Many thanks to those who replied:
robsonk@ebrd.com
peter@nextra.ch
gjy@crc.com
The response was mixed regarding nscd. One admin said use it, one said don't
and the third offered advice on how to determine what was going on! Thanks
to them all.
It should be pointed out that my original understanding of the problem was a
bit confused, so I was corrected about that:
> This not an answer but may help you figure one out, you may be able to
> do it either with a high debug level on nscd or using truss. The
> problem was not quite as described, the problem is that DNS/bind was
> single threaded, nscd is mulithreaded, if you get into a situation
> where there were multiple host cache misses then the lookups would
> block due to the single threaded nature of DNS/bind, (i.e. if nscd
> asked for multiple names this would be done serially rather than in
> parallel), this could/would severely hurt performance.
>From reading the ISC web site BIND is still single-threded, although it
seems this is being worked on and BIND version 9 should be multi-threaded.
This will not be available until (hopefully early) next year. I have not
found anywhere anything saying the Sun's in.named included with Solaris 7 is
multi-threaded. (I know it is 'basically' the sameas BIND but they (Sun) seem
to change some things - I think multi-threading it would have been a *major*
change though :-) )
I also ran the 'top' command and could see the 'THR' (threads) column only
showing 1 for named but a varying figure for nscd. So this seemed to confirm
it.
I would also agree with another quote I was given:
> This is what clinches it for me with concern to abandoning NSCD, it is a
> quote from the sun man page on it:
>
> The nscd interface is included in this release on an uncom-
> mitted basis only, and is subject to change or removal in a
> future minor release.
Admittedly a bit worrying if its interfering with the web or mail servers.
At present we are still using nscd but to try and get around the
single/multi-threaded problem I have changed the nscd.conf parameters to
store more entries and for longer. Hopefully the servers will find the
entries they want in the nscd cache, using multiple-threading, before having
to go to BIND to look it up with its single-threaded nature. We are not
running it on the nameservers themselves.
I think BIND 9 will sort this query out for good :-)
On the issue of 'bufhwm' I referred back to:
http://www.rvs.uni-hannover.de/people/voeckler/tune/EN/tune.html
This is a good (I think) document on some of the things that can be tuned
under Solaris 2. It has been updated a bit for Solaris 7 and seems to have
helped our web and mail servers. Thanks to Jens-S. Vockler for this.
The original question was:
> Can anyone tell me whether running nscd on Solaris 7 server systems - mail,
> www, dns - is a good or bad thing? We disabled it under Solaris 2.6/2.5.1
> since I gather it caused bottlenecks. Under Solaris 7 I am told it is
> threaded and thus there should be no bottlenecks (at least not as much as
> before). If we don't run it then Netscape doesn't work (version 4.61) -
> not such a bad thing but it is used by the web people from their accounts
> on the server. It does also beg the question of what else may not work if
> we disable it. We run apache/squid on the web server, bind on the name
> servers and exim on the mailhub. The web and mail systems run a caching
> dns - which in itself seems a bit pointless if nscd is there (or
> vice-versa really!).
>
> As a side issue we used to up the bufhwm value on the web server under
> Solaris 2.5.1. I gather there were many performance changes in Solaris 7 -
> should this value still be tweaked for web servers? (A url for Solaris 7
> performance tweaks would be nice!)
>
John.
--------------------------------------------------------------------------
John Horne, University of Plymouth, UK Tel: +44 (0)1752 233914
E-mail: jhorne@plymouth.ac.uk
Finger for PGP key: john@jhorne.csd.plymouth.ac.uk
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