[jira] [Commented] (IMPALA-558) HS2::FetchResults sets hasMoreRows in many cases where no more rows are to be returned

["Sahil Takiar (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/IMPALA-558?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16921071#comment-16921071 ] 

Sahil Takiar commented on IMPALA-558:
-------------------------------------

The frequency of this issue should be significantly reduced when result spooling is enabled. The call to {{BufferedPlanRootSink::Send}} no longer blocks waiting for a corresponding call to {{GetNext}}, so {{FlushFinal}} is called immediately after sending the last batch.

However, even with result spooling, the issue could still occur because {{Send}} releases the lock and then {{FlushFinal}} re-acquires it before setting the sender state. So it is possible that the client calls {{GetNext}} before {{FlushFinal}} can set the state to EOS.

This could be fixed by re-factoring the {{PlanRootSink}} interface so that {{Send}} takes in an {{eos}} flag. This would allow {{Send}} to know if the batch being sent, is the last one. It could then set the {{sender_state_}} flag. However, I'm not sure its worth the effort.

> HS2::FetchResults sets hasMoreRows in many cases where no more rows are to be returned
> --------------------------------------------------------------------------------------
>
>                 Key: IMPALA-558
>                 URL: https://issues.apache.org/jira/browse/IMPALA-558
>             Project: IMPALA
>          Issue Type: Sub-task
>          Components: Clients
>    Affects Versions: Impala 1.1
>            Reporter: Henry Robinson
>            Priority: Minor
>              Labels: query-lifecycle
>
> The first call to {{FetchResults}} always sets {{hasMoreRows}} even when 0 rows should be returned. The next call correctly sets {{hasMoreRows == False}}. The upshot is there's always an extra round-trip, although correctness isn't affected.
> {code}
>     execute_statement_req = TCLIService.TExecuteStatementReq()
>     execute_statement_req.sessionHandle = resp.sessionHandle
>     execute_statement_req.statement = "SELECT COUNT(*) FROM functional.alltypes WHERE 1 = 2"
>     execute_statement_resp = self.hs2_client.ExecuteStatement(execute_statement_req)
>     
>     fetch_results_req = TCLIService.TFetchResultsReq()
>     fetch_results_req.operationHandle = execute_statement_resp.operationHandle
>     fetch_results_req.maxRows = 100
>     fetch_results_resp = self.hs2_client.FetchResults(fetch_results_req)
>     
>     assert not fetch_results_resp.hasMoreRows # Fails
> {code}



--
This message was sent by Atlassian Jira
(v8.3.2#803003)

---------------------------------------------------------------------
To unsubscribe, e-mail: issues-all-unsubscribe@impala.apache.org
For additional commands, e-mail: issues-all-help@impala.apache.org