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Re: Great Suggestion for the DNS problem...?
On Tue, 29 Jul 2008, Steven M. Bellovin wrote:
In this situation, UDP uses one query packet and one reply. TCP uses 3 to set up the connection, a query, a reply, and three to tear down the connection. *Plus* the name server will have to keep state for every client, plus TIMEWAIT state, etc. (Exercise left to TCP geek readers: how few packets can you do this in? For example -- send the query with the SYN+ACK, send client FIN with the query, send server FIN with the answer? Bonus points for not leaving the server's side in TIMEWAIT. Exercise for implementers: how sane can your stack be if you're going to support that?)
The bittorrent tracker guys seem to run into problems at around 30kk tracker requests per second (TCP), and they say it's mostly setup/teardown (sy usage in vmstat), the tracker hash lookup doesn't take that much.
They're trying to move to UDP, currently their workload is approx 5% UDP.
I guess TCP DNS workload would be similar in characteristics.
-- Mikael Abrahamsson email: swmike@xxxxxxxxx