Subject: [PATCH v12] Make End-Of-Recovery error less scary

From: Kyotaro Horiguchi <[email-masked]>
Date: Fri, 28 Feb 2020 15:52:58 +0900

When recovery in any type ends, we see a bit scary error message like
"invalid record length" that suggests something serious is
happening. Actually if recovery meets a record with length = 0, that
usually means it finished applying all available WAL records.

Make this message less scary as "reached end of WAL". Instead, raise
the error level for other kind of WAL failure to WARNING.
---
 src/backend/access/transam/xlog.c         |  92 +++++++++++++-----
 src/backend/access/transam/xlogreader.c   |  78 ++++++++++++++++
 src/backend/replication/walreceiver.c     |   7 +-
 src/bin/pg_waldump/pg_waldump.c           |  13 ++-
 src/include/access/xlogreader.h           |   1 +
 src/test/recovery/t/011_crash_recovery.pl | 108 +++++++++++++++++++++-
 6 files changed, 268 insertions(+), 31 deletions(-)

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 958220c495..bf1d40e7cb 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -4480,6 +4480,7 @@ ReadRecord(XLogReaderState *xlogreader, int emode,
 	for (;;)
 	{
 		char	   *errormsg;
+		XLogRecPtr	ErrRecPtr = InvalidXLogRecPtr;
 
 		record = XLogReadRecord(xlogreader, &errormsg);
 		if (record == NULL)
@@ -4495,6 +4496,18 @@ ReadRecord(XLogReaderState *xlogreader, int emode,
 			{
 				abortedRecPtr = xlogreader->abortedRecPtr;
 				missingContrecPtr = xlogreader->missingContrecPtr;
+				ErrRecPtr = abortedRecPtr;
+			}
+			else
+			{
+				/*
+				 * EndRecPtr is the LSN we tried to read but failed. In the
+				 * case of decoding error, it is at the end of the failed
+				 * record but we don't have a means for now to know EndRecPtr
+				 * is pointing to which of the beginning or ending of the
+				 * failed record.
+				 */
+				ErrRecPtr = xlogreader->EndRecPtr;
 			}
 
 			if (readFile >= 0)
@@ -4504,13 +4517,16 @@ ReadRecord(XLogReaderState *xlogreader, int emode,
 			}
 
 			/*
-			 * We only end up here without a message when XLogPageRead()
-			 * failed - in that case we already logged something. In
-			 * StandbyMode that only happens if we have been triggered, so we
-			 * shouldn't loop anymore in that case.
+			 * We only end up here without a message when XLogPageRead() failed
+			 * in that case we already logged something, or just met end-of-WAL
+			 * conditions. In StandbyMode that only happens if we have been
+			 * triggered, so we shouldn't loop anymore in that case. When
+			 * EndOfWAL is true, we don't emit that error if any immediately
+			 * and instead will show it as a part of a decent end-of-wal
+			 * message later.
 			 */
-			if (errormsg)
-				ereport(emode_for_corrupt_record(emode, xlogreader->EndRecPtr),
+			if (!xlogreader->EndOfWAL && errormsg)
+				ereport(emode_for_corrupt_record(emode, ErrRecPtr),
 						(errmsg_internal("%s", errormsg) /* already translated */ ));
 		}
 
