diff --git a/doc/src/sgml/ref/create_table.sgml b/doc/src/sgml/ref/create_table.sgml
index e0b8a4e..c4ac2bd 100644
--- a/doc/src/sgml/ref/create_table.sgml
+++ b/doc/src/sgml/ref/create_table.sgml
@@ -1014,6 +1014,22 @@ CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXI
+
+ wal_compress_update (boolean)
+
+
+ Enables or disables the WAL tuple compression for UPDATE
+ on this table. Default value of this option is false to maintain
+ backward compatability for the command. If true, all the update
+ operations on this table which will place the new tuple on same page
+ as it's original tuple will compress the WAL for new tuple and
+ subsequently reduce the WAL volume. It is recommended to enable
+ this option for tables where UPDATE changes less than
+ 50 percent of tuple data.
+
+
+
+
diff --git a/src/backend/access/common/heaptuple.c b/src/backend/access/common/heaptuple.c
index aea9d40..3bf5728 100644
--- a/src/backend/access/common/heaptuple.c
+++ b/src/backend/access/common/heaptuple.c
@@ -60,6 +60,7 @@
#include "access/sysattr.h"
#include "access/tuptoaster.h"
#include "executor/tuptable.h"
+#include "utils/pg_rbcompress.h"
/* Does att's datatype allow packing into the 1-byte-header varlena format? */
@@ -617,6 +618,44 @@ 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 and generate
+ * encoded wal tuple (EWT), using pgrb. The result is stored
+ * in *encdata.
+ * ----------------
+ */
+bool
+heap_delta_encode(TupleDesc tupleDesc, HeapTuple oldtup, HeapTuple newtup,
+ char *encdata, uint32 *enclen)
+{
+ return pgrb_delta_encode(
+ (char *) newtup->t_data + offsetof(HeapTupleHeaderData, t_bits),
+ newtup->t_len - offsetof(HeapTupleHeaderData, t_bits),
+ (char *) oldtup->t_data + offsetof(HeapTupleHeaderData, t_bits),
+ oldtup->t_len - offsetof(HeapTupleHeaderData, t_bits),
+ encdata, enclen, NULL
+ );
+}
+
+/* ----------------
+ * heap_delta_decode
+ *
+ * Decode a tuple using delta-encoded WAL tuple and old tuple version.
+ * ----------------
+ */
+void
+heap_delta_decode(char *encdata, uint32 enclen, HeapTuple oldtup, HeapTuple newtup)
+{
+ pgrb_delta_decode(encdata, enclen,
+ (char *) newtup->t_data + offsetof(HeapTupleHeaderData, t_bits),
+ MaxHeapTupleSize - offsetof(HeapTupleHeaderData, t_bits),
+ &newtup->t_len,
+ (char *) oldtup->t_data + offsetof(HeapTupleHeaderData, t_bits),
+ oldtup->t_len - offsetof(HeapTupleHeaderData, t_bits));
+}
+
/*
* heap_form_tuple
* construct a tuple from the given values[] and isnull[] arrays,
diff --git a/src/backend/access/common/reloptions.c b/src/backend/access/common/reloptions.c
index fa08c45..2123a61 100644
--- a/src/backend/access/common/reloptions.c
+++ b/src/backend/access/common/reloptions.c
@@ -85,6 +85,14 @@ static relopt_bool boolRelOpts[] =
},
false
},
+ {
+ {
+ "wal_compress_update",
+ "Compress the wal tuple for update operation on this relation",
+ RELOPT_KIND_HEAP
+ },
+ true
+ },
/* list terminator */
{{NULL}}
};
@@ -1175,7 +1183,9 @@ default_reloptions(Datum reloptions, bool validate, relopt_kind kind)
{"check_option", RELOPT_TYPE_STRING,
offsetof(StdRdOptions, check_option_offset)},
{"user_catalog_table", RELOPT_TYPE_BOOL,
- offsetof(StdRdOptions, user_catalog_table)}
+ offsetof(StdRdOptions, user_catalog_table)},
+ {"wal_compress_update", RELOPT_TYPE_BOOL,
+ offsetof(StdRdOptions, wal_compress_update)}
};
options = parseRelOptions(reloptions, validate, kind, &numoptions);
diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index a771ccb..2724188 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_rbcompress.h"
/* GUC variable */
@@ -6597,6 +6598,12 @@ log_heap_update(Relation reln, Buffer oldbuf,
XLogRecPtr recptr;
XLogRecData rdata[7];
Page page = BufferGetPage(newbuf);
+ char *newtupdata;
+ int newtuplen;
+ bool compressed = false;
+
+ /* Structure which holds EWT */
+ char buf[MaxHeapTupleSize];
bool need_tuple_data = RelationIsLogicallyLogged(reln);
/* Caller should not call me on a non-WAL-logged relation */
@@ -6607,6 +6614,37 @@ 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 block in
+ * WAL as in that case there is no saving by reduced WAL size.
