Using command line

You can issue the command provided here to configure entry cache.

About this task

idsldapmodify -D <adminDN> -w <adminPW> -i <filename> 

where <filename> contains: 

dn: cn=Front End, cn=Configuration 
changetype: modify 
replace: ibm-slapdEntryCacheSize
ibm-slapdEntryCacheSize: <value to be set in numerals>