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https://issues.apache.org/jira/browse/HIVE-15908?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15872048#comment-15872048
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Harsh J commented on HIVE-15908:
--------------------------------
After a bit more testing with some slow logging queries, aside of just this
newline flush on the server side, increasing the fetch size in HiveStatement to
a very large value (1000 rows) also helps, as does decreasing the Beeline
Command class's UI-jarring 1 second pause between fetches to something like
100-200 ms.
I'm unsure if such changes are acceptable though, as they'd increase the
running load on the HS2 given overall beeline usage. FWIW, Hue feels more
pleasant to use, and it polls the query logs with a fetch size of 1000 rows
with a dynamic refresh sleep time that begins with 100 ms and scales up to 2s
over time, in increments of 100ms (this works better cause there's more logging
at the beginning of the query than around the end).
> OperationLog's LogFile writer should have autoFlush turned on
> -------------------------------------------------------------
>
> Key: HIVE-15908
> URL: https://issues.apache.org/jira/browse/HIVE-15908
> Project: Hive
> Issue Type: Improvement
> Components: HiveServer2
> Affects Versions: 0.13.0
> Reporter: Harsh J
> Assignee: Harsh J
> Priority: Minor
> Attachments: HIVE-15908.000.patch
>
>
> The HS2 offers an API to fetch Operation Log results from the maintained
> OperationLog file. The reader used inside class OperationLog$LogFile class
> reads line-by-line on its input stream, for any lines available from the OS's
> file input perspective.
> The writer inside the same class uses PrintStream to write to the file in
> parallel. However, the PrintStream constructor used sets PrintStream's
> {{autoFlush}} feature in an OFF state. This causes the BufferedWriter used by
> PrintStream to accumulate 8k worth of bytes in memory as the buffer before
> flushing the writes to disk, causing a slowness in the logs streamed back to
> the client. Every line must be ideally flushed entirely as-its-written, for a
> smoother experience.
> I suggest changing the line inside {{OperationLog$LogFile}} that appears as
> below:
> {code}
> out = new PrintStream(new FileOutputStream(file));
> {code}
> Into:
> {code}
> out = new PrintStream(new FileOutputStream(file), true);
> {code}
> This will cause it to use the described autoFlush feature of PrintStream and
> make for a better reader-log-results-streaming experience:
> https://docs.oracle.com/javase/7/docs/api/java/io/PrintStream.html#PrintStream(java.io.OutputStream,%20boolean)
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