oldtup->t_data;
+	Form_pg_attribute *att = tupleDesc->attrs;
+	bool		hasnulls = HeapTupleHasNulls(oldtup);
+	bits8	   *bp = oldtup->t_data->t_bits;		/* ptr to null bitmap in tuple */
+	bool		slow = false;	/* can we use/set attcacheoff? */
+	char	   *tp;				/* ptr to tuple data */
+	long		off;			/* offset in tuple data */
+	int			natts;
+	int32	   *offsets;
+	int			noffsets;
+	int			attnum;
+	PGLZ_Strategy strategy;
+
+	/*
+	 * Loop through all attributes, if the attribute is modified by the update
+	 * operation, store the [Offset,Length] reffering old tuple version till
+	 * the last unchanged column in the EWT as History Reference, else store
+	 * the [Length,Data] from new tuple version as New Data.
+	 */
+	natts = HeapTupleHeaderGetNatts(oldtup->t_data);
+
+	offsets = palloc(natts * sizeof(int32));
+
+	noffsets = 0;
+
+	/* copied from heap_deform_tuple */
+	tp = (char *) tup + tup->t_hoff;
+	off = 0;
+	for (attnum = 0; attnum < natts; attnum++)
+	{
+		Form_pg_attribute thisatt = att[attnum];
+
+		if (hasnulls && att_isnull(attnum, bp))
+		{
+			slow = true;		/* can't use attcacheoff anymore */
+			continue;
+		}
+
+		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;
+		}
+
+		off = att_addlength_pointer(off, thisatt->attlen, tp + off);
+
+		if (thisatt->attlen <= 0)
+			slow = true;		/* can't use attcacheoff anymore */
+
+		offsets[noffsets++] = off;
+	}
+
+	strategy = *PGLZ_strategy_always;
+	strategy.min_comp_rate = wal_update_compression_ratio;
+
+	return pglz_compress_with_history((char *) oldtup->t_data, oldtup->t_len,
+									  (char *) newtup->t_data, newtup->t_len,
+									  offsets, noffsets, (PGLZ_Header *) encdata,
+									  &strategy);
+}
+
+/* ----------------
+ * heap_delta_decode
+ *
+ *		Decode a tuple using delta-encoded WAL tuple and old tuple version.
+ * ----------------
+ */
+void
+heap_delta_decode(char *encdata, HeapTuple oldtup, HeapTuple newtup)
+{
+	return pglz_decompress_with_history((char *) encdata,
+										newtup->t_data,
+										&newtup->t_len,
+										(char *) oldtup->t_data,
+										oldtup->t_len);
+}
+
 /*
  * heap_form_tuple
  *		construct a tuple from the given values[] and isnull[] arrays,
diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index 57d47e8..789bbe2 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -70,6 +70,7 @@
 #include "utils/snapmgr.h"
 #include "utils/syscache.h"
 #include "utils/tqual.h"
+#include "utils/pg_lzcompress.h"
 
 
 /* GUC variable */
@@ -5765,6 +5766,16 @@ log_heap_update(Relation reln, Buffer oldbuf,
 	XLogRecPtr	recptr;
 	XLogRecData rdata[4];
 	Page		page = BufferGetPage(newbuf);
+	char	   *newtupdata;
+	int			newtuplen;
+	bool		compressed = false;
+
+	/* Structure which holds EWT */
+	struct
+	{
+		PGLZ_Header pglzheader;
+		char		buf[MaxHeapTupleSize];
+	}			buf;
 
 	/* Caller should not call me on a non-WAL-logged relation */
 	Assert(RelationNeedsWAL(reln));
@@ -5774,15 +5785,46 @@ log_heap_update(Relation reln, Buffer oldbuf,
 	else
 		info = XLOG_HEAP_UPDATE;
 
