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https://issues.apache.org/jira/browse/IMPALA-8021?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Work on IMPALA-8021 started by Paul Rogers.
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> Add estimated cardinality to EXPLAIN output
> -------------------------------------------
>
> Key: IMPALA-8021
> URL: https://issues.apache.org/jira/browse/IMPALA-8021
> Project: IMPALA
> Issue Type: Improvement
> Components: Frontend
> Affects Versions: Impala 3.1.0
> Reporter: Paul Rogers
> Assignee: Paul Rogers
> Priority: Minor
>
> The EXPLAIN output provides much useful information in the plan tree. But, it
> lacks a vital piece of information: the expected cardinality at each step.
> All our planning decisions are based on this cardinality; we need it to make
> sense of the generated plan.
> Add cardinality to each node so it appears something like this:
> {noformat}
> HASH JOIN [INNER JOIN, BROADCAST]
> | rows=1.23G
> |
> |--SCAN HDFS [db.table]
> | partitions=2/123 files=2 size=4.56MB rows=7.89M
> {noformat}
> Only the scan and join have interesting cardinality numbers: Exchange nodes
> always have the same as their child. Aggregation may also be useful.
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