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, 72 insertions, 86 deletions

diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index 8e78aafda7c..1c7dac38fc9 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -31,7 +31,9 @@
 #include "access/transam.h"
 #include "access/xact.h"
 #include "access/xlog_internal.h"
+#include "access/xlogutils.h"
 #include "access/xlogreader.h"
+#include "access/xlogrecord.h"
 
 #include "catalog/pg_control.h"
 
@@ -46,8 +48,7 @@ typedef struct XLogRecordBuffer
 {
 	XLogRecPtr	origptr;
 	XLogRecPtr	endptr;
-	XLogRecord	record;
-	char	   *record_data;
+	XLogReaderState *record;
 } XLogRecordBuffer;
 
 /* RMGR Handlers */
@@ -79,17 +80,16 @@ static void DecodeXLogTuple(char *data, Size len, ReorderBufferTupleBuf *tup);
  * context.
  */
 void
-LogicalDecodingProcessRecord(LogicalDecodingContext *ctx, XLogRecord *record)
+LogicalDecodingProcessRecord(LogicalDecodingContext *ctx, XLogReaderState *record)
 {
 	XLogRecordBuffer buf;
 
 	buf.origptr = ctx->reader->ReadRecPtr;
 	buf.endptr = ctx->reader->EndRecPtr;
-	buf.record = *record;
-	buf.record_data = XLogRecGetData(record);
+	buf.record = record;
 
 	/* cast so we get a warning when new rmgrs are added */
-	switch ((RmgrIds) buf.record.xl_rmid)
+	switch ((RmgrIds) XLogRecGetRmid(record))
 	{
 			/*
 			 * Rmgrs we care about for logical decoding. Add new rmgrs in
@@ -135,7 +135,7 @@ LogicalDecodingProcessRecord(LogicalDecodingContext *ctx, XLogRecord *record)
 		case RM_BRIN_ID:
 			break;
 		case RM_NEXT_ID:
-			elog(ERROR, "unexpected RM_NEXT_ID rmgr_id: %u", (RmgrIds) buf.record.xl_rmid);
+			elog(ERROR, "unexpected RM_NEXT_ID rmgr_id: %u", (RmgrIds) XLogRecGetRmid(buf.record));
 	}
 }
 
@@ -146,7 +146,7 @@ static void
 DecodeXLogOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 {
 	SnapBuild  *builder = ctx->snapshot_builder;
-	uint8		info = buf->record.xl_info & ~XLR_INFO_MASK;
+	uint8		info = XLogRecGetInfo(buf->record) & ~XLR_INFO_MASK;
 
 	switch (info)
 	{
@@ -185,8 +185,8 @@ DecodeXactOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 {
 	SnapBuild  *builder = ctx->snapshot_builder;
 	ReorderBuffer *reorder = ctx->reorder;
-	XLogRecord *r = &buf->record;
-	uint8		info = r->xl_info & ~XLR_INFO_MASK;
+	XLogReaderState *r = buf->record;
+	uint8		info = XLogRecGetInfo(r) & ~XLR_INFO_MASK;
 
 	/* no point in doing anything yet, data could not be decoded anyway */
 	if (SnapBuildCurrentState(builder) < SNAPBUILD_FULL_SNAPSHOT)
@@ -200,12 +200,12 @@ DecodeXactOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 				TransactionId *subxacts = NULL;
 				SharedInvalidationMessage *invals = NULL;
 
-				xlrec = (xl_xact_commit *) buf->record_data;
+				xlrec = (xl_xact_commit *) XLogRecGetData(r);
 
 				subxacts = (TransactionId *) &(xlrec->xnodes[xlrec->nrels]);
 				invals = (SharedInvalidationMessage *) &(subxacts[xlrec->nsubxacts]);
 
-				DecodeCommit(ctx, buf, r->xl_xid, xlrec->dbId,
+				DecodeCommit(ctx, buf, XLogRecGetXid(r), xlrec->dbId,
 							 xlrec->xact_time,
 							 xlrec->nsubxacts, subxacts,
 							 xlrec->nmsgs, invals);
@@ -220,7 +220,7 @@ DecodeXactOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 				SharedInvalidationMessage *invals = NULL;
 
 				/* Prepared commits contain a normal commit record... */
-				prec = (xl_xact_commit_prepared *) buf->record_data;
+				prec = (xl_xact_commit_prepared *) XLogRecGetData(r);
 				xlrec = &prec->crec;
 
 				subxacts = (TransactionId *) &(xlrec->xnodes[xlrec->nrels]);
@@ -237,9 +237,9 @@ DecodeXactOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 			{
 				xl_xact_commit_compact *xlrec;
 