+ 	newtupdata = ((char *) newtup->t_data) + offsetof(HeapTupleHeaderData, t_bits);
+	newtuplen = newtup->t_len - offsetof(HeapTupleHeaderData, t_bits);
+
+	/*
+	 * EWT can be generated for all new tuple versions created by Update
+	 * operation. Currently we do it when both the old and new tuple versions
+	 * are on same page, because during recovery if the page containing old
+	 * tuple is corrupt, it should not cascade that corruption to other pages.
+	 * Under the general assumption that for long runs most updates tend to
+	 * create new tuple version on same page, there should not be significant
+	 * impact on WAL reduction or performance.
+	 *
+	 * We should not generate EWT when we need to backup the whole bolck in
+	 * WAL as in that case there is no saving by reduced WAL size.
+	 */
+	if ((oldbuf == newbuf) && !XLogCheckBufferNeedsBackup(newbuf))
+	{
+		/* Delta-encode the new tuple using the old tuple */
+		if (heap_delta_encode(reln->rd_att, oldtup, newtup, (char *) &buf.pglzheader))
+		{
+			compressed = true;
+			newtupdata = (char *) &buf.pglzheader;
+			newtuplen = VARSIZE(&buf.pglzheader);
+		}
+	}
+
+	xlrec.flags = 0;
 	xlrec.target.node = reln->rd_node;
 	xlrec.target.tid = oldtup->t_self;
 	xlrec.old_xmax = HeapTupleHeaderGetRawXmax(oldtup->t_data);
 	xlrec.old_infobits_set = compute_infobits(oldtup->t_data->t_infomask,
 											  oldtup->t_data->t_infomask2);
 	xlrec.new_xmax = HeapTupleHeaderGetRawXmax(newtup->t_data);
-	xlrec.all_visible_cleared = all_visible_cleared;
+	if (all_visible_cleared)
+		xlrec.flags |= XL_HEAP_UPDATE_ALL_VISIBLE_CLEARED;
 	xlrec.newtid = newtup->t_self;
-	xlrec.new_all_visible_cleared = new_all_visible_cleared;
+	if (new_all_visible_cleared)
+		xlrec.flags |= XL_HEAP_UPDATE_NEW_ALL_VISIBLE_CLEARED;
+	if (compressed)
+		xlrec.flags |= XL_HEAP_UPDATE_DELTA_ENCODED;
 
 	rdata[0].data = (char *) &xlrec;
 	rdata[0].len = SizeOfHeapUpdate;
@@ -5809,9 +5851,12 @@ log_heap_update(Relation reln, Buffer oldbuf,
 	rdata[2].buffer_std = true;
 	rdata[2].next = &(rdata[3]);
 
-	/* PG73FORMAT: write bitmap [+ padding] [+ oid] + data */
-	rdata[3].data = (char *) newtup->t_data + offsetof(HeapTupleHeaderData, t_bits);
-	rdata[3].len = newtup->t_len - offsetof(HeapTupleHeaderData, t_bits);
+	/*
+	 * PG73FORMAT: write bitmap [+ padding] [+ oid] + data follows .........
+	 * OR PG93FORMAT [If encoded]: LZ header + Encoded data follows
+	 */
+	rdata[3].data = newtupdata;
+	rdata[3].len = newtuplen;
 	rdata[3].buffer = newbuf;
 	rdata[3].buffer_std = true;
 	rdata[3].next = NULL;
@@ -6614,7 +6659,10 @@ heap_xlog_update(XLogRecPtr lsn, XLogRecord *record, bool hot_update)
 	Page		page;
 	OffsetNumber offnum;
 	ItemId		lp = NULL;
+	HeapTupleData newtup;
+	HeapTupleData oldtup;
 	HeapTupleHeader htup;
+	HeapTupleHeader oldtupdata = NULL;
 	struct
 	{
 		HeapTupleHeaderData hdr;
@@ -6629,7 +6677,7 @@ heap_xlog_update(XLogRecPtr lsn, XLogRecord *record, bool hot_update)
 	 * 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->flags & XL_HEAP_UPDATE_ALL_VISIBLE_CLEARED)
 	{
 		Relation	reln = CreateFakeRelcacheEntry(xlrec->target.node);
 		BlockNumber block = ItemPointerGetBlockNumber(&xlrec->target.tid);
@@ -6689,7 +6737,7 @@ heap_xlog_update(XLogRecPtr lsn, XLogRecord *record, bool hot_update)
 	if (PageGetMaxOffsetNumber(page) < offnum || !ItemIdIsNormal(lp))
 		elog(PANIC, "heap_update_redo: invalid lp");
 
