This error occur in case you have miss used values of memory_target and memory_max_target.
To overcome the same follow the following steps
Step 1. Open the terminal
sqlplus / as sysdba
Step 2. Once yoe are in , it will not allow startup of database;
SQL> startup
ORA-00093: _shared_pool_reserved_min_alloc must be between 4000 and 11744051
Step 3.
SQL>Create pfile='/tmp/init-20121025.ora' from spfile;
Step 4.
SQL>!gedit /tmp/init-20121025.ora
In this file make memory_target and memory_max_target values 0 (Zero). Save the file.
Step 5.
SQL>startup pfile='/tmp/init-20121025.ora'
Database will start.
Step 6.
SQL>Create spfile from pfile='/tmp/init-20121025.ora';
Step 7. Bounce the database
SQL>shutdown immediate
SQL>startup
DONE.
We can then adjust the values of memory_target and memory_max_target accordingly.
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