@@ -4541,11 +4557,14 @@ ReadRecord(XLogReaderState *xlogreader, int emode,
 			/* Great, got a record */
 			return record;
 		}
-		else
+
+		Assert(ErrRecPtr != InvalidXLogRecPtr);
+
+		/* No valid record available from this source */
+		lastSourceFailed = true;
+
+		if (!fetching_ckpt)
 		{
-			/* No valid record available from this source */
-			lastSourceFailed = true;
-
 			/*
 			 * If archive recovery was requested, but we were still doing
 			 * crash recovery, switch to archive recovery and retry using the
@@ -4558,11 +4577,17 @@ ReadRecord(XLogReaderState *xlogreader, int emode,
 			 * we'd have no idea how far we'd have to replay to reach
 			 * consistency.  So err on the safe side and give up.
 			 */
-			if (!InArchiveRecovery && ArchiveRecoveryRequested &&
-				!fetching_ckpt)
+			if (!InArchiveRecovery && ArchiveRecoveryRequested)
 			{
+				/*
+				 * We don't report this as LOG, since we don't stop recovery
+				 * here
+				 */
 				ereport(DEBUG1,
-						(errmsg_internal("reached end of WAL in pg_wal, entering archive recovery")));
+						(errmsg_internal("reached end of WAL at %X/%X on timeline %u in %s during crash recovery, entering archive recovery",
+										 LSN_FORMAT_ARGS(ErrRecPtr),
+										 replayTLI,
+										 xlogSourceNames[currentSource])));
 				InArchiveRecovery = true;
 				if (StandbyModeRequested)
 					StandbyMode = true;
@@ -4610,12 +4635,24 @@ ReadRecord(XLogReaderState *xlogreader, int emode,
 				continue;
 			}
 
-			/* In standby mode, loop back to retry. Otherwise, give up. */
-			if (StandbyMode && !CheckForStandbyTrigger())
-				continue;
-			else
-				return NULL;
+			/*
+			 * recovery ended.
+			 *
+			 * Emit a decent message if we met end-of-WAL. Otherwise we should
+			 * have already emitted an error message.
+			 */
+			if (xlogreader->EndOfWAL)
+				ereport(LOG,
+						(errmsg("reached end of WAL at %X/%X on timeline %u",
+								LSN_FORMAT_ARGS(ErrRecPtr), replayTLI),
+						 (errormsg ? errdetail_internal("%s", errormsg) : 0)));
 		}
+
+		/* In standby mode, loop back to retry. Otherwise, give up. */
+		if (StandbyMode && !CheckForStandbyTrigger())
+			continue;
+		else
+			return NULL;
 	}
 }
 
@@ -7544,7 +7581,7 @@ StartupXLOG(void)
 		else
 		{
 			/* just have to read next record after CheckPoint */
-			record = ReadRecord(xlogreader, LOG, false, replayTLI);
+			record = ReadRecord(xlogreader, WARNING, false, replayTLI);
 		}
 
 		if (record != NULL)
@@ -7782,7 +7819,7 @@ StartupXLOG(void)
 				}
 
 				/* Else, try to fetch the next WAL record */
-				record = ReadRecord(xlogreader, LOG, false, replayTLI);
+				record = ReadRecord(xlogreader, WARNING, false, replayTLI);
 			} while (record != NULL);
 
 			/*
@@ -7842,13 +7879,20 @@ StartupXLOG(void)
 
 			InRedo = false;
 		}
-		else
+		else if (xlogreader->EndOfWAL)
 		{
 			/* there are no WAL records following the checkpoint */
 			ereport(LOG,
 					(errmsg("redo is not required")));
 
 		}
+		else
+		{
+			/* broken record found */
+			ereport(WARNING,
+					(errmsg("redo is skipped"),
+					 errhint("This suggests WAL file corruption. You might need to check the database.")));
+		}
 
 		/*
 		 * This check is intentionally after the above log messages that
@@ -12434,12 +12478,14 @@ retry:
 										 private->replayTLI,
 										 xlogreader->EndRecPtr))
 		{
+			Assert(!StandbyMode);
+
 			if (readFile >= 0)
 				close(readFile);
 			readFile = -1;
 			readLen = 0;
 			readSource = XLOG_FROM_ANY;
-
+			xlogreader->EndOfWAL = true;
 			return -1;
 		}
 	}
@@ -13097,7 +13143,7 @@ emode_for_corrupt_record(int emode, XLogRecPtr RecPtr)
 {
 	static XLogRecPtr lastComplaint = 0;
 
-	if (readSource == XLOG_FROM_PG_WAL && emode == LOG)
+	if (currentSource == XLOG_FROM_PG_WAL && emode <= WARNING)
 	{
 		if (RecPtr == lastComplaint)
 			emode = DEBUG1;
diff --git a/src/backend/access/transam/xlogreader.c b/src/backend/access/transam/xlogreader.c
index 35029cf97d..22982c4de7 100644
--- a/src/backend/access/transam/xlogreader.c
+++ b/src/backend/access/transam/xlogreader.c
@@ -121,6 +121,7 @@ XLogReaderAllocate(int wal_segment_size, const char *waldir,
 		pfree(state);
 		return NULL;
 	}
+	state->EndOfWAL = false;
 	state->errormsg_buf[0] = '\0';
 