-	htup = (HeapTupleHeader) PageGetItem(page, lp);
+	oldtupdata = htup = (HeapTupleHeader) PageGetItem(page, lp);
 
 	htup->t_infomask &= ~(HEAP_XMAX_BITS | HEAP_MOVED);
 	htup->t_infomask2 &= ~HEAP_KEYS_UPDATED;
@@ -6707,7 +6755,7 @@ 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->flags & XL_HEAP_UPDATE_ALL_VISIBLE_CLEARED)
 		PageClearAllVisible(page);
 
 	/*
@@ -6732,7 +6780,7 @@ 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->flags & XL_HEAP_UPDATE_NEW_ALL_VISIBLE_CLEARED)
 	{
 		Relation	reln = CreateFakeRelcacheEntry(xlrec->target.node);
 		BlockNumber block = ItemPointerGetBlockNumber(&xlrec->newtid);
@@ -6795,10 +6843,32 @@ newsame:;
 		   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);
+
+	/*
+	 * If the record is EWT then decode it.
+	 */
+	if (xlrec->flags & XL_HEAP_UPDATE_DELTA_ENCODED)
+	{
+		/*
+		 * PG93FORMAT: Header + Control byte + history reference (2 - 3)bytes
+		 * + New data (1 byte length + variable data)+ ...
+		 */
+		PGLZ_Header *encoded_data = (PGLZ_Header *) (((char *) xlrec) + hsize);
+
+		oldtup.t_data = oldtupdata;
+		newtup.t_data = htup;
+
+		heap_delta_decode((char *) encoded_data, &oldtup, &newtup);
+		newlen = newtup.t_len;
+	}
+	else
+	{
+		/* PG73FORMAT: get bitmap [+ padding] [+ oid] + data */
+		memcpy((char *) htup + offsetof(HeapTupleHeaderData, t_bits),
+			   (char *) xlrec + hsize,
+			   newlen);
+	}
+
 	newlen += offsetof(HeapTupleHeaderData, t_bits);
 	htup->t_infomask2 = xlhdr.t_infomask2;
 	htup->t_infomask = xlhdr.t_infomask;
@@ -6814,7 +6884,7 @@ newsame:;
 	if (offnum == InvalidOffsetNumber)
 		elog(PANIC, "heap_update_redo: failed to add tuple");
 
-	if (xlrec->new_all_visible_cleared)
+	if (xlrec->flags & XL_HEAP_UPDATE_NEW_ALL_VISIBLE_CLEARED)
 		PageClearAllVisible(page);
 
 	freespace = PageGetHeapFreeSpace(page);		/* needed to update FSM below */
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index cf2f6e7..9cd6271 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -1204,6 +1204,28 @@ begin:;
 }
 
 /*
+ * Determine whether the buffer referenced has to be backed up. Since we don't
+ * yet have the insert lock, fullPageWrites and forcePageWrites could change
+ * later, but will not cause any problem because this function is used only to
+ * identify whether EWT is required for WAL update.
+ */
+bool
+XLogCheckBufferNeedsBackup(Buffer buffer)
+{
+	bool		doPageWrites;
+	Page		page;
+
+	page = BufferGetPage(buffer);
+
+	doPageWrites = XLogCtl->Insert.fullPageWrites || XLogCtl->Insert.forcePageWrites;
+
+	if (doPageWrites && PageGetLSN(page) <= RedoRecPtr)
+		return true;			/* buffer requires backup */
+
+	return false;				/* buffer does not need to be backed up */
+}
+
+/*
  * Determine whether the buffer referenced by an XLogRecData item has to
  * be backed up, and if so fill a BkpBlock struct for it.  In any case
  * save the buffer's LSN at *lsn.
diff --git a/src/backend/utils/adt/pg_lzcompress.c b/src/backend/utils/adt/pg_lzcompress.c
index 66c64c1..c6ba6af 100644
--- a/src/backend/utils/adt/pg_lzcompress.c
+++ b/src/backend/utils/adt/pg_lzcompress.c
@@ -373,6 +373,7 @@ do { \
  */
 static inline int
 pglz_find_match(PGLZ_HistEntry **hstart, const char *input, const char *end,
+				const char *historyend,
 				int *lenp, int *offp, int good_match, int good_drop)
 {
 	PGLZ_HistEntry *hent;
@@ -393,7 +394,7 @@ pglz_find_match(PGLZ_HistEntry **hstart, const char *input, const char *end,
 		/*
 		 * Stop if the offset does not fit into our tag anymore.
 		 */
-		thisoff = ip - hp;
+		thisoff = (historyend ? historyend : ip) - hp;
 		if (thisoff >= 0x0fff)
 			break;
 
