[jira] [Commented] (HIVE-10209) FetchTask with VC may fail because ExecMapper.done is true

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

    [ https://issues.apache.org/jira/browse/HIVE-10209?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14394150#comment-14394150 ] 

Chao commented on HIVE-10209:
-----------------------------

Also, sorry if I missing anything obvious, but:
{code}
select * from src where key < 10 limit 1;
{code}

shouldn't need to do a full table scan, right? As long as we've find some row that key is less than 10, we should return immediately.

> FetchTask with VC may fail because ExecMapper.done is true
> ----------------------------------------------------------
>
>                 Key: HIVE-10209
>                 URL: https://issues.apache.org/jira/browse/HIVE-10209
>             Project: Hive
>          Issue Type: Bug
>          Components: Query Processor
>    Affects Versions: 1.1.0
>            Reporter: Chao
>            Assignee: Chao
>
> ExecMapper.done is a static variable, and may cause issues in the following example:
> {code}
> set hive.fetch.task.conversion=minimal;
> select * from src where key < 10 limit 1;
> set hive.fetch.task.conversion=more;
> select *, BLOCK__OFFSET_INSIDE__FILE from src where key < 10;
> {code}
> The second select won't return any result.
> The issue is, the first select query will be converted to a MapRedTask with only a mapper. And, when the task is done, because of the limit operator, ExecMapper.done will be set to true.
> Then, when the second select query begin to execute, it will call {{FetchOperator::getRecordReader()}}, and since here we have virtual column, an instance of {{HiveRecordReader}} will be returned. The problem is, {{HiveRecordReader::doNext()}} will check ExecMapper.done. In this case, since the value is true, it will quit immediately.
> In short, I think making ExecMapper.done static is a bad idea. The first query should in no way affect the second one.



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