 	/*
@@ -292,6 +293,7 @@ XLogReadRecord(XLogReaderState *state, char **errormsg)
 	/* reset error state */
 	*errormsg = NULL;
 	state->errormsg_buf[0] = '\0';
+	state->EndOfWAL = false;
 
 	ResetDecoder(state);
 	state->abortedRecPtr = InvalidXLogRecPtr;
@@ -588,6 +590,15 @@ err:
 		 */
 		state->abortedRecPtr = RecPtr;
 		state->missingContrecPtr = targetPagePtr;
+
+		/*
+		 * If the message is not set yet, that means we failed to load the
+		 * page for the record.  Otherwise do not hide the existing message.
+		 */
+		if (state->errormsg_buf[0] == '\0')
+			report_invalid_record(state,
+								  "missing contrecord at %X/%X",
+								  LSN_FORMAT_ARGS(RecPtr));
 	}
 
 	/*
@@ -730,6 +741,40 @@ ValidXLogRecordHeader(XLogReaderState *state, XLogRecPtr RecPtr,
 					  XLogRecPtr PrevRecPtr, XLogRecord *record,
 					  bool randAccess)
 {
+	if (record->xl_tot_len == 0)
+	{
+		/*
+		 * We are almost sure reaching the end of WAL, make sure that the
+		 * whole page after the record is filled with zeroes.
+		 */
+		char	   *p;
+		char	   *pe;
+
+		/* scan from the beginning of the record to the end of block */
+		p = (char *) record;
+		pe = p + XLOG_BLCKSZ - (RecPtr & (XLOG_BLCKSZ - 1));
+
+		while (*p == 0 && p < pe)
+			p++;
+
+		if (p == pe)
+		{
+			/*
+			 * The page after the record is completely zeroed. That suggests
+			 * we don't have a record after this point. We don't bother
+			 * checking the pages after since they are not zeroed in the case
+			 * of recycled segments.
+			 */
+			report_invalid_record(state, "empty record at %X/%X",
+								  LSN_FORMAT_ARGS(RecPtr));
+
+			/* notify end-of-wal to callers */
+			state->EndOfWAL = true;
+			return false;
+		}
+
+		/* The same condition will be caught as invalid record length */
+	}
 	if (record->xl_tot_len < SizeOfXLogRecord)
 	{
 		report_invalid_record(state,
@@ -836,6 +881,31 @@ XLogReaderValidatePageHeader(XLogReaderState *state, XLogRecPtr recptr,
 
 	XLogSegNoOffsetToRecPtr(segno, offset, state->segcxt.ws_segsize, recaddr);
 
+	StaticAssertStmt(XLOG_PAGE_MAGIC != 0, "XLOG_PAGE_MAGIC is zero");
+
+	if (hdr->xlp_magic == 0)
+	{
+		/* Regard an empty page as End-Of-WAL */
+		int			i;
+
+		for (i = 0; i < XLOG_BLCKSZ && phdr[i] == 0; i++);
+		if (i == XLOG_BLCKSZ)
+		{
+			char		fname[MAXFNAMELEN];
+
+			XLogFileName(fname, state->seg.ws_tli, segno,
+						 state->segcxt.ws_segsize);
+
+			report_invalid_record(state,
+								  "empty page in log segment %s, offset %u",
+								  fname,
+								  offset);
+			state->EndOfWAL = true;
+			return false;
+		}
+
+		/* The same condition will be caught as invalid magic number */
+	}
 	if (hdr->xlp_magic != XLOG_PAGE_MAGIC)
 	{
 		char		fname[MAXFNAMELEN];
@@ -921,6 +991,14 @@ XLogReaderValidatePageHeader(XLogReaderState *state, XLogRecPtr recptr,
 							  LSN_FORMAT_ARGS(hdr->xlp_pageaddr),
 							  fname,
 							  offset);
+
+		/*
+		 * If the page address is less than expected we assume it is an unused
+		 * page in a recycled segment.
+		 */
+		if (hdr->xlp_pageaddr < recaddr)
+			state->EndOfWAL = true;
+
 		return false;
 	}
 
