Paul Rogers created IMPALA-8021:
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Summary: 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
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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