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| <div class="subTitle">org.apache.hadoop.io.file.tfile</div> |
| <h2 title="Class TFile" class="title">Class TFile</h2> |
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| <ul class="inheritance"> |
| <li><a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true" title="class or interface in java.lang">java.lang.Object</a></li> |
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| <ul class="inheritance"> |
| <li>org.apache.hadoop.io.file.tfile.TFile</li> |
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| <pre>@InterfaceAudience.Public |
| @InterfaceStability.Evolving |
| public class <span class="typeNameLabel">TFile</span> |
| extends <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true" title="class or interface in java.lang">Object</a></pre> |
| <div class="block">A TFile is a container of key-value pairs. Both keys and values are type-less |
| bytes. Keys are restricted to 64KB, value length is not restricted |
| (practically limited to the available disk storage). TFile further provides |
| the following features: |
| <ul> |
| <li>Block Compression. |
| <li>Named meta data blocks. |
| <li>Sorted or unsorted keys. |
| <li>Seek by key or by file offset. |
| </ul> |
| The memory footprint of a TFile includes the following: |
| <ul> |
| <li>Some constant overhead of reading or writing a compressed block. |
| <ul> |
| <li>Each compressed block requires one compression/decompression codec for |
| I/O. |
| <li>Temporary space to buffer the key. |
| <li>Temporary space to buffer the value (for TFile.Writer only). Values are |
| chunk encoded, so that we buffer at most one chunk of user data. By default, |
| the chunk buffer is 1MB. Reading chunked value does not require additional |
| memory. |
| </ul> |
| <li>TFile index, which is proportional to the total number of Data Blocks. |
| The total amount of memory needed to hold the index can be estimated as |
| (56+AvgKeySize)*NumBlocks. |
| <li>MetaBlock index, which is proportional to the total number of Meta |
| Blocks.The total amount of memory needed to hold the index for Meta Blocks |
| can be estimated as (40+AvgMetaBlockName)*NumMetaBlock. |
| </ul> |
| <p> |
| The behavior of TFile can be customized by the following variables through |
| Configuration: |
| <ul> |
| <li><b>tfile.io.chunk.size</b>: Value chunk size. Integer (in bytes). Default |
| to 1MB. Values of the length less than the chunk size is guaranteed to have |
| known value length in read time (See |
| <a href="../../../../../../org/apache/hadoop/io/file/tfile/TFile.Reader.Scanner.Entry.html#isValueLengthKnown--"><code>TFile.Reader.Scanner.Entry.isValueLengthKnown()</code></a>). |
| <li><b>tfile.fs.output.buffer.size</b>: Buffer size used for |
| FSDataOutputStream. Integer (in bytes). Default to 256KB. |
| <li><b>tfile.fs.input.buffer.size</b>: Buffer size used for |
| FSDataInputStream. Integer (in bytes). Default to 256KB. |
| </ul> |
| <p> |
| Suggestions on performance optimization. |
| <ul> |
| <li>Minimum block size. We recommend a setting of minimum block size between |
| 256KB to 1MB for general usage. Larger block size is preferred if files are |
| primarily for sequential access. However, it would lead to inefficient random |
| access (because there are more data to decompress). Smaller blocks are good |
| for random access, but require more memory to hold the block index, and may |
| be slower to create (because we must flush the compressor stream at the |
| conclusion of each data block, which leads to an FS I/O flush). Further, due |
| to the internal caching in Compression codec, the smallest possible block |
| size would be around 20KB-30KB. |
| <li>The current implementation does not offer true multi-threading for |
| reading. The implementation uses FSDataInputStream seek()+read(), which is |
| shown to be much faster than positioned-read call in single thread mode. |
| However, it also means that if multiple threads attempt to access the same |
| TFile (using multiple scanners) simultaneously, the actual I/O is carried out |
| sequentially even if they access different DFS blocks. |
| <li>Compression codec. Use "none" if the data is not very compressable (by |
| compressable, I mean a compression ratio at least 2:1). Generally, use "lzo" |
| as the starting point for experimenting. "gz" overs slightly better |
