[Freeipa-users] nsslapd-dbcachesize and database size

[Rich Megginson]

On 10/14/2015 07:09 AM, Andrew E. Bruno wrote:
> 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.

What about your cachememsize?

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

Replication metadata accounts for some of this.  Fragmentation accounts 
for some of this.  You can periodically clean up, but you shouldn't have 
to.  The growth should eventually hit a plateau.

>
> 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?

12% is sort of a starting point.  There isn't a good way to tell how to 
account for replication metadata, fragmentation, etc.  Just monitor 
periodically and adjust as needed.

>
> 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
>