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| <h2 title="Interface BatchScanner" class="title">Interface BatchScanner</h2> |
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| <pre>public interface <span class="typeNameLabel">BatchScanner</span> |
| extends <a href="../../../../../org/apache/accumulo/core/client/ScannerBase.html" title="interface in org.apache.accumulo.core.client">ScannerBase</a></pre> |
| <div class="block">In exchange for possibly <b>returning scanned entries out of order</b>, BatchScanner |
| implementations may scan an Accumulo table more efficiently by |
| <ul> |
| <li>Looking up multiple ranges in parallel. Parallelism is constrained by the number of threads |
| available to the BatchScanner, set in its constructor.</li> |
| <li>Breaking up large ranges into subranges. Often the number and boundaries of subranges are |
| determined by a table's split points.</li> |
| <li>Combining multiple ranges into a single RPC call to a tablet server.</li> |
| </ul> |
| |
| The above techniques lead to better performance than a <a href="../../../../../org/apache/accumulo/core/client/Scanner.html" title="interface in org.apache.accumulo.core.client"><code>Scanner</code></a> in use cases such as |
| <ul> |
| <li>Retrieving many small ranges</li> |
| <li>Scanning a large range that returns many entries</li> |
| <li>Running server-side iterators that perform computation, even if few entries are returned from |
| the scan itself</li> |
| </ul> |
| |
| To re-emphasize, only use a BatchScanner when you do not care whether returned data is in sorted |
| order. Use a <a href="../../../../../org/apache/accumulo/core/client/Scanner.html" title="interface in org.apache.accumulo.core.client"><code>Scanner</code></a> instead when sorted order is important. |
| |
| <p> |
| A BatchScanner instance will use no more threads than provided in the construction of the |
| BatchScanner implementation. Multiple invocations of <code>iterator()</code> will all share the |
| same resources of the instance. A new BatchScanner instance should be created to use allocate |
| additional threads.</div> |
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| <h3>Method Summary</h3> |
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| <tr> |
| <th class="colFirst" scope="col">Modifier and Type</th> |
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| <tr id="i0" class="altColor"> |
| <td class="colFirst"><code>void</code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../org/apache/accumulo/core/client/BatchScanner.html#close--">close</a></span>()</code> |
| <div class="block">Closes any underlying connections on the scanner.</div> |
| </td> |
| </tr> |
| <tr id="i1" class="rowColor"> |
| <td class="colFirst"><code>void</code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../org/apache/accumulo/core/client/BatchScanner.html#setRanges-java.util.Collection-">setRanges</a></span>(<a href="https://docs.oracle.com/javase/8/docs/api/java/util/Collection.html?is-external=true" title="class or interface in java.util">Collection</a><<a href="../../../../../org/apache/accumulo/core/data/Range.html" title="class in org.apache.accumulo.core.data">Range</a>> ranges)</code> |
| <div class="block">Allows scanning over multiple ranges efficiently.</div> |
| </td> |
| </tr> |
| <tr id="i2" class="altColor"> |
| <td class="colFirst"><code>void</code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../org/apache/accumulo/core/client/BatchScanner.html#setTimeout-long-java.util.concurrent.TimeUnit-">setTimeout</a></span>(long timeout, |
| <a href="https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/TimeUnit.html?is-external=true" title="class or interface in java.util.concurrent">TimeUnit</a> timeUnit)</code> |
| <div class="block">This setting determines how long a scanner will automatically retry when a failure occurs.</div> |
| </td> |
| </tr> |
| </table> |
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| <h3>Methods inherited from interface org.apache.accumulo.core.client.<a href="../../../../../org/apache/accumulo/core/client/ScannerBase.html" title="interface in org.apache.accumulo.core.client">ScannerBase</a></h3> |
| <code><a href="../../../../../org/apache/accumulo/core/client/ScannerBase.html#addScanIterator-org.apache.accumulo.core.client.IteratorSetting-">addScanIterator</a>, <a href="../../../../../org/apache/accumulo/core/client/ScannerBase.html#clearClassLoaderContext--">clearClassLoaderContext</a>, <a href="../../../../../org/apache/accumulo/core/client/ScannerBase.html#clearColumns--">clearColumns</a>, <a href="../../../../../org/apache/accumulo/core/client/ScannerBase.html#clearSamplerConfiguration--">clearSamplerConfiguration</a>, <a href="../../../../../org/apache/accumulo/core/client/ScannerBase.html#clearScanIterators--">clearScanIterators</a>, <a href="../../../../../org/apache/accumulo/core/client/ScannerBase.html#fetchColumn-org.apache.accumulo.core.client.IteratorSetting.Column-">fetchColumn</a>, <a href="../../../../../org/apache/accumulo/core/client/ScannerBase.html#fetchColumn-org.apache.hadoop.io.Text-org.apache.hadoop.io.Text-">fetchColumn</a>, <a href="../../../../../org/apache/accumulo/core/client/ScannerBase.html#fetchColumnFamily-org.apache.hadoop.io.Text-">fetchColumnFamily</a>, <a href="../../../../../org/apache/accumulo/core/client/ScannerBase.html#getAuthorizations--">getAuthorizations</a>, <a href="../../../../../org/apache/accumulo/core/client/ScannerBase.html#getBatchTimeout-java.util.concurrent.TimeUnit-">getBatchTimeout</a>, <a href="../../../../../org/apache/accumulo/core/client/ScannerBase.html#getClassLoaderContext--">getClassLoaderContext</a>, <a href="../../../../../org/apache/accumulo/core/client/ScannerBase.html#getSamplerConfiguration--">getSamplerConfiguration</a>, <a