@@ -408,12 +409,12 @@ pglz_find_match(PGLZ_HistEntry **hstart, const char *input, const char *end,
 		thislen = 0;
 		if (len >= 16)
 		{
-			if (memcmp(ip, hp, len) == 0)
+			if ((historyend == NULL || historyend - hp > len) && memcmp(ip, hp, len) == 0)
 			{
 				thislen = len;
 				ip += len;
 				hp += len;
-				while (ip < end && *ip == *hp && thislen < PGLZ_MAX_MATCH)
+				while (ip < end && *ip == *hp && thislen < PGLZ_MAX_MATCH && (historyend == NULL || hp < historyend))
 				{
 					thislen++;
 					ip++;
@@ -423,7 +424,7 @@ pglz_find_match(PGLZ_HistEntry **hstart, const char *input, const char *end,
 		}
 		else
 		{
-			while (ip < end && *ip == *hp && thislen < PGLZ_MAX_MATCH)
+			while (ip < end && *ip == *hp && thislen < PGLZ_MAX_MATCH && (historyend == NULL || hp < historyend))
 			{
 				thislen++;
 				ip++;
@@ -588,7 +589,7 @@ pglz_compress(const char *source, int32 slen, PGLZ_Header *dest,
 		/*
 		 * Try to find a match in the history
 		 */
-		if (pglz_find_match(hist_start, dp, dend, &match_len,
+		if (pglz_find_match(hist_start, dp, dend, NULL, &match_len,
 							&match_off, good_match, good_drop))
 		{
 			/*
@@ -637,6 +638,176 @@ pglz_compress(const char *source, int32 slen, PGLZ_Header *dest,
 	return true;
 }
 