diff --git a/src/backend/replication/walreceiver.c b/src/backend/replication/walreceiver.c
index b39fce8c23..1a7a692bc0 100644
--- a/src/backend/replication/walreceiver.c
+++ b/src/backend/replication/walreceiver.c
@@ -471,10 +471,9 @@ WalReceiverMain(void)
 						else if (len < 0)
 						{
 							ereport(LOG,
-									(errmsg("replication terminated by primary server"),
-									 errdetail("End of WAL reached on timeline %u at %X/%X.",
-											   startpointTLI,
-											   LSN_FORMAT_ARGS(LogstreamResult.Write))));
+									(errmsg("replication terminated by primary server at %X/%X on timeline %u.",
+											LSN_FORMAT_ARGS(LogstreamResult.Write),
+											startpointTLI)));
 							endofwal = true;
 							break;
 						}
diff --git a/src/bin/pg_waldump/pg_waldump.c b/src/bin/pg_waldump/pg_waldump.c
index a6251e1a96..3745e76488 100644
--- a/src/bin/pg_waldump/pg_waldump.c
+++ b/src/bin/pg_waldump/pg_waldump.c
@@ -1176,9 +1176,16 @@ main(int argc, char **argv)
 		exit(0);
 
 	if (errormsg)
-		fatal_error("error in WAL record at %X/%X: %s",
-					LSN_FORMAT_ARGS(xlogreader_state->ReadRecPtr),
-					errormsg);
+	{
+		if (xlogreader_state->EndOfWAL)
+			pg_log_info("end of WAL at %X/%X: %s",
+						LSN_FORMAT_ARGS(xlogreader_state->EndRecPtr),
+						errormsg);
+		else
+			fatal_error("error in WAL record at %X/%X: %s",
+						LSN_FORMAT_ARGS(xlogreader_state->EndRecPtr),
+						errormsg);
+	}
 
 	XLogReaderFree(xlogreader_state);
 
diff --git a/src/include/access/xlogreader.h b/src/include/access/xlogreader.h
index 477f0efe26..7b314ef10e 100644
--- a/src/include/access/xlogreader.h
+++ b/src/include/access/xlogreader.h
@@ -174,6 +174,7 @@ struct XLogReaderState
 	 */
 	XLogRecPtr	ReadRecPtr;		/* start of last record read */
 	XLogRecPtr	EndRecPtr;		/* end+1 of last record read */
+	bool		EndOfWAL;		/* was the last attempt EOW? */
 
 	/*
 	 * Set at the end of recovery: the start point of a partial record at the
diff --git a/src/test/recovery/t/011_crash_recovery.pl b/src/test/recovery/t/011_crash_recovery.pl
index 3892aba3e5..1d7476c309 100644
--- a/src/test/recovery/t/011_crash_recovery.pl
+++ b/src/test/recovery/t/011_crash_recovery.pl
@@ -10,9 +10,11 @@ use PostgreSQL::Test::Cluster;
 use PostgreSQL::Test::Utils;
 use Test::More;
 use Config;
+use IPC::Run;
 
-plan tests => 3;
+plan tests => 11;
 
+my $reached_eow_pat = "reached end of WAL at ";
 my $node = PostgreSQL::Test::Cluster->new('primary');
 $node->init(allows_streaming => 1);
 $node->start;
@@ -50,7 +52,15 @@ is($node->safe_psql('postgres', qq[SELECT pg_xact_status('$xid');]),
 
 # Crash and restart the postmaster
 $node->stop('immediate');
+my $logstart = get_log_size($node);
 $node->start;
+my $max_attempts = 360;
+while ($max_attempts-- >= 0)
+{
+	last if (find_in_log($node, $reached_eow_pat, $logstart));
+	sleep 0.5;
+}
+ok ($max_attempts >= 0, "end-of-wal is logged");
 