href="../../../../../org/apache/accumulo/core/client/ScannerBase.html#getTimeout-java.util.concurrent.TimeUnit-">getTimeout</a>, <a href="../../../../../org/apache/accumulo/core/client/ScannerBase.html#iterator--">iterator</a>, <a href="../../../../../org/apache/accumulo/core/client/ScannerBase.html#removeScanIterator-java.lang.String-">removeScanIterator</a>, <a href="../../../../../org/apache/accumulo/core/client/ScannerBase.html#setBatchTimeout-long-java.util.concurrent.TimeUnit-">setBatchTimeout</a>, <a href="../../../../../org/apache/accumulo/core/client/ScannerBase.html#setClassLoaderContext-java.lang.String-">setClassLoaderContext</a>, <a href="../../../../../org/apache/accumulo/core/client/ScannerBase.html#setSamplerConfiguration-org.apache.accumulo.core.client.sample.SamplerConfiguration-">setSamplerConfiguration</a>, <a href="../../../../../org/apache/accumulo/core/client/ScannerBase.html#updateScanIteratorOption-java.lang.String-java.lang.String-java.lang.String-">updateScanIteratorOption</a></code></li> |
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| <h3>Methods inherited from interface java.lang.<a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Iterable.html?is-external=true" title="class or interface in java.lang">Iterable</a></h3> |
| <code><a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Iterable.html?is-external=true#forEach-java.util.function.Consumer-" title="class or interface in java.lang">forEach</a>, <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Iterable.html?is-external=true#spliterator--" title="class or interface in java.lang">spliterator</a></code></li> |
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| <a name="setRanges-java.util.Collection-"> |
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| <h4>setRanges</h4> |
| <pre>void setRanges(<a href="https://docs.oracle.com/javase/8/docs/api/java/util/Collection.html?is-external=true" title="class or interface in java.util">Collection</a><<a href="../../../../../org/apache/accumulo/core/data/Range.html" title="class in org.apache.accumulo.core.data">Range</a>> ranges)</pre> |
| <div class="block">Allows scanning over multiple ranges efficiently.</div> |
| <dl> |
| <dt><span class="paramLabel">Parameters:</span></dt> |
| <dd><code>ranges</code> - specifies the non-overlapping ranges to query</dd> |
| </dl> |
| </li> |
| </ul> |
| <a name="close--"> |
| <!-- --> |
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| <h4>close</h4> |
| <pre>void close()</pre> |
| <div class="block"><span class="descfrmTypeLabel">Description copied from interface: <code><a href="../../../../../org/apache/accumulo/core/client/ScannerBase.html#close--">ScannerBase</a></code></span></div> |
| <div class="block">Closes any underlying connections on the scanner. This may invalidate any iterators derived |
| from the Scanner, causing them to throw exceptions.</div> |
| <dl> |
| <dt><span class="overrideSpecifyLabel">Specified by:</span></dt> |
| <dd><code><a href="https://docs.oracle.com/javase/8/docs/api/java/lang/AutoCloseable.html?is-external=true#close--" title="class or interface in java.lang">close</a></code> in interface <code><a href="https://docs.oracle.com/javase/8/docs/api/java/lang/AutoCloseable.html?is-external=true" title="class or interface in java.lang">AutoCloseable</a></code></dd> |
| <dt><span class="overrideSpecifyLabel">Specified by:</span></dt> |
| <dd><code><a href="../../../../../org/apache/accumulo/core/client/ScannerBase.html#close--">close</a></code> in interface <code><a href="../../../../../org/apache/accumulo/core/client/ScannerBase.html" title="interface in org.apache.accumulo.core.client">ScannerBase</a></code></dd> |
| </dl> |
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| <a name="setTimeout-long-java.util.concurrent.TimeUnit-"> |
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| <h4>setTimeout</h4> |
| <pre>void setTimeout(long timeout, |
| <a href="https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/TimeUnit.html?is-external=true" title="class or interface in java.util.concurrent">TimeUnit</a> timeUnit)</pre> |
| <div class="block">This setting determines how long a scanner will automatically retry when a failure occurs. By |
| default, a scanner will retry forever. |
| |
| <p> |
| Setting the timeout to zero (with any time unit) or <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Long.html?is-external=true#MAX_VALUE" title="class or interface in java.lang"><code>Long.MAX_VALUE</code></a> (with |
| <a href="https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/TimeUnit.html?is-external=true#MILLISECONDS" title="class or interface in java.util.concurrent"><code>TimeUnit.MILLISECONDS</code></a>) means no timeout. |
| |
| <p> |
| The batch scanner will accomplish as much work as possible before throwing an exception. |
| BatchScanner iterators will throw a <a href="../../../../../org/apache/accumulo/core/client/TimedOutException.html" title="class in org.apache.accumulo.core.client"><code>TimedOutException</code></a> when all needed servers timeout.</div> |
| <dl> |
| <dt><span class="overrideSpecifyLabel">Specified by:</span></dt> |
| <dd><code><a href="../../../../../org/apache/accumulo/core/client/ScannerBase.html#setTimeout-long-java.util.concurrent.TimeUnit-">setTimeout</a></code> in interface <code><a href="../../../../../org/apache/accumulo/core/client/ScannerBase.html" title="interface in org.apache.accumulo.core.client">ScannerBase</a></code></dd> |
| <dt><span class="paramLabel">Parameters:</span></dt> |
| <dd><code>timeout</code> - the length of the timeout</dd> |
| <dd><code>timeUnit</code> - the units of the timeout</dd> |
| </dl> |
| </li> |
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