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| <h1 class="entry-title">Apache Kudu (incubating) Weekly Update April 4, 2016</h1> |
| <p class="meta">Posted 04 Apr 2016 by Todd Lipcon</p> |
| </header> |
| <div class="entry-content"> |
| <p>Welcome to the third edition of the Kudu Weekly Update. This weekly blog post |
| covers ongoing development and news in the Apache Kudu (incubating) project.</p> |
| |
| <!--more--> |
| |
| <p>If you find this post useful, please let us know by emailing the |
| <a href="mailto:user@kudu.incubator.apache.org">kudu-user mailing list</a> or |
| tweeting at <a href="https://twitter.com/ApacheKudu">@ApacheKudu</a>. Similarly, if you’re |
| aware of some Kudu news we missed, let us know so we can cover it in |
| a future post.</p> |
| |
| <h2 id="development-discussions-and-code-in-progress">Development discussions and code in progress</h2> |
| |
| <ul> |
| <li> |
| <p>The 0.8.0 release train is progressing nicely. Jean-Daniel Cryans posted a first |
| release candidate <a href="http://mail-archives.apache.org/mod_mbox/incubator-kudu-dev/201604.mbox/%3CCAGpTDNfA-hsv6xkeNcvwBGarP1sri%2BvBYqYNt70YWeH44_QPSw%40mail.gmail.com%3E">VOTE thread</a> |
| on the dev mailing list. Please download the release candidate and give it a try.</p> |
| </li> |
| <li> |
| <p>Ara Ebrahimi’s implementation of a <a href="https://github.com/apache/incubator-kudu/blob/master/java/kudu-flume-sink/">Kudu sink for Apache Flume</a> |
| was completed this week. Mike Percy worked on some follow-up around documentation and a shaded |
| <em>jar-with-dependencies</em> for easier consumption.</p> |
| </li> |
| <li> |
| <p>Mike also worked on and committed an <a href="http://gerrit.cloudera.org:8080/#/c/2640/">improvement to the Java API</a> |
| so that error results for failed write operations are easier to handle. Previously, |
| clients had to perform string comparisons to know whether an insert failed due |
| to something like a duplicate key constraint rather than some other less expected |
| error.</p> |
| </li> |
| <li> |
| <p>After some early cluster testing of the new implementation of scanner predicates, |
| a few tricky bugs were discovered. The first was around proper handling of inequality |
| predicates on floating point columns. The second involved handling predicates like |
| ‘my_int8_col <= 127’: for non-nullable columns, this predicate is a tautology |
| and can be eliminated. However, for nullable columns, such a predicate is equivalent |
| to ‘my_int8_col IS NOT NULL’. In order to fix this, Dan Burkert added an internal |
| <a href="http://gerrit.cloudera.org:8080/#/c/2671/">implementation of ‘IS NOT NULL’</a>.</p> |
| |
| <p>These bugs also exposed a few gaps in test coverage around predicate handling. Dan |
| added a couple thousand lines worth of new test coverage both from <a href="http://gerrit.cloudera.org:8080/2677">C++</a> |
| and <a href="http://gerrit.cloudera.org:8080/#/c/2591/">Java</a>.</p> |
| |
| <p>These exhaustive tests also identified a <a href="https://issues.apache.org/jira/browse/KUDU-1386">gap in Kudu’s handling of NaN |
| float values</a>. The team |
| elected to leave this as a known issue for now, since usage of NaN is relatively |
| rare.</p> |
| </li> |
| <li> |
| <p>Todd Lipcon fixed a <a href="http://gerrit.cloudera.org:8080/#/c/2483/">bug in Kudu’s implementation of Raft configuration |
| change</a>. |
| This bug could cause tablet replicas to become “stuck” after certain types of network |
| partitions. The fix will be included in the upcoming 0.8 release.</p> |
| </li> |
| <li> |
| <p>Mike Percy has been working on a <a href="http://gerrit.cloudera.org:8080/#/c/2595/">bug</a> |
| where tablet servers fail to start up after their write-ahead logs (WALs) have been |
| truncated. This can happen on certain types of machine crashes, or if the disks |
| fill up under a write workload.</p> |
| </li> |
| <li> |
| <p>Todd Lipcon spent time this week testing Kudu on a small cluster with a 3TB |
| TPC-H dataset. In particular, he was focusing on concurrent query workloads, |
| including scenarios with multiple read-only users in addition to combining |
| a query workload with a write workload. As a result, he identified a few |
| issues around Kudu’s handling of RPCs in overload conditions.</p> |
| |
| <p>In order to improve the behavior on the server side, Todd changed the RPC |
| scheduling algorithm to use an <a href="https://en.wikipedia.org/wiki/Earliest_deadline_first_scheduling">earliest-deadline-first</a> |
| policy. This has the effect of preventing query timeouts: a query which |
| is closest to experiencing a timeout will be scheduled with higher priority |
| over those which have plenty of time left.</p> |
| |
| <p>In addition, this work identified a few bugs in the Kudu C++ client. |
| In particular, in the case where the server was overloaded, the client |
| would sometimes <a href="http://gerrit.cloudera.org:8080/#/c/2654/">incorrectly rewind to the start of the current |
| tablet</a> resulting in incorrect |
| results. In other cases, the client would end up in a <a href="http://gerrit.cloudera.org:8080/#/c/2709/">tight loop sending |
| RPCs to the master</a>. Fixes |
| for both of these issues will be in the upcoming 0.8 release.</p> |
| </li> |
| </ul> |
| |
| <h2 id="upcoming-talks-and-meetups">Upcoming talks and meetups</h2> |
| |
| <ul> |
| <li>Todd Lipcon will be presenting an introductory Kudu talk at <a href="http://www.dataengconf.com/schedule/">DataEngConf</a> |
| on Friday, April 8th.</li> |
| </ul> |
| |
| </div> |
| </article> |
| |
| |
| </div> |
| <div class="col-lg-3 recent-posts"> |
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| <li> <a href="/2021/06/22/apache-kudu-1-15-0-released.html">Apache Kudu 1.15.0 Released</a> </li> |
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| <li> <a href="/2021/01/28/apache-kudu-1-14-0-release.html">Apache Kudu 1.14.0 Released</a> </li> |
| |
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| |
| <li> <a href="/2020/09/21/apache-kudu-1-13-0-release.html">Apache Kudu 1.13.0 released</a> </li> |
| |
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| |
| </ul> |
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