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

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

Tim Armstrong created IMPALA-7214:
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             Summary: 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: Documentation
          Components: Docs
    Affects Versions: Impala 2.12.0
            Reporter: Tim Armstrong
            Assignee: Alex Rodoni


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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