[jira] [Commented] (IMPALA-7214) Lots of misleading/incorrect use of DataNode in Impala docs

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

    [ https://issues.apache.org/jira/browse/IMPALA-7214?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16617793#comment-16617793 ] 

Tim Armstrong commented on IMPALA-7214:
---------------------------------------

This dropped off my radar, sorry about that - I'll make time to take a look soon.

> Lots of misleading/incorrect use of DataNode in Impala docs
> -----------------------------------------------------------
>
>                 Key: IMPALA-7214
>                 URL: https://issues.apache.org/jira/browse/IMPALA-7214
>             Project: IMPALA
>          Issue Type: Bug
>          Components: Docs
>    Affects Versions: Impala 2.12.0
>            Reporter: Tim Armstrong
>            Assignee: Alex Rodoni
>            Priority: Major
>
> The docs tend to conflate DataNodes (a HDFS service) and Impala daemons. I think this stems from the original deployment practice of always colocating Impala daemons with HDFS datanodes so that HDFS data could always be read from a local DataNode. 
> I'm a bit pedantic so the conflation feels wrong to me regardless, but I think this will become increasingly confusing as alternative deployments without colocated HDFS DataNodes become more common (e.g. running against S3, running with a separate HDFS service).
> E.g. picking an example at random:
> {noformat}
>         In Impala 1.4.0 and higher, the <codeph>LIMIT</codeph> clause is now optional (rather than required) for
>         queries that use the <codeph>ORDER BY</codeph> clause. Impala automatically uses a temporary disk work area
>         to perform the sort if the sort operation would otherwise exceed the Impala memory limit for a particular
>         DataNode.
> {noformat}
> This is wrong because the memory limit is for an Impala daemon, which is the process that does the actual sorting. So here I think it should be "Impala daemon" instead of "DataNode".



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