bzr commit into mysql-6.0-falcon-team branch (kevin.lewis:2718) Bug#44911

[Kevin Lewis]

#At file:///C:/Work/bzr/Merge/mysql-6.0-falcon-team/ based on revid:kevin.lewis@stripped

 2718 Kevin Lewis	2009-06-03
      Bug#44911 - More follow-on changes.  
      This assures that there will not be a infinite loop in the case where a lock record is returned from Table::fetch and the transaction becomes CommittedVisible soon after.  This should only occur once.  The next time, it has to be a different lock record.  If the same record is read again, something is fataly wrong.  It happened once while I was making some changes for 43344 because of a mistake. So instead of looping infinitely reading the same record, this patch will issue a fatal error.

    modified:
      storage/falcon/Table.cpp
=== modified file 'storage/falcon/Table.cpp'
--- a/storage/falcon/Table.cpp	2009-06-03 20:49:27 +0000
+++ b/storage/falcon/Table.cpp	2009-06-03 21:01:11 +0000
@@ -3498,6 +3498,7 @@ Record* Table::fetchForUpdate(Transactio
 	//  Find the record that will be locked
 
 	int recordNumber = source->recordNumber;
+	Record* prevSource = NULL;
 
 	// If we already have this locked or updated, get the active version
 
@@ -3555,7 +3556,18 @@ Record* Table::fetchForUpdate(Transactio
 			case CommittedVisible:
 				{
 				if (source->isALock())
+					{
+					// A lock record may heve been read above, and before we called getRelativeState,
+					// the transactino may have committed a change.  It could be visible for 
+					// read committed and write committed isolations.  But if the same lock record 
+					// is read again, it could cause a hang and it should not ever happen.  
+					// So prevent an unlikely hang with a FATAL message.
+
+					if (prevSource == source)
+						FATAL("Table::fetchForUpdate found a committed visible lock record.");
+
 					break;  // need to re-fetch the base record
+					}
 
 				if (source->isDeleted())
 					{
@@ -3605,6 +3617,7 @@ Record* Table::fetchForUpdate(Transactio
 				throw SQLError(RUNTIME_ERROR, "unexpected transaction state %d", state);
 			}
 
+		prevSource = source;  // Don't ever folow this pointer!
 		source->release(REC_HISTORY);
 
 		source = fetch(recordNumber);


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