Bug #28429 Replication: ldap style Automatic query forwarding for writing queries to master
Submitted: 14 May 2007 23:07 Modified: 11 Nov 2008 16:26
Reporter: Michael Hafen Email Updates:
Status: Verified Impact on me:
Category:MySQL Proxy Severity:S4 (Feature request)
Version:Any OS:Any
Assigned to: Assigned Account CPU Architecture:Any

[14 May 2007 23:07] Michael Hafen
If I remember correctly LDAP will automatically forward a query which causes a change to the directory from a slave to it's master.  This seems to me like a good way to achieve transparent scaling-out for web applications that aren't coded for separate read / write servers.

This could be especially helpful for lazy programmers, like myself, that would rather not modify an application, where even possible, to allow for separate read / write servers.

This could also be a good alternative to scaling-up, which can be very costly after a point.  Instead replication slaves are put in place to act as passive servers, and pass any writing request on up to the master server.

How to repeat:
Just a feature request

Suggested fix:
This could be implemented either at the client library and/or replication server level.

At the client level, the replication slave would return a reference to it's master when it received a query that would change or lock some part of the database.  The client would then have to follow that reference, possible several references in a replication chain or circle, to find a master to take the writing query.  If I remember right this is the way LDAP implements it.

On the other hand this could be implemented just at the replicate server level.  When a replication slave got such a request it would itself forward that request to it's master.

Either way there would have to be a method to watch for the query being forwarded to a master that has already seen it.  This could be a problem anytime there is something like a master - master cluster.  Possibly include the replication id of each server that has seen the request as part of the packet.  Then if a server got the packet and saw it's id in the chain, it would assume it safe to go ahead and run the query itself.
[11 Nov 2008 16:26] Susanne Ebrecht
Many thanks for pointing this out. This is a nice idea.
[24 Nov 2008 14:17] Sven Sandberg
I think this is a job for MySQL Proxy, not core replication (and Mats agreed). Changing lead and category.