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     <h1 class="entry-title">Predicate Improvements in Kudu 0.8</h1>
     <p class="meta">Posted 19 Apr 2016 by Dan Burkert</p>
   </header>
   <div class="entry-content">
     <p>The recently released Kudu version 0.8 ships with a host of new improvements to
 scan predicates. Performance and usability have been improved, especially for
 tables taking advantage of <a href="http://kudu.apache.org/docs/schema_design.html#data-distribution">advanced partitioning
 options</a>.</p>

 <!--more-->

 <h2 id="scan-optimizations-in-the-server-and-c-client">Scan Optimizations in the Server and C++ Client</h2>

 <p>The server and C++ client have gotten more sophisticated in how they handle and
 optimize scan constraints. Constraints specified in the predicates and lower
 and upper bound primary keys are better unified, resulting in more predicates
 being pushed into primary key bounds, which can turn full table scans with
 predicates into much more efficient bounded scans.</p>

 <p>Additionally, the server and C++ client now recognize more opportunities to
 prune entire tablets during scans. For example, for the following schema and
 query Kudu will now be able to skip scanning 15 out of the 16 tablets in the
 table:</p>

 <div class="highlight"><pre><code class="language-sql" data-lang="sql"><span class="c1">-- create a table with 16 tablets</span>
 <span class="k">CREATE</span> <span class="k">TABLE</span> <span class="n">users</span> <span class="p">(</span><span class="n">id</span> <span class="n">INT64</span><span class="p">,</span> <span class="n">name</span> <span class="n">STRING</span><span class="p">,</span> <span class="n">address</span> <span class="n">STRING</span><span class="p">)</span>
 <span class="n">DISTRIBUTE</span> <span class="k">BY</span> <span class="n">HASH</span> <span class="p">(</span><span class="n">id</span><span class="p">)</span> <span class="k">INTO</span> <span class="mi">16</span> <span class="n">BUCKETS</span><span class="p">;</span>

 <span class="c1">-- scan over a single tablet</span>
 <span class="k">SELECT</span> <span class="n">id</span><span class="p">,</span> <span class="n">name</span><span class="p">,</span> <span class="n">address</span> <span class="k">FROM</span> <span class="n">users</span>
 <span class="k">WHERE</span> <span class="n">id</span> <span class="o">=</span> <span class="mi">876932</span><span class="p">;</span></code></pre></div>

 <p>For a deeper look at the newly implemented scan and partition pruning
 optimizations, see the associated <a href="https://github.com/apache/incubator-kudu/blob/master/docs/design-docs/scan-optimization-partition-pruning.md">design
 document</a>.
 These optimizations will eventually be incorporated into the Java client as
 well, but until that time they are still used on the server side for scans
 initiated by Java clients. If you would like to help with this effort, let us
 know on the <a href="https://issues.apache.org/jira/browse/KUDU-1065">JIRA issue</a>.</p>

 <h2 id="redesigned-predicate-api-in-the-java-client">Redesigned Predicate API in the Java Client</h2>

 <p>The Java client has a new way to express scan predicates: the
 <a href="http://kudu.apache.org/apidocs/org/kududb/client/KuduPredicate.html"><code>KuduPredicate</code></a>.
 The API matches the corresponding C++ API more closely, and adds support for
 specifying exclusive, as well as inclusive, range predicates. The existing
 <a href="http://kudu.apache.org/apidocs/org/kududb/client/ColumnRangePredicate.html"><code>ColumnRangePredicate</code></a>
 API has been deprecated, and will be removed soon. Example of transitioning from
 the old to new API:</p>

 <div class="highlight"><pre><code class="language-java" data-lang="java"><span class="n">ColumnSchema</span> <span class="n">myIntColumnSchema</span> <span class="o">=</span> <span class="o">...;</span>
 <span class="n">KuduScanner</span><span class="o">.</span><span class="na">KuduScannerBuilder</span> <span class="n">scannerBuilder</span> <span class="o">=</span> <span class="o">...;</span>