+ */
+
+ if (RelationIsEnabledForWalCompression(reln) &&
+ (oldbuf == newbuf) &&
+ !XLogCheckBufferNeedsBackup(newbuf))
+ {
+ uint32 enclen;
+
+ /* Delta-encode the new tuple using the old tuple */
+ if (heap_delta_encode(reln->rd_att, oldtup, newtup, buf, &enclen))
+ {
+ compressed = true;
+ newtupdata = buf;
+ newtuplen = enclen;
+ }
+ }
+
xlrec.target.node = reln->rd_node;
xlrec.target.tid = oldtup->t_self;
xlrec.old_xmax = HeapTupleHeaderGetRawXmax(oldtup->t_data);
@@ -6619,6 +6657,8 @@ log_heap_update(Relation reln, Buffer oldbuf,
xlrec.newtid = newtup->t_self;
if (new_all_visible_cleared)
xlrec.flags |= XLOG_HEAP_NEW_ALL_VISIBLE_CLEARED;
+ if (compressed)
+ xlrec.flags |= XLOG_HEAP_DELTA_ENCODED;
rdata[0].data = (char *) &xlrec;
rdata[0].len = SizeOfHeapUpdate;
@@ -6634,7 +6674,7 @@ log_heap_update(Relation reln, Buffer oldbuf,
xlhdr.header.t_infomask2 = newtup->t_data->t_infomask2;
xlhdr.header.t_infomask = newtup->t_data->t_infomask;
xlhdr.header.t_hoff = newtup->t_data->t_hoff;
- xlhdr.t_len = newtup->t_len - offsetof(HeapTupleHeaderData, t_bits);
+ xlhdr.t_len = newtuplen;
/*
* As with insert records, we need not store the rdata[2] segment
@@ -6647,10 +6687,13 @@ 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 OR
+ * PG94FORMAT [If encoded]: Control byte + history reference (2 - 3)bytes
+ * + literal byte + ...
+ */
+ rdata[3].data = newtupdata;
+ rdata[3].len = newtuplen;
rdata[3].buffer = need_tuple_data ? InvalidBuffer : newbuf;
rdata[3].buffer_std = true;
rdata[3].next = NULL;
@@ -7739,7 +7782,10 @@ 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;
@@ -7814,7 +7860,7 @@ 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;
@@ -7923,10 +7969,31 @@ newsame:;
Assert(newlen <= MaxHeapTupleSize);
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 & XLOG_HEAP_DELTA_ENCODED)
+ {
+ /*
+ * PG94FORMAT: Control byte + history reference (2 - 3)bytes
+ * + literal byte + ...
