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7TFile (Hadoop 0.20.1 API)
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79  SUMMARY:&nbsp;<A HREF="#nested_class_summary">NESTED</A>&nbsp;|&nbsp;<A HREF="#field_summary">FIELD</A>&nbsp;|&nbsp;CONSTR&nbsp;|&nbsp;<A HREF="#method_summary">METHOD</A></FONT></TD>
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90<FONT SIZE="-1">
91org.apache.hadoop.io.file.tfile</FONT>
92<BR>
93Class TFile</H2>
94<PRE>
95<A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true" title="class or interface in java.lang">java.lang.Object</A>
96  <IMG SRC="../../../../../../resources/inherit.gif" ALT="extended by "><B>org.apache.hadoop.io.file.tfile.TFile</B>
97</PRE>
98<HR>
99<DL>
100<DT><PRE>public class <B>TFile</B><DT>extends <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true" title="class or interface in java.lang">Object</A></DL>
101</PRE>
102
103<P>
104A TFile is a container of key-value pairs. Both keys and values are type-less
105 bytes. Keys are restricted to 64KB, value length is not restricted
106 (practically limited to the available disk storage). TFile further provides
107 the following features:
108 <ul>
109 <li>Block Compression.
110 <li>Named meta data blocks.
111 <li>Sorted or unsorted keys.
112 <li>Seek by key or by file offset.
113 </ul>
114 The memory footprint of a TFile includes the following:
115 <ul>
116 <li>Some constant overhead of reading or writing a compressed block.
117 <ul>
118 <li>Each compressed block requires one compression/decompression codec for
119 I/O.
120 <li>Temporary space to buffer the key.
121 <li>Temporary space to buffer the value (for TFile.Writer only). Values are
122 chunk encoded, so that we buffer at most one chunk of user data. By default,
123 the chunk buffer is 1MB. Reading chunked value does not require additional
124 memory.
125 </ul>
126 <li>TFile index, which is proportional to the total number of Data Blocks.
127 The total amount of memory needed to hold the index can be estimated as
128 (56+AvgKeySize)*NumBlocks.
129 <li>MetaBlock index, which is proportional to the total number of Meta
130 Blocks.The total amount of memory needed to hold the index for Meta Blocks
131 can be estimated as (40+AvgMetaBlockName)*NumMetaBlock.
132 </ul>
133 <p>
134 The behavior of TFile can be customized by the following variables through
135 Configuration:
136 <ul>
137 <li><b>tfile.io.chunk.size</b>: Value chunk size. Integer (in bytes). Default
138 to 1MB. Values of the length less than the chunk size is guaranteed to have
139 known value length in read time (See
140 <A HREF="../../../../../../org/apache/hadoop/io/file/tfile/TFile.Reader.Scanner.Entry.html#isValueLengthKnown()"><CODE>TFile.Reader.Scanner.Entry.isValueLengthKnown()</CODE></A>).
141 <li><b>tfile.fs.output.buffer.size</b>: Buffer size used for
142 FSDataOutputStream. Integer (in bytes). Default to 256KB.
143 <li><b>tfile.fs.input.buffer.size</b>: Buffer size used for
144 FSDataInputStream. Integer (in bytes). Default to 256KB.
145 </ul>
146 <p>
147 Suggestions on performance optimization.
148 <ul>
149 <li>Minimum block size. We recommend a setting of minimum block size between
150 256KB to 1MB for general usage. Larger block size is preferred if files are
151 primarily for sequential access. However, it would lead to inefficient random
152 access (because there are more data to decompress). Smaller blocks are good
153 for random access, but require more memory to hold the block index, and may
154 be slower to create (because we must flush the compressor stream at the
155 conclusion of each data block, which leads to an FS I/O flush). Further, due
156 to the internal caching in Compression codec, the smallest possible block
157 size would be around 20KB-30KB.
158 <li>The current implementation does not offer true multi-threading for
159 reading. The implementation uses FSDataInputStream seek()+read(), which is
160 shown to be much faster than positioned-read call in single thread mode.
161 However, it also means that if multiple threads attempt to access the same
162 TFile (using multiple scanners) simultaneously, the actual I/O is carried out
163 sequentially even if they access different DFS blocks.
164 <li>Compression codec. Use "none" if the data is not very compressable (by
165 compressable, I mean a compression ratio at least 2:1). Generally, use "lzo"
166 as the starting point for experimenting. "gz" overs slightly better
167 compression ratio over "lzo" but requires 4x CPU to compress and 2x CPU to
168 decompress, comparing to "lzo".
