Thanks for an interesting presentation.
I’d like to point out that Memcached is not a real cluster. Whenever you add multiple Memcached servers to a “pool”, the Memcache(d) extension in PHP simply divides up the cache into multiple, equally-sized portions. But the different Memcached servers themselves are completely unaware of each other.
This imitates a cluster when accessing it, but it has some severe implications – if you have 3 machines in a pool and one goes down, suddenly 1/3 of your cache is gone and once the timeout is reached on the still active servers the cache will be redistributed amongst the remaining nodes. Now that the remaining servers rebalance there will be a redistribution in the storage and suddenly all keys are invalidated.
In practice a cache flush is hardly noticeable but on large-scale production this is a huge headache, and scaling Memcached over too many machines can be a death sentence for your stability.
Fill in your details below or click an icon to log in:
You are commenting using your WordPress.com account. ( Log Out / Change )
You are commenting using your Twitter account. ( Log Out / Change )
You are commenting using your Facebook account. ( Log Out / Change )
You are commenting using your Google+ account. ( Log Out / Change )
Connecting to %s
Notify me of new comments via email.
Notify me of new posts via email.
November 3, 2014
The challenges of scaling WordPress depend on many factors. This session centers on three factors that are most often overlooked or misunderstood:
1. Choosing the right caching system
2. Tuning and clustering mysql
3. Tuning apache
Presentation Slides »
WordCamp NYC 2014 58
Mikel King 2