Pre-General Availability Draft: 2018-02-22
This section outlines advantages the
daemon_memcached plugin. The combination of
InnoDB tables and memcached
offers advantages over using either by themselves.
Direct access to the
InnoDBstorage engine avoids the parsing and planning overhead of SQL.
Running memcached in the same process space as the MySQL server avoids the network overhead of passing requests back and forth.
Data written using the memcached protocol is transparently written to an
InnoDBtable, without going through the MySQL SQL layer. You can control frequency of writes to achieve higher raw performance when updating non-critical data.
Data requested through the memcached protocol is transparently queried from an
InnoDBtable, without going through the MySQL SQL layer.
Subsequent requests for the same data is served from the
InnoDBbuffer pool. The buffer pool handles the in-memory caching. You can tune performance of data-intensive operations using
Data can be unstructured or structured, depending on the type of application. You can create a new table for data, or use existing tables.
InnoDBcan handle composing and decomposing multiple column values into a single memcached item value, reducing the amount of string parsing and concatenation required in your application. For example, you can store the string value
2|4|6|8in the memcached cache, and have
InnoDBsplit the value based on a separator character, then store the result in four numeric columns.
The transfer between memory and disk is handled automatically, simplifying application logic.
Data is stored in a MySQL database to protect against crashes, outages, and corruption.
You can access the underlying
InnoDBtable through SQL for reporting, analysis, ad hoc queries, bulk loading, multi-step transactional computations, set operations such as union and intersection, and other operations suited to the expressiveness and flexibility of SQL.
You can ensure high availability by using the
daemon_memcachedplugin on a master server in combination with MySQL replication.
The integration of memcached with MySQL provides a way to make in-memory data persistent, so you can use it for more significant kinds of data. You can use more
incr, and similar write operations in your application without concern that data could be lost. You can stop and start the memcached server without losing updates made to cached data. To guard against unexpected outages, you can take advantage of
InnoDBcrash recovery, replication, and backup capabilities.
InnoDBdoes fast primary key lookups is a natural fit for memcached single-item queries. The direct, low-level database access path used by the
daemon_memcachedplugin is much more efficient for key-value lookups than equivalent SQL queries.
The serialization features of memcached, which can turn complex data structures, binary files, or even code blocks into storeable strings, offer a simple way to get such objects into a database.
Because you can access the underlying data through SQL, you can produce reports, search or update across multiple keys, and call functions such as
MAX()on memcached data. All of these operations are expensive or complicated using memcached by itself.
You do not need to manually load data into memcached at startup. As particular keys are requested by an application, values are retrieved from the database automatically, and cached in memory using the
Because memcached consumes relatively little CPU, and its memory footprint is easy to control, it can run comfortably alongside a MySQL instance on the same system.
Because data consistency is enforced by mechanisms used for regular
InnoDBtables, you do not have to worry about stale memcached data or fallback logic to query the database in the case of a missing key.