[kudu-CR] [java] Clean up AsyncKuduSession

["Will Berkeley (Code Review)" <ge...@cloudera.org>]

Will Berkeley has uploaded a new patch set (#2). ( http://gerrit.cloudera.org:8080/13336 )

Change subject: [java] Clean up AsyncKuduSession
......................................................................

[java] Clean up AsyncKuduSession

This makes several improvements to AsyncKuduSession code.

1. I replaced a lot of wordy callback definitions with Java 8 lambdas.
2. I renamed the member variable and method parameter names for ones
   that were mutation-buffer-space-related. The new names reflect that
   the buffers are measured in number of ops, not size in bytes. I
   couldn't rename the methods because that would break API
   compatibility.
3. I renamed 'interval' to 'intervalMillis', following naming best
   practice, unless it would break compatibility.
4. I added some helper functions and simplified logic in a few places.
5. I removed all of the "low watermark rejections". Previously, the
   AsyncKuduSession tracked a low watermark percentage (default 0.5)
   and, once the buffer was more full than that percentage and there's
   an ongoing flush, new operations were rejected out of apply with a
   PleaseThrottleException with a probability scaling linearly from 0
   to 1 as the buffer went from the watermark to full. I don't think
   this makes sense, however, as it simply means doing more work to fill
   the buffer. Applications ought to just fill the buffer as fast as
   possible, and then wait to apply more. The PleaseThrottleException
   provides a deferred that applications can wait on until there is
   buffer space available. In fact, this was causing bad behavior in the
   synchronous KuduSession, which, in its apply, would fill the buffer
   until the first PleaseThrottleException (high chance of this being
   before the buffer is full) and then it would wait until the
   outstanding flush was finished before returning, holding up preparing
   more ops for flush for basically no reason.
6. I removed the test for the watermark behavior.

Change-Id: I0c901af497b3a4195c78b62c61d31aa00866a993
---
M java/kudu-client/src/main/java/org/apache/kudu/client/AsyncKuduSession.java
M java/kudu-client/src/main/java/org/apache/kudu/client/KuduSession.java
M java/kudu-client/src/main/java/org/apache/kudu/client/SessionConfiguration.java
M java/kudu-client/src/test/java/org/apache/kudu/client/TestAsyncKuduSession.java
4 files changed, 113 insertions(+), 171 deletions(-)


  git pull ssh://gerrit.cloudera.org:29418/kudu refs/changes/36/13336/2
-- 
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Gerrit-Project: kudu
Gerrit-Branch: master
Gerrit-MessageType: newpatchset
Gerrit-Change-Id: I0c901af497b3a4195c78b62c61d31aa00866a993
Gerrit-Change-Number: 13336
Gerrit-PatchSet: 2
Gerrit-Owner: Will Berkeley <wd...@gmail.com>