| compression ratio over "lzo" but requires 4x CPU to compress and 2x CPU to |
| decompress, comparing to "lzo". |
| <li>File system buffering, if the underlying FSDataInputStream and |
| FSDataOutputStream is already adequately buffered; or if applications |
| reads/writes keys and values in large buffers, we can reduce the sizes of |
| input/output buffering in TFile layer by setting the configuration parameters |
| "tfile.fs.input.buffer.size" and "tfile.fs.output.buffer.size". |
| </ul> |
| |
| Some design rationale behind TFile can be found at <a |
| href=https://issues.apache.org/jira/browse/HADOOP-3315>Hadoop-3315</a>.</div> |
| </li> |
| </ul> |
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| <h3>Nested Class Summary</h3> |
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| <caption><span>Nested Classes</span><span class="tabEnd"> </span></caption> |
| <tr> |
| <th class="colFirst" scope="col">Modifier and Type</th> |
| <th class="colLast" scope="col">Class and Description</th> |
| </tr> |
| <tr class="altColor"> |
| <td class="colFirst"><code>static class </code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../org/apache/hadoop/io/file/tfile/TFile.Reader.html" title="class in org.apache.hadoop.io.file.tfile">TFile.Reader</a></span></code> |
| <div class="block">TFile Reader.</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/hadoop/io/file/tfile/TFile.Writer.html" title="class in org.apache.hadoop.io.file.tfile">TFile.Writer</a></span></code> |
| <div class="block">TFile Writer.</div> |
| </td> |
| </tr> |
| </table> |
| </li> |
| </ul> |
| <!-- =========== FIELD SUMMARY =========== --> |
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| <h3>Field Summary</h3> |
| <table class="memberSummary" border="0" cellpadding="3" cellspacing="0" summary="Field Summary table, listing fields, and an explanation"> |
| <caption><span>Fields</span><span class="tabEnd"> </span></caption> |
| <tr> |
| <th class="colFirst" scope="col">Modifier and Type</th> |
| <th class="colLast" scope="col">Field and Description</th> |
| </tr> |
| <tr class="altColor"> |
| <td class="colFirst"><code>static <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</a></code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../org/apache/hadoop/io/file/tfile/TFile.html#COMPARATOR_JCLASS">COMPARATOR_JCLASS</a></span></code> |
| <div class="block">comparator prefix: java class</div> |
| </td> |
| </tr> |
| <tr class="rowColor"> |
| <td class="colFirst"><code>static <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</a></code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../org/apache/hadoop/io/file/tfile/TFile.html#COMPARATOR_MEMCMP">COMPARATOR_MEMCMP</a></span></code> |
| <div class="block">comparator: memcmp</div> |
| </td> |
| </tr> |
| <tr class="altColor"> |
| <td class="colFirst"><code>static <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</a></code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../org/apache/hadoop/io/file/tfile/TFile.html#COMPRESSION_GZ">COMPRESSION_GZ</a></span></code> |
| <div class="block">compression: gzip</div> |
| </td> |
| </tr> |
| <tr class="rowColor"> |
| <td class="colFirst"><code>static <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</a></code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../org/apache/hadoop/io/file/tfile/TFile.html#COMPRESSION_LZO">COMPRESSION_LZO</a></span></code> |
| <div class="block">compression: lzo</div> |
| </td> |
| </tr> |
| <tr class="altColor"> |
| <td class="colFirst"><code>static <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</a></code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../org/apache/hadoop/io/file/tfile/TFile.html#COMPRESSION_NONE">COMPRESSION_NONE</a></span></code> |
| <div class="block">compression: none</div> |
| </td> |
| </tr> |
| </table> |
| </li> |
| </ul> |
| <!-- ========== METHOD SUMMARY =========== --> |
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| <h3>Method Summary</h3> |
| <table class="memberSummary" border="0" cellpadding="3" cellspacing="0" summary="Method Summary table, listing methods, and an explanation"> |
| <caption><span id="t0" class="activeTableTab"><span>All Methods</span><span class="tabEnd"> </span></span><span id="t1" class="tableTab"><span><a href="javascript:show(1);">Static Methods</a></span><span class="tabEnd"> </span></span><span id="t4" class="tableTab"><span><a href="javascript:show(8);">Concrete Methods</a></span><span class="tabEnd"> </span></span></caption> |
