This content originally appeared on DEV Community and was authored by Vahid Yousefzadeh
In Oracle 21c, you can define the value of a parameter using environment variables or even by referencing other database parameters. This provides more flexibility and automation when configuring your database.
For example, suppose you want to allocate 50% of the SGA space to the buffer cache (as a minimum). You can easily do this using Oracle’s new feature:
SQL> show parameter sga_target
NAME TYPE VALUE
———————————— ———– ——————————
sga_target big integer 3568M
SQL> alter system set db_cache_size=‘sga_target*50/100’;
System altered.
SQL> show parameter db_cache_size
NAME TYPE VALUE
———————————— ———– ——————————
db_cache_size big integer 1792M
As you can see, the parameter value is dynamically calculated based on another parameter (sga_target).
Below is another example that demonstrates how to use environment variables:
[oracle@oLinux7 ~]$ mkdir /oracle21c/DATADATA
[oracle@oLinux7 ~]$ export DATADATA=/oracle21c/DATADATA
Then, inside SQL*Plus:
SQL> alter system set db_create_file_dest=’$DATADATA‘;
System altered.
SQL> create tablespace tttt;
Tablespace created.
SQL> select name from v$datafile where name like ‘%DATADATA%’;
NAME
——————————————————————————–
/oracle21c/DATADATA/DB21C/datafile/o1_mf_tttt_lh6domx8_.dbf
SQL> show parameter db_create_file_dest
NAME TYPE VALUE
———————————— ———– ——————————
db_create_file_dest string $DATADATA
As shown above, Oracle successfully interprets the environment variable $DATADATA when setting or displaying the parameter value.
This content originally appeared on DEV Community and was authored by Vahid Yousefzadeh
Vahid Yousefzadeh | Sciencx (2025-10-12T18:10:41+00:00) Expression-Based Parameter Value Feature in Oracle 21c. Retrieved from https://www.scien.cx/2025/10/12/expression-based-parameter-value-feature-in-oracle-21c/
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