169 <li>File system buffering, if the underlying FSDataInputStream and
170 FSDataOutputStream is already adequately buffered; or if applications
171 reads/writes keys and values in large buffers, we can reduce the sizes of
172 input/output buffering in TFile layer by setting the configuration parameters
173 "tfile.fs.input.buffer.size" and "tfile.fs.output.buffer.size".
174 </ul>
175 
176 Some design rationale behind TFile can be found at <a
177 href=https://issues.apache.org/jira/browse/HADOOP-3315>Hadoop-3315</a>.
178<P>
179
180<P>
181<HR>
182
183<P>
184<!-- ======== NESTED CLASS SUMMARY ======== -->
185
186<A NAME="nested_class_summary"><!-- --></A>
187<TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY="">
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189<TH ALIGN="left" COLSPAN="2"><FONT SIZE="+2">
190<B>Nested Class Summary</B></FONT></TH>
191</TR>
192<TR BGCOLOR="white" CLASS="TableRowColor">
193<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
194<CODE>static&nbsp;class</CODE></FONT></TD>
195<TD><CODE><B><A HREF="../../../../../../org/apache/hadoop/io/file/tfile/TFile.Reader.html" title="class in org.apache.hadoop.io.file.tfile">TFile.Reader</A></B></CODE>
196
197<BR>
198&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;TFile Reader.</TD>
199</TR>
200<TR BGCOLOR="white" CLASS="TableRowColor">
201<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
202<CODE>static&nbsp;class</CODE></FONT></TD>
203<TD><CODE><B><A HREF="../../../../../../org/apache/hadoop/io/file/tfile/TFile.Writer.html" title="class in org.apache.hadoop.io.file.tfile">TFile.Writer</A></B></CODE>
204
205<BR>
206&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;TFile Writer.</TD>
207</TR>
208</TABLE>
209&nbsp;<!-- =========== FIELD SUMMARY =========== -->
210
211<A NAME="field_summary"><!-- --></A>
212<TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY="">
213<TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor">
214<TH ALIGN="left" COLSPAN="2"><FONT SIZE="+2">
215<B>Field Summary</B></FONT></TH>
216</TR>
217<TR BGCOLOR="white" CLASS="TableRowColor">
218<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
219<CODE>static&nbsp;<A HREF="http://java.sun.com/javase/6/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</A></CODE></FONT></TD>
220<TD><CODE><B><A HREF="../../../../../../org/apache/hadoop/io/file/tfile/TFile.html#COMPARATOR_JCLASS">COMPARATOR_JCLASS</A></B></CODE>
221
222<BR>
223&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;comparator prefix: java class</TD>
224</TR>
225<TR BGCOLOR="white" CLASS="TableRowColor">
226<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
227<CODE>static&nbsp;<A HREF="http://java.sun.com/javase/6/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</A></CODE></FONT></TD>
228<TD><CODE><B><A HREF="../../../../../../org/apache/hadoop/io/file/tfile/TFile.html#COMPARATOR_MEMCMP">COMPARATOR_MEMCMP</A></B></CODE>
229
230<BR>
231&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;comparator: memcmp</TD>
232</TR>
233<TR BGCOLOR="white" CLASS="TableRowColor">
234<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
235<CODE>static&nbsp;<A HREF="http://java.sun.com/javase/6/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</A></CODE></FONT></TD>
236<TD><CODE><B><A HREF="../../../../../../org/apache/hadoop/io/file/tfile/TFile.html#COMPRESSION_GZ">COMPRESSION_GZ</A></B></CODE>
237
238<BR>
239&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;compression: gzip</TD>
240</TR>
241<TR BGCOLOR="white" CLASS="TableRowColor">
242<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
243<CODE>static&nbsp;<A HREF="http://java.sun.com/javase/6/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</A></CODE></FONT></TD>
244<TD><CODE><B><A HREF="../../../../../../org/apache/hadoop/io/file/tfile/TFile.html#COMPRESSION_LZO">COMPRESSION_LZO</A></B></CODE>
245
246<BR>
247&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;compression: lzo</TD>
248</TR>
249<TR BGCOLOR="white" CLASS="TableRowColor">
250<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
251<CODE>static&nbsp;<A HREF="http://java.sun.com/javase/6/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</A></CODE></FONT></TD>
252<TD><CODE><B><A HREF="../../../../../../org/apache/hadoop/io/file/tfile/TFile.html#COMPRESSION_NONE">COMPRESSION_NONE</A></B></CODE>
253
254<BR>
255&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;compression: none</TD>
256</TR>
