max-cache-size (was: no subject)

[gagadget at free.fr]

Selon John Wobus <jw354 at cornell.edu>:

> If you can solve the problem with more memory, that could be your best
> solution.  I used max-cache-size for a while, but eventually discovered
> the cache was not actually growing indefinitely.  The problem was that
> we
> needed just a bit more memory for the cache size to stabilize.  This
> was not at all evident from the memory-usage statistics we gathered
> before the memory upgrade.  But a modest memory upgrade indeed
> solved our problem.  I believe that using the max-cache-size also
> causes bind to spend more CPU on cache management.
>
> However, I can imagine situations where merely adding
> a bit of memory would not be enough.  For example, if someone is doing
> some serious spidering using your nameserver, then the eventual
> stable cache size could be extremely large.  However I believe there
> are people on this list who have very large and diverse user-bases, yet
> the cache sizes in their nameservers do stabilize at a reasonable
> amount.

I don't really understand how named allocate new amount of memory for cache as
named don't seem to know how to release it and don't seem to have limit.

> Your figure of '2M', though, is very small and suggests you are in
> a situation where your resources are very limited.

I put such a small value because I wanted to test this parameter. I originaly
put '64M' and noticed bind would take the exact same amount of memory without
any parameter.

I did that :
BIND 8.4.6 -> named process take 10mb of memory
BIND 9.4.2 no max-cache-size -> named process take 60mb of memory and "rndc
dumpdb -cache" generates a 56Mb file
BIND 9.4.2 + max-cache-size 'anything you want M' -> same as above

My DNS servers have only 128 Mb of ram, so I would like to limit bind to grow
too widely in ram.

> Bind also uses memory for other functions besides the cache
> itself.  If you limit the cache, e.g. to 2M, then I'm guessing
> other uses of memory become dominant, and a change, say, between
> 2M and 10M might not be very visible in terms of memory size.
> Some other bind uses of memory might even grow with usage,
> in a similar manner to the cache: perhaps someone on this list can
> comment on that.  If you really are attempting to run with severely
> limited
> resources, possibly other parameters could be adjusted to reduce
> memory usage, e.g. number of simultaneous recursive clients
> supported.

Thank you for answering precisely John,
Gael.

> John Wobus
>
> On May 23, 2008, at 5:32 AM, gagadget at free.fr wrote:
>
> >
> > Hello everybody,
> >
> > I am running BIND 9.4.2 and I want to limit the cache size of the
> > named process
> > because It tends to grow indefinitly.
> >
> > In order to do that, I put the following line in global option section
> > :
> >
> > max-cache-size 2M ;
> >
> > The problem is : this parameter does not seem to work at all because
> > with or
> > without it, the size of named is the same. Doing a "rndc dumpdb
> > -cache" show a
> > named_dump.db file size of about 60Mb which is much more than 2Mb as
> > set in
> > named.conf.
> >
> > Am I missing something or the parameter is not used by named ?
> >
> > Regards,
> > Gael.
> >
>
>
>