Recommended setup with large cache memory

[Attila Nagy]

Kevin Darcy wrote:
> typical ISP). Having thus disclaimed, I think that _theoretically_ you 
> could try cleaning *more* frequently (each cleaning should then have 
> less impact on performance because there are fewer entries to purge on 
> each pass) and/or setting/lowering max-cache-ttl and/or max-ncache-ttl 
That depends. I didn't look the source, but if it walks through the 
entries every time to get the expired ones out, doing cleaning more 
often on a large dataset will be slower.
BTW, it seems that the cleaning takes about the same time, even in the 
very early morning, when the load is about 4-5 lower than in the daytime 
peak.
So I guess the needed time is based on the number of cached entries and 
not on the number of expired entries.

> You could also consider some sort of clustering/load-balancing solution, 
> but again, like max-cache-ttl/max-ncache-ttl tuning, your issue there is 
> what impact is the lower cache hit ratio going to have, and is that 
> impact even worse than just having the nameserver get slow once in a 
> while when its doing its cleaning...
We have many nameservers, it is just embarassing to do cleaning on them. 
And getting each one out of the pool just for this is insane.

BTW, currently I have a zero cleaning interval and the memory usage of 
bind seems to be capped. Higher than the limit, I set, but it doesn't 
grow, which is good.

> P.S. It would be nice if there was a way to initiate a cache cleaning 
> through rndc. Then cleaning-interval could be set to 0 in named.conf and 
> a cron job could be set up to do the cleaning on a set time-of-day 
> schedule, during hours when the impact on customers would be minimal. In 
To be honest, I am not interested in regular, user or server initiated 
cleaning. The current method (which I thought is not working), which 
caps the usage and drops the records, without eating the CPU is much better.

-- 
Attila Nagy                                   e-mail: Attila.Nagy at fsn.hu
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