the way to calculate the cache size

[tem_dl]

Hi All,
I’m tuning my LDAP DB (BDB type).
I’m reading at http://www.openldap.org/doc/admin24/tuning.html#Berkeley DB Cache

#(Number of hash buckets + number of overflow pages + number of duplicate pages) * page size / 2
                #The objectClass index for my example database is 5.9MB and uses 3 hash buckets and 656 duplicate pages. So:
                #              ( 3 + 656 ) * 4KB / 2 =~ 1.3MB.
#With only this index enabled, I'd figure at least a 4MB cache for this backend. (Of course you're using a single cache shared among all of 
#the database files, so the cache pages will most likely get used for something other than what you accounted for, but this gives you a 
#fighting chance.)”

I understand that: with each index ( in this case only objectclass is indexed), we must calculate their cache size individually and sum every them. (1)
- I can specify “Number of hash buckets” & “Cache Size “ (2)by command

#db_stat-4.4 -m | head -n 25
32771    Number of hash buckets used for page location
Pool file: <index>.bdb
<number>           page size

- I can specify “Number of overflow pages” & “Number of duplicate pages” by command

#db_stat-4.4 -d *.bdb (3)
0              Number of tree duplicate page
0              Number of tree overflow pages

(1) Did I understand right?
(2) Which page size will we use, some of index file use 4K page size, others use 16K page size?
(3) Do must I run for each index or *.bdb is still ok?

Could anyone help me? This chapter is not clearly huh?

Thank for reading