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https://issues.apache.org/jira/browse/HIVE-17634?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16185323#comment-16185323
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Vineet Garg commented on HIVE-17634:
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[~kellyzly] We decided to estimate stats only if they don't exist in metastore.
So if user has explicitly turned off {{hive.stats.fetch.column.stats}} we
assume user is not interested in statistics (either from metastore or
estimated) for physical planning. Estimate statistics is mostly for preventing
falling back to non-cbo in case of missing statistics,it is better to always
use stats from metastore if they exist.
I am not convinced why would user not want to fetch stats from metastore and
instead rely upon estimated statistics?
> Use properties from HiveConf about "fetchColStats" and "fetchPartStats" in
> RelOptHiveTable#updateColStats
> ---------------------------------------------------------------------------------------------------------
>
> Key: HIVE-17634
> URL: https://issues.apache.org/jira/browse/HIVE-17634
> Project: Hive
> Issue Type: Bug
> Reporter: liyunzhang_intel
> Assignee: liyunzhang_intel
> Attachments: HIVE-17634.patch
>
>
> in
> [RelOptHiveTable#updateColStats|https://github.com/apache/hive/blob/master/ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/RelOptHiveTable.java#L309],
> we set {{fetchColStats}},{{fetchPartStats}} as true when call
> {{StatsUtils.collectStatistics}}
> {code}
> if (!hiveTblMetadata.isPartitioned()) {
> // 2.1 Handle the case for unpartitioned table.
> try {
> Statistics stats = StatsUtils.collectStatistics(hiveConf, null,
> hiveTblMetadata, hiveNonPartitionCols,
> nonPartColNamesThatRqrStats,
> colStatsCached, nonPartColNamesThatRqrStats, true, true);
> ...
> {code}
> This will cause querying columns statistic from metastore even we set
> {{hive.stats.fetch.column.stats}} and {{hive.stats.fetch.partition.stats}} as
> false in HiveConf. If we these two properties as false, we can not any
> column statistics from metastore. Suggest to set the properties from
> HiveConf.
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