+ */
+ oldtup.t_data = oldtupdata;
+ oldtup.t_len = ItemIdGetLength(lp);
+ newtup.t_data = htup;
+
+ heap_delta_decode((char *) xlrec + hsize, newlen, &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.header.t_infomask2;
htup->t_infomask = xlhdr.header.t_infomask;
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 7f63185..5d874eb 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -2332,6 +2332,28 @@ XLogRecPtrToBytePos(XLogRecPtr ptr)
}
/*
+ * 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 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/Makefile b/src/backend/utils/adt/Makefile
index 1ae9fa0..04dc17c 100644
--- a/src/backend/utils/adt/Makefile
+++ b/src/backend/utils/adt/Makefile
@@ -26,7 +26,7 @@ OBJS = acl.o arrayfuncs.o array_selfuncs.o array_typanalyze.o \
rowtypes.o regexp.o regproc.o ruleutils.o selfuncs.o \
tid.o timestamp.o varbit.o varchar.o varlena.o version.o xid.o \
network.o mac.o inet_cidr_ntop.o inet_net_pton.o \
- ri_triggers.o pg_lzcompress.o pg_locale.o formatting.o \
+ ri_triggers.o pg_lzcompress.o pg_rbcompress.o pg_locale.o formatting.o \
ascii.o quote.o pgstatfuncs.o encode.o dbsize.o genfile.o trigfuncs.o \
tsginidx.o tsgistidx.o tsquery.o tsquery_cleanup.o tsquery_gist.o \
tsquery_op.o tsquery_rewrite.o tsquery_util.o tsrank.o \
diff --git a/src/backend/utils/adt/pg_rbcompress.c b/src/backend/utils/adt/pg_rbcompress.c
new file mode 100644
index 0000000..2b6254b
--- /dev/null
+++ b/src/backend/utils/adt/pg_rbcompress.c
@@ -0,0 +1,667 @@
+/* ----------
+ * pg_rbcompress.c -
+ *
+ * This is a delta encoding scheme specific to PostgreSQL and designed
+ * to compress similar tuples. It can be used as it is or extended for
+ * other purpose in PostgrSQL if required.
+ *
+ * It uses a simple history table to represent history data (old tuple)
+ * and then compress source string (new tuple) using the history data.
+ * It uses LZ compression format to store encoded string except for
+ * using PGLZ_Header.
+ *
+ *
+ * The decompression algorithm works exactly same as LZ, except
+ * for processing of its PGLZ_Header.
+ *
+ * Copyright (c) 1999-2014, PostgreSQL Global Development Group
+ *
+ * src/backend/utils/adt/pg_rbcompress.c
+ * ----------
+ */
+#include "postgres.h"
+
+#include
+
+#include "utils/pg_rbcompress.h"
+
+
+/* ----------
+ * Local definitions
+ * ----------
+ */
+#define PGRB_MAX_HISTORY_LISTS 8192 /* must be power of 2 */
+#define PGRB_HISTORY_SIZE 4096
+#define PGRB_MAX_MATCH 273
+#define PGRB_CHUNK_SIZE 4
+
+
+
+/* ----------
+ * The provided standard strategies
+ * ----------
+ */
+static const PGRB_Strategy strategy_default_data = {
+ 32, /* Data chunks less than 32 bytes are not
+ * compressed */
+ INT_MAX, /* No upper limit on what we'll try to
+ * compress */
+ 25, /* Require 25% compression rate, or not worth
+ * it */
+ 1024, /* Give up if no compression in the first 1KB */
+ 128, /* Stop history lookup if a match of 128 bytes
+ * is found */
+ 50 /* Lower good match size by 50% at every loop
+ * iteration */
+};
+const PGRB_Strategy *const PGRB_strategy_default = &strategy_default_data;
+
+
+/* ----------
+ * Statically allocated work arrays for history
+ * ----------
+ */
+static int16 hist_start[PGRB_MAX_HISTORY_LISTS];
+static uint16 rb_hist_entries[PGRB_HISTORY_SIZE + 1];
+
+/*
+ * Element 0 in hist_entries is unused, and means 'invalid'. Likewise,
+ * INVALID_ENTRY_PTR in next/prev pointers mean 'invalid'.
+ */
+#define INVALID_ENTRY 0
+
+
+/* ----------
+ * pgrb_hist_idx -
+ *
+ * Computes the history table slot for the lookup by the next 4
+ * characters in the input.
+ *
+ * NB: because we use the next 4 characters, we are not guaranteed to
+ * find 3-character matches; they very possibly will be in the wrong
+ * hash list. This seems an acceptable tradeoff for spreading out the
+ * hash keys more.
