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From "Harsh J (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HIVE-15908) OperationLog's LogFile writer should have autoFlush turned on
Date Tue, 14 Feb 2017 07:25:41 GMT
Harsh J created HIVE-15908:
------------------------------

             Summary: 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
            Reporter: Harsh J
            Assignee: Harsh J
            Priority: Minor


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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