acache config

[JINMEI Tatuya / 神明達哉]

>>>>> On Fri, 23 Jun 2006 15:21:57 +0200, 
>>>>> Mipam <mipam at ibb.net> said:

> I am trying to read more on the acache section in 9.4.0.
> However, it's hard to read about this, because there is so little material
> available.

Did you read ARM (bind-9.4.0aX/doc/arm)?  If not, you'll find more
information about acache there.  I'm going to provide some short
answers below in case you've not read ARM yet.

> Currently i only know the acache-enable option, but i didn't see
> it in the named.conf.5 manual. The only variable in the named.conf.5
> concerning acache is max-acache-size. So where to enable the acache 
> with the acache-enable option, also in named.conf or?

Yes, in the options section.

> Secondly, in the current bind version already a lot of info is cached.
> What additional info is cached with the acache section?

The cached information currently (i.e., before acache) used in BIND is
DNS resource records which are in general necessary for DNS protocol
operations.  acache is a completely different beast: acache caches
the content of the additional section for a given NS RR so that named
can build response packets containing the NS RR in the authority
section more efficiently.  It's just for optimization purpose, and
is irrelevant to the DNS protocols.

> I guess the performance gain by this is mainily on bind servers hosting
> a lot of domain names?

Not really.  It is mainly on BIND servers that mainly serves
delegations with many NS RRs.  One major example is a root DNS server.

On the other hand, acache is not so beneficial for a server that
serves a lot of "leaf" domain names (such as "www.foo.example") with a
small number of NS RRs in the corresponding zone.

Some additional remarks:
- if you are interested in the implementation details of acache, you
  can find some additional information in
  bind-9.4.0aX/lib/dns/include/dns/acache.h
- bind-9.4.0a5 has memory leak related to acache.  If you seriously
  want to try acache, you'll need to use 9.4.0a6.

					JINMEI, Tatuya
					Communication Platform Lab.
					Corporate R&D Center, Toshiba Corp.
					jinmei at isl.rdc.toshiba.co.jp