ODM I/O normally bypasses the file system cache and directly reads from and writes to disk. Cached ODM enables some I/O to use caching and read ahead, which can improve ODM I/O performance. Cached ODM performs a conditional form of caching that is based on per-I/O hints from Oracle. The hints indicate what Oracle does with the data. ODM uses these hints to perform caching and read ahead for some reads, but ODM avoids caching other reads, even for the same file.
Cached ODM can be configured in two ways. The primary configuration method is to turn caching on or off for all I/O on a per-file basis. The secondary configuration method is to adjust the ODM cachemap. The cachemap maps file type and I/O type combinations into caching advisories.