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help / color / mirror / Atom feedFrom: Anthonin Bonnefoy <[email protected]>
To: Mircea Cadariu <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Cc: Japin Li <[email protected]>
Subject: Re: Propagate XLogFindNextRecord error to callers
Date: Wed, 11 Feb 2026 09:43:51 +0100
Message-ID: <CAO6_XqrUzBT70kE20uHH=FWyfGJaTDMwqv++yNppdusywsG8-w@mail.gmail.com> (raw)
In-Reply-To: <[email protected]>
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On Mon, Feb 9, 2026 at 1:15 PM Mircea Cadariu <[email protected]> wrote:
> In XLogNextRecord, right before the above code, we do *errormsg = NULL. Should this be done also in XLogFindNextRecord in the patch?
>
> If so, what about even extracting a helper method which will be called from both places?
XLogReadRecord may already have consumed errormsg_deferred and set
errormsg. We can't set it to NULL, or that would erase a valid error
message.
A simplification would have been to remove processing the deferred
error processing from XLogNextRecord and leave it to
XLogFindNextRecord, but there are some calls to XLogNextRecord (like
in xlogprefetcher.c), so being able to get the error message when
calling XLogNextRecord is necessary.
> A nit for the commit message: Propage -> Propagate
Fixed
Attachments:
[application/octet-stream] v4-0001-Propagate-errormsg-to-XLogFindNextRecord-caller.patch (8.2K, 2-v4-0001-Propagate-errormsg-to-XLogFindNextRecord-caller.patch)
download | inline diff:
From 9bd8a70bb090f20182c9a21c26dcf803c0e61026 Mon Sep 17 00:00:00 2001
From: Anthonin Bonnefoy <[email protected]>
Date: Fri, 12 Dec 2025 09:56:00 +0100
Subject: Propagate errormsg to XLogFindNextRecord caller
Currently, XLogFindNextRecord errormsg is ignored and callers will only
output a generic 'could not find a valid record' message without
details.
Additionally, invalid page header won't go through XLogReadRecord,
leaving the error in state->errormsg_buf.
This patch propagates XLogFindNextRecord's error message to the callers
and displays it. In case of an invalid page header, the errormsg is
filled with errormsg_buf content.
---
contrib/pg_walinspect/pg_walinspect.c | 16 ++++++++++++----
src/backend/access/transam/xlogreader.c | 16 +++++++++++++---
src/backend/postmaster/walsummarizer.c | 17 ++++++++++++-----
src/bin/pg_waldump/pg_waldump.c | 12 +++++++++---
src/bin/pg_waldump/t/001_basic.pl | 23 +++++++++++++++++++++++
src/include/access/xlogreader.h | 2 +-
6 files changed, 70 insertions(+), 16 deletions(-)
diff --git a/contrib/pg_walinspect/pg_walinspect.c b/contrib/pg_walinspect/pg_walinspect.c
index 716a0922c6b..98dd31b69bb 100644
--- a/contrib/pg_walinspect/pg_walinspect.c
+++ b/contrib/pg_walinspect/pg_walinspect.c
@@ -97,6 +97,7 @@ InitXLogReaderState(XLogRecPtr lsn)
XLogReaderState *xlogreader;
ReadLocalXLogPageNoWaitPrivate *private_data;
XLogRecPtr first_valid_record;
+ char *errormsg;
/*
* Reading WAL below the first page of the first segments isn't allowed.
@@ -124,12 +125,19 @@ InitXLogReaderState(XLogRecPtr lsn)
errdetail("Failed while allocating a WAL reading processor.")));
/* first find a valid recptr to start from */
- first_valid_record = XLogFindNextRecord(xlogreader, lsn);
+ first_valid_record = XLogFindNextRecord(xlogreader, lsn, &errormsg);
if (!XLogRecPtrIsValid(first_valid_record))
- ereport(ERROR,
- errmsg("could not find a valid record after %X/%08X",
- LSN_FORMAT_ARGS(lsn)));
+ {
+ if (errormsg)
+ ereport(ERROR,
+ errmsg("could not find a valid record after %X/%08X: %s",
+ LSN_FORMAT_ARGS(lsn), errormsg));
+ else
+ ereport(ERROR,
+ errmsg("could not find a valid record after %X/%08X",
+ LSN_FORMAT_ARGS(lsn)));
+ }
return xlogreader;
}
diff --git a/src/backend/access/transam/xlogreader.c b/src/backend/access/transam/xlogreader.c
index 03ada8aa0c5..5a151bbf27f 100644
--- a/src/backend/access/transam/xlogreader.c
+++ b/src/backend/access/transam/xlogreader.c
@@ -1391,12 +1391,11 @@ XLogReaderResetError(XLogReaderState *state)
* XLogReadRecord() will read the next valid record.
