Remove read_page callback from XLogReader.

Previously, the XLogReader module would fetch new input data using a
callback function.  Redesign the interface so that it tells the caller
to insert more data with a special return value instead.  This API suits
later patches for prefetching, encryption and maybe other future
projects that would otherwise require continually extending the callback
interface.

As incidental cleanup work, move global variables readOff, readLen and
readSegNo inside XlogReaderState.

Author: Kyotaro HORIGUCHI <[email protected]>
Author: Heikki Linnakangas <[email protected]> (parts of earlier version)
Reviewed-by: Antonin Houska <[email protected]>
Reviewed-by: Alvaro Herrera <[email protected]>
Reviewed-by: Takashi Menjo <[email protected]>
Reviewed-by: Andres Freund <[email protected]>
Reviewed-by: Thomas Munro <[email protected]>
Discussion: https://postgr.es/m/20190418.210257.43726183.horiguchi.kyotaro%40lab.ntt.co.jp

1 files changed, 24 insertions, 18 deletions

diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 4bf8a18e01e..52fe9aba660 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -580,10 +580,7 @@ StartReplication(StartReplicationCmd *cmd)
 
 	/* create xlogreader for physical replication */
 	xlogreader =
-		XLogReaderAllocate(wal_segment_size, NULL,
-						   XL_ROUTINE(.segment_open = WalSndSegmentOpen,
-									  .segment_close = wal_segment_close),
-						   NULL);
+		XLogReaderAllocate(wal_segment_size, NULL, wal_segment_close);
 
 	if (!xlogreader)
 		ereport(ERROR,
@@ -806,10 +803,12 @@ StartReplication(StartReplicationCmd *cmd)
  * which has to do a plain sleep/busy loop, because the walsender's latch gets
  * set every time WAL is flushed.
  */
-static int
-logical_read_xlog_page(XLogReaderState *state, XLogRecPtr targetPagePtr, int reqLen,
-					   XLogRecPtr targetRecPtr, char *cur_page)
+static bool
+logical_read_xlog_page(XLogReaderState *state)
 {
+	XLogRecPtr		targetPagePtr = state->readPagePtr;
+	int				reqLen		  = state->reqLen;
+	char		   *cur_page	  = state->readBuf;
 	XLogRecPtr	flushptr;
 	int			count;
 	WALReadError errinfo;
@@ -826,7 +825,10 @@ logical_read_xlog_page(XLogReaderState *state, XLogRecPtr targetPagePtr, int req
 
 	/* fail if not (implies we are going to shut down) */
 	if (flushptr < targetPagePtr + reqLen)
-		return -1;
+	{
+		XLogReaderSetInputData(state, -1);
+		return false;
+	}
 
 	if (targetPagePtr + XLOG_BLCKSZ <= flushptr)
 		count = XLOG_BLCKSZ;	/* more than one block available */
@@ -834,7 +836,7 @@ logical_read_xlog_page(XLogReaderState *state, XLogRecPtr targetPagePtr, int req
 		count = flushptr - targetPagePtr;	/* part of the page available */
 
 	/* now actually read the data, we know it's there */
-	if (!WALRead(state,
+	if (!WALRead(state, WalSndSegmentOpen, wal_segment_close,
 				 cur_page,
 				 targetPagePtr,
 				 XLOG_BLCKSZ,
@@ -854,7 +856,8 @@ logical_read_xlog_page(XLogReaderState *state, XLogRecPtr targetPagePtr, int req
 	XLByteToSeg(targetPagePtr, segno, state->segcxt.ws_segsize);
 	CheckXLogRemoved(segno, state->seg.ws_tli);
 
-	return count;
+	XLogReaderSetInputData(state, count);
+	return true;
 }
 
 /*
@@ -1007,9 +1010,8 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 
 		ctx = CreateInitDecodingContext(cmd->plugin, NIL, need_full_snapshot,
 										InvalidXLogRecPtr,
-										XL_ROUTINE(.page_read = logical_read_xlog_page,
-												   .segment_open = WalSndSegmentOpen,
-												   .segment_close = wal_segment_close),
+										logical_read_xlog_page,
+										wal_segment_close,
 										WalSndPrepareWrite, WalSndWriteData,
 										WalSndUpdateProgress);
 
@@ -1167,9 +1169,8 @@ StartLogicalReplication(StartReplicationCmd *cmd)
 	 */
 	logical_decoding_ctx =
 		CreateDecodingContext(cmd->startpoint, cmd->options, false,
-							  XL_ROUTINE(.page_read = logical_read_xlog_page,
-										 .segment_open = WalSndSegmentOpen,
-										 .segment_close = wal_segment_close),
+							  logical_read_xlog_page,
+							  wal_segment_close,
 							  WalSndPrepareWrite, WalSndWriteData,
 							  WalSndUpdateProgress);
 	xlogreader = logical_decoding_ctx->reader;
@@ -2745,7 +2746,7 @@ XLogSendPhysical(void)
 	enlargeStringInfo(&output_message, nbytes);
 
 retry:
-	if (!WALRead(xlogreader,
+	if (!WALRead(xlogreader, WalSndSegmentOpen, wal_segment_close,
 				 &output_message.data[output_message.len],
 				 startptr,
 				 nbytes,
@@ -2843,7 +2844,12 @@ XLogSendLogical(void)
 	 */
 	WalSndCaughtUp = false;
 
-	record = XLogReadRecord(logical_decoding_ctx->reader, &errm);
+	while (XLogReadRecord(logical_decoding_ctx->reader, &record, &errm) ==
+		   XLREAD_NEED_DATA)
+	{
+		if (!logical_decoding_ctx->page_read(logical_decoding_ctx->reader))
+			break;
+	}
 
 	/* xlog record was invalid */
 	if (errm != NULL)