+ * ----------
+ */
+#define pgrb_hist_idx(_s, _pos, _mask) ( \
+ (((_s)[_pos - 3] << 6) ^ ((_s)[_pos - 2] << 4) ^ \
+ ((_s)[_pos - 1] << 2) ^ (_s)[_pos]) & (_mask) \
+ )
+
+
+/* The same, calculated in a rolling fashion */
+#define pgrb_hash_init(_p,hindex) \
+ hindex = ((_p)[0] << 4) ^ ((_p)[1] << 2) ^ ((_p)[2])
+
+#define pgrb_hash_roll(_p, hindex) \
+ hindex = (hindex << 2) ^ (_p)[3]
+
+#define pgrb_hash_unroll(_p, hindex) \
+ hindex = hindex ^ ((_p)[0] << 6)
+
+
+
+/* ----------
+ * pgrb_out_ctrl -
+ *
+ * Outputs the last and allocates a new control byte if needed.
+ * ----------
+ */
+#define pgrb_out_ctrl(__ctrlp,__ctrlb,__ctrl,__buf) \
+do { \
+ if ((__ctrl & 0xff) == 0) \
+ { \
+ *(__ctrlp) = __ctrlb; \
+ __ctrlp = (__buf)++; \
+ __ctrlb = 0; \
+ __ctrl = 1; \
+ } \
+} while (0)
+
+
+/* ----------
+ * pgrb_out_literal -
+ *
+ * Outputs a literal byte to the destination buffer including the
+ * appropriate control bit.
+ * ----------
+ */
+#define pgrb_out_literal(_ctrlp,_ctrlb,_ctrl,_buf,_byte) \
+do { \
+ pgrb_out_ctrl(_ctrlp,_ctrlb,_ctrl,_buf); \
+ *(_buf)++ = (unsigned char)(_byte); \
+ _ctrl <<= 1; \
+} while (0)
+
+
+/* ----------
+ * pgrb_out_tag -
+ *
+ * Outputs a backward reference tag of 2-4 bytes (depending on
+ * offset and length) to the destination buffer including the
+ * appropriate control bit.
+ * ----------
+ */
+#define pgrb_out_tag(_ctrlp,_ctrlb,_ctrl,_buf,_len,_off) \
+do { \
+ pgrb_out_ctrl(_ctrlp,_ctrlb,_ctrl,_buf); \
+ _ctrlb |= _ctrl; \
+ _ctrl <<= 1; \
+ if (_len > 17) \
+ { \
+ (_buf)[0] = (unsigned char)((((_off) & 0xf00) >> 4) | 0x0f); \
+ (_buf)[1] = (unsigned char)(((_off) & 0xff)); \
+ (_buf)[2] = (unsigned char)((_len) - 18); \
+ (_buf) += 3; \
+ } else { \
+ (_buf)[0] = (unsigned char)((((_off) & 0xf00) >> 4) | ((_len) - 3)); \
+ (_buf)[1] = (unsigned char)((_off) & 0xff); \
+ (_buf) += 2; \
+ } \
+} while (0)
+
+
+/* ----------
+ * pgrb_find_match -
+ *
+ * ----------
+ */
+static inline int
+pgrb_find_match(int16 *hstart, const char *hbegin,
+ const char* input_chunk_start,
+ int16 *lenp, int16 *offp,
+ const char *hend, int hindex,
+ int good_match, int good_drop)
+{
+ const char *hp;
+ const char *ip;
+ int16 history_chunk_size;
+ int32 len = 0;
+ int32 off = 0;
+ int16 hoff;
+
+
+ hoff = hstart[hindex];
+
+ /* We use offset 0 to mean invalid entries. */
+ while (hoff != INVALID_ENTRY)
+ {
+ int32 thisoff;
+ int32 thislen;
+ int32 maxlen;
+
+ thislen = 0;
+
+ hp = hbegin + hoff;
+ ip = input_chunk_start;
+
+ maxlen = PGRB_MAX_MATCH;
+ if (hend - hp < maxlen)
+ maxlen = hend - hp;
+
+ /*
+ * we cannot get a bigger chunk if the maximum length for
+ * start of match position is less than already found match
+ * length.
+ */
+ if (len > maxlen)
+ break;
+
+ thisoff = hend - hp;
+ if (thisoff >= 0x0fff)
+ break;
+
+ /*
+ * Determine length of match. A better match must be larger than the
+ * best so far. And if we already have a match of 16 or more bytes,
+ * it's worth the call overhead to use memcmp() to check if this match
+ * is equal for the same size. After that we must fallback to
+ * chunk by chunk comparison to know the exact position where
+ * the diff occurred.
