Sahil Takiar created IMPALA-9225:
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Summary: Retryable queries should spool all results before
returning any to the client
Key: IMPALA-9225
URL: https://issues.apache.org/jira/browse/IMPALA-9225
Project: IMPALA
Issue Type: Sub-task
Reporter: Sahil Takiar
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 included 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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