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NoSQL to MySQL with Memcached

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The ever increasing performance demands of web-based services has
generated significant interest in providing NoSQL access methods to
MySQL - enabling users to maintain all of the advantages of their
existing relational database infrastructure, while providing blazing
fast performance for simple queries, using an API to complement regular
SQL access to their data.

The HandlerSocket
development at DeNA is a great example of community innovation, with a
solution implemented as a custom plug-in and protocol for the MySQL
server daemon.

We are hearing the community say they want NotOnly SQL - they want
their trusted SQL RDBMS - plus, they want NoSQL techniques to access
that data. So, we are previewing our NotOnlySQL solution for MySQL -
delivered via memcached - with implementations to access both the
InnoDB and MySQL Cluster (NDB) storage engines.

The purpose of this blog is to provide more detail on the Memcached API for MySQL, specifically covering:

  • Design rationale
  • Implementation
  • Getting started

Design Rationale

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.

Over and above performance, there are a number of additional potential benefits in this approach for both developers and DBAs:

  • Preserves investments in memcached infrastructure by
    re-using existing memcached clients and eliminates the need for
    application changes.
  • Access to the full range of memcached
    client libraries and platforms, providing maximum deployment
    flexibility and consistently high performance across all supported
    environments.
  • Extends memcached functionality by
    integrating persistent, crash-safe, transactional database back-ends
    offering ACID compliance, rich query support and extensive management
    and monitoring tools.
  • Reduces service disruption caused by
    cache re-population after an outage (note that buffer pool reloading
    enhancements planned for a future milestone release will further
    improve recovery performance by warming the cache)
  • Simplifies web infrastructure by compressing the caching and database layers into a single data tier, managed by MySQL.
  • Reduces
    development and administration effort by eliminating the cache
    invalidation and data consistency checking required to ensure
    synchronization between the database and cache when updates are
    committed.
  • Eliminates duplication of data between the
    cache and database, enabling simpler re-use of data across multiple
    applications, and reducing memory footprint.
  • Flexibility
    to concurrently access the same data set with SQL, allowing complex
    queries to be run while simultaneously supporting Key-Value operations
    from memcached.

Of course, the memcached implementations for InnoDB and MySQL
Cluster are still in their early phases of development (though MySQL
Cluster is more mature at this stage), and so neither is suitable for
production deployment. Nonetheless, developers can at least get a taste
of what is possible as these features evolve.

Implementation

The initial memcached API implementations for InnoDB and MySQL
Cluster take slightly different approaches, which are discussed below.

Note that both implementations are dependent on memcached 1.6.

Memcached and InnoDB

As illustrated in Figure 1, memcached protocol access for InnoDB is
implemented via a memcached daemon plug-in to the mysqld process, with
the memcached protocol mapped to the native InnoDB API.


Figure 1: Memcached API Implementation for InnoDB

Figure 1: Memcached API Implementation for InnoDB

With the memcached daemon running in the same process space, users
get very low latency access to their data while also leveraging the
scalability enhancements delivered with InnoDB 1.2 (which has been
introduced as part of the MySQL 5.6.2 Development Milestone Release),
and a simple deployment and management model. Multiple web /
application servers can remotely access the memcached / InnoDB server
to get direct access to a shared data set.

Note that in the current InnoDB implementation, updates made by
memcached applications are not written to the binlog. Binlogging
capability is something that the engineering team plan to add in a
future milestone release which would deliver against more of the
benefits identified in the "Design Rationale" section above.

With simultaneous SQL access, users can maintain all the advanced
functionality offered by InnoDB including support for foreign keys, XA
transactions and complex JOIN operations.

Looking forward, the MySQL engineering team plans to develop the
same implementation model used by MySQL Cluster with the memcached
server running in a separate process space (discussed below). Users can
then choose whichever implementation model makes the most sense for
their specific use-case.

Learn more »

You can download the code now from http://labs.mysql.com and select the appropriate build:

  • Binary: mysql-5.6.2-labs-innodb-memcached-linux-x86_64.tar.gz
  • Source: mysql-5.6.2-labs-innodb-memcached.tar.gz

Memcached and MySQL Cluster (NDB)

Like memcached, MySQL Cluster provides a distributed hash table with
in-memory performance for caching, which can now be accessed via the
simple memcached API.


Figure 2: Memcached API Implementation for MySQL Cluster (NDB)

Figure 2: Memcached API Implementation for MySQL Cluster (NDB)

Unlike the initial InnoDB implementation discussed above, a MySQL
Cluster plug-in is installed within the memcached server as an
"memcached driver for NDB" which can access the NDB API to directly
query the data nodes, as illustrated in the diagram above.

With the memcached server running in a separate process space, a
single MySQL Cluster instance can serve multiple memcached
applications, and scale-out on demand with transparent auto-sharding,
in-memory data and the ability to add nodes on-line to a running
cluster, without interruption to service.

Users can also take advantage of 99.999% uptime and high write performance properties of MySQL Cluster to support update-intensive services with extreme availability requirements.

As all updates from memcached applications pass through the NDB API,
the binlog injector thread captures and writes events to the binary log
for onward replication to slave systems.

As well as having memcached access to MySQL Cluster, users have the
additional flexibility of maintaining their own dedicated memcached
caching layer for data with the following properties:

  • Read-intensive (rarely updated)
  • Response-time sensitive
  • Does not require persistence
  • Simple key-value access patterns

The Memcached API adds another direct NoSQL access method to MySQL
Cluster, which already includes C++ (NDB API), Java, JPA, LDAP and
HTTP/REST interfaces, all of which can be used concurrently with the
SQL interface to serve a broad range of web, telecoms and embedded
use-cases handling the simplest to the most complex queries.

Learn more about the memcached implementation for MySQL Cluster »

You can also read the blog from the engineer who developed this capability and also take a look at his presentation from the O'Reilly MySQL Conference.

You can download the code now from http://labs.mysql.com and select the source build: mysql-cluster-7.2-labs-memcached

Summary

Explosions in data volumes and internet penetration rates are
driving a seemingly insatiable demand for ever-higher levels of
database performance. By directly implementing memcached API support to
InnoDB and MySQL Cluster, developers and DBAs can preserve the rich
functionality of relational databases and SQL, while also having
options to integrate simple and fast access methods provided by the one
of the most widely adopted NoSQL protocols.

Let us know what you think of these enhancements directly in
comments for each blog. We look forward to working with the community
to perfect these new features.


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