+ */
+ if (len >= 16)
+ {
+ if (memcmp(ip, hp, len) == 0)
+ {
+ thislen = len;
+ ip += len;
+ hp += len;
+ while (*ip == *hp && thislen < maxlen)
+ {
+ history_chunk_size = PGRB_CHUNK_SIZE;
+ while (history_chunk_size > 0)
+ {
+ if (*hp++ != *ip++)
+ break;
+ else
+ --history_chunk_size;
+ }
+
+ /* consider only complete chunk matches. */
+ if (history_chunk_size == 0)
+ thislen += PGRB_CHUNK_SIZE;
+ }
+ }
+ }
+ else
+ {
+ while (*ip == *hp && thislen < maxlen)
+ {
+ history_chunk_size = PGRB_CHUNK_SIZE;
+ while (history_chunk_size > 0)
+ {
+ if (*hp++ != *ip++)
+ break;
+ else
+ --history_chunk_size;
+ }
+
+ /* consider only complete chunk matches. */
+ if (history_chunk_size == 0)
+ thislen += PGRB_CHUNK_SIZE;
+ }
+ }
+
+ /*
+ * Remember this match as the best (if it is)
+ */
+ if (thislen > len)
+ {
+ len = thislen;
+ off = thisoff;
+ }
+
+ /*
+ * Advance to the next history entry
+ */
+ hoff = rb_hist_entries[hoff];
+
+ /*
+ * Be happy with lesser good matches the more entries we visited. But
+ * no point in doing calculation if we're at end of list.
+ */
+ if (hoff != INVALID_ENTRY)
+ {
+ if (len >= good_match)
+ break;
+ good_match -= (good_match * good_drop) / 100;
+ }
+ }
+
+ /*
+ * Return match information only if it results at least in one chunk
+ * reduction.
+ */
+ if (len >= PGRB_CHUNK_SIZE)
+ {
+ *lenp = len;
+ *offp = off;
+ return 1;
+ }
+
+ return 0;
+}
+
+static int
+choose_hash_size(int slen)
+{
+ int hashsz;
+
+ /*
+ * Experiments suggest that these hash sizes work pretty well. A large
+ * hash table minimizes collision, but has a higher startup cost. For a
+ * small input, the startup cost dominates. The table size must be a power
+ * of two.
+ */
+ if (slen < 128)
+ hashsz = 512;
+ else if (slen < 256)
+ hashsz = 1024;
+ else if (slen < 512)
+ hashsz = 2048;
+ else if (slen < 1024)
+ hashsz = 4096;
+ else
+ hashsz = 8192;
+ return hashsz;
+}
+
+/* ----------
+ * Chunkwise Delta Encoding - Compresses source data by referring history.
+ *
+ * source is the input data to be compressed
+ * slen is the length of source data
+ * history is the data which is used as reference for compression
+ * hlen is the length of history data
+ * The encoded result is written to dest, and its length is returned in
+ * finallen.
+ * The return value is TRUE if compression succeeded,
+ * FALSE if not; in the latter case the contents of dest
+ * are undefined.
+ * ----------
+ */
+bool
+pgrb_delta_encode(const char *source, int32 slen,
+ const char *history, int32 hlen,
+ char *dest, uint32 *finallen,
+ const PGRB_Strategy *strategy)
+{
+ unsigned char *bp = ((unsigned char *) dest);
+ unsigned char *bstart = bp;
+ const char *dp = source;
+ const char *dend = source + slen;
+ const char *dp_unmatched_chunk_start;
+ const char *dp_unmatched_start;
+ const char *hp = history;
+ const char *hend = history + hlen;
+ const char *hend_tmp;
+ unsigned char ctrl_dummy = 0;
+ unsigned char *ctrlp = &ctrl_dummy;
+ unsigned char ctrlb = 0;
+ unsigned char ctrl = 0;
+ bool found_match = false;
+ int16 match_len = 0;
+ int16 match_off;
+ int32 result_size;
+ int32 result_max;
+ int32 result_min;
+ int32 need_rate;
+ int32 good_match;
+ int32 good_drop;
+ int hashsz;
+ int mask;
+ int32 hindex;
+ int16 skip_bytes = 4;
+ int hoff;
+
+ /*
+ * Tuples of length greater than PGRB_HISTORY_SIZE are not allowed for
+ * delta encode as this is the maximum size of history offset.