 <span class="c1">// Old predicate API</span>
 <span class="n">ColumnRangePredicate</span> <span class="n">predicate</span> <span class="o">=</span> <span class="k">new</span> <span class="nf">ColumnRangePredicate</span><span class="o">(</span><span class="n">myIntColumnSchema</span><span class="o">);</span>
 <span class="n">predicate</span><span class="o">.</span><span class="na">setLowerBound</span><span class="o">(</span><span class="mi">20</span><span class="o">);</span>
 <span class="n">scannerBuilder</span><span class="o">.</span><span class="na">addColumnRangePredicate</span><span class="o">(</span><span class="n">predicate</span><span class="o">);</span>

 <span class="c1">// New predicate API</span>
 <span class="n">scannerBuilder</span><span class="o">.</span><span class="na">newPredicate</span><span class="o">(</span>
     <span class="n">KuduPredicate</span><span class="o">.</span><span class="na">newComparisonPredicate</span><span class="o">(</span><span class="n">myIntColumnSchema</span><span class="o">,</span> <span class="n">ComparisonOp</span><span class="o">.</span><span class="na">GREATER_EQUAL</span><span class="o">,</span> <span class="mi">20</span><span class="o">));</span></code></pre></div>

 <h2 id="under-the-covers-changes">Under the Covers Changes</h2>

 <p>The scan optimizations in the server and C++ client, and the new <code>KuduPredicate</code>
 API in the Java client are made possible by an overhaul of how predicates are
 handled internally. A new protobuf message type,
 <a href="https://github.com/apache/incubator-kudu/blob/master/src/kudu/common/common.proto#L273"><code>ColumnPredicatePB</code></a>
 has been introduced, and will allow more column predicate types to be introduced
 in the future. If you are interested in contributing to Kudu but don’t know
 where to start, consider adding a new predicate type; for example the <code>IS NULL</code>,
 <code>IS NOT NULL</code>, <code>IN</code>, and <code>LIKE</code> predicates types are currently not implemented.</p>

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	<article>
	<header>
	<h1 class="entry-title">Predicate Improvements in Kudu 0.8</h1>
	<p class="meta">Posted 19 Apr 2016 by Dan Burkert</p>
	</header>
	<div class="entry-content">
	<p>The recently released Kudu version 0.8 ships with a host of new improvements to
	scan predicates. Performance and usability have been improved, especially for
	tables taking advantage of <a href="http://kudu.apache.org/docs/schema_design.html#data-distribution">advanced partitioning
	options</a>.</p>

	<!--more-->

	<h2 id="scan-optimizations-in-the-server-and-c-client">Scan Optimizations in the Server and C++ Client</h2>

	<p>The server and C++ client have gotten more sophisticated in how they handle and
	optimize scan constraints. Constraints specified in the predicates and lower
	and upper bound primary keys are better unified, resulting in more predicates
	being pushed into primary key bounds, which can turn full table scans with
	predicates into much more efficient bounded scans.</p>

	<p>Additionally, the server and C++ client now recognize more opportunities to
	prune entire tablets during scans. For example, for the following schema and
	query Kudu will now be able to skip scanning 15 out of the 16 tablets in the
	table:</p>

	<div class="highlight"><pre><code class="language-sql" data-lang="sql"><span class="c1">-- create a table with 16 tablets</span>
	<span class="k">CREATE</span> <span class="k">TABLE</span> <span class="n">users</span> <span class="p">(</span><span class="n">id</span> <span class="n">INT64</span><span class="p">,</span> <span class="n">name</span> <span class="n">STRING</span><span class="p">,</span> <span class="n">address</span> <span class="n">STRING</span><span class="p">)</span>
	<span class="n">DISTRIBUTE</span> <span class="k">BY</span> <span class="n">HASH</span> <span class="p">(</span><span class="n">id</span><span class="p">)</span> <span class="k">INTO</span> <span class="mi">16</span> <span class="n">BUCKETS</span><span class="p">;</span>

