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From: Kyotaro Horiguchi <horiguchi.kyotaro@lab.ntt.co.jp>
Subject: [PATCH 1/2] Allow switch WAL source midst of record.
Date: Thu, 7 Sep 2017 12:14:55 +0900

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


----Next_Part(Thu_Sep_07_12_33_47_2017_696)--
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Content-Transfer-Encoding: 7bit
Content-Disposition: inline; filename="0002-Debug-assistant-code.patch"

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  Subject: Re: [PATCH 1/2] Allow switch WAL source midst of record.
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