The init.ora file may be made to contain all of the necessary information to start an Oracle instance, but the config.ora file is sometimes used to segragate the configuration information into a separate file.

The init.ora file (and spfile) determines many Oracle operating system environment attributes, such as

1. memory allocated for data,
2. memory allocated for statements,
3. resources allocated for I/O, and
4. other crucial performance-related parameters.

Each version of Oracle continues to add to the total number of initialization parameters. In Oracle 10g Release 2 there are now 1381 (257 documented and 1124 hidden) different initialization parameters (these numbers vary slightly on different versions of Oracle and platforms). As you might expect, an entire book could be written on how to set and tune each parameter; this book focuses on the key parameters that affect database performance. The key to an optimized Oracle database is often the architecture of the system and the parameters that set the environment for the database

The statistics-gathering operations can run either serially or in parallel. You can specify the degree of parallelism with the DEGREE argument to the DBMS_STATS gathering procedures. The database can use parallel statistics gathering in conjunction with sampling. Oracle recommends setting the DEGREE parameter to DBMS_STATS.AUTO_DEGREE. This setting allows Oracle Database to choose an appropriate degree of parallelism based on the size of the object and the settings for the parallel-related init.ora parameters. Note that certain types of index statistics are not gathered in parallel, including cluster indexes, domain indexes, and bitmap join indexes.

For partitioned tables and indexes, DBMS_STATS can gather separate statistics for each partition and global statistics for the entire table or index. Similarly, for composite partitioning, DBMS_STATS can gather separate statistics for subpartitions, partitions, and the entire table or index.