Oracle derived parameters Oracle Database Tips by Donald BurlesonJuly 9, 2015

Oracle derived parameters

There are many internal parameters inside Oracle that are automatically calculated, and parameters that are derived from the values of other parameters.  (Note:  this list of derived parameters is NOT release-specific.  Check to ensure that this parameter is valid for your release of Oracle).  Here are some common Oracle parameters that are derived from other parameters:

• _enqueue_hash_chains- The default value is derived from processes parameter.

• db_block_checkpoint_batch - This parameter specifies the number of blocks that the DBWR writes in one batch when performing a checkpoint. Setting this value too high causes the system to flood the I/O devices during the checkpoint, severely degrades performance, and increases response times--maybe to unacceptable levels.

• enqueue_resources - This parameter specifies the number of resources that can be locked by the lock manager. The default value is derived from processes and is usually sufficient.

• nls_currency - This parameter is derived from nls_territory, and specifies the string to use as the local currency symbol for the L number format element.

• nls_date_format - This parameter is derived from nls_territory and defines the default date format to use with the to_char and to_date functions. The value of this parameter is any valid date format mask.

• nls_iso_currency - Derived from nls_territory, this parameter defines the string to use as the international currency symbol for the C number format element.

• nls_numeric_characters - This is derived from nls_territory, and defines the characters to be used as the group separator and decimal.

• nls_sort - Derived from nls_language, this parameter is set to BINARY, the collating sequence for ORDER BY is based on the numeric values of the characters. A linguistic sort decides the order based on the defined linguistic sort. A binary sort is much more efficient and uses much less overhead.

• sessions - This parameter specifies the total number of user and system sessions, and is set to 1.1 times the value of the processes parameter.