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7LocalDirAllocator (Hadoop 0.20.1 API)
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91org.apache.hadoop.fs</FONT>
92<BR>
93Class LocalDirAllocator</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.fs.LocalDirAllocator</B>
97</PRE>
98<HR>
99<DL>
100<DT><PRE>public class <B>LocalDirAllocator</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>
104An implementation of a round-robin scheme for disk allocation for creating
105 files. The way it works is that it is kept track what disk was last
106 allocated for a file write. For the current request, the next disk from
107 the set of disks would be allocated if the free space on the disk is
108 sufficient enough to accomodate the file that is being considered for
109 creation. If the space requirements cannot be met, the next disk in order
110 would be tried and so on till a disk is found with sufficient capacity.
111 Once a disk with sufficient space is identified, a check is done to make
112 sure that the disk is writable. Also, there is an API provided that doesn't
113 take the space requirements into consideration but just checks whether the
114 disk under consideration is writable (this should be used for cases where
115 the file size is not known apriori). An API is provided to read a path that
116 was created earlier. That API works by doing a scan of all the disks for the
117 input pathname.
118 This implementation also provides the functionality of having multiple
119 allocators per JVM (one for each unique functionality or context, like
120 mapred, dfs-client, etc.). It ensures that there is only one instance of
121 an allocator per context per JVM.
122 Note:
123 1. The contexts referred above are actually the configuration items defined
124 in the Configuration class like "mapred.local.dir" (for which we want to
125 control the dir allocations). The context-strings are exactly those
126 configuration items.
127 2. This implementation does not take into consideration cases where
128 a disk becomes read-only or goes out of space while a file is being written
129 to (disks are shared between multiple processes, and so the latter situation
130 is probable).
131 3. In the class implementation, "Disk" is referred to as "Dir", which
132 actually points to the configured directory on the Disk which will be the
133 parent for all file write/read allocations.
134<P>
135
136<P>
137<HR>
138
139<P>
140
141<!-- ======== CONSTRUCTOR SUMMARY ======== -->
142
143<A NAME="constructor_summary"><!-- --></A>
144<TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY="">
145<TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor">
146<TH ALIGN="left" COLSPAN="2"><FONT SIZE="+2">
147<B>Constructor Summary</B></FONT></TH>
148</TR>
149<TR BGCOLOR="white" CLASS="TableRowColor">
150<TD><CODE><B><A HREF="../../../../org/apache/hadoop/fs/LocalDirAllocator.html#LocalDirAllocator(java.lang.String)">LocalDirAllocator</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;contextCfgItemName)</CODE>
151
152<BR>
153&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Create an allocator object</TD>
154</TR>
155</TABLE>
156&nbsp;
157<!-- ========== METHOD SUMMARY =========== -->
158
159<A NAME="method_summary"><!-- --></A>
160<TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY="">
161<TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor">
162<TH ALIGN="left" COLSPAN="2"><FONT SIZE="+2">
163<B>Method Summary</B></FONT></TH>
164</TR>
165<TR BGCOLOR="white" CLASS="TableRowColor">
166<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
167<CODE>&nbsp;<A HREF="http://java.sun.com/javase/6/docs/api/java/io/File.html?is-external=true" title="class or interface in java.io">File</A></CODE></FONT></TD>
168<TD><CODE><B><A HREF="../../../../org/apache/hadoop/fs/LocalDirAllocator.html#createTmpFileForWrite(java.lang.String, long, org.apache.hadoop.conf.Configuration)">createTmpFileForWrite</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;pathStr,
169                      long&nbsp;size,
170                      <A HREF="../../../../org/apache/hadoop/conf/Configuration.html" title="class in org.apache.hadoop.conf">Configuration</A>&nbsp;conf)</CODE>
