Revamp the WAL record format.

Each WAL record now carries information about the modified relation and
block(s) in a standardized format. That makes it easier to write tools that
need that information, like pg_rewind, prefetching the blocks to speed up
recovery, etc.

There's a whole new API for building WAL records, replacing the XLogRecData
chains used previously. The new API consists of XLogRegister* functions,
which are called for each buffer and chunk of data that is added to the
record. The new API also gives more control over when a full-page image is
written, by passing flags to the XLogRegisterBuffer function.

This also simplifies the XLogReadBufferForRedo() calls. The function can dig
the relation and block number from the WAL record, so they no longer need to
be passed as arguments.

For the convenience of redo routines, XLogReader now disects each WAL record
after reading it, copying the main data part and the per-block data into
MAXALIGNed buffers. The data chunks are not aligned within the WAL record,
but the redo routines can assume that the pointers returned by XLogRecGet*
functions are. Redo routines are now passed the XLogReaderState, which
contains the record in the already-disected format, instead of the plain
XLogRecord.

The new record format also makes the fixed size XLogRecord header smaller,
by removing the xl_len field. The length of the "main data" portion is now
stored at the end of the WAL record, and there's a separate header after
XLogRecord for it. The alignment padding at the end of XLogRecord is also
removed. This compansates for the fact that the new format would otherwise
be more bulky than the old format.

Reviewed by Andres Freund, Amit Kapila, Michael Paquier, Alvaro Herrera,
Fujii Masao.

1 files changed, 28 insertions, 49 deletions

diff --git a/src/backend/commands/sequence.c b/src/backend/commands/sequence.c
index cb8b27a93c0..ba5b938863c 100644
--- a/src/backend/commands/sequence.c
+++ b/src/backend/commands/sequence.c
@@ -372,20 +372,16 @@ fill_seq_with_data(Relation rel, HeapTuple tuple)
 	{
 		xl_seq_rec	xlrec;
 		XLogRecPtr	recptr;
-		XLogRecData rdata[2];
+
+		XLogBeginInsert();
+		XLogRegisterBuffer(0, buf, REGBUF_WILL_INIT);
 
 		xlrec.node = rel->rd_node;
-		rdata[0].data = (char *) &xlrec;
-		rdata[0].len = sizeof(xl_seq_rec);
-		rdata[0].buffer = InvalidBuffer;
-		rdata[0].next = &(rdata[1]);
 
-		rdata[1].data = (char *) tuple->t_data;
-		rdata[1].len = tuple->t_len;
-		rdata[1].buffer = InvalidBuffer;
-		rdata[1].next = NULL;
+		XLogRegisterData((char *) &xlrec, sizeof(xl_seq_rec));
+		XLogRegisterData((char *) tuple->t_data, tuple->t_len);
 
-		recptr = XLogInsert(RM_SEQ_ID, XLOG_SEQ_LOG, rdata);
+		recptr = XLogInsert(RM_SEQ_ID, XLOG_SEQ_LOG);
 
 		PageSetLSN(page, recptr);
 	}
@@ -454,21 +450,17 @@ AlterSequence(AlterSeqStmt *stmt)
 	{
 		xl_seq_rec	xlrec;
 		XLogRecPtr	recptr;
-		XLogRecData rdata[2];
 		Page		page = BufferGetPage(buf);
 
+		XLogBeginInsert();
+		XLogRegisterBuffer(0, buf, REGBUF_WILL_INIT);
+
 		xlrec.node = seqrel->rd_node;
-		rdata[0].data = (char *) &xlrec;
-		rdata[0].len = sizeof(xl_seq_rec);
-		rdata[0].buffer = InvalidBuffer;
-		rdata[0].next = &(rdata[1]);
+		XLogRegisterData((char *) &xlrec, sizeof(xl_seq_rec));
 
-		rdata[1].data = (char *) seqtuple.t_data;
-		rdata[1].len = seqtuple.t_len;
-		rdata[1].buffer = InvalidBuffer;
-		rdata[1].next = NULL;
+		XLogRegisterData((char *) seqtuple.t_data, seqtuple.t_len);
 
-		recptr = XLogInsert(RM_SEQ_ID, XLOG_SEQ_LOG, rdata);
+		recptr = XLogInsert(RM_SEQ_ID, XLOG_SEQ_LOG);
 
 		PageSetLSN(page, recptr);
 	}
@@ -706,7 +698,6 @@ nextval_internal(Oid relid)
 	{
 		xl_seq_rec	xlrec;
 		XLogRecPtr	recptr;
-		XLogRecData rdata[2];
 
