Revert recovery prefetching feature.

This set of commits has some bugs with known fixes, but at this late
stage in the release cycle it seems best to revert and resubmit next
time, along with some new automated test coverage for this whole area.

Commits reverted:

dc88460c: Doc: Review for "Optionally prefetch referenced data in recovery."
1d257577: Optionally prefetch referenced data in recovery.
f003d9f8: Add circular WAL decoding buffer.
323cbe7c: Remove read_page callback from XLogReader.

Remove the new GUC group WAL_RECOVERY recently added by a55a9847, as the
corresponding section of config.sgml is now reverted.

Discussion: https://postgr.es/m/CAOuzzgrn7iKnFRsB4MHp3UisEQAGgZMbk_ViTN4HV4-Ksq8zCg%40mail.gmail.com

1 files changed, 15 insertions, 34 deletions

diff --git a/src/backend/access/transam/xlogutils.c b/src/backend/access/transam/xlogutils.c
index 4d5c9bb08f5..d17d660f460 100644
--- a/src/backend/access/transam/xlogutils.c
+++ b/src/backend/access/transam/xlogutils.c
@@ -335,13 +335,11 @@ XLogReadBufferForRedoExtended(XLogReaderState *record,
 	RelFileNode rnode;
 	ForkNumber	forknum;
 	BlockNumber blkno;
-	Buffer		recent_buffer;
 	Page		page;
 	bool		zeromode;
 	bool		willinit;
 
-	if (!XLogRecGetRecentBuffer(record, block_id, &rnode, &forknum, &blkno,
-								&recent_buffer))
+	if (!XLogRecGetBlockTag(record, block_id, &rnode, &forknum, &blkno))
 	{
 		/* Caller specified a bogus block_id */
 		elog(PANIC, "failed to locate backup block with ID %d", block_id);
@@ -352,7 +350,7 @@ XLogReadBufferForRedoExtended(XLogReaderState *record,
 	 * going to initialize it. And vice versa.
 	 */
 	zeromode = (mode == RBM_ZERO_AND_LOCK || mode == RBM_ZERO_AND_CLEANUP_LOCK);
-	willinit = (record->record->blocks[block_id].flags & BKPBLOCK_WILL_INIT) != 0;
+	willinit = (record->blocks[block_id].flags & BKPBLOCK_WILL_INIT) != 0;
 	if (willinit && !zeromode)
 		elog(PANIC, "block with WILL_INIT flag in WAL record must be zeroed by redo routine");
 	if (!willinit && zeromode)
@@ -363,8 +361,7 @@ XLogReadBufferForRedoExtended(XLogReaderState *record,
 	{
 		Assert(XLogRecHasBlockImage(record, block_id));
 		*buf = XLogReadBufferExtended(rnode, forknum, blkno,
-									  get_cleanup_lock ? RBM_ZERO_AND_CLEANUP_LOCK : RBM_ZERO_AND_LOCK,
-									  recent_buffer);
+									  get_cleanup_lock ? RBM_ZERO_AND_CLEANUP_LOCK : RBM_ZERO_AND_LOCK);
 		page = BufferGetPage(*buf);
 		if (!RestoreBlockImage(record, block_id, page))
 			elog(ERROR, "failed to restore block image");
@@ -393,8 +390,7 @@ XLogReadBufferForRedoExtended(XLogReaderState *record,
 	}
 	else
 	{
-		*buf = XLogReadBufferExtended(rnode, forknum, blkno, mode,
-									  recent_buffer);
+		*buf = XLogReadBufferExtended(rnode, forknum, blkno, mode);
 		if (BufferIsValid(*buf))
 		{
 			if (mode != RBM_ZERO_AND_LOCK && mode != RBM_ZERO_AND_CLEANUP_LOCK)
@@ -441,8 +437,7 @@ XLogReadBufferForRedoExtended(XLogReaderState *record,
  */
 Buffer
 XLogReadBufferExtended(RelFileNode rnode, ForkNumber forknum,
-					   BlockNumber blkno, ReadBufferMode mode,
-					   Buffer recent_buffer)
+					   BlockNumber blkno, ReadBufferMode mode)
 {
 	BlockNumber lastblock;
 	Buffer		buffer;
@@ -450,15 +445,6 @@ XLogReadBufferExtended(RelFileNode rnode, ForkNumber forknum,
 
