Oracle 5.0 Reference Manual page 1358

• If you use the in-memory cache to hold transient information, or as a read-only cache for information
also stored in a database, the failure of any
can fall back to an alternative lookup method using database queries, and reload the data into RAM
on a different server.
The typical usage environment is to modify your application so that information is read from the cache
provided by memcached. If the information is not in memcached, then the data is loaded from the
MySQL database and written into the cache so that future requests for the same object benefit from the
cached data.
For a typical deployment layout, see
Figure 15.4.
In the example structure, any of the clients can contact one of the
given key. Each client is configured to talk to all of the servers shown in the illustration. Within the
client, when the request is made to store the information, the key used to reference the data is hashed
and this hash is then used to select one of the
server takes place on the client before the server is contacted, keeping the process lightweight.
The same algorithm is used again when a client requests the same key. The same key generates
the same hash, and the same
method, the cached data is spread among all of the
is accessible from any client. The result is a distributed, memory-based, cache that can return
information, particularly complex data and structures, much faster than natively reading the information
from the database.
The data held within a traditional
means there is no persistence of data), and the RAM cache is always populated from the backing store
(a MySQL database). If a
database.
Integration with MySQL Storage Engines
memcached
In April 2011, MySQL announced the preview of a new memcached interface for the InnoDB and
MySQL Cluster storage engines.
Using the memcached API, web services can directly access the InnoDB and MySQL Cluster storage
engines without transformations to SQL, ensuring low latency and high throughput for read/write
queries. Operations such as SQL parsing are eliminated and more of the server's hardware resources
(CPU, memory and I/O) are dedicated to servicing the query within the storage engine itself. The
memcached
Integration with MySQL Storage Engines
memcached
Architecture Overview
memcached
memcached
memcached
memcached
data can be persisted to disk while still cached in memory for fast retrieval.
server is not critical. For persistent data, you
memcached
Figure 15.4, "memcached
servers. The selection of the
memcached
server is selected as the source for the data. Using this
memcached
server is never stored on disk (only in RAM, which
server fails, the data can always be recovered from the MySQL
1338
Architecture Overview".
servers to request a
memcached
servers, and the cached information
memcached