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Memcached Object Cache
Multisite Sites Redirecting (5 posts)

  1. Ed
    Member
    Posted 1 year ago #

    Not sure how to replicate this apart from leaving it running on a large multisite install, but after so long some blogs start redirecting to other blogs on visit, i.e. when you visit subdomain1.blog.com it will go to blog.com instead. Disabling the object-cache.php fixes it, so it's definitely that.

    This is using the latest version of the Memcached object-cache.php and WordPress. I will also say that we are using multisite networks split into 3 different sub-networks, not sure if that will have an impact, but only one physical WordPress install uses the object-cache.php and Memcached server, it's not shared with anything else.

    The APC object cache used to do the same thing, but we are on a multiple server set up now so can't test that anymore. Although using APC object-cache used to improve the speed of WordPress throughout, the Memcached one seems to add 300ms-10s to the loading time of pages, especially the admin area.

    If anyone could shed any light on the situation I'd be grateful.

    Cheers,

    Ed

    http://wordpress.org/extend/plugins/memcached/

  2. Mike Bijon
    Member
    Posted 1 year ago #

    Do you know your cache hit ratio?

    Memcache does add latency compared to a single server APC. Depending on your network traffic 10-20ms is possible. But 300ms makes it sounds like it's skipping the cache and hitting the DB.

  3. Ed
    Member
    Posted 1 year ago #

    The hit ratio was quite high actually. I heard it does at a small bit of latency but it has added up to 10 seconds in places. I've had to disable it for now as it was redirecting pages. Hitting the DB is relatively quick looking at our stats, so the 10 seconds, in my mind, wouldn't relate to that.

    Cheers,

    Ed

  4. Matt Martz
    Member
    Plugin Author

    Posted 1 year ago #

    One thing that you can do to test things, is to edit object-cache.php and uncomment the line to log failures to a log file as seen at: http://plugins.trac.wordpress.org/browser/memcached/tags/2.0.2/object-cache.php#L355

    In my experience, you see this when the server cannot communicate with the memcached server.

    One thing to note, you can still run APC along side this plugin, taking advantage of opcode caching done by APC, and letting memcached handle object caching.

    One other thing to note, is that unless you need the cache on another server, or you are using multiple servers, there's no sense in using memcached. memcached is best used for multiple web servers, or where the load due to caching has caused you to need to move it elsewhere. APC is the best bet for single web server configurations.

    Although your mention that both the APC object cache and memcached causes this issue, of redirecting, is quite odd. You are the first person I have had mention that. I'd be looking to other plugins or code that could be causing conflicts also.

  5. Ed
    Member
    Posted 1 year ago #

    Hi Matt,

    I'll give that a go.

    We're on a multi-server set up at the moment, hence using Memcached, we're also using APC for the opcode cache. It's interesting you say it can't connect, I'll monitor it to see if there are any connection issues, although they're both running locally but connecting via external IPs in wp-config.php.

    Cheers,
    Ed

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