memcached namespace about mcrouter

[alikhtarov]

@Testinos can you provide an example of how that feature would look like? One thing I can think of is adding a prefix for every key based on pool information, so for example get key sent to mcrouter would result in get user:key sent to memcached - do you mean something like that?

Note that mcrouter already supports sending to different destinations depending on the key prefix, so for example you can send get a:key to 'a' servers and get b:key to 'b' servers - see https://github.com/facebook/mcrouter/wiki/Prefix-routing-setup

[Testinos]

@alikhtarov mysql memcached present namespace, namespace it is dedicated tables in database for storage data.
Example:
mysql memcached database(database: memcached, tables "sessions", "default")
telnet 127.0.0.1 11211 (one connection for next 4 steps)

1. get @@sessions (set namespace)
2. set test (set key for "sessions" namespace)
3. get @@default
4. set test1 (set key for "default" namespace)

referer: http://dev.mysql.com/doc/refman/5.6/en/innodb-memcached-intro.html (ctrl + F "Namespaces")

[alikhtarov]

@Testinos I see. Mcrouter will already pass through those commands ("get @@namespace") to the server, so you can just proxy those requests to a mysql memcached server directly and everything will work as expected. Do you have a use case in mind where mcrouter itself should handle namespace logic?

[exception0x876]

@alikhtarov thing is mcrouter uses connection pooling as stated in documentation and namespaces work per connection. So mcrouter should know which namespace to use on a destination connection based on source connection namespace.

[Testinos]

@exception0x876, All right.
So possible improve this in mcrouter?

[Testinos]

I see implementation this, example:
*I have 4 namespace
Announce this 4 namespaces in mcrouter config, without depending Route Handles.
For every announce namespace create dedicated connection pool to memcached servers, and so if client after connect to mcrouter send command ("get @@namespace") send all traffic from this source connection to specially connection pool with command ("get @@namespace".)

[alikhtarov]

So you can already do requests like "get @@namespace.key" using prefix routing. But there's no way to maintain state per connection like you suggest. Adding support for this is not trivial, as currently there's no correspondence between client and server connections in mcrouter by design, so that clients can share the server connections. This means that every request/reply pair is independent. If a client sends "get @@namespace", and we forward it to the server, all other clients sharing the server connection will be affected.

[Testinos]

Thanks for reply.