171
172<BR>
173&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Creates a temporary file in the local FS.</TD>
174</TR>
175<TR BGCOLOR="white" CLASS="TableRowColor">
176<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
177<CODE>&nbsp;<A HREF="../../../../org/apache/hadoop/fs/Path.html" title="class in org.apache.hadoop.fs">Path</A></CODE></FONT></TD>
178<TD><CODE><B><A HREF="../../../../org/apache/hadoop/fs/LocalDirAllocator.html#getLocalPathForWrite(java.lang.String, org.apache.hadoop.conf.Configuration)">getLocalPathForWrite</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;pathStr,
179                     <A HREF="../../../../org/apache/hadoop/conf/Configuration.html" title="class in org.apache.hadoop.conf">Configuration</A>&nbsp;conf)</CODE>
180
181<BR>
182&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Get a path from the local FS.</TD>
183</TR>
184<TR BGCOLOR="white" CLASS="TableRowColor">
185<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
186<CODE>&nbsp;<A HREF="../../../../org/apache/hadoop/fs/Path.html" title="class in org.apache.hadoop.fs">Path</A></CODE></FONT></TD>
187<TD><CODE><B><A HREF="../../../../org/apache/hadoop/fs/LocalDirAllocator.html#getLocalPathForWrite(java.lang.String, long, org.apache.hadoop.conf.Configuration)">getLocalPathForWrite</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;pathStr,
188                     long&nbsp;size,
189                     <A HREF="../../../../org/apache/hadoop/conf/Configuration.html" title="class in org.apache.hadoop.conf">Configuration</A>&nbsp;conf)</CODE>
190
191<BR>
192&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Get a path from the local FS.</TD>
193</TR>
194<TR BGCOLOR="white" CLASS="TableRowColor">
195<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
196<CODE>&nbsp;<A HREF="../../../../org/apache/hadoop/fs/Path.html" title="class in org.apache.hadoop.fs">Path</A></CODE></FONT></TD>
197<TD><CODE><B><A HREF="../../../../org/apache/hadoop/fs/LocalDirAllocator.html#getLocalPathToRead(java.lang.String, org.apache.hadoop.conf.Configuration)">getLocalPathToRead</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;pathStr,
198                   <A HREF="../../../../org/apache/hadoop/conf/Configuration.html" title="class in org.apache.hadoop.conf">Configuration</A>&nbsp;conf)</CODE>
199
200<BR>
201&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Get a path from the local FS for reading.</TD>
202</TR>
203<TR BGCOLOR="white" CLASS="TableRowColor">
204<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
205<CODE>&nbsp;boolean</CODE></FONT></TD>
206<TD><CODE><B><A HREF="../../../../org/apache/hadoop/fs/LocalDirAllocator.html#ifExists(java.lang.String, org.apache.hadoop.conf.Configuration)">ifExists</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;pathStr,
207         <A HREF="../../../../org/apache/hadoop/conf/Configuration.html" title="class in org.apache.hadoop.conf">Configuration</A>&nbsp;conf)</CODE>
208
209<BR>
210&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;We search through all the configured dirs for the file's existence
211  and return true when we find</TD>
212</TR>
213<TR BGCOLOR="white" CLASS="TableRowColor">
214<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
215<CODE>static&nbsp;boolean</CODE></FONT></TD>
216<TD><CODE><B><A HREF="../../../../org/apache/hadoop/fs/LocalDirAllocator.html#isContextValid(java.lang.String)">isContextValid</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;contextCfgItemName)</CODE>
217
218<BR>
219&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Method to check whether a context is valid</TD>
220</TR>
221</TABLE>
222&nbsp;<A NAME="methods_inherited_from_class_java.lang.Object"><!-- --></A>
223<TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY="">
224<TR BGCOLOR="#EEEEFF" CLASS="TableSubHeadingColor">
225<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>
226</TR>
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229</TR>
230</TABLE>
231&nbsp;
232<P>
233
234<!-- ========= CONSTRUCTOR DETAIL ======== -->
235
