Initial RPC to submit a query and fetch the query handle can take quite long time to return as it can do various operations for planning and submission that involve executing Catalog Operations like Rename, Alter Table Recover partition that can take time on tables with many partitions(https://github.com/apache/impala/blob/1231208da7104c832c13f272d1e5b8f554d29337/be/src/exec/catalog-op-executor.cc#L92). Attached is the profile of one such DDL query (with few fields hidden).
These RPCs are:
One of the side effects of such RPC taking long time is that clients such as impala-shell using AWS NLB can get stuck for ever. The reason is NLB tracks and closes connections after 350s and cannot be configured. But after closing the connection it doesn;t send TCP RST to the client. Only when client tries to send data or packets NLB issues back TCP RST to indicate connection is not alive. Documentation is here: https://docs.aws.amazon.com/elasticloadbalancing/latest/network/network-load-balancers.html#connection-idle-timeout. Hence the impala-shell waiting for RPC to return gets stuck indefinitely.
Hence, we may need to evaluate techniques for RPCs to return query handle after
- Creating Driver: https://github.com/apache/impala/blob/b28da054f3595bb92873433211438306fc22fbc7/be/src/service/impala-server.cc#L1150
- Register Query: https://github.com/apache/impala/blob/b28da054f3595bb92873433211438306fc22fbc7/be/src/service/impala-server.cc#L1168
and execute later parts of RPC asynchronously in different thread without blocking the RPC. That way clients can get query handle and poll for it for state and results.