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| <h2 title="Interface BloomFilter" class="title">Interface BloomFilter</h2> |
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| <dt>All Superinterfaces:</dt> |
| <dd><a href="../../../../../org/apache/hadoop/hbase/util/BloomFilterBase.html" title="interface in org.apache.hadoop.hbase.util">BloomFilterBase</a></dd> |
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| <dt>All Known Implementing Classes:</dt> |
| <dd><a href="../../../../../org/apache/hadoop/hbase/io/hfile/CompoundBloomFilter.html" title="class in org.apache.hadoop.hbase.io.hfile">CompoundBloomFilter</a></dd> |
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| <pre>@InterfaceAudience.Private |
| public interface <a href="../../../../../src-html/org/apache/hadoop/hbase/util/BloomFilter.html#line.77">BloomFilter</a> |
| extends <a href="../../../../../org/apache/hadoop/hbase/util/BloomFilterBase.html" title="interface in org.apache.hadoop.hbase.util">BloomFilterBase</a></pre> |
| <div class="block">Implements a <i>Bloom filter</i>, as defined by Bloom in 1970. |
| <p> |
| The Bloom filter is a data structure that was introduced in 1970 and that has |
| been adopted by the networking research community in the past decade thanks |
| to the bandwidth efficiencies that it offers for the transmission of set |
| membership information between networked hosts. A sender encodes the |
| information into a bit vector, the Bloom filter, that is more compact than a |
| conventional representation. Computation and space costs for construction are |
| linear in the number of elements. The receiver uses the filter to test |
| whether various elements are members of the set. Though the filter will |
| occasionally return a false positive, it will never return a false negative. |
| When creating the filter, the sender can choose its desired point in a |
| trade-off between the false positive rate and the size. |
| |
| <p> |
| Originally inspired by <a href="http://www.one-lab.org/">European Commission |
| One-Lab Project 034819</a>. |
| |
| Bloom filters are very sensitive to the number of elements inserted into |
| them. For HBase, the number of entries depends on the size of the data stored |
| in the column. Currently the default region size is 256MB, so entry count ~= |
| 256MB / (average value size for column). Despite this rule of thumb, there is |
| no efficient way to calculate the entry count after compactions. Therefore, |
| it is often easier to use a dynamic bloom filter that will add extra space |
| instead of allowing the error rate to grow. |
| |
| ( http://www.eecs.harvard.edu/~michaelm/NEWWORK/postscripts/BloomFilterSurvey |
| .pdf ) |
| |
| m denotes the number of bits in the Bloom filter (bitSize) n denotes the |
| number of elements inserted into the Bloom filter (maxKeys) k represents the |
| number of hash functions used (nbHash) e represents the desired false |
| positive rate for the bloom (err) |
| |
| If we fix the error rate (e) and know the number of entries, then the optimal |
| bloom size m = -(n * ln(err) / (ln(2)^2) ~= n * ln(err) / ln(0.6185) |
| |
| The probability of false positives is minimized when k = m/n ln(2).</div> |
| <dl> |
| <dt><span class="seeLabel">See Also:</span></dt> |
| <dd><a href="../../../../../org/apache/hadoop/hbase/util/BloomFilter.html" title="interface in org.apache.hadoop.hbase.util"><code>The general behavior of a filter</code></a>, |
| <a |
| href="http://portal.acm.org/citation.cfm?id=362692&dl=ACM&coll=portal"> |
| Space/Time Trade-Offs in Hash Coding with Allowable Errors</a>, |
| <a href="../../../../../org/apache/hadoop/hbase/util/BloomFilterWriter.html" title="interface in org.apache.hadoop.hbase.util"><code>for the ability to add elements to a Bloom filter</code></a></dd> |
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| <tr id="i0" class="altColor"> |
| <td class="colFirst"><code>boolean</code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../org/apache/hadoop/hbase/util/BloomFilter.html#contains-byte:A-int-int-org.apache.hadoop.hbase.nio.ByteBuff-">contains</a></span>(byte[] buf, |
| int offset, |
| int length, |
| <a href="../../../../../org/apache/hadoop/hbase/nio/ByteBuff.html" title="class in org.apache.hadoop.hbase.nio">ByteBuff</a> bloom)</code> |
| <div class="block">Check if the specified key is contained in the bloom filter.</div> |
