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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