257</TABLE>
258&nbsp;
259<!-- ========== METHOD SUMMARY =========== -->
260
261<A NAME="method_summary"><!-- --></A>
262<TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY="">
263<TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor">
264<TH ALIGN="left" COLSPAN="2"><FONT SIZE="+2">
265<B>Method Summary</B></FONT></TH>
266</TR>
267<TR BGCOLOR="white" CLASS="TableRowColor">
268<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
269<CODE>static&nbsp;<A HREF="http://java.sun.com/javase/6/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</A>[]</CODE></FONT></TD>
270<TD><CODE><B><A HREF="../../../../../../org/apache/hadoop/io/file/tfile/TFile.html#getSupportedCompressionAlgorithms()">getSupportedCompressionAlgorithms</A></B>()</CODE>
271
272<BR>
273&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Get names of supported compression algorithms.</TD>
274</TR>
275<TR BGCOLOR="white" CLASS="TableRowColor">
276<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
277<CODE>static&nbsp;void</CODE></FONT></TD>
278<TD><CODE><B><A HREF="../../../../../../org/apache/hadoop/io/file/tfile/TFile.html#main(java.lang.String[])">main</A></B>(<A HREF="http://java.sun.com/javase/6/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</A>[]&nbsp;args)</CODE>
279
280<BR>
281&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Dumping the TFile information.</TD>
282</TR>
283<TR BGCOLOR="white" CLASS="TableRowColor">
284<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
285<CODE>static&nbsp;<A HREF="http://java.sun.com/javase/6/docs/api/java/util/Comparator.html?is-external=true" title="class or interface in java.util">Comparator</A>&lt;<A HREF="../../../../../../org/apache/hadoop/io/file/tfile/RawComparable.html" title="interface in org.apache.hadoop.io.file.tfile">RawComparable</A>&gt;</CODE></FONT></TD>
286<TD><CODE><B><A HREF="../../../../../../org/apache/hadoop/io/file/tfile/TFile.html#makeComparator(java.lang.String)">makeComparator</A></B>(<A HREF="http://java.sun.com/javase/6/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</A>&nbsp;name)</CODE>
287
288<BR>
289&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Make a raw comparator from a string name.</TD>
290</TR>
291</TABLE>
292&nbsp;<A NAME="methods_inherited_from_class_java.lang.Object"><!-- --></A>
293<TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY="">
294<TR BGCOLOR="#EEEEFF" CLASS="TableSubHeadingColor">
295<TH ALIGN="left"><B>Methods inherited from class java.lang.<A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true" title="class or interface in java.lang">Object</A></B></TH>
296</TR>
297<TR BGCOLOR="white" CLASS="TableRowColor">
298<TD><CODE><A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true#clone()" title="class or interface in java.lang">clone</A>, <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true#equals(java.lang.Object)" title="class or interface in java.lang">equals</A>, <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true#finalize()" title="class or interface in java.lang">finalize</A>, <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true#getClass()" title="class or interface in java.lang">getClass</A>, <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true#hashCode()" title="class or interface in java.lang">hashCode</A>, <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true#notify()" title="class or interface in java.lang">notify</A>, <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true#notifyAll()" title="class or interface in java.lang">notifyAll</A>, <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true#toString()" title="class or interface in java.lang">toString</A>, <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true#wait()" title="class or interface in java.lang">wait</A>, <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true#wait(long)" title="class or interface in java.lang">wait</A>, <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Object.html?is-external=true#wait(long, int)" title="class or interface in java.lang">wait</A></CODE></TD>
299</TR>
300</TABLE>
301&nbsp;
302<P>
303
304<!-- ============ FIELD DETAIL =========== -->
305
306<A NAME="field_detail"><!-- --></A>
307<TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY="">
308<TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor">
309<TH ALIGN="left" COLSPAN="1"><FONT SIZE="+2">
310<B>Field Detail</B></FONT></TH>
311</TR>
312</TABLE>
313
