Hello,
At Wed, 6 Sep 2017 12:23:53 -0700, Andres Freund <and...@anarazel.de> wrote in
<20170906192353.ufp2dq7wm5fd6...@alap3.anarazel.de>
> On 2017-09-06 17:36:02 +0900, Kyotaro HORIGUCHI wrote:
> > The problem is that the current ReadRecord needs the first one of
> > a series of continuation records from the same source with the
> > other part, the master in the case.
>
> What's the problem with that? We can easily keep track of the beginning
> of a record, and only confirm the address before that.
After failure while reading a record locally, ReadRecored tries
streaming to read from the beginning of a record, which is not on
the master, then retry locally and.. This loops forever.
> > A (or the) solution closed in the standby side is allowing to
> > read a seris of continuation records from muliple sources.
>
> I'm not following. All we need to use is the beginning of the relevant
> records, that's easy enough to keep track of. We don't need to read the
> WAL or anything.
The beginning is already tracked and nothing more to do.
I reconsider that way and found that it doesn't need such
destructive refactoring.
The first *problem* was WaitForWALToBecomeAvaialble requests the
beginning of a record, which is not on the page the function has
been told to fetch. Still tliRecPtr is required to determine the
TLI to request, it should request RecPtr to be streamed.
The rest to do is let XLogPageRead retry other sources
immediately. To do this I made ValidXLogPageHeader@xlogreader.c
public (and renamed to XLogReaderValidatePageHeader).
The patch attached fixes the problem and passes recovery
tests. However, the test for this problem is not added. It needs
to go to the last page in a segment then put a record continues
to the next segment, then kill the standby after receiving the
previous segment but before receiving the whole record.
regards,
--
Kyotaro Horiguchi
NTT Open Source Software Center
>From 8932a390bd3d1acfe5722bc62f42fc7e381ca617 Mon Sep 17 00:00:00 2001
From: Kyotaro Horiguchi <horiguchi.kyot...@lab.ntt.co.jp>
Date: Thu, 7 Sep 2017 12:14:55 +0900
Subject: [PATCH 1/2] Allow switch WAL source midst of record.
The corrent recovery machinary assumes the whole of a record is
avaiable from single source. This prevents a standby from restarting
under a certain condition. This patch allows source switching during
reading a series of continuation records.
---
src/backend/access/transam/xlog.c | 7 ++++++-
src/backend/access/transam/xlogreader.c | 12 +++++-------
src/include/access/xlogreader.h | 5 +++++
3 files changed, 16 insertions(+), 8 deletions(-)
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index df4843f..eef3a97 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -11566,6 +11566,11 @@ retry:
Assert(reqLen <= readLen);
*readTLI = curFileTLI;
+
+ if (!XLogReaderValidatePageHeader(xlogreader, targetPagePtr,
+ (XLogPageHeader) readBuf))
+ goto next_record_is_invalid;
+
return readLen;
next_record_is_invalid:
@@ -11700,7 +11705,7 @@ WaitForWALToBecomeAvailable(XLogRecPtr RecPtr, bool randAccess,
}
else
{
- ptr = tliRecPtr;
+ ptr = RecPtr;
tli = tliOfPointInHistory(tliRecPtr, expectedTLEs);
if (curFileTLI > 0 && tli < curFileTLI)
diff --git a/src/backend/access/transam/xlogreader.c b/src/backend/access/transam/xlogreader.c
index 0781a7b..aa05e3f 100644
--- a/src/backend/access/transam/xlogreader.c
+++ b/src/backend/access/transam/xlogreader.c
@@ -27,8 +27,6 @@
static bool allocate_recordbuf(XLogReaderState *state, uint32 reclength);
-static bool ValidXLogPageHeader(XLogReaderState *state, XLogRecPtr recptr,
- XLogPageHeader hdr);
static bool ValidXLogRecordHeader(XLogReaderState *state, XLogRecPtr RecPtr,
XLogRecPtr PrevRecPtr, XLogRecord *record, bool randAccess);
static bool ValidXLogRecord(XLogReaderState *state, XLogRecord *record,
@@ -545,7 +543,7 @@ ReadPageInternal(XLogReaderState *state, XLogRecPtr pageptr, int reqLen)
hdr = (XLogPageHeader) state->readBuf;
- if (!ValidXLogPageHeader(state, targetSegmentPtr, hdr))
+ if (!XLogReaderValidatePageHeader(state, targetSegmentPtr, hdr))
goto err;
}
@@ -582,7 +580,7 @@ ReadPageInternal(XLogReaderState *state, XLogRecPtr pageptr, int reqLen)
/*
* Now that we know we have the full header, validate it.
