Regarding Consistent Hashing....

Ajinkya Nahar ajinkya at
Thu Aug 30 06:03:53 UTC 2007



Basically, we are using Amazon's EC2 servers as memcached servers. 


So as and when we see an increase in traffic/load, we expect to add more EC2
servers to the memcached cloud. And when the traffic/load subsides (lets say
after a week or so), we might remove a few servers from the cloud. 


In such a scenario, if using normal hashing, I believe we would have to
flush everything when adding/removing memcached servers. 


Do you think doing this might cause the system to go in a spin and might be
a risky proposition, and so we should rather consider using consistent


Or do you think this is not a big deal and we should rather use the regular
hashing (which is more stable)?


Please let me know your comments on this.





-----Original Message-----
From: Mikael Johansson [mailto:mikael at] 
Sent: Thursday, August 30, 2007 11:03 AM
To: Ajinkya Nahar
Cc: memcached at; sunil at; 'Nishith Shah'
Subject: Re: Regarding Consistent Hashing....




I believe there's already people using consistent hashing on large

installs out there. As to the pecl/memcache client the code is not

released and still in CVS, but it is stable (and certainly ready to be

evaluated/tested), also a release is coming up so you can either wait

for that or build from source like


 cvs -d :pserver:cvsread at checkout pecl/memcache

 cd pecl/memcache



 make && make install


Enable it by setting an php.ini entry like


 memcache.hash_strategy = consistent


Please note that the consistent hashing implementation might still

change in the future when a standard is reached on the subject.




Ajinkya Nahar wrote:

> Hi all,


> I want to know whether consistent hashing technique can be used in

> production environment.


> Is it still too young or is it of production quality?


> Also, what configuration needs to be done in the PHP client when using

> consistent hashing?


> Please let me know.


> Thanks in advance.


> Regards,


> Ajinkya





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