New in Oracle 21c is the ability to use an expression to derive the value of an initialization parameter.
Oracle 21c allows us to base the value of a particular parameter which is derived from the existing value of some other parameter – or even based on the value of an environment variable.
So now the Oracle 21c database is able to automatically adjust the value of a parameter in response to environmental changes – or even when some other parameter value changes.
An example is to have the Shared Pool size always based on what the value of the SGA is. So regardless of what the SGA size is, the Shared Pool will always be 20% of that value.
############################################################################## Configure parameter shared_pool_size to be 20% of SGA ############################################################################### SQL> show parameter sga_target NAME TYPE VALUE ------------------------------------ ----------- ------------------------------ sga_target big integer 3G SQL> alter system set shared_pool_size='sga_target*20/100' scope=both; System altered. SQL> show parameter shared_pool_size NAME TYPE VALUE ------------------------------------ ----------- ------------------------------ shared_pool_size big integer 624M ############################################################################### Configure parameter job_queue_processes to be the higher value of 50 or 20% of the value of parameter processes ############################################################################### SQL> show parameter processes NAME TYPE VALUE ------------------------------------ ----------- ------------------------------ processes integer 200 SQL> alter system set job_queue_processes='max(50,processes*20/100)' scope=both; System altered. SQL> show parameter job_queu NAME TYPE VALUE ------------------------------------ ----------- ------------------------------ job_queue_processes integer 50 SQL> alter system set processes=300 scope=spfile; System altered. SQL> shutdown immediate; Database closed. Database dismounted. ORACLE instance shut down. SQL> startup; ORACLE instance started. Total System Global Area 3221225216 bytes Fixed Size 9690880 bytes Variable Size 1929379840 bytes Database Buffers 1258291200 bytes Redo Buffers 23863296 bytes Database mounted. Database opened. SQL> show parameter job_queu NAME TYPE VALUE ------------------------------------ ----------- ------------------------------ job_queue_processes integer 60 ############################################################################### Configure parameter diagnostic_dest to be based on environment variable DIAG ############################################################################### [oracle@db21c homes]$ cd /home/oracle [oracle@db21c ~]$ mkdir diag [oracle@db21c ~]$ export DIAG=/home/oracle SQL> alter system set diagnostic_dest='$DIAG' scope=both; System altered. SQL> show parameter diagnostic NAME TYPE VALUE ------------------------------------ ----------- ------------------------------ diagnostic_dest string $DIAG SQL> alter system switch logfile; System altered. [oracle@db21c ~]$ cd $DIAG [oracle@db21c db21c_syd1tp]$ pwd /home/oracle [oracle@db21c diag]$ ls diag [oracle@db21c diag]$ cd diag/ [oracle@db21c diag]$ ls rdbms [oracle@db21c diag]$ cd rdbms/db21c_syd1tp/ [oracle@db21c db21c_syd1tp]$ ls db21c i_1.mif