-				xlrec = (xl_xact_commit_compact *) buf->record_data;
+				xlrec = (xl_xact_commit_compact *) XLogRecGetData(r);
 
-				DecodeCommit(ctx, buf, r->xl_xid, InvalidOid,
+				DecodeCommit(ctx, buf, XLogRecGetXid(r), InvalidOid,
 							 xlrec->xact_time,
 							 xlrec->nsubxacts, xlrec->subxacts,
 							 0, NULL);
@@ -250,11 +250,11 @@ DecodeXactOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 				xl_xact_abort *xlrec;
 				TransactionId *sub_xids;
 
-				xlrec = (xl_xact_abort *) buf->record_data;
+				xlrec = (xl_xact_abort *) XLogRecGetData(r);
 
 				sub_xids = (TransactionId *) &(xlrec->xnodes[xlrec->nrels]);
 
-				DecodeAbort(ctx, buf->origptr, r->xl_xid,
+				DecodeAbort(ctx, buf->origptr, XLogRecGetXid(r),
 							sub_xids, xlrec->nsubxacts);
 				break;
 			}
@@ -265,7 +265,7 @@ DecodeXactOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 				TransactionId *sub_xids;
 
 				/* prepared abort contain a normal commit abort... */
-				prec = (xl_xact_abort_prepared *) buf->record_data;
+				prec = (xl_xact_abort_prepared *) XLogRecGetData(r);
 				xlrec = &prec->arec;
 
 				sub_xids = (TransactionId *) &(xlrec->xnodes[xlrec->nrels]);
@@ -282,7 +282,7 @@ DecodeXactOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 				int			i;
 				TransactionId *sub_xid;
 
-				xlrec = (xl_xact_assignment *) buf->record_data;
+				xlrec = (xl_xact_assignment *) XLogRecGetData(r);
 
 				sub_xid = &xlrec->xsub[0];
 
@@ -316,14 +316,14 @@ static void
 DecodeStandbyOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 {
 	SnapBuild  *builder = ctx->snapshot_builder;
-	XLogRecord *r = &buf->record;
-	uint8		info = r->xl_info & ~XLR_INFO_MASK;
+	XLogReaderState *r = buf->record;
+	uint8		info = XLogRecGetInfo(r) & ~XLR_INFO_MASK;
 
 	switch (info)
 	{
 		case XLOG_RUNNING_XACTS:
 			{
-				xl_running_xacts *running = (xl_running_xacts *) buf->record_data;
+				xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
 
 				SnapBuildProcessRunningXacts(builder, buf->origptr, running);
 
@@ -352,8 +352,8 @@ DecodeStandbyOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 static void
 DecodeHeap2Op(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 {
-	uint8		info = buf->record.xl_info & XLOG_HEAP_OPMASK;
-	TransactionId xid = buf->record.xl_xid;
+	uint8		info = XLogRecGetInfo(buf->record) & XLOG_HEAP_OPMASK;
+	TransactionId xid = XLogRecGetXid(buf->record);
 	SnapBuild  *builder = ctx->snapshot_builder;
 
 	/* no point in doing anything yet */
@@ -370,7 +370,7 @@ DecodeHeap2Op(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 			{
 				xl_heap_new_cid *xlrec;
 
-				xlrec = (xl_heap_new_cid *) buf->record_data;
+				xlrec = (xl_heap_new_cid *) XLogRecGetData(buf->record);
 				SnapBuildProcessNewCid(builder, xid, buf->origptr, xlrec);
 
 				break;
@@ -405,8 +405,8 @@ DecodeHeap2Op(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 static void
 DecodeHeapOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 {
-	uint8		info = buf->record.xl_info & XLOG_HEAP_OPMASK;
-	TransactionId xid = buf->record.xl_xid;
+	uint8		info = XLogRecGetInfo(buf->record) & XLOG_HEAP_OPMASK;
+	TransactionId xid = XLogRecGetXid(buf->record);
 	SnapBuild  *builder = ctx->snapshot_builder;
 
 	/* no point in doing anything yet */
@@ -576,34 +576,35 @@ DecodeAbort(LogicalDecodingContext *ctx, XLogRecPtr lsn, TransactionId xid,
 static void
 DecodeInsert(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 {
-	XLogRecord *r = &buf->record;
+	XLogReaderState *r = buf->record;
 	xl_heap_insert *xlrec;
 	ReorderBufferChange *change;
+	RelFileNode target_node;
 
-	xlrec = (xl_heap_insert *) buf->record_data;
+	xlrec = (xl_heap_insert *) XLogRecGetData(r);
 