	<span class="c1">-- scan over a single tablet</span>
	<span class="k">SELECT</span> <span class="n">id</span><span class="p">,</span> <span class="n">name</span><span class="p">,</span> <span class="n">address</span> <span class="k">FROM</span> <span class="n">users</span>
	<span class="k">WHERE</span> <span class="n">id</span> <span class="o">=</span> <span class="mi">876932</span><span class="p">;</span></code></pre></div>

	<p>For a deeper look at the newly implemented scan and partition pruning
	optimizations, see the associated <a href="https://github.com/apache/incubator-kudu/blob/master/docs/design-docs/scan-optimization-partition-pruning.md">design
	document</a>.
	These optimizations will eventually be incorporated into the Java client as
	well, but until that time they are still used on the server side for scans
	initiated by Java clients. If you would like to help with this effort, let us
	know on the <a href="https://issues.apache.org/jira/browse/KUDU-1065">JIRA issue</a>.</p>

	<h2 id="redesigned-predicate-api-in-the-java-client">Redesigned Predicate API in the Java Client</h2>

	<p>The Java client has a new way to express scan predicates: the
	<a href="http://kudu.apache.org/apidocs/org/kududb/client/KuduPredicate.html"><code>KuduPredicate</code></a>.
	The API matches the corresponding C++ API more closely, and adds support for
	specifying exclusive, as well as inclusive, range predicates. The existing
	<a href="http://kudu.apache.org/apidocs/org/kududb/client/ColumnRangePredicate.html"><code>ColumnRangePredicate</code></a>
	API has been deprecated, and will be removed soon. Example of transitioning from
	the old to new API:</p>

	<div class="highlight"><pre><code class="language-java" data-lang="java"><span class="n">ColumnSchema</span> <span class="n">myIntColumnSchema</span> <span class="o">=</span> <span class="o">...;</span>
	<span class="n">KuduScanner</span><span class="o">.</span><span class="na">KuduScannerBuilder</span> <span class="n">scannerBuilder</span> <span class="o">=</span> <span class="o">...;</span>

	<span class="c1">// Old predicate API</span>
	<span class="n">ColumnRangePredicate</span> <span class="n">predicate</span> <span class="o">=</span> <span class="k">new</span> <span class="nf">ColumnRangePredicate</span><span class="o">(</span><span class="n">myIntColumnSchema</span><span class="o">);</span>
	<span class="n">predicate</span><span class="o">.</span><span class="na">setLowerBound</span><span class="o">(</span><span class="mi">20</span><span class="o">);</span>
	<span class="n">scannerBuilder</span><span class="o">.</span><span class="na">addColumnRangePredicate</span><span class="o">(</span><span class="n">predicate</span><span class="o">);</span>

	<span class="c1">// New predicate API</span>
	<span class="n">scannerBuilder</span><span class="o">.</span><span class="na">newPredicate</span><span class="o">(</span>
	<span class="n">KuduPredicate</span><span class="o">.</span><span class="na">newComparisonPredicate</span><span class="o">(</span><span class="n">myIntColumnSchema</span><span class="o">,</span> <span class="n">ComparisonOp</span><span class="o">.</span><span class="na">GREATER_EQUAL</span><span class="o">,</span> <span class="mi">20</span><span class="o">));</span></code></pre></div>

	<h2 id="under-the-covers-changes">Under the Covers Changes</h2>

	<p>The scan optimizations in the server and C++ client, and the new <code>KuduPredicate</code>
	API in the Java client are made possible by an overhaul of how predicates are
	handled internally. A new protobuf message type,
	<a href="https://github.com/apache/incubator-kudu/blob/master/src/kudu/common/common.proto#L273"><code>ColumnPredicatePB</code></a>
	has been introduced, and will allow more column predicate types to be introduced
	in the future. If you are interested in contributing to Kudu but don’t know
	where to start, consider adding a new predicate type; for example the <code>IS NULL</code>,
	<code>IS NOT NULL</code>, <code>IN</code>, and <code>LIKE</code> predicates types are currently not implemented.</p>

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