236<A NAME="constructor_detail"><!-- --></A>
237<TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY="">
238<TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor">
239<TH ALIGN="left" COLSPAN="1"><FONT SIZE="+2">
240<B>Constructor Detail</B></FONT></TH>
241</TR>
242</TABLE>
243
244<A NAME="LocalDirAllocator(java.lang.String)"><!-- --></A><H3>
245LocalDirAllocator</H3>
246<PRE>
247public <B>LocalDirAllocator</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;contextCfgItemName)</PRE>
248<DL>
249<DD>Create an allocator object
250<P>
251<DL>
252<DT><B>Parameters:</B><DD><CODE>contextCfgItemName</CODE> - </DL>
253</DL>
254
255<!-- ============ METHOD DETAIL ========== -->
256
257<A NAME="method_detail"><!-- --></A>
258<TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY="">
259<TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor">
260<TH ALIGN="left" COLSPAN="1"><FONT SIZE="+2">
261<B>Method Detail</B></FONT></TH>
262</TR>
263</TABLE>
264
265<A NAME="getLocalPathForWrite(java.lang.String, org.apache.hadoop.conf.Configuration)"><!-- --></A><H3>
266getLocalPathForWrite</H3>
267<PRE>
268public <A HREF="../../../../org/apache/hadoop/fs/Path.html" title="class in org.apache.hadoop.fs">Path</A> <B>getLocalPathForWrite</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;pathStr,
269                                 <A HREF="../../../../org/apache/hadoop/conf/Configuration.html" title="class in org.apache.hadoop.conf">Configuration</A>&nbsp;conf)
270                          throws <A HREF="http://java.sun.com/javase/6/docs/api/java/io/IOException.html?is-external=true" title="class or interface in java.io">IOException</A></PRE>
271<DL>
272<DD>Get a path from the local FS. This method should be used if the size of
273  the file is not known apriori. We go round-robin over the set of disks
274  (via the configured dirs) and return the first complete path where
275  we could create the parent directory of the passed path.
276<P>
277<DD><DL>
278<DT><B>Parameters:</B><DD><CODE>pathStr</CODE> - the requested path (this will be created on the first
279  available disk)<DD><CODE>conf</CODE> - the Configuration object
280<DT><B>Returns:</B><DD>the complete path to the file on a local disk
281<DT><B>Throws:</B>
282<DD><CODE><A HREF="http://java.sun.com/javase/6/docs/api/java/io/IOException.html?is-external=true" title="class or interface in java.io">IOException</A></CODE></DL>
283</DD>
284</DL>
285<HR>
286
287<A NAME="getLocalPathForWrite(java.lang.String, long, org.apache.hadoop.conf.Configuration)"><!-- --></A><H3>
288getLocalPathForWrite</H3>
289<PRE>
290public <A HREF="../../../../org/apache/hadoop/fs/Path.html" title="class in org.apache.hadoop.fs">Path</A> <B>getLocalPathForWrite</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;pathStr,
291                                 long&nbsp;size,
292                                 <A HREF="../../../../org/apache/hadoop/conf/Configuration.html" title="class in org.apache.hadoop.conf">Configuration</A>&nbsp;conf)
293                          throws <A HREF="http://java.sun.com/javase/6/docs/api/java/io/IOException.html?is-external=true" title="class or interface in java.io">IOException</A></PRE>
294<DL>
295<DD>Get a path from the local FS. Pass size as -1 if not known apriori. We
296  round-robin over the set of disks (via the configured dirs) and return
297  the first complete path which has enough space
298<P>
299<DD><DL>
300<DT><B>Parameters:</B><DD><CODE>pathStr</CODE> - the requested path (this will be created on the first
301  available disk)<DD><CODE>size</CODE> - the size of the file that is going to be written<DD><CODE>conf</CODE> - the Configuration object
302<DT><B>Returns:</B><DD>the complete path to the file on a local disk
303<DT><B>Throws:</B>
304<DD><CODE><A HREF="http://java.sun.com/javase/6/docs/api/java/io/IOException.html?is-external=true" title="class or interface in java.io">IOException</A></CODE></DL>
305</DD>
306</DL>
307<HR>
308
309<A NAME="getLocalPathToRead(java.lang.String, org.apache.hadoop.conf.Configuration)"><!-- --></A><H3>
310getLocalPathToRead</H3>
311<PRE>
