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https://issues.apache.org/jira/browse/HIVE-15339?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15760933#comment-15760933
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Jesus Camacho Rodriguez commented on HIVE-15339:
------------------------------------------------
[~rajesh.balamohan], last patch LGTM. +1
> Batch metastore calls to get column stats for fields needed in
> FilterSelectivityEstimator
> -----------------------------------------------------------------------------------------
>
> Key: HIVE-15339
> URL: https://issues.apache.org/jira/browse/HIVE-15339
> Project: Hive
> Issue Type: Improvement
> Reporter: Rajesh Balamohan
> Assignee: Rajesh Balamohan
> Priority: Minor
> Attachments: HIVE-15339.1.patch, HIVE-15339.3.patch,
> HIVE-15339.4.patch, HIVE-15339.5.patch, HIVE-15339.6.patch
>
>
> Based on query pattern, {{FilterSelectivityEstimator}} gets column statistics
> from metastore in multiple calls. For instance, in the following query, it
> ends up getting individual column statistics for for flights multiple number
> of times.
> When the table has large number of partitions, getting statistics for columns
> via multiple calls can be very expensive. This would adversely impact the
> overall compilation time. The following query took 14 seconds to compile.
> {noformat}
> SELECT COUNT(`flights`.`flightnum`) AS `cnt_flightnum_ok`,
> YEAR(`flights`.`dateofflight`) AS `yr_flightdate_ok`
> FROM `flights` as `flights`
> JOIN `airlines` ON (`flights`.`uniquecarrier` = `airlines`.`code`)
> JOIN `airports` as `source_airport` ON (`flights`.`origin` =
> `source_airport`.`iata`)
> JOIN `airports` as `dest_airport` ON (`flights`.`dest` =
> `dest_airport`.`iata`)
> GROUP BY YEAR(`flights`.`dateofflight`);
> {noformat}
> It may be helpful to club all columns that need statistics and fetch these
> details in single remote call.
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