 	/* only interested in our database */
-	if (xlrec->target.node.dbNode != ctx->slot->data.database)
+	XLogRecGetBlockTag(r, 0, &target_node, NULL, NULL);
+	if (target_node.dbNode != ctx->slot->data.database)
 		return;
 
 	change = ReorderBufferGetChange(ctx->reorder);
 	change->action = REORDER_BUFFER_CHANGE_INSERT;
-	memcpy(&change->data.tp.relnode, &xlrec->target.node, sizeof(RelFileNode));
+	memcpy(&change->data.tp.relnode, &target_node, sizeof(RelFileNode));
 
 	if (xlrec->flags & XLOG_HEAP_CONTAINS_NEW_TUPLE)
 	{
-		Assert(r->xl_len > (SizeOfHeapInsert + SizeOfHeapHeader));
+		Size		tuplelen;
+		char	   *tupledata = XLogRecGetBlockData(r, 0, &tuplelen);
 
 		change->data.tp.newtuple = ReorderBufferGetTupleBuf(ctx->reorder);
 
-		DecodeXLogTuple((char *) xlrec + SizeOfHeapInsert,
-						r->xl_len - SizeOfHeapInsert,
-						change->data.tp.newtuple);
+		DecodeXLogTuple(tupledata, tuplelen, change->data.tp.newtuple);
 	}
 
 	change->data.tp.clear_toast_afterwards = true;
 
-	ReorderBufferQueueChange(ctx->reorder, r->xl_xid, buf->origptr, change);
+	ReorderBufferQueueChange(ctx->reorder, XLogRecGetXid(r), buf->origptr, change);
 }
 
 /*
@@ -615,62 +616,47 @@ DecodeInsert(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 static void
 DecodeUpdate(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 {
-	XLogRecord *r = &buf->record;
+	XLogReaderState *r = buf->record;
 	xl_heap_update *xlrec;
-	xl_heap_header_len xlhdr;
 	ReorderBufferChange *change;
 	char	   *data;
+	Size		datalen;
+	RelFileNode target_node;
 
-	xlrec = (xl_heap_update *) buf->record_data;
+	xlrec = (xl_heap_update *) XLogRecGetData(r);
 
 	/* only interested in our database */
-	if (xlrec->target.node.dbNode != ctx->slot->data.database)
+	XLogRecGetBlockTag(r, 0, &target_node, NULL, NULL);
+	if (target_node.dbNode != ctx->slot->data.database)
 		return;
 
 	change = ReorderBufferGetChange(ctx->reorder);
 	change->action = REORDER_BUFFER_CHANGE_UPDATE;
-	memcpy(&change->data.tp.relnode, &xlrec->target.node, sizeof(RelFileNode));
-
-	/* caution, remaining data in record is not aligned */
-	data = buf->record_data + SizeOfHeapUpdate;
+	memcpy(&change->data.tp.relnode, &target_node, sizeof(RelFileNode));
 
 	if (xlrec->flags & XLOG_HEAP_CONTAINS_NEW_TUPLE)
 	{
-		Assert(r->xl_len > (SizeOfHeapUpdate + SizeOfHeapHeaderLen));
-
-		memcpy(&xlhdr, data, sizeof(xlhdr));
-		data += offsetof(xl_heap_header_len, header);
+		data = XLogRecGetBlockData(r, 0, &datalen);
 
 		change->data.tp.newtuple = ReorderBufferGetTupleBuf(ctx->reorder);
 
-		DecodeXLogTuple(data,
-						xlhdr.t_len + SizeOfHeapHeader,
-						change->data.tp.newtuple);
-		/* skip over the rest of the tuple header */
-		data += SizeOfHeapHeader;
-		/* skip over the tuple data */
-		data += xlhdr.t_len;
+		DecodeXLogTuple(data, datalen, change->data.tp.newtuple);
 	}
 
 	if (xlrec->flags & XLOG_HEAP_CONTAINS_OLD)
 	{
-		memcpy(&xlhdr, data, sizeof(xlhdr));
-		data += offsetof(xl_heap_header_len, header);
+		/* caution, remaining data in record is not aligned */
+		data = XLogRecGetData(r) + SizeOfHeapUpdate;
+		datalen = XLogRecGetDataLen(r) - SizeOfHeapUpdate;
 
 		change->data.tp.oldtuple = ReorderBufferGetTupleBuf(ctx->reorder);
 
-		DecodeXLogTuple(data,
-						xlhdr.t_len + SizeOfHeapHeader,
-						change->data.tp.oldtuple);
-#ifdef NOT_USED
-		data += SizeOfHeapHeader;
-		data += xlhdr.t_len;
-#endif
+		DecodeXLogTuple(data, datalen, change->data.tp.oldtuple);
 	}
 
 	change->data.tp.clear_toast_afterwards = true;
 
