Github user gcaragea commented on a diff in the pull request:
https://github.com/apache/incubator-hawq/pull/146#discussion_r46597216
--- Diff: src/backend/cdb/cdbmetadatacache.c ---
@@ -619,6 +619,9 @@ BlockLocation *GetHdfsFileBlockLocations(const
HdfsFileInfo *file_info, uint64_t
if (cache_entry->block_num <= 1)
{
// only one file, re-fetch
+ LWLockRelease(MetadataCacheLock);
+
+ LWLockAcquire(MetadataCacheLock, LW_EXCLUSIVE);
--- End diff --
Can this create deadlock situations? Upgrading locks usually is a tricky
situation, can lead to a situation where:
- proc A has SHARED lock on foo and bar
- proc B has SHARED lock on foo and bar
- proc A requests EXCLUSIVE lock on foo and gets it
- proc B requests EXCLUSIVE lock on bar and gets it
- proc A requests EXCLUSIVE lock on bar and waits
- proc B requests EXCLUSIVE lock on foo and waits - deadlock
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