Blocker Description
Right now the entire method of HiveMetastoreCatalog.lookupRelation has a lock (https://github.com/apache/spark/blob/branch-1.3/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveMetastoreCatalog.scala#L173) and the scope of lock will cover resolving data source tables (https://github.com/apache/spark/blob/branch-1.3/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveMetastoreCatalog.scala#L93). So, lookupRelation can be extremely expensive when we are doing expensive operations like parquet schema discovery. So, we should use fine-grained lock for lookupRelation.