 		/*
 		 * We don't log the current state of the tuple, but rather the state
@@ -714,6 +705,8 @@ nextval_internal(Oid relid)
 		 * that many future WAL records, at the cost that we lose those
 		 * sequence values if we crash.
 		 */
+		XLogBeginInsert();
+		XLogRegisterBuffer(0, buf, REGBUF_WILL_INIT);
 
 		/* set values that will be saved in xlog */
 		seq->last_value = next;
@@ -721,17 +714,11 @@ nextval_internal(Oid relid)
 		seq->log_cnt = 0;
 
 		xlrec.node = seqrel->rd_node;
-		rdata[0].data = (char *) &xlrec;
-		rdata[0].len = sizeof(xl_seq_rec);
-		rdata[0].buffer = InvalidBuffer;
-		rdata[0].next = &(rdata[1]);
 
-		rdata[1].data = (char *) seqtuple.t_data;
-		rdata[1].len = seqtuple.t_len;
-		rdata[1].buffer = InvalidBuffer;
-		rdata[1].next = NULL;
+		XLogRegisterData((char *) &xlrec, sizeof(xl_seq_rec));
+		XLogRegisterData((char *) seqtuple.t_data, seqtuple.t_len);
 
-		recptr = XLogInsert(RM_SEQ_ID, XLOG_SEQ_LOG, rdata);
+		recptr = XLogInsert(RM_SEQ_ID, XLOG_SEQ_LOG);
 
 		PageSetLSN(page, recptr);
 	}
@@ -894,21 +881,16 @@ do_setval(Oid relid, int64 next, bool iscalled)
 	{
 		xl_seq_rec	xlrec;
 		XLogRecPtr	recptr;
-		XLogRecData rdata[2];
 		Page		page = BufferGetPage(buf);
 
-		xlrec.node = seqrel->rd_node;
-		rdata[0].data = (char *) &xlrec;
-		rdata[0].len = sizeof(xl_seq_rec);
-		rdata[0].buffer = InvalidBuffer;
-		rdata[0].next = &(rdata[1]);
+		XLogBeginInsert();
+		XLogRegisterBuffer(0, buf, REGBUF_WILL_INIT);
 
-		rdata[1].data = (char *) seqtuple.t_data;
-		rdata[1].len = seqtuple.t_len;
-		rdata[1].buffer = InvalidBuffer;
-		rdata[1].next = NULL;
+		xlrec.node = seqrel->rd_node;
+		XLogRegisterData((char *) &xlrec, sizeof(xl_seq_rec));
+		XLogRegisterData((char *) seqtuple.t_data, seqtuple.t_len);
 
-		recptr = XLogInsert(RM_SEQ_ID, XLOG_SEQ_LOG, rdata);
+		recptr = XLogInsert(RM_SEQ_ID, XLOG_SEQ_LOG);
 
 		PageSetLSN(page, recptr);
 	}
@@ -1552,9 +1534,10 @@ pg_sequence_parameters(PG_FUNCTION_ARGS)
 
 
 void
-seq_redo(XLogRecPtr lsn, XLogRecord *record)
+seq_redo(XLogReaderState *record)
 {
-	uint8		info = record->xl_info & ~XLR_INFO_MASK;
+	XLogRecPtr	lsn = record->EndRecPtr;
+	uint8		info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
 	Buffer		buffer;
 	Page		page;
 	Page		localpage;
@@ -1563,14 +1546,10 @@ seq_redo(XLogRecPtr lsn, XLogRecord *record)
 	xl_seq_rec *xlrec = (xl_seq_rec *) XLogRecGetData(record);
 	sequence_magic *sm;
 
-	/* Backup blocks are not used in seq records */
-	Assert(!(record->xl_info & XLR_BKP_BLOCK_MASK));
-
 	if (info != XLOG_SEQ_LOG)
 		elog(PANIC, "seq_redo: unknown op code %u", info);
 
-	buffer = XLogReadBuffer(xlrec->node, 0, true);
-	Assert(BufferIsValid(buffer));
+	buffer = XLogInitBufferForRedo(record, 0);
 	page = (Page) BufferGetPage(buffer);
 
 	/*
@@ -1589,7 +1568,7 @@ seq_redo(XLogRecPtr lsn, XLogRecord *record)
 	sm->magic = SEQ_MAGIC;
 
 	item = (char *) xlrec + sizeof(xl_seq_rec);
-	itemsz = record->xl_len - sizeof(xl_seq_rec);
+	itemsz = XLogRecGetDataLen(record) - sizeof(xl_seq_rec);
 
 	if (PageAddItem(localpage, (Item) item, itemsz,
 					FirstOffsetNumber, false, false) == InvalidOffsetNumber)