[Freeipa-users] nsslapd-dbcachesize and database size

[Rich Megginson]

On 10/14/2015 08:35 AM, Andrew E. Bruno wrote:
> On Wed, Oct 14, 2015 at 07:59:23AM -0600, Rich Megginson wrote:
>> 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?
> We have nsslapd-cachememsize set at 2G for the cn=userRoot. According to
> dbmon.sh it looked OK and we didn't think it needed to be increased:
>
> dbcachefree 6123847680 free% 95.055 roevicts 0 hit% 99 pagein 34260 pageout 308661
>
>         dbname      count          free  free%    size
> changelog:ent         84        158342   30.9  4210.2
> changelog:dn       29716            58    0.0    74.0
>   userroot:ent       8446    2091021433   97.4  6685.1
>   userroot:dn        8446     523272268   99.8   120.3
>      ipaca:ent        100        673516   47.9  7338.6
>      ipaca:dn         100       1399359   99.4    80.1

Yes, looks good.

>
>
> The changelog:dn seems to vary so much not sure how to tune that one. Any
> suggestions? It's almost always 0% free.

I wouldn't worry about it, for now.

>
>>> 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.
> Great, Thanks Rich!