1 files changed, 37 insertions, 17 deletions

diff --git a/src/backend/access/transam/xlogreader.c b/src/backend/access/transam/xlogreader.c
index fcb08720c0a..018fdf3d34e 100644
--- a/src/backend/access/transam/xlogreader.c
+++ b/src/backend/access/transam/xlogreader.c
@@ -10,9 +10,11 @@
  *
  * NOTES
  *		See xlogreader.h for more notes on this facility.
+ *
+ *		This file is compiled as both front-end and backend code, so it
+ *		may not use ereport, server-defined static variables, etc.
  *-------------------------------------------------------------------------
  */
-
 #include "postgres.h"
 
 #include "access/transam.h"
@@ -192,7 +194,7 @@ XLogReadRecord(XLogReaderState *state, XLogRecPtr RecPtr, char **errormsg)
 {
 	XLogRecord *record;
 	XLogRecPtr	targetPagePtr;
-	bool		randAccess = false;
+	bool		randAccess;
 	uint32		len,
 				total_len;
 	uint32		targetRecOff;
@@ -200,6 +202,13 @@ XLogReadRecord(XLogReaderState *state, XLogRecPtr RecPtr, char **errormsg)
 	bool		gotheader;
 	int			readOff;
 
+	/*
+	 * randAccess indicates whether to verify the previous-record pointer of
+	 * the record we're reading.  We only do this if we're reading
+	 * sequentially, which is what we initially assume.
+	 */
+	randAccess = false;
+
 	/* reset error state */
 	*errormsg = NULL;
 	state->errormsg_buf[0] = '\0';
@@ -208,6 +217,7 @@ XLogReadRecord(XLogReaderState *state, XLogRecPtr RecPtr, char **errormsg)
 
 	if (RecPtr == InvalidXLogRecPtr)
 	{
+		/* No explicit start point; read the record after the one we just read */
 		RecPtr = state->EndRecPtr;
 
 		if (state->ReadRecPtr == InvalidXLogRecPtr)
@@ -223,11 +233,13 @@ XLogReadRecord(XLogReaderState *state, XLogRecPtr RecPtr, char **errormsg)
 	else
 	{
 		/*
+		 * Caller supplied a position to start at.
+		 *
 		 * In this case, the passed-in record pointer should already be
 		 * pointing to a valid record starting position.
 		 */
 		Assert(XRecOffIsValid(RecPtr));
-		randAccess = true;		/* allow readPageTLI to go backwards too */
+		randAccess = true;
 	}
 
 	state->currRecPtr = RecPtr;
@@ -309,8 +321,10 @@ XLogReadRecord(XLogReaderState *state, XLogRecPtr RecPtr, char **errormsg)
 		/* XXX: more validation should be done here */
 		if (total_len < SizeOfXLogRecord)
 		{
-			report_invalid_record(state, "invalid record length at %X/%X",
-								  (uint32) (RecPtr >> 32), (uint32) RecPtr);
+			report_invalid_record(state,
+						"invalid record length at %X/%X: wanted %lu, got %u",
+								  (uint32) (RecPtr >> 32), (uint32) RecPtr,
+								  SizeOfXLogRecord, total_len);
 			goto err;
 		}
 		gotheader = false;
@@ -463,12 +477,10 @@ XLogReadRecord(XLogReaderState *state, XLogRecPtr RecPtr, char **errormsg)
 err:
 
 	/*
-	 * Invalidate the xlog page we've cached. We might read from a different
-	 * source after failure.
+	 * Invalidate the read state. We might read from a different source after
+	 * failure.
 	 */
-	state->readSegNo = 0;
-	state->readOff = 0;
-	state->readLen = 0;
+	XLogReaderInvalReadState(state);
 
 	if (state->errormsg_buf[0] != '\0')
 		*errormsg = state->errormsg_buf;
@@ -572,7 +584,7 @@ ReadPageInternal(XLogReaderState *state, XLogRecPtr pageptr, int reqLen)
 	if (!ValidXLogPageHeader(state, pageptr, hdr))
 		goto err;
 
-	/* update cache information */
+	/* update read state information */
 	state->readSegNo = targetSegNo;
 	state->readOff = targetPageOff;
 	state->readLen = readLen;
@@ -580,10 +592,19 @@ ReadPageInternal(XLogReaderState *state, XLogRecPtr pageptr, int reqLen)
 	return readLen;
 
 err:
+	XLogReaderInvalReadState(state);
+	return -1;
+}
+
+/*
+ * Invalidate the xlogreader's read state to force a re-read.
+ */
+void
+XLogReaderInvalReadState(XLogReaderState *state)
+{
 	state->readSegNo = 0;
 	state->readOff = 0;
 	state->readLen = 0;
-	return -1;
 }
 
 /*
@@ -600,8 +621,9 @@ ValidXLogRecordHeader(XLogReaderState *state, XLogRecPtr RecPtr,
 	if (record->xl_tot_len < SizeOfXLogRecord)
 	{
 		report_invalid_record(state,
-							  "invalid record length at %X/%X",
-							  (uint32) (RecPtr >> 32), (uint32) RecPtr);
+						"invalid record length at %X/%X: wanted %lu, got %u",
+							  (uint32) (RecPtr >> 32), (uint32) RecPtr,
+							  SizeOfXLogRecord, record->xl_tot_len);
 		return false;
 	}
 	if (record->xl_rmid > RM_MAX_ID)
@@ -907,11 +929,9 @@ XLogFindNextRecord(XLogReaderState *state, XLogRecPtr RecPtr)
 err:
 out:
 	/* Reset state to what we had before finding the record */
-	state->readSegNo = 0;
-	state->readOff = 0;
-	state->readLen = 0;
 	state->ReadRecPtr = saved_state.ReadRecPtr;
 	state->EndRecPtr = saved_state.EndRecPtr;
+	XLogReaderInvalReadState(state);
 
 	return found;
 }