+/*
+ * Like pglz_compress, but performs delta encoding rather than compression.
+ * The back references are offsets from the end of history data, rather
+ * than current output position. 'hoffsets' is an array of offsets in the
+ * history to consider. We could scan the whole history string for possible
+ * matches, but if the caller has some information on which offsets are
+ * likely to be interesting (attribute boundaries, when encoding tuples, for
+ * example), this is a lot faster.
+ */
+bool
+pglz_compress_with_history(const char *source, int32 slen, const char *history,
+						   int32 hlen,
+						   int32 *hoffsets,
+						   int32 nhoffsets,
+						   PGLZ_Header *dest, const PGLZ_Strategy *strategy)
+{
+	unsigned char *bp = ((unsigned char *) dest) + sizeof(PGLZ_Header);
+	unsigned char *bstart = bp;
+	int			hist_next = 0;
+	bool		hist_recycle = false;
+	const char *dp = source;
+	const char *dend = source + slen;
+	unsigned char ctrl_dummy = 0;
+	unsigned char *ctrlp = &ctrl_dummy;
+	unsigned char ctrlb = 0;
+	unsigned char ctrl = 0;
+	bool		found_match = false;
+	int32		match_len;
+	int32		match_off;
+	int32		good_match;
+	int32		good_drop;
+	int32		result_size;
+	int32		result_max;
+	int			i;
+	int32		need_rate;
+	const char *historyend = history + hlen;
+
+	/*
+	 * Our fallback strategy is the default.
+	 */
+	if (strategy == NULL)
+		strategy = PGLZ_strategy_default;
+
+	/*
+	 * If the strategy forbids compression (at all or if source chunk size out
+	 * of range), fail.
+	 */
+	if (strategy->match_size_good <= 0 ||
+		slen < strategy->min_input_size ||
+		slen > strategy->max_input_size)
+		return false;
+
+	/*
+	 * Save the original source size in the header.
+	 */
+	dest->rawsize = slen;
+
+	/*
+	 * Limit the match parameters to the supported range.
+	 */
+	good_match = strategy->match_size_good;
+	if (good_match > PGLZ_MAX_MATCH)
+		good_match = PGLZ_MAX_MATCH;
+	else if (good_match < 17)
+		good_match = 17;
+
+	good_drop = strategy->match_size_drop;
+	if (good_drop < 0)
+		good_drop = 0;
+	else if (good_drop > 100)
+		good_drop = 100;
+
+	need_rate = strategy->min_comp_rate;
+	if (need_rate < 0)
+		need_rate = 0;
+	else if (need_rate > 99)
+		need_rate = 99;
+
+	/*
+	 * Compute the maximum result size allowed by the strategy, namely the
+	 * input size minus the minimum wanted compression rate.  This had better
+	 * be <= slen, else we might overrun the provided output buffer.
+	 */
+	if (slen > (INT_MAX / 100))
+	{
+		/* Approximate to avoid overflow */
+		result_max = (slen / 100) * (100 - need_rate);
+	}
+	else
+		result_max = (slen * (100 - need_rate)) / 100;
+
+	/*
+	 * Initialize the history lists to empty.  We do not need to zero the
+	 * hist_entries[] array; its entries are initialized as they are used.
+	 */
+	memset(hist_start, 0, sizeof(hist_start));
+
+	/* Populate the history hash from the history string */
+	for (i = 0; i < nhoffsets; i++)
+	{
+		const char *hp = history + hoffsets[i];
+
+		/* Add this offset to history */
+		pglz_hist_add(hist_start, hist_entries,
+					  hist_next, hist_recycle,
+					  hp, historyend);
+	}
+
+	/*
+	 * Compress the source directly into the output buffer.
+	 */
+	dp = source;
+	while (dp < dend)
+	{
+		/*
+		 * If we already exceeded the maximum result size, fail.
+		 *
+		 * We check once per loop; since the loop body could emit as many as 4
+		 * bytes (a control byte and 3-byte tag), PGLZ_MAX_OUTPUT() had better
+		 * allow 4 slop bytes.
+		 */
+		if (bp - bstart >= result_max)
+			return false;
+
+		/*
+		 * Try to find a match in the history
+		 */
+		if (pglz_find_match(hist_start, dp, dend, historyend, &match_len,
+							&match_off, good_match, good_drop))
+		{
+			/*
+			 * Create the tag and add history entries for all matched
+			 * characters.
+			 */
+			pglz_out_tag(ctrlp, ctrlb, ctrl, bp, match_len, match_off);
+			dp += match_len;
+			found_match = true;
+		}
+		else
+		{
+			/*
+			 * No match found. Copy one literal byte.
+			 */
+			pglz_out_literal(ctrlp, ctrlb, ctrl, bp, *dp);
+			dp++;				/* Do not do this ++ in the line above! */
+			/* The macro would do it four times - Jan.	*/
+		}
+	}
+
+	if (!found_match)
+		return false;
+
+	/*
+	 * Write out the last control byte and check that we haven't overrun the
+	 * output size allowed by the strategy.
+	 */
+	*ctrlp = ctrlb;
+	result_size = bp - bstart;
+
+#ifdef DELTA_DEBUG
+	elog(LOG, "old %d new %d compressed %d", hlen, slen, result_size);
+#endif
+
+	/*
+	 * Success - need only fill in the actual length of the compressed datum.
+	 */
+	SET_VARSIZE_COMPRESSED(dest, result_size + sizeof(PGLZ_Header));
+
+	return true;
+}
 
 /* ----------
  * pglz_decompress -
@@ -647,15 +818,39 @@ pglz_compress(const char *source, int32 slen, PGLZ_Header *dest,
 void
 pglz_decompress(const PGLZ_Header *source, char *dest)
 {
+	pglz_decompress_with_history((char *) source, dest, NULL, NULL, 0);
+}
+
+/* ----------
+ * pglz_decompress_with_history -
+ *
+ *		Decompresses source into dest.
+ *		To decompress, it uses history if provided.
+ * ----------
+ */
+void
+pglz_decompress_with_history(const char *source, char *dest, uint32 *destlen,
+							 const char *history, int hlen)
+{
+	PGLZ_Header src;
 	const unsigned char *sp;
 	const unsigned char *srcend;
 	unsigned char *dp;
 	unsigned char *destend;
+	const char *historyend = history + hlen;
+
+	/* To avoid the unaligned access of PGLZ_Header */
+	memcpy((char *) &src, source, sizeof(PGLZ_Header));
 
 	sp = ((const unsigned char *) source) + sizeof(PGLZ_Header);
-	srcend = ((const unsigned char *) source) + VARSIZE(source);
+	srcend = ((const unsigned char *) source) + VARSIZE(&src);
 	dp = (unsigned char *) dest;
-	destend = dp + source->rawsize;
+	destend = dp + src.rawsize;
+
+	if (destlen)
+	{
+		*destlen = src.rawsize;
+	}
 
 	while (sp < srcend && dp < destend)
 	{
@@ -699,26 +894,38 @@ pglz_decompress(const PGLZ_Header *source, char *dest)
 					break;
 				}
 
