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java.lang.Object org.apache.hadoop.io.MapFile
@InterfaceAudience.Public @InterfaceStability.Stable public class MapFile
A file-based map from keys to values.
A map is a directory containing two files, the data
file,
containing all keys and values in the map, and a smaller index
file, containing a fraction of the keys. The fraction is determined by
MapFile.Writer.getIndexInterval()
.
The index file is read entirely into memory. Thus key implementations should try to keep themselves small.
Map files are created by adding entries in-order. To maintain a large
database, perform updates by copying the previous version of a database and
merging in a sorted change list, to create a new version of the database in
a new file. Sorting large change lists can be done with SequenceFile.Sorter
.
Nested Class Summary | |
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static class |
MapFile.Reader
Provide access to an existing map. |
static class |
MapFile.Writer
Writes a new map. |
Field Summary | |
---|---|
static String |
DATA_FILE_NAME
The name of the data file. |
static String |
INDEX_FILE_NAME
The name of the index file. |
Constructor Summary | |
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protected |
MapFile()
|
Method Summary | |
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static void |
delete(FileSystem fs,
String name)
Deletes the named map file. |
static long |
fix(FileSystem fs,
Path dir,
Class<? extends Writable> keyClass,
Class<? extends Writable> valueClass,
boolean dryrun,
Configuration conf)
This method attempts to fix a corrupt MapFile by re-creating its index. |
static void |
main(String[] args)
|
static void |
rename(FileSystem fs,
String oldName,
String newName)
Renames an existing map directory. |
Methods inherited from class java.lang.Object |
---|
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Field Detail |
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public static final String INDEX_FILE_NAME
public static final String DATA_FILE_NAME
Constructor Detail |
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protected MapFile()
Method Detail |
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public static void rename(FileSystem fs, String oldName, String newName) throws IOException
IOException
public static void delete(FileSystem fs, String name) throws IOException
IOException
public static long fix(FileSystem fs, Path dir, Class<? extends Writable> keyClass, Class<? extends Writable> valueClass, boolean dryrun, Configuration conf) throws Exception
fs
- filesystemdir
- directory containing the MapFile data and indexkeyClass
- key class (has to be a subclass of Writable)valueClass
- value class (has to be a subclass of Writable)dryrun
- do not perform any changes, just report what needs to be done
Exception
public static void main(String[] args) throws Exception
Exception
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