[Freeipa-users] nsslapd-dbcachesize and database size

[Andrew E. Bruno]

The load average on our freeipa replicas started to spike over the
last few days and we narrowed it down to a dbcache issue. Following the
guidelines here: https://github.com/richm/scripts/wiki/dbmon.sh

We saw that the dbcachefree was 2.0% which indicates a lot of page
churn. Sure enough our nsslapd-dbcachesize was set to 2G and the size of
our database and index files was 3.1G: 

$ du -sh /var/lib/dirsrv/slapd-[domain]/db/
3.1G

Once we increased nsslapd-dbcachesize to 6G load average went back to
normal and query response times improved. Interestingly, when we
restarted the dirsrv process the database size went down to 1.7G

$ du -sh /var/lib/dirsrv/slapd-[domain]/db/
1.7G

When we initially deployed freeipa, the size of our database and indexes
was about 400M which is why we set nsslapd-dbcachesize to 2G. 

A few questions:

1. What causes the increase in size of
/var/lib/dirsrv/slapd-[domain]/db/*  and should we periodically clean up?

2. How do you tune nsslapd-dbcachesize to account for this growth? The
dbmon.sh wiki suggests a 12% overhead but our db files and indexes seem
to grow much larger? 

We're running: 
- ipa-server-4.1.0-18.el7.centos.4.x86_64 and
- 389-ds-base-1.3.3.1-20.el7_1.x86_64

Thanks,

--Andrew