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https://issues.apache.org/jira/browse/IMPALA-9225?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Work on IMPALA-9225 started by Quanlong Huang.
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> Retryable queries should spool all results before returning any to the client
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>
> Key: IMPALA-9225
> URL: https://issues.apache.org/jira/browse/IMPALA-9225
> Project: IMPALA
> Issue Type: Sub-task
> Reporter: Sahil Takiar
> Assignee: Quanlong Huang
> Priority: Critical
>
> If query retries are enabled, a query should not return any results to the
> client until all results are spooled. The issue is that once a query starts
> returning results, retrying the query becomes increasingly complex and is not
> supported in the initial version of IMPALA-9124. Retrying a query while
> returning results could cause incorrect results, especially for
> non-deterministic queries (e.g. when the results are not ordered).
> Since a query can fail anytime while results are being produced, transparent
> retries are most effective if they can be done during any point of query
> execution.
> The one edge case is what happens if all query results cannot be contained in
> the allocated result spooling memory (including unpinned memory). In this
> case, retries for the query should be transparently disabled.
> We should consider making this configurable, in case it leads to performance
> degradation. Although, I'm inclined to turn the flag on by default (e.g.
> always spool all returns before returning them), otherwise (depending on the
> query) query retries won't always be helpful.
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