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https://issues.apache.org/jira/browse/KUDU-1291?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15823465#comment-15823465
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Haijie Hong commented on KUDU-1291:
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Hi, I'm confused about how to get the cardinality of a column? Should we set a
threshold(such as cardinality / number of rows) to determine whether we should
optimize it?
> Efficiently support predicates on non-prefix key components
> -----------------------------------------------------------
>
> Key: KUDU-1291
> URL: https://issues.apache.org/jira/browse/KUDU-1291
> Project: Kudu
> Issue Type: Sub-task
> Components: perf, tablet
> Reporter: Todd Lipcon
>
> In a lot of workloads, users have a compound primary key where the first
> component (or few components) is low cardinality. For example, a time series
> workload may have (year, month, day, entity_id, timestamp) as a primary key.
> A metrics or log storage workload might have (hostname, timestamp).
> It's common to want to do cross-user or cross-date analytics like 'WHERE
> timestamp BETWEEN <a> and <b>' without specifying any predicate for the first
> column(s) of the PK. Currently, we do not execute this efficiently, but
> rather scan the whole table evaluating the predicate.
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