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Mysql has memory based data engines, which means it keeps the data in RAM.

There are two types of memory storage engine in Mysql as far as I know that use memory,

One is Memory engine itself The not very cool feature of this storage engine is that only creates virtual tables which means if the server is restarted the data is lost

The other one is Cluster storage engine This doesn't have the drawback of the previous engine, it uses memory but it also keeps a file based record of data.

Now the question is if your Database is already using RAM to store and process data, do you need to add another caching engine like Memcached in order to boost your product's performance?

How fast is a memory engined database compared to Memcached?

Does Memcache add any features to your products that a memory engined database doesn't?

Plus memory engined database gives you more features like being able to request queries, compared to Memcached which will only let you get raw data, so Memcached is kind of like a database engine that only supports SELECT command.

Am I missing something?

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It depends how you use memcached. If you use it to cache a rendered HTML page that took 30 SQL queries to build, then it will give you a performance boost even over an in-memory database.

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A (relational) database and caching service are complementary. As pointed out, they have different design goals and use-cases. (And yet I find the core advantage of a database missing in the post.)

Memcached (and other caches) offer some benefits that can not be realized under an ACID database model. This is a trade-off but such caches are designed for maximum distribution and minimum latency. Memcached is not a database: it is a distributed key-value store with some eviction policies. Because it is merely a key-value store it can "skip" many of the steps in querying database data -- at the expensive of only directly supporting 1-1 operations. No joins, no relationships, a single result, etc.

Remember, a cache is just that: a cache. It is not a reliable information store nor does it offer the data-integrity/consistency found in a (relational) database. Even cache systems which can "persist" data do not necessarily have ACID guarantees (heck, even MyISAM isn't fully ACID!). Some cache systems offer much stronger synchronization/consistency guarantees; memcached is not such a system.

The bottomline is, be because of memcache's simple design and model, it will win in latency and distribution over the realm it operates on. How much? Well, that depends...

...first, pick approach(es) with the required features and guarantees and then benchmark the approaches to determine which one(s) are suitable (or "best suited") for the task. (There might not even be a need to use a cache or "memory database" at all or the better approach might be to use a "No SQL" design.)

Happy coding.

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Memcached can store up to 1mb of data. What it does is that it leverages the db load in such way that you don't even connect to the db in order to ask it for data. Majority of websites have a small amount of data that they display to the user (in terms of textual data, not the files themselves).

So to answer - yes, it's a good idea to have Memcached too since it can help you so you don't even connect to the db, which removes some overhead at the start.

On the other hand, there's plethora of engines available for MySQL. Personally, I wouldn't use memory engine for many reasons - one of them being the loss of data. InnoDB, the default MySQL engine as of recent release - already stores the working data set in the memory (controlled by innodb_buffer_pool variable) and it's incredibly fast if the dataset can fit in the memory. There's also TokuDB engine that surpasses InnoDB in terms of scaling, both better than memory engine. However, it's always a good thing to cache the data that's frequently accessed and rarely changed.

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