Best practices for compressing files in an Oracle database
Even though an Oracle database runs without any errors when files are compressed, increased I/O to compressed files decreases database performance. Use the following guidelines for compressing Oracle datafiles:
Do not compress database control files.
Do not compress files belonging to TEMPORARY tablespaces.
Do not compress files belonging to SYSTEM and SYSAUX tablespace.
Monitor the I/O activity on compressed files periodically and uncompress the files if I/O activity increases.