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| <tr id="i0" class="altColor"> |
| <td class="colFirst"><code>static <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</a>[]</code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../org/apache/hadoop/io/file/tfile/TFile.html#getSupportedCompressionAlgorithms--">getSupportedCompressionAlgorithms</a></span>()</code> |
| <div class="block">Get names of supported compression algorithms.</div> |
| </td> |
| </tr> |
| <tr id="i1" class="rowColor"> |
| <td class="colFirst"><code>static void</code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../org/apache/hadoop/io/file/tfile/TFile.html#main-java.lang.String:A-">main</a></span>(<a href="https://docs.oracle.com/javase/8/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</a>[] args)</code> |
| <div class="block">Dumping the TFile information.</div> |
| </td> |
| </tr> |
| <tr id="i2" class="altColor"> |
| <td class="colFirst"><code>static <a href="https://docs.oracle.com/javase/8/docs/api/java/util/Comparator.html?is-external=true" title="class or interface in java.util">Comparator</a><<a href="../../../../../../org/apache/hadoop/io/file/tfile/RawComparable.html" title="interface in org.apache.hadoop.io.file.tfile">RawComparable</a>></code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../org/apache/hadoop/io/file/tfile/TFile.html#makeComparator-java.lang.String-">makeComparator</a></span>(<a href="https://docs.oracle.com/javase/8/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</a> name)</code> |
| <div class="block">Make a raw comparator from a string name.</div> |
| </td> |
| </tr> |
| </table> |
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| <!-- --> |
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| <h3>Methods inherited from class java.lang.<a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true" title="class or interface in java.lang">Object</a></h3> |
| <code><a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true#clone--" title="class or interface in java.lang">clone</a>, <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true#equals-java.lang.Object-" title="class or interface in java.lang">equals</a>, <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true#finalize--" title="class or interface in java.lang">finalize</a>, <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true#getClass--" title="class or interface in java.lang">getClass</a>, <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true#hashCode--" title="class or interface in java.lang">hashCode</a>, <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true#notify--" title="class or interface in java.lang">notify</a>, <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true#notifyAll--" title="class or interface in java.lang">notifyAll</a>, <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true#toString--" title="class or interface in java.lang">toString</a>, <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true#wait--" title="class or interface in java.lang">wait</a>, <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true#wait-long-" title="class or interface in java.lang">wait</a>, <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html?is-external=true#wait-long-int-" title="class or interface in java.lang">wait</a></code></li> |
| </ul> |
| </li> |
| </ul> |
| </li> |
| </ul> |
| </div> |
| <div class="details"> |
| <ul class="blockList"> |
| <li class="blockList"> |
| <!-- ============ FIELD DETAIL =========== --> |
| <ul class="blockList"> |
| <li class="blockList"><a name="field.detail"> |
| <!-- --> |
| </a> |
| <h3>Field Detail</h3> |
| <a name="COMPRESSION_GZ"> |
| <!-- --> |
| </a> |
| <ul class="blockList"> |
| <li class="blockList"> |
| <h4>COMPRESSION_GZ</h4> |
| <pre>public static final <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</a> COMPRESSION_GZ</pre> |
| <div class="block">compression: gzip</div> |
| <dl> |
| <dt><span class="seeLabel">See Also:</span></dt> |
| <dd><a href="../../../../../../constant-values.html#org.apache.hadoop.io.file.tfile.TFile.COMPRESSION_GZ">Constant Field Values</a></dd> |
| </dl> |
| </li> |
| </ul> |
| <a name="COMPRESSION_LZO"> |
| <!-- --> |
| </a> |
| <ul class="blockList"> |
