[jira] [Work started] (IMPALA-8021) Add estimated cardinality to EXPLAIN output

["Paul Rogers (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/IMPALA-8021?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Work on IMPALA-8021 started by Paul Rogers.
-------------------------------------------
> 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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