+ */
+ if (hlen >= PGRB_HISTORY_SIZE || hlen < 4)
+ return false;
+
+ /*
+ * Our fallback strategy is the default.
+ */
+ if (strategy == NULL)
+ strategy = PGRB_strategy_default;
+
+ /*
+ * Limit the match parameters to the supported range.
+ */
+ good_match = strategy->match_size_good;
+ if (good_match > PGRB_MAX_MATCH)
+ good_match = PGRB_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;
+
+ /*
+ * 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;
+
+ 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);
+ result_min = (slen / 100) * need_rate;
+ }
+ else
+ {
+ result_max = (slen * (100 - need_rate)) / 100;
+ result_min = (slen * (need_rate)) / 100;
+ }
+
+ hashsz = choose_hash_size(hlen/PGRB_CHUNK_SIZE);
+ mask = hashsz - 1;
+
+ /*
+ * Initialize the history lists to empty. We do not need to zero the
+ * rb_hist_entries[] array; its entries are initialized as they are used.
+ */
+ memset(hist_start, INVALID_ENTRY, hashsz * sizeof(int16));
+
+ /*
+ * Form the history table using fixed PGRB_CHUNK_SIZE bytes.
+ */
+ hoff = hlen - 4;
+ hend_tmp = hend - 4;
+ while (hend_tmp - 4 > hp)
+ {
+ hindex = pgrb_hist_idx(hp, hoff, mask);
+
+ /*
+ * Need to position offset to 4 bytes prior, before storing in
+ * history table as the hash calculation is done from that location.
+ */
+ hoff -= PGRB_CHUNK_SIZE;
+
+ /* add this offset to the history table */
+ rb_hist_entries[hoff+1] = hist_start[hindex];
+ hist_start[hindex] = hoff+1;
+
+ hend_tmp -= PGRB_CHUNK_SIZE;
+ }
+
+
+ /*
+ * Loop through the input. To optimize the encoding we don't
+ * copy any unmatched bytes till we find a match.
+ */
+ match_off = 0;
+ dp_unmatched_chunk_start = dp;
+ dp_unmatched_start = dp;
+ pgrb_hash_init(dp, hindex);
+ while (dp < dend - 4)
+ {
+ /* If we already exceeded the maximum result size, fail. */
+ if (bp - bstart >= result_max ||
+ dp - dp_unmatched_start >= result_max)
+ return false;
+
+ /*
+ * If we don't find any match till result minimum size,
+ * then fall out.
+ */
+ if (!found_match && dend - dp <= result_min)
+ return false;
+
+ /*
+ * Try to find a match in the history
+ */
+ pgrb_hash_roll(dp, hindex);
+
+ if (pgrb_find_match(hist_start, history, dp,
+ &match_len, &match_off,
+ hend, (hindex & mask),
+ good_match, good_drop))
+ {
+ while (dp_unmatched_start < dp)
+ {
+ pgrb_out_literal(ctrlp, ctrlb, ctrl, bp, *dp_unmatched_start);
+ dp_unmatched_start++;
+ }
+ /*
+ * Create the tag and add history entries for all matched
+ * characters.
+ */
+ pgrb_out_tag(ctrlp, ctrlb, ctrl, bp, match_len, match_off);
+ pgrb_hash_unroll(dp, hindex);
+ dp += match_len;
+ dp_unmatched_start = dp;
+ dp_unmatched_chunk_start = dp;
+ found_match = true;
+ }
+ else
+ {
+ pgrb_hash_unroll(dp, hindex);
+ /*
+ * If we don't find any match for first 4 bytes, then skip 4 bytes
+ * and if we don't find match again for next 8 bytes, then skip 8
+ * bytes and keep on doing the same until we find first match.
+ * There is a chance that we miss some bytes for compression, but
+ * it should not effect much as we are doing this only till we find
+ * first match.
