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thundering herd problem [Was Re: Questions about LVS-TUN

To: "LinuxVirtualServer.org users mailing list." <lvs-users@xxxxxxxxxxxxxxxxxxxxxx>
Subject: thundering herd problem [Was Re: Questions about LVS-TUN
Cc: Horms <horms@xxxxxxxxxxxx>
From: Joseph Mack NA3T <jmack@xxxxxxxx>
Date: Sat, 16 Dec 2006 07:32:44 -0800 (PST)
On Tue, 12 Dec 2006, Bill Omer wrote:


For example.  Say you have 1000 people connected via telnet (those
connections could be from terminals, wireless scanners etc..) across
10 servers.  Thats 100 users per server when it is weighted.  If you
were using rr, if one server dies then the rest of the servers will
pick up 10 extra users each.  When the dead server is restored, you
will have 9 servers with over a hundred users and 1 server with hardly
any connections.  That is a poor utilization of resources and could
take a day to recover.

It should only take the average time for connections to expire. Is that about a day for you?

You could use wrr with w=2 for the new server, till the number of connections is about right.

The thundering herd problem is one of allocating resources.
Say you bring up a new realserver and using lc scheduling 1000 people connect to a database in seconds on the new machine, then you're going to have problems. In your case if all new connections (say 100 connections) go to one machine, over what time interval would that happen?

Joe

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Joseph Mack NA3T EME(B,D), FM05lw North Carolina
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