| <li class="blockList"> |
| <h4>COMPRESSION_LZO</h4> |
| <pre>public static final <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</a> COMPRESSION_LZO</pre> |
| <div class="block">compression: lzo</div> |
| <dl> |
| <dt><span class="seeLabel">See Also:</span></dt> |
| <dd><a href="../../../../../../constant-values.html#org.apache.hadoop.io.file.tfile.TFile.COMPRESSION_LZO">Constant Field Values</a></dd> |
| </dl> |
| </li> |
| </ul> |
| <a name="COMPRESSION_NONE"> |
| <!-- --> |
| </a> |
| <ul class="blockList"> |
| <li class="blockList"> |
| <h4>COMPRESSION_NONE</h4> |
| <pre>public static final <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</a> COMPRESSION_NONE</pre> |
| <div class="block">compression: none</div> |
| <dl> |
| <dt><span class="seeLabel">See Also:</span></dt> |
| <dd><a href="../../../../../../constant-values.html#org.apache.hadoop.io.file.tfile.TFile.COMPRESSION_NONE">Constant Field Values</a></dd> |
| </dl> |
| </li> |
| </ul> |
| <a name="COMPARATOR_MEMCMP"> |
| <!-- --> |
| </a> |
| <ul class="blockList"> |
| <li class="blockList"> |
| <h4>COMPARATOR_MEMCMP</h4> |
| <pre>public static final <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</a> COMPARATOR_MEMCMP</pre> |
| <div class="block">comparator: memcmp</div> |
| <dl> |
| <dt><span class="seeLabel">See Also:</span></dt> |
| <dd><a href="../../../../../../constant-values.html#org.apache.hadoop.io.file.tfile.TFile.COMPARATOR_MEMCMP">Constant Field Values</a></dd> |
| </dl> |
| </li> |
| </ul> |
| <a name="COMPARATOR_JCLASS"> |
| <!-- --> |
| </a> |
| <ul class="blockListLast"> |
| <li class="blockList"> |
| <h4>COMPARATOR_JCLASS</h4> |
| <pre>public static final <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</a> COMPARATOR_JCLASS</pre> |
| <div class="block">comparator prefix: java class</div> |
| <dl> |
| <dt><span class="seeLabel">See Also:</span></dt> |
| <dd><a href="../../../../../../constant-values.html#org.apache.hadoop.io.file.tfile.TFile.COMPARATOR_JCLASS">Constant Field Values</a></dd> |
| </dl> |
| </li> |
| </ul> |
| </li> |
| </ul> |
| <!-- ============ METHOD DETAIL ========== --> |
| <ul class="blockList"> |
| <li class="blockList"><a name="method.detail"> |
| <!-- --> |
| </a> |
| <h3>Method Detail</h3> |
| <a name="makeComparator-java.lang.String-"> |
| <!-- --> |
| </a> |
| <ul class="blockList"> |
| <li class="blockList"> |
| <h4>makeComparator</h4> |
| <pre>public static <a href="https://docs.oracle.com/javase/8/docs/api/java/util/Comparator.html?is-external=true" title="class or interface in java.util">Comparator</a><<a href="../../../../../../org/apache/hadoop/io/file/tfile/RawComparable.html" title="interface in org.apache.hadoop.io.file.tfile">RawComparable</a>> makeComparator(<a href="https://docs.oracle.com/javase/8/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</a> name)</pre> |
| <div class="block">Make a raw comparator from a string name.</div> |
| <dl> |
| <dt><span class="paramLabel">Parameters:</span></dt> |
| <dd><code>name</code> - Comparator name</dd> |
| <dt><span class="returnLabel">Returns:</span></dt> |
| <dd>A RawComparable comparator.</dd> |
| </dl> |
| </li> |
| </ul> |
| <a name="getSupportedCompressionAlgorithms--"> |
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| </a> |
| <ul class="blockList"> |
| <li class="blockList"> |
| <h4>getSupportedCompressionAlgorithms</h4> |
| <pre>public static <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</a>[] getSupportedCompressionAlgorithms()</pre> |
| <div class="block">Get names of supported compression algorithms. The names are acceptable by |
| TFile.Writer.</div> |
| <dl> |
| <dt><span class="returnLabel">Returns:</span></dt> |
| <dd>Array of strings, each represents a supported compression |
| algorithm. Currently, the following compression algorithms are |
| supported. |
| <ul> |
| <li>"none" - No compression. |
| <li>"lzo" - LZO compression. |
| <li>"gz" - GZIP compression. |
| </ul></dd> |
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| <pre>public static void main(<a href="https://docs.oracle.com/javase/8/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</a>[] args)</pre> |
| <div class="block">Dumping the TFile information.</div> |
| <dl> |
| <dt><span class="paramLabel">Parameters:</span></dt> |
| <dd><code>args</code> - A list of TFile paths.</dd> |
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