*/
XLogRecPtr
-XLogFindNextRecord(XLogReaderState *state, XLogRecPtr RecPtr)
+XLogFindNextRecord(XLogReaderState *state, XLogRecPtr RecPtr, char **errormsg)
{
XLogRecPtr tmpRecPtr;
XLogRecPtr found = InvalidXLogRecPtr;
XLogPageHeader header;
- char *errormsg;
Assert(XLogRecPtrIsValid(RecPtr));
@@ -1481,7 +1480,7 @@ XLogFindNextRecord(XLogReaderState *state, XLogRecPtr RecPtr)
* or we just jumped over the remaining data of a continuation.
*/
XLogBeginRead(state, tmpRecPtr);
- while (XLogReadRecord(state, &errormsg) != NULL)
+ while (XLogReadRecord(state, errormsg) != NULL)
{
/* past the record we've found, break out */
if (RecPtr <= state->ReadRecPtr)
@@ -1496,6 +1495,17 @@ XLogFindNextRecord(XLogReaderState *state, XLogRecPtr RecPtr)
err:
XLogReaderInvalReadState(state);
+ /*
+ * we may have reported errors due to invalid WAL header, propagate the
+ * error message to the caller.
+ */
+ if (state->errormsg_deferred)
+ {
+ if (state->errormsg_buf[0] != '\0')
+ *errormsg = state->errormsg_buf;
+ state->errormsg_deferred = false;
+ }
+
return InvalidXLogRecPtr;
}
diff --git a/src/backend/postmaster/walsummarizer.c b/src/backend/postmaster/walsummarizer.c
index 2d8f57099fd..f50976a7f76 100644
--- a/src/backend/postmaster/walsummarizer.c
+++ b/src/backend/postmaster/walsummarizer.c
@@ -917,6 +917,7 @@ SummarizeWAL(TimeLineID tli, XLogRecPtr start_lsn, bool exact,
WalSummaryIO io;
BlockRefTable *brtab = CreateEmptyBlockRefTable();
bool fast_forward = true;
+ char *errormsg;
/* Initialize private data for xlogreader. */
private_data = palloc0_object(SummarizerReadLocalXLogPrivate);
@@ -968,7 +969,7 @@ SummarizeWAL(TimeLineID tli, XLogRecPtr start_lsn, bool exact,
}
else
{
- summary_start_lsn = XLogFindNextRecord(xlogreader, start_lsn);
+ summary_start_lsn = XLogFindNextRecord(xlogreader, start_lsn, &errormsg);
if (!XLogRecPtrIsValid(summary_start_lsn))
{
/*
@@ -997,9 +998,16 @@ SummarizeWAL(TimeLineID tli, XLogRecPtr start_lsn, bool exact,
switch_lsn = xlogreader->EndRecPtr;
}
else
- ereport(ERROR,
- errmsg("could not find a valid record after %X/%08X",
- LSN_FORMAT_ARGS(start_lsn)));
+ {
+ if (errormsg)
+ ereport(ERROR,
+ errmsg("could not find a valid record after %X/%08X: %s",
+ LSN_FORMAT_ARGS(start_lsn), errormsg));
+ else
+ ereport(ERROR,
+ errmsg("could not find a valid record after %X/%08X",
+ LSN_FORMAT_ARGS(start_lsn)));
+ }
}
/* We shouldn't go backward. */
@@ -1012,7 +1020,6 @@ SummarizeWAL(TimeLineID tli, XLogRecPtr start_lsn, bool exact,
while (1)
{
int block_id;
- char *errormsg;
XLogRecord *record;
uint8 rmid;
diff --git a/src/bin/pg_waldump/pg_waldump.c b/src/bin/pg_waldump/pg_waldump.c
index f3446385d6a..503ba76e559 100644
--- a/src/bin/pg_waldump/pg_waldump.c
+++ b/src/bin/pg_waldump/pg_waldump.c
@@ -1212,11 +1212,17 @@ main(int argc, char **argv)
pg_fatal("out of memory while allocating a WAL reading processor");
