[ 
https://issues.apache.org/jira/browse/IMPALA-5029?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
 ]

Tim Armstrong reassigned IMPALA-5029:
-------------------------------------

    Assignee:     (was: Alexander Behm)

> Remove un-necessary exchange operators from scan+agg queries when hosts=1
> -------------------------------------------------------------------------
>
>                 Key: IMPALA-5029
>                 URL: https://issues.apache.org/jira/browse/IMPALA-5029
>             Project: IMPALA
>          Issue Type: Bug
>          Components: Frontend
>    Affects Versions: Impala 2.6.0
>            Reporter: Mostafa Mokhtar
>            Priority: Minor
>
> Lightweight queries that constitute a small scan followed by an aggregate and 
> hosts=1 can be optimized by doing a final aggregate opposed to streaming -> 
> exchange -> Final
> {code}
> select count (distinct n_nationkey) from nation
> {code}
> Plan
> {code}
> +----------------------------------------------------------+
> | Explain String                                           |
> +----------------------------------------------------------+
> | Estimated Per-Host Requirements: Memory=36.00MB VCores=2 |
> |                                                          |
> | PLAN-ROOT SINK                                           |
> | |                                                        |
> | 06:AGGREGATE [FINALIZE]                                  |
> | |  output: count:merge(n_nationkey)                      |
> | |  hosts=1 per-host-mem=unavailable                      |
> | |  tuple-ids=2 row-size=8B cardinality=1                 |
> | |                                                        |
> | 05:EXCHANGE [UNPARTITIONED]                              |
> | |  hosts=1 per-host-mem=unavailable                      |
> | |  tuple-ids=2 row-size=8B cardinality=1                 |
> | |                                                        |
> | 02:AGGREGATE                                             |
> | |  output: count(n_nationkey)                            |
> | |  hosts=1 per-host-mem=10.00MB                          |
> | |  tuple-ids=2 row-size=8B cardinality=1                 |
> | |                                                        |
> | 04:AGGREGATE                                             |
> | |  group by: n_nationkey                                 |
> | |  hosts=1 per-host-mem=10.00MB                          |
> | |  tuple-ids=1 row-size=8B cardinality=25                |
> | |                                                        |
> | 03:EXCHANGE [HASH(n_nationkey)]                          |
> | |  hosts=1 per-host-mem=0B                               |
> | |  tuple-ids=1 row-size=8B cardinality=25                |
> | |                                                        |
> | 01:AGGREGATE [STREAMING]                                 |
> | |  group by: n_nationkey                                 |
> | |  hosts=1 per-host-mem=10.00MB                          |
> | |  tuple-ids=1 row-size=8B cardinality=25                |
> | |                                                        |
> | 00:SCAN HDFS [tpch_300_parquet.nation, RANDOM]           |
> |    partitions=1/1 files=1 size=2.19KB                    |
> |    table stats: 25 rows total                            |
> |    column stats: all                                     |
> |    hosts=1 per-host-mem=16.00MB                          |
> |    tuple-ids=0 row-size=8B cardinality=25                |
> +----------------------------------------------------------+
> {code}



--
This message was sent by Atlassian JIRA
(v7.6.3#76005)

---------------------------------------------------------------------
To unsubscribe, e-mail: issues-all-unsubscr...@impala.apache.org
For additional commands, e-mail: issues-all-h...@impala.apache.org

Reply via email to