-				/*
-				 * Now we copy the bytes specified by the tag from OUTPUT to
-				 * OUTPUT. It is dangerous and platform dependent to use
-				 * memcpy() here, because the copied areas could overlap
-				 * extremely!
-				 */
-				while (len--)
+				if (history)
+				{
+					/*
+					 * Now we copy the bytes specified by the tag from history
+					 * to OUTPUT.
+					 */
+					memcpy(dp, historyend - off, len);
+					dp += len;
+				}
+				else
 				{
-					*dp = dp[-off];
-					dp++;
+					/*
+					 * Now we copy the bytes specified by the tag from OUTPUT
+					 * to OUTPUT. It is dangerous and platform dependent to
+					 * use memcpy() here, because the copied areas could
+					 * overlap extremely!
+					 */
+					while (len--)
+					{
+						*dp = dp[-off];
+						dp++;
+					}
 				}
 			}
 			else
 			{
 				/*
-				 * An unset control bit means LITERAL BYTE. So we just copy
-				 * one from INPUT to OUTPUT.
+				 * An unset control bit means LITERAL BYTE. So we just
+				 * copy one from INPUT to OUTPUT.
 				 */
-				if (dp >= destend)		/* check for buffer overrun */
-					break;		/* do not clobber memory */
+				if (dp >= destend)	/* check for buffer overrun */
+					break;	/* do not clobber memory */
 
 				*dp++ = *sp++;
 			}
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 6128694..9a37b2d 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -123,6 +123,7 @@ extern int	CommitSiblings;
 extern char *default_tablespace;
 extern char *temp_tablespaces;
 extern bool synchronize_seqscans;
+extern int	wal_update_compression_ratio;
 extern int	ssl_renegotiation_limit;
 extern char *SSLCipherSuites;
 
@@ -2382,6 +2383,17 @@ static struct config_int ConfigureNamesInt[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		/* Not for general use */
+		{"wal_update_compression_ratio", PGC_USERSET, DEVELOPER_OPTIONS,
+			gettext_noop("Sets the compression ratio of delta record for wal update"),
+			NULL,
+		},
+		&wal_update_compression_ratio,
+		25, 1, 99,
+		NULL, NULL, NULL
+	},
+
 	/* End-of-list marker */
 	{
 		{NULL, 0, 0, NULL, NULL}, NULL, 0, 0, 0, NULL, NULL, NULL
diff --git a/src/include/access/heapam_xlog.h b/src/include/access/heapam_xlog.h
index 270924a..1825292 100644
--- a/src/include/access/heapam_xlog.h
+++ b/src/include/access/heapam_xlog.h
@@ -147,13 +147,22 @@ typedef struct xl_heap_update
 	TransactionId old_xmax;		/* xmax of the old tuple */
 	TransactionId new_xmax;		/* xmax of the new tuple */
 	ItemPointerData newtid;		/* new inserted tuple id */
-	uint8		old_infobits_set;	/* infomask bits to set on old tuple */
-	bool		all_visible_cleared;	/* PD_ALL_VISIBLE was cleared */
-	bool		new_all_visible_cleared;		/* same for the page of newtid */
+	uint8		old_infobits_set;		/* infomask bits to set on old tuple */
+	int			flags;			/* flag bits, see below */
 	/* 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 XL_HEAP_UPDATE_ALL_VISIBLE_CLEARED		0x01	/* Indicates as old
+														 * page's all visible
+														 * bit is cleared */
+#define XL_HEAP_UPDATE_NEW_ALL_VISIBLE_CLEARED	0x02	/* Indicates as new
+														 * page's all visible
+														 * bit is cleared */
+#define XL_HEAP_UPDATE_DELTA_ENCODED			0x04	/* Indicates as the
+														 * update operation is
+														 * delta encoded */
+
+#define SizeOfHeapUpdate	(offsetof(xl_heap_update, flags) + sizeof(int))
 