314<A NAME="COMPRESSION_GZ"><!-- --></A><H3>
315COMPRESSION_GZ</H3>
316<PRE>
317public static final <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</A> <B>COMPRESSION_GZ</B></PRE>
318<DL>
319<DD>compression: gzip
320<P>
321<DL>
322<DT><B>See Also:</B><DD><A HREF="../../../../../../constant-values.html#org.apache.hadoop.io.file.tfile.TFile.COMPRESSION_GZ">Constant Field Values</A></DL>
323</DL>
324<HR>
325
326<A NAME="COMPRESSION_LZO"><!-- --></A><H3>
327COMPRESSION_LZO</H3>
328<PRE>
329public static final <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</A> <B>COMPRESSION_LZO</B></PRE>
330<DL>
331<DD>compression: lzo
332<P>
333<DL>
334<DT><B>See Also:</B><DD><A HREF="../../../../../../constant-values.html#org.apache.hadoop.io.file.tfile.TFile.COMPRESSION_LZO">Constant Field Values</A></DL>
335</DL>
336<HR>
337
338<A NAME="COMPRESSION_NONE"><!-- --></A><H3>
339COMPRESSION_NONE</H3>
340<PRE>
341public static final <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</A> <B>COMPRESSION_NONE</B></PRE>
342<DL>
343<DD>compression: none
344<P>
345<DL>
346<DT><B>See Also:</B><DD><A HREF="../../../../../../constant-values.html#org.apache.hadoop.io.file.tfile.TFile.COMPRESSION_NONE">Constant Field Values</A></DL>
347</DL>
348<HR>
349
350<A NAME="COMPARATOR_MEMCMP"><!-- --></A><H3>
351COMPARATOR_MEMCMP</H3>
352<PRE>
353public static final <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</A> <B>COMPARATOR_MEMCMP</B></PRE>
354<DL>
355<DD>comparator: memcmp
356<P>
357<DL>
358<DT><B>See Also:</B><DD><A HREF="../../../../../../constant-values.html#org.apache.hadoop.io.file.tfile.TFile.COMPARATOR_MEMCMP">Constant Field Values</A></DL>
359</DL>
360<HR>
361
362<A NAME="COMPARATOR_JCLASS"><!-- --></A><H3>
363COMPARATOR_JCLASS</H3>
364<PRE>
365public static final <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</A> <B>COMPARATOR_JCLASS</B></PRE>
366<DL>
367<DD>comparator prefix: java class
368<P>
369<DL>
370<DT><B>See Also:</B><DD><A HREF="../../../../../../constant-values.html#org.apache.hadoop.io.file.tfile.TFile.COMPARATOR_JCLASS">Constant Field Values</A></DL>
371</DL>
372
373<!-- ============ METHOD DETAIL ========== -->
374
375<A NAME="method_detail"><!-- --></A>
376<TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY="">
377<TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor">
378<TH ALIGN="left" COLSPAN="1"><FONT SIZE="+2">
379<B>Method Detail</B></FONT></TH>
380</TR>
381</TABLE>
382
383<A NAME="makeComparator(java.lang.String)"><!-- --></A><H3>
384makeComparator</H3>
385<PRE>
386public static <A HREF="http://java.sun.com/javase/6/docs/api/java/util/Comparator.html?is-external=true" title="class or interface in java.util">Comparator</A>&lt;<A HREF="../../../../../../org/apache/hadoop/io/file/tfile/RawComparable.html" title="interface in org.apache.hadoop.io.file.tfile">RawComparable</A>&gt; <B>makeComparator</B>(<A HREF="http://java.sun.com/javase/6/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</A>&nbsp;name)</PRE>
387<DL>
388<DD>Make a raw comparator from a string name.
389<P>
390<DD><DL>
391<DT><B>Parameters:</B><DD><CODE>name</CODE> - Comparator name
392<DT><B>Returns:</B><DD>A RawComparable comparator.</DL>
393</DD>
394</DL>
395<HR>
396
397<A NAME="getSupportedCompressionAlgorithms()"><!-- --></A><H3>
398getSupportedCompressionAlgorithms</H3>
399<PRE>
400public static <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</A>[] <B>getSupportedCompressionAlgorithms</B>()</PRE>
401<DL>
402<DD>Get names of supported compression algorithms. The names are acceptable by
403 TFile.Writer.
404<P>
405<DD><DL>
406
407<DT><B>Returns:</B><DD>Array of strings, each represents a supported compression
408         algorithm. Currently, the following compression algorithms are
409         supported.
410         <ul>
411         <li>"none" - No compression.
412         <li>"lzo" - LZO compression.
413         <li>"gz" - GZIP compression.
414         </ul></DL>
415</DD>
416</DL>
417<HR>
418
419<A NAME="main(java.lang.String[])"><!-- --></A><H3>
420main</H3>
421<PRE>
422public static void <B>main</B>(<A HREF="http://java.sun.com/javase/6/docs/api/java/lang/String.html?is-external=true" title="class or interface in java.lang">String</A>[]&nbsp;args)</PRE>
423<DL>
424<DD>Dumping the TFile information.
425<P>
426<DD><DL>
427<DT><B>Parameters:</B><DD><CODE>args</CODE> - A list of TFile paths.</DL>
428</DD>
429</DL>
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