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https://issues.apache.org/jira/browse/PIG-3347?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13887236#comment-13887236
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Daniel Dai commented on PIG-3347:
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UID is to track column lineage so in logical optimizer, so that we can freely
move operate up and down, ProjectionPatcher will reposition the column
according to uid, even if the column get reordered. A new source of data should
have a new UID, that's the case for nested LOForEach/LODistinct, since they are
not directly derived from the previous operator, instead, it is a new field
generated by the foreach.
> Store invocation brings side effect
> -----------------------------------
>
> Key: PIG-3347
> URL: https://issues.apache.org/jira/browse/PIG-3347
> Project: Pig
> Issue Type: Bug
> Components: grunt
> Affects Versions: 0.11
> Environment: local mode
> Reporter: Sergey
> Assignee: Daniel Dai
> Priority: Critical
> Fix For: 0.12.1
>
> Attachments: PIG-3347-1.patch
>
>
> The problem is that intermediate 'store' invocation "changes" the final store
> output. Looks like it brings some kind of side effect. We did use 'local'
> mode to run script
> here is the input data:
> 1
> 1
> Here is the script:
> {code}
> a = load 'test';
> a_group = group a by $0;
> b = foreach a_group {
> a_distinct = distinct a.$0;
> generate group, a_distinct;
> }
> --store b into 'b';
> c = filter b by SIZE(a_distinct) == 1;
> store c into 'out';
> {code}
> We expect output to be:
> 1 1
> The output is empty file.
> Uncomment {code}--store b into 'b';{code} line and see the diffrence.
> Yuo would get expected output.
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