 /*
  * This is what we need to know about vacuum page cleanup/redirect
diff --git a/src/include/access/htup_details.h b/src/include/access/htup_details.h
index cd01ecd..042c8b9 100644
--- a/src/include/access/htup_details.h
+++ b/src/include/access/htup_details.h
@@ -687,6 +687,11 @@ extern HeapTuple heap_modify_tuple(HeapTuple tuple,
 extern void heap_deform_tuple(HeapTuple tuple, TupleDesc tupleDesc,
 				  Datum *values, bool *isnull);
 
+extern bool heap_delta_encode(TupleDesc tupleDesc, HeapTuple oldtup,
+				HeapTuple newtup, char *encdata);
+extern void heap_delta_decode (char *encdata, HeapTuple oldtup,
+				HeapTuple newtup);
+
 /* these three are deprecated versions of the three above: */
 extern HeapTuple heap_formtuple(TupleDesc tupleDescriptor,
 			   Datum *values, char *nulls);
diff --git a/src/include/access/xlog.h b/src/include/access/xlog.h
index 72e3242..15f5d5d 100644
--- a/src/include/access/xlog.h
+++ b/src/include/access/xlog.h
@@ -261,6 +261,7 @@ typedef struct CheckpointStatsData
 extern CheckpointStatsData CheckpointStats;
 
 extern XLogRecPtr XLogInsert(RmgrId rmid, uint8 info, XLogRecData *rdata);
+extern bool XLogCheckBufferNeedsBackup(Buffer buffer);
 extern void XLogFlush(XLogRecPtr RecPtr);
 extern bool XLogBackgroundFlush(void);
 extern bool XLogNeedsFlush(XLogRecPtr RecPtr);
diff --git a/src/include/utils/pg_lzcompress.h b/src/include/utils/pg_lzcompress.h
index 4af24a3..7a32803 100644
--- a/src/include/utils/pg_lzcompress.h
+++ b/src/include/utils/pg_lzcompress.h
@@ -107,6 +107,8 @@ extern const PGLZ_Strategy *const PGLZ_strategy_always;
  */
 extern bool pglz_compress(const char *source, int32 slen, PGLZ_Header *dest,
 			  const PGLZ_Strategy *strategy);
+extern bool pglz_compress_with_history(const char *source, int32 slen, const char *history, int32 hlen, int32 *hoffsets, int32 noffsets, PGLZ_Header *dest, const PGLZ_Strategy *strategy);
 extern void pglz_decompress(const PGLZ_Header *source, char *dest);
+extern void pglz_decompress_with_history(const char *source, char *dest, uint32 *destlen, const char *history, int hlen);
 
 #endif   /* _PG_LZCOMPRESS_H_ */
diff --git a/src/test/regress/expected/update.out b/src/test/regress/expected/update.out
index 71b856f..af46df2 100644
--- a/src/test/regress/expected/update.out
+++ b/src/test/regress/expected/update.out
@@ -97,3 +97,73 @@ SELECT a, b, char_length(c) FROM update_test;
 (2 rows)
 