 # Make sure we really got a new xid
 cmp_ok($node->safe_psql('postgres', 'SELECT pg_current_xact_id()'),
@@ -62,3 +72,99 @@ is($node->safe_psql('postgres', qq[SELECT pg_xact_status('$xid');]),
 
 $stdin .= "\\q\n";
 $tx->finish;    # wait for psql to quit gracefully
+
+my $segsize = $node->safe_psql('postgres',
+	   qq[SELECT setting FROM pg_settings WHERE name = 'wal_segment_size';]);
+
+# make sure no records afterwards go to the next segment
+$node->safe_psql('postgres', qq[
+				 SELECT pg_switch_wal();
+				 CHECKPOINT;
+				 CREATE TABLE t();
+]);
+$node->stop('immediate');
+
+# identify REDO WAL file
+my $cmd = "pg_controldata -D " . $node->data_dir();
+$cmd = ['pg_controldata', '-D', $node->data_dir()];
+$stdout = '';
+$stderr = '';
+IPC::Run::run $cmd, '>', \$stdout, '2>', \$stderr;
+ok($stdout =~ /^Latest checkpoint's REDO WAL file:[ \t] *(.+)$/m,
+   "checkpoint file is identified");
+my $chkptfile = $1;
+
+# identify the last record
+my $walfile = $node->data_dir() . "/pg_wal/$chkptfile";
+$cmd = ['pg_waldump', $walfile];
+$stdout = '';
+$stderr = '';
+my $lastrec;
+IPC::Run::run $cmd, '>', \$stdout, '2>', \$stderr;
+foreach my $l (split(/\r?\n/, $stdout))
+{
+	$lastrec = $l;
+}
+ok(defined $lastrec, "last WAL record is extracted");
+ok($stderr =~ /end of WAL at ([0-9A-F\/]+): .* at \g1/,
+   "pg_waldump emits the correct ending message");
+
+# read the last record LSN excluding leading zeroes
+ok ($lastrec =~ /, lsn: 0\/0*([1-9A-F][0-9A-F]+),/,
+	"LSN of the last record identified");
+my $lastlsn = $1;
+
+# corrupt the last record
+my $offset = hex($lastlsn) % $segsize;
+open(my $segf, '+<', $walfile) or die "failed to open $walfile\n";
+seek($segf, $offset, 0);  # halfway break the last record
+print $segf "\0\0\0\0";
+close($segf);
+
+# pg_waldump complains about the corrupted record
+$stdout = '';
+$stderr = '';
+IPC::Run::run $cmd, '>', \$stdout, '2>', \$stderr;
+ok($stderr =~ /fatal: error in WAL record at 0\/$lastlsn: .* at 0\/$lastlsn/,
+   "pg_waldump emits the correct error message");
+
+# also server complains
+$logstart = get_log_size($node);
+$node->start;
+$max_attempts = 360;
+while ($max_attempts-- >= 0)
+{
+	last if (find_in_log($node, "WARNING:  invalid record length at 0/$lastlsn: wanted [0-9]+, got 0",
+						 $logstart));
+	sleep 0.5;
+}
+ok($max_attempts >= 0, "header error is logged at $lastlsn");
+
+# no end-of-wal message should be seen this time
+ok(!find_in_log($node, $reached_eow_pat, $logstart),
+   "false log message is not emitted");
+
+$node->stop('immediate');
+
+#### helper routines
+# return the size of logfile of $node in bytes
+sub get_log_size
+{
+	my ($node) = @_;
+
+	return (stat $node->logfile)[7];
+}
+
+# find $pat in logfile of $node after $off-th byte
+sub find_in_log
+{
+	my ($node, $pat, $off) = @_;
+
+	$off = 0 unless defined $off;
+	my $log = PostgreSQL::Test::Utils::slurp_file($node->logfile);
+	return 0 if (length($log) <= $off);
+
+	$log = substr($log, $off);
+
+	return $log =~ m/$pat/;
+}
-- 
2.27.0

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