[jira] [Comment Edited] (IMPALA-11263) Coordinator hang when cancelling a query

["Wenzhe Zhou (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/IMPALA-11263?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17526742#comment-17526742 ] 

Wenzhe Zhou edited comment on IMPALA-11263 at 4/23/22 7:38 AM:
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In Coordinator::BackendState::Cancel(), if exec_rpc_sent_ equals true and exec_done_ equals false (that means Coordinator::BackendState::ExecAsync() is called, but callback function  Coordinator::BackendState::ExecCompleteCb() is not called), we will call RpcController::Cancel() to cancel Exec() RPC then call WaitOnExecLocked() to wait callback function Coordinator::BackendState::ExecCompleteCb() to be called. 
From above log message,  Coordinator::BackendState::Cancel() for the 4-th backend hang after calling WaitOnExecLocked(). That means the callback function was not called.
Coordinator::BackendState::ExecCompleteCb() should be called if RPC is finished successfully, finished with error, cancelled, or timeout.

RpcController::Cancel() schedule a cancellation task for reactor thread pool. When reactor thread execute the task with function ReactorThread::CancelOutboundCall(). The function call Connection::CancelOutboundCall() and OutboundCall::Cancel().  Connection::CancelOutboundCall() reset car->call as null so that Connection::HandleOutboundCallTimeout() will skip to call OutboundCall::SetTimedOut().  OutboundCall::Cancel() will not call OutboundCall::SetCancelled() if its state is SENDING. OutboundCall::SetCancelled() will be called until OutboundCall:SetSent() is called. So if the RPC is cancelled when OutboundCall.state_ is in SENDING state,  OutboundCall::SetTimedOut() will not be called when the timeout of outbound call  is handled in Connection::HandleOutboundCallTimeout(), and OutboundCall::SetCancelled() will not be called if notification of transfer finishing (CallTransferCallbacks::NotifyTransferFinished()) is not received after sending a RPC call on the wire.
Coordinator::BackendState::ExecCompleteCb() will not be called if OutboundCall::SetCancelled() and OutboundCall::SetTimedOut() are not called.
That means in case the CallTransferCallbacks::NotifyTransferFinished() is not called after sending a RPC call on the wire, Coordinator::BackendState::ExecCompleteCb() will not be called, which lead Coordinator::BackendState::WaitOnExecLocked() to wait indefinitely. 

Connection::ProcessOutboundTransfers() call OutboundCall::SetSending() to set OutboundCall::state_ as SENDING when starting transfer. It then call  OutboundTransfer::SendBuffer() to send data through socket. 
OutboundTransfer::SendBuffer() call socket->Writev() to send data. If socket->Writev() return error, the function will return error without calling CallTransferCallbacks::NotifyTransferFinished() so OutboundCall::SetSent() will not be called.
This means if socket write fails, OutboundCall.state_ will stay in SENDING state and OutboundCall::SetCancelled() will not be called. 
This is the case that Coordinator::BackendState::WaitOnExecLocked() wait indefinitely.


was (Author: wzhou):
In Coordinator::BackendState::Cancel(), if exec_rpc_sent_ equals true and exec_done_ equals false (that means Coordinator::BackendState::ExecAsync() is called, but callback function  Coordinator::BackendState::ExecCompleteCb() is not called), we will call RpcController::Cancel() to cancel Exec() RPC then call WaitOnExecLocked() to wait callback function Coordinator::BackendState::ExecCompleteCb() to be called. 
From above log message,  Coordinator::BackendState::Cancel() for the 4-th backend hang after calling WaitOnExecLocked(). That means the callback function was not called.
Coordinator::BackendState::ExecCompleteCb() should be called if RPC is finished successfully, finished with error, cancelled, or timeout.

RpcController::Cancel() schedule a cancellation task for reactor thread pool. When reactor thread execute the task with function ReactorThread::CancelOutboundCall(). The function call Connection::CancelOutboundCall() and OutboundCall::Cancel().  Connection::CancelOutboundCall() reset car->call as null so that Connection::HandleOutboundCallTimeout() will skip to call OutboundCall::SetTimedOut().  OutboundCall::Cancel() will not call OutboundCall::SetCancelled() if its state is SENDING. OutboundCall::SetCancelled() will be called until OutboundCall:SetSent() is called. So if the RPC is cancelled when OutboundCall.state_ is in SENDING state,  OutboundCall::SetTimedOut() will not be called when the timeout of outbound call  is handled in Connection::HandleOutboundCallTimeout(), and OutboundCall::SetCancelled() will not be called if notification of transfer finishing is not received after sending a RPC call on the wire.
Coordinator::BackendState::ExecCompleteCb() will not be called if OutboundCall::SetCancelled() and OutboundCall::SetTimedOut() are not called.
That means in case the notification of transfer finishing is missing after sending a RPC call on the wire, Coordinator::BackendState::ExecCompleteCb() will not be called, which lead Coordinator::BackendState::WaitOnExecLocked() to wait indefinitely. 


> Coordinator hang when cancelling a query
> ----------------------------------------
>
>                 Key: IMPALA-11263
>                 URL: https://issues.apache.org/jira/browse/IMPALA-11263
>             Project: IMPALA
>          Issue Type: Bug
>          Components: Backend
>            Reporter: Wenzhe Zhou
>            Assignee: Wenzhe Zhou
>            Priority: Major
>
> In a rare case, callback function Coordinator::BackendState::ExecCompleteCb() was not called for the corresponding ExecQueryFInstances RPC somehow. This caused coordinator waited indefinitely when cancelling the query.



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