Search Again: Re: Capacity & RAM From: Men & Mice Support Date: Monday, November 15, 1999 Time: 10:26:00 pm At 11:50 AM -0800 11/15/99, Peter Lalor wrote: >The only problem we've had is with Funnel Web analysis of very large >Web server logs. We find that Funnel Web generates a DNS load >exceeding 1 mb/s and that it effectively brings QuickDNS to it's >knees, no matter what hardware we've run it on. That said, large >Unix iron doesn't appreciate it much either. We've had other reports of this. In essence, as near as we can tell, the sequence of events goes something like this: o FunnelWeb gives QDNS a rapid-fire series of requests. o QDNS tries to resolve each one as it comes in. o Each request generally requires a dozen or more outgoing queries (root servers, class A subnet, class B subnet, class C subnet, PTR record; some go directly to class C, but some have classless subnet delegation beyond that). Caching is not generally very useful for this, since most of the addresses to be looked up are from different blocks of IP addresses. For those cases where caching works, it only takes an average of about 4 queries. o Doing the math on the bandwidth, if FunnelWeb is giving QDNS 1 Mb/s in queries, that equates to approx. 12 x 1 Mb/s = 12 Mb/s. That's generally more bandwidth than is available. o As a result, the network becomes flooded. This means that, once an outside server responds to a query, it may take several seconds for that query to get through the queue. o Since QDNS ends up waiting for hundreds of queries to resolve simultaneously, its multithreading system gets overloaded. Multithreading overhead becomes a massive computational exercise, overloading even powerful hardware. Also, the cache becomes filled with essentially useless reverse lookup entries; if you have plenty of RAM allocated to QDNS, then this is no big deal, but otherwise, some or all of the useful cache entries are purged. ____________________________________________________________________ Chris Buxton cbuxton@menandmice.com Men & Mice http://www.menandmice.com Makers of: QuickDNS Pro

Messages In This Thread: Re: Capacity & RAM by Kurt Anderson on Nov 5, 1999 at 5:26:00 pm Re: Capacity & RAM by eric@micromaniac.com on Nov 5, 1999 at 5:47:00 pm Re: Capacity & RAM by Men & Mice Support on Nov 5, 1999 at 8:51:00 pm Re: Capacity & RAM by andrew kagan on Nov 5, 1999 at 9:55:00 pm Re: Capacity & RAM by Men & Mice Support on Nov 5, 1999 at 10:39:00 pm Re: Capacity & RAM by Peter Lalor on Nov 8, 1999 at 7:52:00 pm Re: Capacity & RAM by Jerry Pasker-Systems Admin. on Nov 8, 1999 at 8:14:00 pm Re: Capacity & RAM by Men & Mice Support on Nov 8, 1999 at 10:17:00 pm Re: Capacity & RAM by Peter Lalor on Nov 15, 1999 at 7:50:00 pm Re: Capacity & RAM by Men & Mice Support on Nov 15, 1999 at 10:26:00 pm