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https://issues.apache.org/jira/browse/IMPALA-5095?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15930805#comment-15930805
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Alexander Behm commented on IMPALA-5095:
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The last tricky case can be solved by returning two rows from the scan, one
with the int_col slot having the min value, and another row with int_col having
the max value.
> Use parquet::Statistics for simple min/max aggregates
> -----------------------------------------------------
>
> Key: IMPALA-5095
> URL: https://issues.apache.org/jira/browse/IMPALA-5095
> Project: IMPALA
> Issue Type: Sub-task
> Components: Backend
> Affects Versions: Impala 2.8.0
> Reporter: Alexander Behm
> Labels: parquet, perfomance, ramp-up
>
> {code}
> select min(int_col), max(bigint_col) from parquet_table;
> select min(int_col), max(bigint_col) from parquet_table group by
> partition_col;
> select min(int_col), max(int_col) from parquet_table; <--- case a little
> trickier because int_col refd twice
> {code}
> The slot values for int_col and bigint_col can be directly filled in from the
> parquet::Statistics, assuming stats are available for both columns. No
> columns need to be scanned/materialized.
> This JIRA focuses on implementing this optimization in the simple case where
> all scanned columns feed into min/max aggregates and where all columns have
> parquet::Statistics. Those conditions can be relaxed, but should be addressed
> separately.
> This optimization opportunity must be detected by the planner and is not
> applicable when there are scan predicates.
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