312public <A HREF="../../../../org/apache/hadoop/fs/Path.html" title="class in org.apache.hadoop.fs">Path</A> <B>getLocalPathToRead</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;pathStr,
313                               <A HREF="../../../../org/apache/hadoop/conf/Configuration.html" title="class in org.apache.hadoop.conf">Configuration</A>&nbsp;conf)
314                        throws <A HREF="http://java.sun.com/javase/6/docs/api/java/io/IOException.html?is-external=true" title="class or interface in java.io">IOException</A></PRE>
315<DL>
316<DD>Get a path from the local FS for reading. We search through all the
317  configured dirs for the file's existence and return the complete
318  path to the file when we find one
319<P>
320<DD><DL>
321<DT><B>Parameters:</B><DD><CODE>pathStr</CODE> - the requested file (this will be searched)<DD><CODE>conf</CODE> - the Configuration object
322<DT><B>Returns:</B><DD>the complete path to the file on a local disk
323<DT><B>Throws:</B>
324<DD><CODE><A HREF="http://java.sun.com/javase/6/docs/api/java/io/IOException.html?is-external=true" title="class or interface in java.io">IOException</A></CODE></DL>
325</DD>
326</DL>
327<HR>
328
329<A NAME="createTmpFileForWrite(java.lang.String, long, org.apache.hadoop.conf.Configuration)"><!-- --></A><H3>
330createTmpFileForWrite</H3>
331<PRE>
332public <A HREF="http://java.sun.com/javase/6/docs/api/java/io/File.html?is-external=true" title="class or interface in java.io">File</A> <B>createTmpFileForWrite</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;pathStr,
333                                  long&nbsp;size,
334                                  <A HREF="../../../../org/apache/hadoop/conf/Configuration.html" title="class in org.apache.hadoop.conf">Configuration</A>&nbsp;conf)
335                           throws <A HREF="http://java.sun.com/javase/6/docs/api/java/io/IOException.html?is-external=true" title="class or interface in java.io">IOException</A></PRE>
336<DL>
337<DD>Creates a temporary file in the local FS. Pass size as -1 if not known
338  apriori. We round-robin over the set of disks (via the configured dirs)
339  and select the first complete path which has enough space. A file is
340  created on this directory. The file is guaranteed to go away when the
341  JVM exits.
342<P>
343<DD><DL>
344<DT><B>Parameters:</B><DD><CODE>pathStr</CODE> - prefix for the temporary file<DD><CODE>size</CODE> - the size of the file that is going to be written<DD><CODE>conf</CODE> - the Configuration object
345<DT><B>Returns:</B><DD>a unique temporary file
346<DT><B>Throws:</B>
347<DD><CODE><A HREF="http://java.sun.com/javase/6/docs/api/java/io/IOException.html?is-external=true" title="class or interface in java.io">IOException</A></CODE></DL>
348</DD>
349</DL>
350<HR>
351
352<A NAME="isContextValid(java.lang.String)"><!-- --></A><H3>
353isContextValid</H3>
354<PRE>
355public static boolean <B>isContextValid</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;contextCfgItemName)</PRE>
356<DL>
357<DD>Method to check whether a context is valid
358<P>
359<DD><DL>
360<DT><B>Parameters:</B><DD><CODE>contextCfgItemName</CODE> -
361<DT><B>Returns:</B><DD>true/false</DL>
362</DD>
363</DL>
364<HR>
365
366<A NAME="ifExists(java.lang.String, org.apache.hadoop.conf.Configuration)"><!-- --></A><H3>
367ifExists</H3>
368<PRE>
369public boolean <B>ifExists</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;pathStr,
370                        <A HREF="../../../../org/apache/hadoop/conf/Configuration.html" title="class in org.apache.hadoop.conf">Configuration</A>&nbsp;conf)</PRE>
371<DL>
372<DD>We search through all the configured dirs for the file's existence
373  and return true when we find
374<P>
375<DD><DL>
376<DT><B>Parameters:</B><DD><CODE>pathStr</CODE> - the requested file (this will be searched)<DD><CODE>conf</CODE> - the Configuration object
377<DT><B>Returns:</B><DD>true if files exist. false otherwise
378<DT><B>Throws:</B>
379<DD><CODE><A HREF="http://java.sun.com/javase/6/docs/api/java/io/IOException.html?is-external=true" title="class or interface in java.io">IOException</A></CODE></DL>
380</DD>
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