Evaluating Memcached for our site. Looking for advice.

[Rob Sharp]

On Mon, 2007-10-22 at 13:53 +0800, K J wrote:

>         In our case, not really. It really depends on your current
>         caching codebase. The only problem is the (current) lack of a
>         consistent hashing algorithm [1] but YMMV. 
>         
>  
> What is the consistent hashing part and why is it a bad thing?
>  

The wiki explains the issue pretty well:

http://www.socialtext.net/memcached/index.cgi?faq#how_does_memcached_handle_failover

"With default clients adding or removing servers will invalidate all of
your cache! Since the list of servers to hash against has changed, most
of your keys will likely hash to different servers. It's like restarting
all of your nodes at the same time."

With a consistent hashing algorithm, node removal will not invalidate
your cache, causing much less of an issue should you need to remove a
node from the server pool.

Hope that helps,
Rob.

Rob Sharp
Development Lead 

telephone: 02 9282 4038
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