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!
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