 DROP TABLE update_test;
+--
+-- Test to update continuos and non continuos columns
+--
+DROP TABLE IF EXISTS update_test;
+NOTICE:  table "update_test" does not exist, skipping
+CREATE TABLE update_test (
+		bser bigserial,
+		bln boolean,
+		ename VARCHAR(25),
+		perf_f float(8),
+		grade CHAR,
+		dept CHAR(5) NOT NULL,
+		dob DATE,
+		idnum INT,
+		addr VARCHAR(30) NOT NULL,
+		destn CHAR(6),
+		Gend CHAR,
+		samba BIGINT,
+		hgt float,
+		ctime TIME
+);
+INSERT INTO update_test VALUES (
+		nextval('update_test_bser_seq'::regclass),
+		TRUE,
+		'Test',
+		7.169,
+		'B',
+		'CSD',
+		'2000-01-01',
+		520,
+		'road2,
+		streeeeet2,
+		city2',
+		'dcy2',
+		'M',
+		12000,
+		50.4,
+		'00:00:00.0'
+);
+SELECT * from update_test;
+ bser | bln | ename | perf_f | grade | dept  |    dob     | idnum |            addr             | destn  | gend | samba | hgt  |  ctime   
+------+-----+-------+--------+-------+-------+------------+-------+-----------------------------+--------+------+-------+------+----------
+    1 | t   | Test  |  7.169 | B     | CSD   | 01-01-2000 |   520 | road2,                     +| dcy2   | M    | 12000 | 50.4 | 00:00:00
+      |     |       |        |       |       |            |       |                 streeeeet2,+|        |      |       |      | 
+      |     |       |        |       |       |            |       |                 city2       |        |      |       |      | 
+(1 row)
+
+-- update first column
+UPDATE update_test SET bser = bser - 1 + 1;
+-- update middle column
+UPDATE update_test SET perf_f = 8.9;
+-- update last column
+UPDATE update_test SET ctime = '00:00:00.1';
+-- update 3 continuos columns
+UPDATE update_test SET destn = 'dcy2', samba = 0 WHERE Gend = 'M' and dept = 'CSD';
+-- update two non continuos columns
+UPDATE update_test SET destn = 'moved', samba = 0;
+UPDATE update_test SET bln = FALSE, hgt = 10.1;
+-- update causing some column alignment difference
+UPDATE update_test SET ename = 'Tes';
+UPDATE update_test SET dept = 'Test';
+SELECT * from update_test;
+ bser | bln | ename | perf_f | grade | dept  |    dob     | idnum |            addr             | destn  | gend | samba | hgt  |   ctime    
+------+-----+-------+--------+-------+-------+------------+-------+-----------------------------+--------+------+-------+------+------------
+    1 | f   | Tes   |    8.9 | B     | Test  | 01-01-2000 |   520 | road2,                     +| moved  | M    |     0 | 10.1 | 00:00:00.1
+      |     |       |        |       |       |            |       |                 streeeeet2,+|        |      |       |      | 
+      |     |       |        |       |       |            |       |                 city2       |        |      |       |      | 
+(1 row)
+
+DROP TABLE update_test;
diff --git a/src/test/regress/sql/update.sql b/src/test/regress/sql/update.sql
index a8a028f..1806992 100644
--- a/src/test/regress/sql/update.sql
+++ b/src/test/regress/sql/update.sql
@@ -59,3 +59,70 @@ UPDATE update_test SET c = repeat('x', 10000) WHERE c = 'car';
 SELECT a, b, char_length(c) FROM update_test;
 
 DROP TABLE update_test;
+
+
+--
+-- Test to update continuos and non continuos columns
+--
+
+DROP TABLE IF EXISTS update_test;
+CREATE TABLE update_test (
+		bser bigserial,
+		bln boolean,
+		ename VARCHAR(25),
+		perf_f float(8),
+		grade CHAR,
+		dept CHAR(5) NOT NULL,
+		dob DATE,
+		idnum INT,
+		addr VARCHAR(30) NOT NULL,
+		destn CHAR(6),
+		Gend CHAR,
+		samba BIGINT,
+		hgt float,
+		ctime TIME
+);
+
+INSERT INTO update_test VALUES (
+		nextval('update_test_bser_seq'::regclass),
+		TRUE,
+		'Test',
+		7.169,
+		'B',
+		'CSD',
+		'2000-01-01',
+		520,
+		'road2,
+		streeeeet2,
+		city2',
+		'dcy2',
+		'M',
+		12000,
+		50.4,
+		'00:00:00.0'
+);
+
+SELECT * from update_test;
+
+-- update first column
+UPDATE update_test SET bser = bser - 1 + 1;
+
+-- update middle column
+UPDATE update_test SET perf_f = 8.9;
+
+-- update last column
+UPDATE update_test SET ctime = '00:00:00.1';
+
+-- update 3 continuos columns
+UPDATE update_test SET destn = 'dcy2', samba = 0 WHERE Gend = 'M' and dept = 'CSD';
+
+-- update two non continuos columns
+UPDATE update_test SET destn = 'moved', samba = 0;
+UPDATE update_test SET bln = FALSE, hgt = 10.1;
+
+-- update causing some column alignment difference
+UPDATE update_test SET ename = 'Tes';
+UPDATE update_test SET dept = 'Test';
+
+SELECT * from update_test;
+DROP TABLE update_test;