memcached replication

Marcus Bointon marcus at
Wed Sep 5 07:55:42 UTC 2007

On 5 Sep 2007, at 06:22, Dustin Sallings wrote:

> 	Doesn't this mean that you will sometimes write a value to a  
> cache, and then later read a value back and get something other  
> than the latest value you wrote?  Getting known stale values seems  
> worse than not getting something from the cache.

I was thinking that. It might be better to deny the existence of the  
key until replication is complete, or make the write synchronous from  
the client's point of view. I think glusterfs has some kind of  
transactional integrity for replication between nodes. Alternatively,  
make the client responsible for writing to replicated servers, which  
is more scalable. PHPDance does this on top of sharedance. It's not  
very efficient, but it is reliable.

Interestingly, though it doesn't get much press, MySQL replication  
suffers the same problem - there is no transactional integrity  
between replicated nodes - if you write to a master, then immediately  
read from a slave, you may not get back what you just wrote. The fix  
there is not to do it and use a unified front end like sequoia instead.

Marcus Bointon
Synchromedia Limited: Creators of
UK resellers of info at hand CRM solutions
marcus at |

More information about the memcached mailing list