Make some xlogreader messages more accurate

When you have some invalid WAL, you often get a message like "wanted
24, got 0".  This is a bit incorrect, since it really wanted *at
least* 24, not exactly 24.  This updates the messages to that effect,
and also adds that detail to one message where it was available but
not printed.

Reviewed-by: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Reviewed-by: Jeevan Ladhe <jeevanladhe.os@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/726d782b-5e45-0c3e-d775-6686afe9aa83%40enterprisedb.com

Author: petere

src/backend/access/transam/xlogreader.c

@@ -623,8 +623,9 @@ XLogDecodeNextRecord(XLogReaderState *state, bool nonblocking)
 	}
 	else if (targetRecOff < pageHeaderSize)
 	{
-		report_invalid_record(state, "invalid record offset at %X/%X",
-							  LSN_FORMAT_ARGS(RecPtr));
+		report_invalid_record(state, "invalid record offset at %X/%X: expected at least %u, got %u",
+							  LSN_FORMAT_ARGS(RecPtr),
+							  pageHeaderSize, targetRecOff);
 		goto err;
 	}
 
@@ -672,7 +673,7 @@ XLogDecodeNextRecord(XLogReaderState *state, bool nonblocking)
 		if (total_len < SizeOfXLogRecord)
 		{
 			report_invalid_record(state,
-								  "invalid record length at %X/%X: wanted %u, got %u",
+								  "invalid record length at %X/%X: expected at least %u, got %u",
 								  LSN_FORMAT_ARGS(RecPtr),
 								  (uint32) SizeOfXLogRecord, total_len);
 			goto err;
@@ -1119,7 +1120,7 @@ ValidXLogRecordHeader(XLogReaderState *state, XLogRecPtr RecPtr,
 	if (record->xl_tot_len < SizeOfXLogRecord)
 	{
 		report_invalid_record(state,
-							  "invalid record length at %X/%X: wanted %u, got %u",
+							  "invalid record length at %X/%X: expected at least %u, got %u",
 							  LSN_FORMAT_ARGS(RecPtr),
 							  (uint32) SizeOfXLogRecord, record->xl_tot_len);
 		return false;