+ */
+ if (dp - dp_unmatched_chunk_start >= skip_bytes)
+ {
+ dp += skip_bytes;
+ dp_unmatched_chunk_start = dp;
+ skip_bytes *= 2;
+ }
+ else
+ dp++;
+ }
+ }
+
+ /* Handle the last few bytes as literals */
+ while (dp_unmatched_start < dend)
+ {
+ pgrb_out_literal(ctrlp, ctrlb, ctrl, bp, *dp_unmatched_start);
+ dp_unmatched_start++; /* Do not do this ++ in the line above! */
+ }
+
+ /*
+ * 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.
+ */
+ *finallen = result_size;
+
+ return true;
+}
+
+/* ----------
+ * pgrb_delta_decode
+ *
+ * Decompresses source into dest.
+ * ----------
+ */
+void
+pgrb_delta_decode(const char *source, uint32 srclen,
+ char *dest, uint32 destlen, uint32 *finallen,
+ const char *history, uint32 histlen)
+{
+ const unsigned char *sp;
+ const unsigned char *srcend;
+ unsigned char *dp;
+ unsigned char *destend;
+ const char *hend;
+
+ sp = ((const unsigned char *) source);
+ srcend = ((const unsigned char *) source) + srclen;
+ dp = (unsigned char *) dest;
+ destend = dp + destlen;
+ hend = history + histlen;
+
+ while (sp < srcend && dp < destend)
+ {
+ /*
+ * Read one control byte and process the next 8 items (or as many as
+ * remain in the compressed input).
+ */
+ unsigned char ctrl = *sp++;
+ int ctrlc;
+
+ for (ctrlc = 0; ctrlc < 8 && sp < srcend; ctrlc++)
+ {
+ if (ctrl & 1)
+ {
+ /*
+ * Otherwise it contains the match length minus 3 and the
+ * upper 4 bits of the offset. The next following byte
+ * contains the lower 8 bits of the offset. If the length is
+ * coded as 18, another extension tag byte tells how much
+ * longer the match really was (0-255).
+ */
+ int32 len;
+ int32 off;
+
+ len = (sp[0] & 0x0f) + 3;
+ off = ((sp[0] & 0xf0) << 4) | sp[1];
+ sp += 2;
+ if (len == 18)
+ len += *sp++;
+
+ /*
+ * Check for output buffer overrun, to ensure we don't clobber
+ * memory in case of corrupt input. Note: we must advance dp
+ * here to ensure the error is detected below the loop. We
+ * don't simply put the elog inside the loop since that will
+ * probably interfere with optimization.
+ */
+ if (dp + len > destend)
+ {
+ dp += len;
+ break;
+ }
+
+ /*
+ * Now we copy the bytes specified by the tag from history to
+ * OUTPUT. We can safely use memcpy here because source and
+ * destination strings will not overlap as in case of LZ.
+ */
+ memcpy(dp, hend - off, len);
+ dp += len;
+ }
+ else
+ {
+ /*
+ * 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 */
+
+ *dp++ = *sp++;
+ }
+
+ /*
+ * Advance the control bit
+ */
+ ctrl >>= 1;
+ }
+ }
+
+ /*
+ * Check we decompressed the right amount.
+ */
+ if (sp != srcend)
+ elog(PANIC, "compressed data is corrupt");
+
+ /*
+ * That's it.
