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From Ted Dunning <ted.dunn...@gmail.com>
Subject Re: Adding observers
Date Wed, 21 Jul 2010 17:39:56 GMT
On Wed, Jul 21, 2010 at 10:30 AM, Avinash Lakshman <
avinash.lakshman@gmail.com> wrote:

> (1) Is it possible to increase the number of observers in the cluster
> dynamically?

Not quite, but practically speaking you can do as good as this.

In general, pretty much any ZK configuration change can be done without
service interruption by using a rolling restart.

> (2) How many observers can I add given that I will seldom write into the
> cluster but will have a lot of reads coming into the system? Can I run a
> cluster with say 100 observers?

Others will give more authoritative answers, but I am pretty sure that the
limitation on the number of observers is strictly related to write rate x
number of observers.  This is related to the fact that writes need to come
from the current master.  It isn't hard to imagine how to write a reflector
that watches for all changes and writes these to a secondary cluster.  That
would essentially eliminate the limit on number of observers.  Something
like that may already be possible within the current system (I couldn't say
since I haven't looked into observers that much).

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