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| <div class="subTitle">org.apache.beam.sdk.extensions.zetasketch</div> |
| <h2 title="Class HllCount" class="title">Class HllCount</h2> |
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| <ul class="inheritance"> |
| <li>java.lang.Object</li> |
| <li> |
| <ul class="inheritance"> |
| <li>org.apache.beam.sdk.extensions.zetasketch.HllCount</li> |
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| <pre><a href="../../../../../../org/apache/beam/sdk/annotations/Experimental.html" title="annotation in org.apache.beam.sdk.annotations">@Experimental</a> |
| public final class <span class="typeNameLabel">HllCount</span> |
| extends java.lang.Object</pre> |
| <div class="block"><code>PTransform</code>s to compute HyperLogLogPlusPlus (HLL++) sketches on data streams based on the |
| <a href="https://github.com/google/zetasketch">ZetaSketch</a> implementation. |
| |
| <p>HLL++ is an algorithm implemented by Google that estimates the count of distinct elements in a |
| data stream. HLL++ requires significantly less memory than the linear memory needed for exact |
| computation, at the cost of a small error. Cardinalities of arbitrary breakdowns can be computed |
| using the HLL++ sketch. See this <a |
| href="http://static.googleusercontent.com/media/research.google.com/en/us/pubs/archive/40671.pdf">published |
| paper</a> for details about the algorithm. |
| |
| <p>HLL++ functions are also supported in <a |
| href="https://cloud.google.com/bigquery/docs/reference/standard-sql/hll_functions">Google Cloud |
| BigQuery</a>. The <code>HllCount PTransform</code>s provided here produce and consume sketches |
| compatible with BigQuery. |
| |
| <p>For detailed design of this class, see https://s.apache.org/hll-in-beam. |
| |
| <h3>Examples</h3> |
| |
| <h4>Example 1: Create long-type sketch for a <code>PCollection<Long></code> and specify precision</h4> |
| |
| <pre><code> |
| PCollection<Long> input = ...; |
| int p = ...; |
| PCollection<byte[]> sketch = input.apply(HllCount.Init.forLongs().withPrecision(p).globally()); |
| </code></pre> |
| |
| <h4>Example 2: Create bytes-type sketch for a <code>PCollection<KV<String, byte[]>></code></h4> |
| |
| <pre><code> |
| PCollection<KV<String, byte[]>> input = ...; |
| PCollection<KV<String, byte[]>> sketch = input.apply(HllCount.Init.forBytes().perKey()); |
| </code></pre> |
| |
| <h4>Example 3: Merge existing sketches in a <code>PCollection<byte[]></code> into a new one</h4> |
| |
| <pre><code> |
| PCollection<byte[]> sketches = ...; |
| PCollection<byte[]> mergedSketch = sketches.apply(HllCount.MergePartial.globally()); |
| </code></pre> |
| |
| <h4>Example 4: Estimates the count of distinct elements in a <code>PCollection<String></code></h4> |
| |
| <pre><code> |
| PCollection<String> input = ...; |
| PCollection<Long> countDistinct = |
| input.apply(HllCount.Init.forStrings().globally()).apply(HllCount.Extract.globally()); |
| </code></pre> |
| |
| Note: Currently HllCount does not work on FnAPI workers. See <a |
| href="https://issues.apache.org/jira/browse/BEAM-7879">Jira ticket [BEAM-7879]</a>.</div> |
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| <tr class="altColor"> |
| <td class="colFirst"><code>static class </code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../org/apache/beam/sdk/extensions/zetasketch/HllCount.Extract.html" title="class in org.apache.beam.sdk.extensions.zetasketch">HllCount.Extract</a></span></code> |
| <div class="block">Provides <code>PTransform</code>s to extract the estimated count of distinct elements (as <code>Long</code>s) from each HLL++ sketch.</div> |
| </td> |
| </tr> |
| <tr class="rowColor"> |
| <td class="colFirst"><code>static class </code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../org/apache/beam/sdk/extensions/zetasketch/HllCount.Init.html" title="class in org.apache.beam.sdk.extensions.zetasketch">HllCount.Init</a></span></code> |
| <div class="block">Provides <code>PTransform</code>s to aggregate inputs into HLL++ sketches.</div> |
| </td> |
| </tr> |
| <tr class="altColor"> |
| <td class="colFirst"><code>static class </code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../org/apache/beam/sdk/extensions/zetasketch/HllCount.MergePartial.html" title="class in org.apache.beam.sdk.extensions.zetasketch">HllCount.MergePartial</a></span></code> |
| <div class="block">Provides <code>PTransform</code>s to merge HLL++ sketches into a new sketch.</div> |
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| <td class="colFirst"><code>static int</code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../org/apache/beam/sdk/extensions/zetasketch/HllCount.html#DEFAULT_PRECISION">DEFAULT_PRECISION</a></span></code> |
