[Pdns-users] max-cache-entries

[Mark Moseley]

On 7/6/06, bert hubert <bert.hubert at netherlabs.nl> wrote:
>
> On Thu, Jul 06, 2006 at 11:03:14AM -0700, Mark Moseley wrote:
> > Just a quick question regarding the excellent pdns-recursor:
>
> Thanks :-)
>
> > To save myself a number of days of trial and error, I'm curious if
> there's a
> > rough conversion for max-cache-entries => memory limit of cache.
> Obviously
> > it's not going to be exact but is there a maximum limit in bytes of each
> > cache entry, so that max-cache-entry x max-cache-entries = Max memory
> used
> > for cache?
>
> No, there is no hard and fast rule. *Actual* memory use depends on a lot
> of
> things, including c++ compiler, operating system paging strategy, access
> patterns.
>
> From what I know, 4 million cache entries correspond to around 1G of
> memory
> used. From my measurements, there is not a lot of benefit of using more
> than
> 4 or 5 million entries, generally.
>
> On 64 bit systems, some more memory will be needed because of the 8 byte
> pointers. This has been confirmed by some large operators.
>
> Tinydns is able to do exact bytewise limiting of memory usage, which is
> very
> impressive. I've pondered doing something like it but it requires a lot of
> very tricky coding, so the current cache entries limit will have to do.
>
> Good luck!
>
> --
> http://www.PowerDNS.com      Open source, database driven DNS Software
> http://netherlabs.nl              Open and Closed source services
>


Cool, that gives me round numbers to work with. Thanks for the info!
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