/* first find a valid recptr to start from */
- first_record = XLogFindNextRecord(xlogreader_state, private.startptr);
+ first_record = XLogFindNextRecord(xlogreader_state, private.startptr, &errormsg);
if (!XLogRecPtrIsValid(first_record))
- pg_fatal("could not find a valid record after %X/%08X",
- LSN_FORMAT_ARGS(private.startptr));
+ {
+ if (errormsg)
+ pg_fatal("could not find a valid record after %X/%08X: %s",
+ LSN_FORMAT_ARGS(private.startptr), errormsg);
+ else
+ pg_fatal("could not find a valid record after %X/%08X",
+ LSN_FORMAT_ARGS(private.startptr));
+ }
/*
* Display a message that we're skipping data if `from` wasn't a pointer
diff --git a/src/bin/pg_waldump/t/001_basic.pl b/src/bin/pg_waldump/t/001_basic.pl
index 5db5d20136f..1898848e418 100644
--- a/src/bin/pg_waldump/t/001_basic.pl
+++ b/src/bin/pg_waldump/t/001_basic.pl
@@ -6,6 +6,7 @@ use warnings FATAL => 'all';
use PostgreSQL::Test::Cluster;
use PostgreSQL::Test::Utils;
use Test::More;
+use File::Copy;
program_help_ok('pg_waldump');
program_version_ok('pg_waldump');
@@ -236,6 +237,28 @@ command_fails_like(
qr/error: error in WAL record at/,
'errors are shown with --quiet');
+# Wrong WAL version. We copy an existing wal file and set the
+# page's magic value to 0000.
+{
+ my $broken_wal_dir = PostgreSQL::Test::Utils::tempdir_short();
+ my $broken_wal = "$broken_wal_dir/$start_walfile";
+ copy($node->data_dir . '/pg_wal/' . $start_walfile, $broken_wal)
+ || die "copying $start_walfile $!";
+
+ my $fh;
+ open($fh, '+<', $broken_wal);
+ sysseek($fh, 0, 0)
+ or BAIL_OUT("sysseek failed: $!");
+ syswrite($fh, pack("S", 0))
+ or BAIL_OUT("syswrite failed: $!");
+ close($fh);
+
+ command_fails_like(
+ [ 'pg_waldump', $broken_wal ],
+ qr/invalid magic number 0000/i,
+ 'detailed error message shown for invalid WAL page magic'
+ );
+}
# Test for: Display a message that we're skipping data if `from`
# wasn't a pointer to the start of a record.
diff --git a/src/include/access/xlogreader.h b/src/include/access/xlogreader.h
index 80f1a548e08..567df33ac8e 100644
--- a/src/include/access/xlogreader.h
+++ b/src/include/access/xlogreader.h
@@ -342,7 +342,7 @@ extern void XLogReaderSetDecodeBuffer(XLogReaderState *state,
/* Position the XLogReader to given record */
extern void XLogBeginRead(XLogReaderState *state, XLogRecPtr RecPtr);
-extern XLogRecPtr XLogFindNextRecord(XLogReaderState *state, XLogRecPtr RecPtr);
+extern XLogRecPtr XLogFindNextRecord(XLogReaderState *state, XLogRecPtr RecPtr, char **errormsg);
/* Return values from XLogPageReadCB. */
typedef enum XLogPageReadResult
--
2.52.0
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To: [email protected]
Cc: [email protected], [email protected], [email protected]
Subject: Re: Propagate XLogFindNextRecord error to callers
In-Reply-To: <CAO6_XqrUzBT70kE20uHH=FWyfGJaTDMwqv++yNppdusywsG8-w@mail.gmail.com>
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