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 <horiguchi.kyotaro@lab.ntt.co.jp>
Author: Heikki Linnakangas <hlinnaka@iki.fi> (parts of earlier version)
Reviewed-by: Antonin Houska <ah@cybertec.at>
Reviewed-by: Alvaro Herrera <alvherre@2ndquadrant.com>
Reviewed-by: Takashi Menjo <takashi.menjo@gmail.com>
Reviewed-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Thomas Munro <thomas.munro@gmail.com>
Discussion: https://postgr.es/m/20190418.210257.43726183.horiguchi.kyotaro%40lab.ntt.co.jp

1 files changed, 14 insertions, 10 deletions

diff --git a/src/backend/access/transam/xlogutils.c b/src/backend/access/transam/xlogutils.c
index d17d660f460..e5de26dce54 100644
--- a/src/backend/access/transam/xlogutils.c
+++ b/src/backend/access/transam/xlogutils.c
@@ -686,8 +686,7 @@ XLogTruncateRelation(RelFileNode rnode, ForkNumber forkNum,
 void
 XLogReadDetermineTimeline(XLogReaderState *state, XLogRecPtr wantPage, uint32 wantLength)
 {
-	const XLogRecPtr lastReadPage = (state->seg.ws_segno *
-									 state->segcxt.ws_segsize + state->segoff);
+	const XLogRecPtr lastReadPage = state->readPagePtr;
 
 	Assert(wantPage != InvalidXLogRecPtr && wantPage % XLOG_BLCKSZ == 0);
 	Assert(wantLength <= XLOG_BLCKSZ);
@@ -702,7 +701,7 @@ XLogReadDetermineTimeline(XLogReaderState *state, XLogRecPtr wantPage, uint32 wa
 	 * current TLI has since become historical.
 	 */
 	if (lastReadPage == wantPage &&
-		state->readLen != 0 &&
+		state->page_verified &&
 		lastReadPage + state->readLen >= wantPage + Min(wantLength, XLOG_BLCKSZ - 1))
 		return;
 
@@ -824,10 +823,12 @@ wal_segment_close(XLogReaderState *state)
  * exists for normal backends, so we have to do a check/sleep/repeat style of
  * loop for now.
  */
-int
-read_local_xlog_page(XLogReaderState *state, XLogRecPtr targetPagePtr,
-					 int reqLen, XLogRecPtr targetRecPtr, char *cur_page)
+bool
+read_local_xlog_page(XLogReaderState *state)
 {
+	XLogRecPtr	targetPagePtr = state->readPagePtr;
+	int			reqLen		  = state->reqLen;
+	char	   *cur_page	  = state->readBuf;
 	XLogRecPtr	read_upto,
 				loc;
 	TimeLineID	tli;
@@ -926,7 +927,8 @@ read_local_xlog_page(XLogReaderState *state, XLogRecPtr targetPagePtr,
 	else if (targetPagePtr + reqLen > read_upto)
 	{
 		/* not enough data there */
-		return -1;
+		XLogReaderSetInputData(state,  -1);
+		return false;
 	}
 	else
 	{
@@ -939,12 +941,14 @@ read_local_xlog_page(XLogReaderState *state, XLogRecPtr targetPagePtr,
 	 * as 'count', read the whole page anyway. It's guaranteed to be
 	 * zero-padded up to the page boundary if it's incomplete.
 	 */
-	if (!WALRead(state, cur_page, targetPagePtr, XLOG_BLCKSZ, tli,
-				 &errinfo))
+	if (!WALRead(state, wal_segment_open, wal_segment_close,
+				 cur_page, targetPagePtr, XLOG_BLCKSZ, tli, &errinfo))
 		WALReadRaiseError(&errinfo);
 
 	/* number of valid bytes in the buffer */
-	return count;
+	state->readPagePtr = targetPagePtr;
+	XLogReaderSetInputData(state, count);
+	return true;
 }
 
 /*