October 2018
Beginner
220 pages
5h 33m
English
Content preview from Apache Hadoop 3 Quick Start Guide
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MapFile and its variants
While the SequenceFile class offers <key, value> to store any data elements, MapFile provides <Key, Value>, as well as an index file of keys. The index file is used for faster access to the keys of each Map. The following diagram shows the storage pattern of MapFile:
SequenceFile provides a sequential pattern for reading and writing data, as HDFS supports an append-only mechanism, whereas MapFile can provide random access capability. The index file contains the fractions of the keys; this is determined by the MapFile.Writer.getIndexInterval() method. The index file is loaded in memory for faster access. You can read ...
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