how to set an optimal cachesize into openldap

Hello

My openldap server is always crashed with segmentation fault exit.
exemple slapd[6814]: segfault at 8 rip 4af0f2 rsp 451c0530 error 4

I want to tune this server by putting a better cachesize.

The size of the openldap database into system is  125 MB

The siize of id2entry file is about 22M
The size of db2intery file is 6,7M

I read on the Administration openldap guide that i can execute db_stat -m to
look on the cachesize used by slapd.
This size is increasing every hour.
In the morning it was on about 240 M on the evening, it increase until 400 M


What does it mean and how to deal with that

Thanks