Re: performance tuning

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On Mon, 2017-11-20 at 09:42 -0600, Sergei Gerasenko wrote:
> Hi William,
> 
> > So to really answer that I should explain the LDAP data model.
> > 
> > You have a set of objects, in a tree database. The RootDSE (you can
> > search with -b '' -s base by the way with ldapsearch) is the ...
> > well,
> > root. Under than you have "suffixes", like dc=com and
> > dc=example,dc=com. 
> 
> Confirmed
> 
> > So we connect those "suffixes" with "mapping trees". Think
> > "routers"
> > that connect a suffix to a backend of some kind.
> > 
> > Then that backend stories entries: that's the "userRoot". It's a
> > backend which is connected by a mapping tree to route queries to
> > it.
> 
> Ok, so when issue requests for entries under dc=example,dc=com and
> they get translated by a mapping tree to a physical db file. I
> noticed that if I specify the base dn as “cn=config”, I don’t see
> user account data for example. When I bind under “dc=example,dc=com”
> however, I do! Is that because when I bind under cn=config, I don’t
> go through a mapping tree, but when I bind with "dc=example,dc=com” I
> do? I of course use our company name instead of “dc=example,dc=com”.

cn=config is special, that's why :) You should generally ignore it for
these discussions about backends and databases. 

> 
> > You can really get an idea of this by looking at what's in
> > "userRoot".
> > If you look at:
> > 
> > cd /var/lib/dirsrv/slapd-<inst>/db/userRoot
> > 
> > dbscan -f id2entry.db | less
> 
> Nice
> 
> > So having your entrycache "as large or larger" than id2entry.db is
> > a
> > great idea, because then you never need to incur the performance
> > penalty of accessing id2entry.
> 
> Great info again. Quick question though. There are at least two types
> of cache I’ve seen: the entry cache, and the dn cache. I think the
> entry cache corresponds to id2entry.db, right? What corresponds to
> the dn cache?

So if you look at the entries from id2entry you'll notice that they
don't have dn's rdns. IE:

uid=william

Rather than:

uid=william,ou=People,....

So the entries in id2entry are just the "objects". They are associated
into a tree by the parentid attribute. So for example:

dc=example,dc=com
entryid: 1

ou=People
parentid: 1
entryid: 2

So ou=People has a parent of "entry 1".

The dncache exists to cache these relation ships: because we have to
"walk up" a number of entries to work out entryid -> dn, it's better to
cache this result if we can. Again, this saves accessing id2entry,
which can be a costly operation. 

So here, we'd cache entryid: 2 with a dn of ou=People,dc=example,dc=com

Does that help? 

> 
> Also: do ipa services need to be stopped when using the ipa-backup
> utility?

I can't answer that I have not used IPA in many years. Please ask the
freeipa-users list for help on that topic, or refer to the
documentation on access.redhat.com (redhat IDM correlates to FreeIPA).

> 
> Thanks again,
>   Sergei
> _______________________________________________
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> rg
-- 
Sincerely,

William Brown
Software Engineer
Red Hat, Australia/Brisbane
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