error: unknown directive "dbcachesize" inside backend database definition

["B M" <bobtuffet@hotmail.com>]

i'm running OpenLDAP 2.2.17 and Berkeley DB 4.2.52.2, and am getting this 
error in my slapd.conf:

unknown directive "dbcachesize" inside backend database definition

isn't dbcachesize a backend database directive?  i googled this error and 
found nothing.  while doing some reasearch, i came across the following 
page:

http://www.zytrax.com/books/ldap/ch6/bdb.html#db-config

it makes no mention of the dbcachesize directive, although it does mention 
the cachesize directive (which i'm using as well and appears to be 
recognized by slapd).  instead, it mentions a DB_CONFIG file where it looks 
like i can put a separate set_cachesize parameter in that will apply to the 
DB backend.

is dbcachesize an obsolete option?  should i be using a DB_CONFIG file 
instead?  if so, what other options might i need to include in my DB_CONFIG 
file?