bind cache size

[Jim Reid]

>>>>> "Tim" == Tim Jones <tim.jones at ntli.net> writes:

    Tim> Is there a significant limit at which to set up cache
    Tim> cleaning, currently we don't explicitly set this up and the
    Tim> cache grows to about 750Mb is a week. Then settles down at
    Tim> that size.

    Tim> Is the theoretical max. cache size we should allow the server
    Tim> to grow to.

There's no "theoretical" maximum cache size. How big the cache gets is
largely a function of the names that are looked up and the values of
their TTLs. The more names that get looked up and the bigger their
TTLS, the bigger the cache. Most people find that the name server's
cache grows steadily for 1-2 weeks and then stabilises at however much
memory is then being used. Most RRs tend not to have TTL's longer
than one or two weeks. So if your server is using 750Mb, that's
probably what's needed to cache the names your clients are looking
up. This is a bit big, but then you said you're getting 1500 queries a
second. I haven't heard of ISP's name servers caches bigger than 250Mb
until now.

BTW, reducing the cache cleaning interval probably has no impact on
the size of the cache. It just indicates how often the name server
does garbage collection to free up the memory held by expired RRs. If
it runs more frequently, the chances are that the clients will lookup
the expired and deleted names, causing them to be looked up and cached
all over again.