Setting Compression on Files

Compression is set at the directory level. Any files written by a Hadoop application, whether via the file APIs or over NFS, are compressed according to the settings for the directory where the file is written. Sub-directories on which compression has not been explicitly set inherit the compression settings of the directory that contains them.

If you change a directory's compression settings after writing a file, the file will keep the old compression settings—that is, if you write a file in an uncompressed directory and then turn compression on, the file does not automatically end up compressed, and vice versa. Further writes to the file will use the file's existing compression setting.