| </td> |
| </tr> |
| <tr id="i1" class="rowColor"> |
| <td class="colFirst"><code>boolean</code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../org/apache/hadoop/hbase/util/BloomFilter.html#contains-org.apache.hadoop.hbase.Cell-org.apache.hadoop.hbase.nio.ByteBuff-org.apache.hadoop.hbase.regionserver.BloomType-">contains</a></span>(<a href="../../../../../org/apache/hadoop/hbase/Cell.html" title="interface in org.apache.hadoop.hbase">Cell</a> keyCell, |
| <a href="../../../../../org/apache/hadoop/hbase/nio/ByteBuff.html" title="class in org.apache.hadoop.hbase.nio">ByteBuff</a> bloom, |
| <a href="../../../../../org/apache/hadoop/hbase/regionserver/BloomType.html" title="enum in org.apache.hadoop.hbase.regionserver">BloomType</a> type)</code> |
| <div class="block">Check if the specified key is contained in the bloom filter.</div> |
| </td> |
| </tr> |
| <tr id="i2" class="altColor"> |
| <td class="colFirst"><code>boolean</code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../org/apache/hadoop/hbase/util/BloomFilter.html#supportsAutoLoading--">supportsAutoLoading</a></span>()</code> </td> |
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| <h3>Methods inherited from interface org.apache.hadoop.hbase.util.<a href="../../../../../org/apache/hadoop/hbase/util/BloomFilterBase.html" title="interface in org.apache.hadoop.hbase.util">BloomFilterBase</a></h3> |
| <code><a href="../../../../../org/apache/hadoop/hbase/util/BloomFilterBase.html#getByteSize--">getByteSize</a>, <a href="../../../../../org/apache/hadoop/hbase/util/BloomFilterBase.html#getKeyCount--">getKeyCount</a>, <a href="../../../../../org/apache/hadoop/hbase/util/BloomFilterBase.html#getMaxKeys--">getMaxKeys</a></code></li> |
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| <h4>contains</h4> |
| <pre>boolean <a href="../../../../../src-html/org/apache/hadoop/hbase/util/BloomFilter.html#line.87">contains</a>(<a href="../../../../../org/apache/hadoop/hbase/Cell.html" title="interface in org.apache.hadoop.hbase">Cell</a> keyCell, |
| <a href="../../../../../org/apache/hadoop/hbase/nio/ByteBuff.html" title="class in org.apache.hadoop.hbase.nio">ByteBuff</a> bloom, |
| <a href="../../../../../org/apache/hadoop/hbase/regionserver/BloomType.html" title="enum in org.apache.hadoop.hbase.regionserver">BloomType</a> type)</pre> |
| <div class="block">Check if the specified key is contained in the bloom filter.</div> |
| <dl> |
| <dt><span class="paramLabel">Parameters:</span></dt> |
| <dd><code>keyCell</code> - the key to check for the existence of</dd> |
| <dd><code>bloom</code> - bloom filter data to search. This can be null if auto-loading |
| is supported.</dd> |
| <dd><code>type</code> - The type of Bloom ROW/ ROW_COL</dd> |
| <dt><span class="returnLabel">Returns:</span></dt> |
| <dd>true if matched by bloom, false if not</dd> |
| </dl> |
| </li> |
| </ul> |
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| <h4>contains</h4> |
| <pre>boolean <a href="../../../../../src-html/org/apache/hadoop/hbase/util/BloomFilter.html#line.98">contains</a>(byte[] buf, |
| int offset, |
| int length, |
| <a href="../../../../../org/apache/hadoop/hbase/nio/ByteBuff.html" title="class in org.apache.hadoop.hbase.nio">ByteBuff</a> bloom)</pre> |
| <div class="block">Check if the specified key is contained in the bloom filter.</div> |
| <dl> |
| <dt><span class="paramLabel">Parameters:</span></dt> |
| <dd><code>buf</code> - data to check for existence of</dd> |
| <dd><code>offset</code> - offset into the data</dd> |
| <dd><code>length</code> - length of the data</dd> |
| <dd><code>bloom</code> - bloom filter data to search. This can be null if auto-loading |
| is supported.</dd> |
| <dt><span class="returnLabel">Returns:</span></dt> |
| <dd>true if matched by bloom, false if not</dd> |
| </dl> |
| </li> |
| </ul> |
| <a name="supportsAutoLoading--"> |
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| <h4>supportsAutoLoading</h4> |
| <pre>boolean <a href="../../../../../src-html/org/apache/hadoop/hbase/util/BloomFilter.html#line.104">supportsAutoLoading</a>()</pre> |
| <dl> |
| <dt><span class="returnLabel">Returns:</span></dt> |
| <dd>true if this Bloom filter can automatically load its data |
| and thus allows a null byte buffer to be passed to contains()</dd> |
| </dl> |
| </li> |
| </ul> |
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