[
https://issues.apache.org/jira/browse/PIG-4148?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Cheolsoo Park updated PIG-4148:
-------------------------------
Attachment: PIG-4148-1.patch
The patch changes the number of samples to parallelism x per-task sample size.
> Tez order-by is often skewed because FindQuantiles UDF is called with small
> number
> ----------------------------------------------------------------------------------
>
> Key: PIG-4148
> URL: https://issues.apache.org/jira/browse/PIG-4148
> Project: Pig
> Issue Type: Sub-task
> Components: tez
> Reporter: Cheolsoo Park
> Assignee: Cheolsoo Park
> Fix For: 0.14.0
>
> Attachments: PIG-4148-1.patch
>
>
> In Tez, FindQuantiles UDF is called with a smaller number of samples than MR
> resulting in skew in range partitions.
> For example, I have a job that runs sampling with a parallelism of 300. Since
> each task samples 100 records, the total sample should be 30K. But
> FindQuantiles UDF is called with only 300 records-
> {code}
> # Plan on vertex
> POValueOutputTez - scope-282 -> [scope-283]
> |
> |---New For Each(false)[tuple] - scope-281
> | |
> |
> POUserFunc(org.apache.pig.backend.hadoop.executionengine.tez.FindQuantilesTez)[tuple]
> - scope-280
> | |
> | |---Project[tuple][*] - scope-279
> |
> |---New For Each(false,false)[tuple] - scope-278
> | |
> | Constant(300) - scope-277 <--- 300 should be 30K!
> | |
> | Project[bag][1] - scope-275
> |
> |---Package(Packager)[tuple]{bytearray} - scope-274
> {code}
> This is because we set the number of samples to the parallelism of the
> sampling vertex.
> {code}
> // We temporarily set it to rp and will adjust it at runtime, because the
> final degree of parallelism
> // is unknown until we are ready to submit it. See PIG-2779.
> rpce.setValue(rp);
> {code}
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
