Memcached and Slave database

[VitorHP]

Hi,

I recently installed memcached in my host, but instead of increase the performace and decrease the load in the host, my website turned slower than before i install memcached.

That is the correct config to memcached works well?

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Other question: With slave database the load in my website would decrease, or this slave databse is only a 'backup system' of master database?

With a 'slave database' in another host, that would happened?

Thanks.

[Andy Huang]

It's worth while to note that vBulletin currently only uses memcache for things in datastore. This is usually <8mb in size unless you have A LOT of plugins, users groups, forums, and customized style. If you allocated too much into memcache, then maybe memcache is hogging memory space that could be used by your forums. It would be a good idea to check how much memory you need for it, and allocate at most double that amount in case of random changes outgrow its limit.

Memcache should also be on the same server, or a server very close to your main web server. That is to say, you will notice massive performance delay if you've got a server in California housing your web contents, and another server in New York with your memcache. This is because your webserver will need to contact your other server and go through internet traffic just like everyone else to fetch these information, and it would more than often be slower than reading things locally, for obvious reasons.

It is also worth while to note that things like APC will work almost just as great if you have configured your forum to use file cache, as APC will cache the datastore file cache, which will help make things generally perform better. If this is the case, you may wish to omit memcache all together, and have the few extra mb of memory for other things.

Slave database server should be pointing to mysql replicated database server. These database server will be used by vBulletin only for reading stuff. IE: If I need to search for something, or pull out the thread, vBulletin will go to the slave database server; if I am posting a reply like I am doing now, vBulletin will go to the master server. This effectively helps reduce the stress on the master server, so the writing tasks doesn't get locked up by intensive reading tasks. The slave server needs to be configured to replicate information from the master server, so the changes (IE: new posts) can be accessed. I think -- never had any chance to test performance of this -- it would be best if the two servers are physically close to each other, too.