| <div class="block">The default <code>precision</code> value used in <a href="../../../../../../org/apache/beam/sdk/extensions/zetasketch/HllCount.Init.Builder.html#withPrecision-int-"><code>HllCount.Init.Builder.withPrecision(int)</code></a> is |
| 15.</div> |
| </td> |
| </tr> |
| <tr class="rowColor"> |
| <td class="colFirst"><code>static int</code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../org/apache/beam/sdk/extensions/zetasketch/HllCount.html#MAXIMUM_PRECISION">MAXIMUM_PRECISION</a></span></code> |
| <div class="block">The maximum <code>precision</code> value you can set in <a href="../../../../../../org/apache/beam/sdk/extensions/zetasketch/HllCount.Init.Builder.html#withPrecision-int-"><code>HllCount.Init.Builder.withPrecision(int)</code></a> is |
| 24.</div> |
| </td> |
| </tr> |
| <tr class="altColor"> |
| <td class="colFirst"><code>static int</code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../org/apache/beam/sdk/extensions/zetasketch/HllCount.html#MINIMUM_PRECISION">MINIMUM_PRECISION</a></span></code> |
| <div class="block">The minimum <code>precision</code> value you can set in <a href="../../../../../../org/apache/beam/sdk/extensions/zetasketch/HllCount.Init.Builder.html#withPrecision-int-"><code>HllCount.Init.Builder.withPrecision(int)</code></a> is |
| 10.</div> |
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| <td class="colFirst"><code>static byte[]</code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../org/apache/beam/sdk/extensions/zetasketch/HllCount.html#getSketchFromByteBuffer-java.nio.ByteBuffer-">getSketchFromByteBuffer</a></span>(java.nio.ByteBuffer bf)</code> |
| <div class="block">Converts the passed-in sketch from <code>ByteBuffer</code> to <code>byte[]</code>, mapping <code>null |
| ByteBuffer</code>s (representing empty sketches) to empty <code>byte[]</code>s.</div> |
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| <h4>MINIMUM_PRECISION</h4> |
| <pre>public static final int MINIMUM_PRECISION</pre> |
| <div class="block">The minimum <code>precision</code> value you can set in <a href="../../../../../../org/apache/beam/sdk/extensions/zetasketch/HllCount.Init.Builder.html#withPrecision-int-"><code>HllCount.Init.Builder.withPrecision(int)</code></a> is |
| 10.</div> |
| <dl> |
| <dt><span class="seeLabel">See Also:</span></dt> |
| <dd><a href="../../../../../../constant-values.html#org.apache.beam.sdk.extensions.zetasketch.HllCount.MINIMUM_PRECISION">Constant Field Values</a></dd> |
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| <h4>MAXIMUM_PRECISION</h4> |
| <pre>public static final int MAXIMUM_PRECISION</pre> |
| <div class="block">The maximum <code>precision</code> value you can set in <a href="../../../../../../org/apache/beam/sdk/extensions/zetasketch/HllCount.Init.Builder.html#withPrecision-int-"><code>HllCount.Init.Builder.withPrecision(int)</code></a> is |
| 24.</div> |
| <dl> |
| <dt><span class="seeLabel">See Also:</span></dt> |
| <dd><a href="../../../../../../constant-values.html#org.apache.beam.sdk.extensions.zetasketch.HllCount.MAXIMUM_PRECISION">Constant Field Values</a></dd> |
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| <h4>DEFAULT_PRECISION</h4> |
| <pre>public static final int DEFAULT_PRECISION</pre> |
| <div class="block">The default <code>precision</code> value used in <a href="../../../../../../org/apache/beam/sdk/extensions/zetasketch/HllCount.Init.Builder.html#withPrecision-int-"><code>HllCount.Init.Builder.withPrecision(int)</code></a> is |
| 15.</div> |
| <dl> |
| <dt><span class="seeLabel">See Also:</span></dt> |
| <dd><a href="../../../../../../constant-values.html#org.apache.beam.sdk.extensions.zetasketch.HllCount.DEFAULT_PRECISION">Constant Field Values</a></dd> |
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| <h4>getSketchFromByteBuffer</h4> |
| <pre>public static byte[] getSketchFromByteBuffer(<a href="https://static.javadoc.io/com.google.code.findbugs/jsr305/3.0.2/javax/annotation/Nullable.html?is-external=true" title="class or interface in javax.annotation">@Nullable</a> |
| java.nio.ByteBuffer bf)</pre> |
| <div class="block">Converts the passed-in sketch from <code>ByteBuffer</code> to <code>byte[]</code>, mapping <code>null |
| ByteBuffer</code>s (representing empty sketches) to empty <code>byte[]</code>s. |
| |
| <p>Utility method to convert sketches materialized with ZetaSQL/BigQuery to valid inputs for |
| Beam <code>HllCount</code> transforms.</div> |
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