presto-hive/src/main/java/io/prestosql/plugin/hive/metastore/SemiTransactionalHiveMetastore.java/SemiTransactionalHiveMetastore/setExclusive
class SemiTransactionalHiveMetastore:    @GuardedBy("this")
    private void setExclusive(ExclusiveOperation exclusiveOperation)
    {
        checkHoldsLock();

        if (state != State.EMPTY) {
            throw new PrestoException(NOT_SUPPORTED, "Unsupported combination of operations in a single transaction");
        }
        state = State.EXCLUSIVE_OPERATION_BUFFERED;
        bufferedExclusiveOperation = exclusiveOperation;
    }