ORA-00064: object is too large to allocate on this O/S (1,20005328,network connections) is encountered on database startup when open_links_per_instance parameter value is set high enough like 1500 or more than 400.
As per Oracle doc this is not a bug. To fix this issue either you need to increase the size of SGA or else decrease the value of open_links_per_instance.
I encountered this error when I set this value to 1500 and SGA was allocated to 8GB. After setting this parameter I was not able to start the database. So I created pfile from spfile and change the value of open_links_per_instance and started the database from the new pfile.
alter system set open_links_per_instance=1500 scope=spfile;
Steps to resolve ORA-00064
STEP1: Login to the database and create pfile from spfile.
sqlplus / as sysdba
create pfile='location/initsid.ora' from spfile;
STEP2: Open newly created pfile using vi editor and reduce the value of open_links_per_instance .
STEP 3: Start the database using new pfile.
SQLPLUS> startup pfile='location/initsid.ora';
SQLPLUS> create spfile from pfile='location/initsid.ora';
SQLPLUS> shut immediate;
SQLPLUS> startup;
Above we have reduced the value of alter system set open_links_per_instance but if you don’t want to reduce it then increase the value of SGA.