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https://issues.apache.org/jira/browse/IMPALA-12101?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Csaba Ringhofer closed IMPALA-12101.
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Resolution: Invalid
> Inconsistent speeds with result spooling
> ----------------------------------------
>
> Key: IMPALA-12101
> URL: https://issues.apache.org/jira/browse/IMPALA-12101
> Project: IMPALA
> Issue Type: Bug
> Components: Backend, Clients
> Reporter: Csaba Ringhofer
> Priority: Major
> Labels: performance
>
> Noticed a case when enabling result spooling makes query execution much
> slower:
> impala-shell -B -q "set spool_query_results=1; select cast(l_shipdate as
> timestamp) from tpch_parquet.lineitem;" > /dev/null
> Fetched 6001215 row(s) in 23.81s
> impala-shell -B -q "set spool_query_results=0; select cast(l_shipdate as
> timestamp) from tpch_parquet.lineitem;" > /dev/null
> Fetched 6001215 row(s) in 9.92s
> Using beeswax leads to completely different results:
> impala-shell --protocol=beeswax -B -q "set spool_query_results=1; select
> cast(l_shipdate as timestamp) from tpch_parquet.lineitem;" > /dev/null
> Fetched 6001215 row(s) in 10.32s
> impala-shell --protocol=beeswax -B -q "set spool_query_results=0; select
> cast(l_shipdate as timestamp) from tpch_parquet.lineitem;" > /dev/null
> Fetched 6001215 row(s) in 11.87s
> This anomaly seems to occur when both the client and the coordinator needs
> significant time to process the returned rows.
> Note that the slow result generation from timestamps (and dates) is a known
> performance issue in the coordinator - most time is spent in converting
> dates/timestamps to strings. On the other side I don't understand how
> enabling result spooling can slow down a query.
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