*/
- if (!ValidXLogPageHeader(state, pageptr, hdr))
+ if (!XLogReaderValidatePageHeader(state, pageptr, hdr))
goto err;
/* update read state information */
@@ -709,9 +707,9 @@ ValidXLogRecord(XLogReaderState *state, XLogRecord *record, XLogRecPtr recptr)
/*
* Validate a page header
*/
-static bool
-ValidXLogPageHeader(XLogReaderState *state, XLogRecPtr recptr,
- XLogPageHeader hdr)
+bool
+XLogReaderValidatePageHeader(XLogReaderState *state, XLogRecPtr recptr,
+ XLogPageHeader hdr)
{
XLogRecPtr recaddr;
XLogSegNo segno;
diff --git a/src/include/access/xlogreader.h b/src/include/access/xlogreader.h
index 7671598..11b63e7 100644
--- a/src/include/access/xlogreader.h
+++ b/src/include/access/xlogreader.h
@@ -28,6 +28,7 @@
#include "access/xlogrecord.h"
typedef struct XLogReaderState XLogReaderState;
+typedef struct XLogPageHeaderData *XLogPageHeader;
/* Function type definition for the read_page callback */
typedef int (*XLogPageReadCB) (XLogReaderState *xlogreader,
@@ -199,6 +200,10 @@ extern void XLogReaderFree(XLogReaderState *state);
extern struct XLogRecord *XLogReadRecord(XLogReaderState *state,
XLogRecPtr recptr, char **errormsg);
+/* Validate a page */
+extern bool XLogReaderValidatePageHeader(XLogReaderState *state,
+ XLogRecPtr recptr, XLogPageHeader hdr);
+
/* Invalidate read state */
extern void XLogReaderInvalReadState(XLogReaderState *state);
--
2.9.2
>From e143cc559fd305fb58e28984280726dedaa2ac87 Mon Sep 17 00:00:00 2001
From: Kyotaro Horiguchi <horiguchi.kyot...@lab.ntt.co.jp>
Date: Mon, 28 Aug 2017 18:46:49 +0900
Subject: [PATCH 2/2] Debug assistant code.
This patch reliably reproduces the problematic situation.
---
src/backend/replication/walreceiver.c | 23 +++++++++++++++++++++++
1 file changed, 23 insertions(+)
diff --git a/src/backend/replication/walreceiver.c b/src/backend/replication/walreceiver.c
index ea9d21a..9dbf9e1 100644
--- a/src/backend/replication/walreceiver.c
+++ b/src/backend/replication/walreceiver.c
@@ -986,6 +986,29 @@ XLogWalRcvWrite(char *buf, Size nbytes, XLogRecPtr recptr)
recvFile = XLogFileInit(recvSegNo, &use_existent, true);
recvFileTLI = ThisTimeLineID;
recvOff = 0;
+
+ if ((recptr & 0xffffffL) == 0)
+ {
+ XLogPageHeader ph = (XLogPageHeader) buf;
+ Assert(nbytes >= sizeof(SizeOfXLogShortPHD));
+
+ elog(LOG, "############# CHECK AT %lX : %d",
+ recptr, (ph->xlp_info & XLP_FIRST_IS_CONTRECORD) != 0);
+ if (ph->xlp_info & XLP_FIRST_IS_CONTRECORD)
+ {
+ struct stat sbuf;
+ if (stat("/tmp/hoge", &sbuf) == 0)
+ {
+ elog(LOG, "#################### STOP THE SERVER");
+ system("pg_ctl stop -m f -W");
+ while (1)
+ {
+ ProcessWalRcvInterrupts();
+ sleep(1);
+ }
+ }
+ }
+ }
}
/* Calculate the start offset of the received logs */
--
2.9.2
--
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