-	ReorderBufferQueueChange(ctx->reorder, r->xl_xid, buf->origptr, change);
+	ReorderBufferQueueChange(ctx->reorder, XLogRecGetXid(r), buf->origptr, change);
 }
 
 /*
@@ -681,36 +667,38 @@ DecodeUpdate(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 static void
 DecodeDelete(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 {
-	XLogRecord *r = &buf->record;
+	XLogReaderState *r = buf->record;
 	xl_heap_delete *xlrec;
 	ReorderBufferChange *change;
+	RelFileNode target_node;
 
-	xlrec = (xl_heap_delete *) buf->record_data;
+	xlrec = (xl_heap_delete *) XLogRecGetData(r);
 
 	/* only interested in our database */
-	if (xlrec->target.node.dbNode != ctx->slot->data.database)
+	XLogRecGetBlockTag(r, 0, &target_node, NULL, NULL);
+	if (target_node.dbNode != ctx->slot->data.database)
 		return;
 
 	change = ReorderBufferGetChange(ctx->reorder);
 	change->action = REORDER_BUFFER_CHANGE_DELETE;
 
-	memcpy(&change->data.tp.relnode, &xlrec->target.node, sizeof(RelFileNode));
+	memcpy(&change->data.tp.relnode, &target_node, sizeof(RelFileNode));
 
 	/* old primary key stored */
 	if (xlrec->flags & XLOG_HEAP_CONTAINS_OLD)
 	{
-		Assert(r->xl_len > (SizeOfHeapDelete + SizeOfHeapHeader));
+		Assert(XLogRecGetDataLen(r) > (SizeOfHeapDelete + SizeOfHeapHeader));
 
 		change->data.tp.oldtuple = ReorderBufferGetTupleBuf(ctx->reorder);
 
 		DecodeXLogTuple((char *) xlrec + SizeOfHeapDelete,
-						r->xl_len - SizeOfHeapDelete,
+						XLogRecGetDataLen(r) - SizeOfHeapDelete,
 						change->data.tp.oldtuple);
 	}
 
 	change->data.tp.clear_toast_afterwards = true;
 
-	ReorderBufferQueueChange(ctx->reorder, r->xl_xid, buf->origptr, change);
+	ReorderBufferQueueChange(ctx->reorder, XLogRecGetXid(r), buf->origptr, change);
 }
 
 /*
@@ -721,27 +709,24 @@ DecodeDelete(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 static void
 DecodeMultiInsert(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 {
-	XLogRecord *r = &buf->record;
+	XLogReaderState *r = buf->record;
 	xl_heap_multi_insert *xlrec;
 	int			i;
 	char	   *data;
-	bool		isinit = (r->xl_info & XLOG_HEAP_INIT_PAGE) != 0;
+	char	   *tupledata;
+	Size		tuplelen;
+	RelFileNode rnode;
 
-	xlrec = (xl_heap_multi_insert *) buf->record_data;
+	xlrec = (xl_heap_multi_insert *) XLogRecGetData(r);
 
 	/* only interested in our database */
-	if (xlrec->node.dbNode != ctx->slot->data.database)
+	XLogRecGetBlockTag(r, 0, &rnode, NULL, NULL);
+	if (rnode.dbNode != ctx->slot->data.database)
 		return;
 
-	data = buf->record_data + SizeOfHeapMultiInsert;
-
-	/*
-	 * OffsetNumbers (which are not of interest to us) are stored when
-	 * XLOG_HEAP_INIT_PAGE is not set -- skip over them.
-	 */
-	if (!isinit)
-		data += sizeof(OffsetNumber) * xlrec->ntuples;
+	tupledata = XLogRecGetBlockData(r, 0, &tuplelen);
 
+	data = tupledata;
 	for (i = 0; i < xlrec->ntuples; i++)
 	{
 		ReorderBufferChange *change;
@@ -751,7 +736,7 @@ DecodeMultiInsert(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 
 		change = ReorderBufferGetChange(ctx->reorder);
 		change->action = REORDER_BUFFER_CHANGE_INSERT;
-		memcpy(&change->data.tp.relnode, &xlrec->node, sizeof(RelFileNode));
+		memcpy(&change->data.tp.relnode, &rnode, sizeof(RelFileNode));
 
 		/*
 		 * CONTAINS_NEW_TUPLE will always be set currently as multi_insert
@@ -806,9 +791,10 @@ DecodeMultiInsert(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 		else
 			change->data.tp.clear_toast_afterwards = false;
 
-		ReorderBufferQueueChange(ctx->reorder, r->xl_xid,
+		ReorderBufferQueueChange(ctx->reorder, XLogRecGetXid(r),
 								 buf->origptr, change);
 	}
+	Assert(data == tupledata + tuplelen);
 }
 
 /*