+ */
+ *finallen = ((char *) dp - dest);
+}
diff --git a/src/include/access/heapam_xlog.h b/src/include/access/heapam_xlog.h
index d4383ab..df64096 100644
--- a/src/include/access/heapam_xlog.h
+++ b/src/include/access/heapam_xlog.h
@@ -67,6 +67,7 @@
#define XLOG_HEAP_CONTAINS_OLD_TUPLE (1<<2)
#define XLOG_HEAP_CONTAINS_OLD_KEY (1<<3)
#define XLOG_HEAP_CONTAINS_NEW_TUPLE (1<<4)
+#define XLOG_HEAP_DELTA_ENCODED (1<<5)
/* convenience macro for checking whether any form of old tuple was logged */
#define XLOG_HEAP_CONTAINS_OLD \
diff --git a/src/include/access/htup_details.h b/src/include/access/htup_details.h
index a3eba98..abb5620 100644
--- a/src/include/access/htup_details.h
+++ b/src/include/access/htup_details.h
@@ -740,6 +740,11 @@ 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, uint32 *enclen);
+extern void heap_delta_decode (char *encdata, uint32 enclen, 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 11ab277..87402b0 100644
--- a/src/include/access/xlog.h
+++ b/src/include/access/xlog.h
@@ -279,6 +279,7 @@ 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_rbcompress.h b/src/include/utils/pg_rbcompress.h
new file mode 100644
index 0000000..d5105db
--- /dev/null
+++ b/src/include/utils/pg_rbcompress.h
@@ -0,0 +1,79 @@
+/* ----------
+ * pg_rbcompress.h -
+ *
+ * Definitions for the PostgreSQL specific encoding scheme
+ *
+ * src/include/utils/pg_rbcompress.h
+ * ----------
+ */
+
+#ifndef _PG_RBCOMPRESS_H_
+#define _PG_RBCOMPRESS_H_
+
+
+/* ----------
+ * PGRB_Strategy -
+ *
+ * Some values that control the compression algorithm.
+ *
+ * min_input_size Minimum input data size to consider compression.
+ *
+ * max_input_size Maximum input data size to consider compression.
+ *
+ * min_comp_rate Minimum compression rate (0-99%) to require.
+ * Regardless of min_comp_rate, the output must be
+ * smaller than the input, else we don't store
+ * compressed.
+ *
+ * first_success_by Abandon compression if we find no compressible
+ * data within the first this-many bytes.
+ *
+ * match_size_good The initial GOOD match size when starting history
+ * lookup. When looking up the history to find a
+ * match that could be expressed as a tag, the
+ * algorithm does not always walk back entirely.
+ * A good match fast is usually better than the
+ * best possible one very late. For each iteration
+ * in the lookup, this value is lowered so the
+ * longer the lookup takes, the smaller matches
+ * are considered good.
+ *
+ * match_size_drop The percentage by which match_size_good is lowered
+ * after each history check. Allowed values are
+ * 0 (no change until end) to 100 (only check
+ * latest history entry at all).
+ * ----------
+ */
+typedef struct PGRB_Strategy
+{
+ int32 min_input_size;
+ int32 max_input_size;
+ int32 min_comp_rate;
+ int32 first_success_by;
+ int32 match_size_good;
+ int32 match_size_drop;
+} PGRB_Strategy;
+
+
+/* ----------
+ * The standard strategies
+ *
+ * PGRB_strategy_default Recommended default strategy for WAL
+ * compression.
+ * ----------
+ */
+extern const PGRB_Strategy *const PGRB_strategy_default;
+
+
+/* ----------
+ * Global function declarations
+ * ----------
+ */
+extern bool pgrb_delta_encode(const char *source, int32 slen,
+ const char *history, int32 hlen,
+ char *dest, uint32 *finallen, const PGRB_Strategy *strategy);
+extern void pgrb_delta_decode(const char *source, uint32 srclen,
+ char *dest, uint32 destlen, uint32 *finallen,
+ const char *history, uint32 histlen);
+
+#endif /* _PG_RBCOMPRESS_H_ */
diff --git a/src/include/utils/rel.h b/src/include/utils/rel.h
index 9b8a4c9..717b90b 100644
--- a/src/include/utils/rel.h
+++ b/src/include/utils/rel.h
@@ -218,6 +218,7 @@ typedef struct StdRdOptions
bool security_barrier; /* for views */
int check_option_offset; /* for views */
bool user_catalog_table; /* use as an additional catalog relation */
+ bool wal_compress_update; /* compress wal tuple for update */
} StdRdOptions;
#define HEAP_MIN_FILLFACTOR 10
@@ -296,6 +297,15 @@ typedef struct StdRdOptions
((StdRdOptions *) (relation)->rd_options)->user_catalog_table : false)
/*
+ * RelationIsEnabledForWalCompression
+ * Returns whether the wal for update operation on relation can
+ * be compressed.
+ */
+#define RelationIsEnabledForWalCompression(relation) \
+ ((relation)->rd_options ? \
+ ((StdRdOptions *) (relation)->rd_options)->wal_compress_update : true)
+
+/*
* RelationIsValid
* True iff relation descriptor is valid.
*/
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;