 	Assert(blkno != P_NEW);
 
-	/* Do we have a clue where the buffer might be already? */
-	if (BufferIsValid(recent_buffer) &&
-		mode == RBM_NORMAL &&
-		ReadRecentBuffer(rnode, forknum, blkno, recent_buffer))
-	{
-		buffer = recent_buffer;
-		goto recent_buffer_fast_path;
-	}
-
 	/* Open the relation at smgr level */
 	smgr = smgropen(rnode, InvalidBackendId);
 
@@ -517,7 +503,6 @@ XLogReadBufferExtended(RelFileNode rnode, ForkNumber forknum,
 		}
 	}
 
-recent_buffer_fast_path:
 	if (mode == RBM_NORMAL)
 	{
 		/* check that page has been initialized */
@@ -701,7 +686,8 @@ XLogTruncateRelation(RelFileNode rnode, ForkNumber forkNum,
 void
 XLogReadDetermineTimeline(XLogReaderState *state, XLogRecPtr wantPage, uint32 wantLength)
 {
-	const XLogRecPtr lastReadPage = state->readPagePtr;
+	const XLogRecPtr lastReadPage = (state->seg.ws_segno *
+									 state->segcxt.ws_segsize + state->segoff);
 
 	Assert(wantPage != InvalidXLogRecPtr && wantPage % XLOG_BLCKSZ == 0);
 	Assert(wantLength <= XLOG_BLCKSZ);
@@ -716,7 +702,7 @@ XLogReadDetermineTimeline(XLogReaderState *state, XLogRecPtr wantPage, uint32 wa
 	 * current TLI has since become historical.
 	 */
 	if (lastReadPage == wantPage &&
-		state->page_verified &&
+		state->readLen != 0 &&
 		lastReadPage + state->readLen >= wantPage + Min(wantLength, XLOG_BLCKSZ - 1))
 		return;
 
@@ -838,12 +824,10 @@ wal_segment_close(XLogReaderState *state)
  * exists for normal backends, so we have to do a check/sleep/repeat style of
  * loop for now.
  */
-bool
-read_local_xlog_page(XLogReaderState *state)
+int
+read_local_xlog_page(XLogReaderState *state, XLogRecPtr targetPagePtr,
+					 int reqLen, XLogRecPtr targetRecPtr, char *cur_page)
 {
-	XLogRecPtr	targetPagePtr = state->readPagePtr;
-	int			reqLen		  = state->reqLen;
-	char	   *cur_page	  = state->readBuf;
 	XLogRecPtr	read_upto,
 				loc;
 	TimeLineID	tli;
@@ -942,8 +926,7 @@ read_local_xlog_page(XLogReaderState *state)
 	else if (targetPagePtr + reqLen > read_upto)
 	{
 		/* not enough data there */
-		XLogReaderSetInputData(state,  -1);
-		return false;
+		return -1;
 	}
 	else
 	{
@@ -956,14 +939,12 @@ read_local_xlog_page(XLogReaderState *state)
 	 * 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, wal_segment_open, wal_segment_close,
-				 cur_page, targetPagePtr, XLOG_BLCKSZ, tli, &errinfo))
+	if (!WALRead(state, cur_page, targetPagePtr, XLOG_BLCKSZ, tli,
+				 &errinfo))
 		WALReadRaiseError(&errinfo);
 
 	/* number of valid bytes in the buffer */
-	state->readPagePtr = targetPagePtr;
-	XLogReaderSetInputData(state, count);
-	return true;
+	return count;
 }
 
 /*