You notice a message from OpenLDAP
Extend the maximum size of the database (default value in UCS is 2147483648 bytes):
ucr set ldap/database/mdb/maxsize: 3000000000 systemctl restart slapd
Read the comments from man slapd-maxsize regarding this parameter. Setting it to high might increase memory usage.
Specify the maximum size of the database in bytes. A memory map of this size is allocated at startup time and the database will not be allowed to grow beyond this size. The default is 10485760 bytes. This setting may be changed upward if the configured limit needs to be increased.
Note: It is important to set this to as large a value as possible, (relative to anticipated growth of the actual data over time) since growing the size later may not be practical when the system is under heavy load.