How to maintain cache update on different memcached servers?

[Bash Coder]

When B goes down you have no failover memcache.  That's OK, because you
don't *need* it anyway - it's just a helper to take load off your database.
If B fails your app goes directly to the database for its data until the
cache server B is back up.  When the server comes back up, it starts to
build it's cache again from scratch.

This is not high availability stuff here -- there's no redundancy or
failover.  But that's OK, because it's just an optimization layer - it isn't
the database.  As to the hashing, I think it just takes a checksum of the
query and does a mod(memcache_server_count).  That way the same query is
cached on the same memcached every time.

- Bash

-- 
http://bashcoder.com

On 10/31/06, howard chen <howachen at gmail.com> wrote:
>
> On 11/1/06, Andrew Pile <andrew at connectedventures.com> wrote:
> > That is NOT how it works. The data is not stored evenly on all
> > servers, it is hashed and sent to one server.
> >
> > On Oct 31, 2006, at 11:26 AM, Jehiah Czebotar wrote:
> >
> > >> so, correct me if i am wrong...
> > >>
> > >> 1. on each memcached server, i start the memcached deamon as they are
> > >> separetely server, they don't know each other, e.g.
> > >> ./memcached -d -m 2048 -l 10.0.0.40 -p 11211
> > >>
> > >> 2. during connection from client, add all the servers...
> > >> e.g.
> > >>
> > >> $memcache = new Memcache;
> > >> $memcache->addServer('memcache_host', 11211);
> > >> $memcache->addServer('memcache_host2', 11211);
> > >>
> > >> 3. the memcached objects will be stored evenly on all these server,
> > >> and i can get it using Memcache::get , without specifying the server
> > >> host
> > >>
> > >
> > > correct: that is exactly it.
> > >
> > > (just make sure the memory you are configuring memcached to use (2048)
> > > is not larger than the actuall free RAM on your machines)
> > >
> > > --
> > > Jehiah
> >
> >
>
> yes, this is the point, how does hashing work?
>
> e.g.
>
> originally three servers, A, B, C
>
> an object is hashed to server B
>
> but server B was downed, and it will hashed to server C when receive
> another request ? what will happen if server B up again?
>
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