MySQL memcached support

Amazon RDS supports using the memcached interface to InnoDB tables that was introduced in MySQL 5.6. The memcached API enables applications to use InnoDB tables in a manner similar to NoSQL key-value data stores.

The memcached interface is a simple, key-based cache. Applications use memcached to insert, manipulate, and retrieve key-value data pairs from the cache. MySQL 5.6 introduced a plugin that implements a daemon service that exposes data from InnoDB tables through the memcached protocol. For more information about the MySQL memcached plugin, see InnoDB integration with memcached.

To enable memcached support for an RDS for MySQL DB instance

1. Determine the security group to use for controlling access to the memcached interface. If the set of applications already using the SQL interface are the same set that will access the memcached interface, you can use the existing VPC security group used by the SQL interface. If a different set of applications will access the memcached interface, define a new VPC or DB security group. For more information about managing security groups, see Controlling access with security groups

2. Create a custom DB option group, selecting MySQL as the engine type and version. For more information about creating an option group, see Creating an option group.

3. Add the MEMCACHED option to the option group. Specify the port that the memcached interface will use, and the security group to use in controlling access to the interface. For more information about adding options, see Adding an option to an option group.

4. Modify the option settings to configure the memcached parameters, if necessary. For more information about how to modify option settings, see Modifying an option setting.

5. Apply the option group to an instance. Amazon RDS enables memcached support for that instance when the option group is applied:

   • You enable memcached support for a new instance by specifying the custom option group when you launch the instance. For more information about launching a MySQL instance, see Creating an Amazon RDS DB instance.

   • You enable memcached support for an existing instance by specifying the custom option group when you modify the instance. For more information about modifying a DB instance, see Modifying an Amazon RDS DB instance.

6. Specify which columns in your MySQL tables can be accessed through the memcached interface. The memcached plug-in creates a catalog table named containers in a dedicated database named innodb_memcache. You insert a row into the containers table to map an InnoDB table for access through memcached. You specify a column in the InnoDB table that is used to store the memcached key values, and one or more columns that are used to store the data values associated with the key. You also specify a name that a memcached application uses to refer to that set of columns. For details on inserting rows in the containers table, see InnoDB memcached plugin internals. For an example of mapping an InnoDB table and accessing it through memcached, see Writing applications for the InnoDB memcached plugin.

7. If the applications accessing the memcached interface are on different computers or EC2 instances than the applications using the SQL interface, add the connection information for those computers to the VPC security group associated with the MySQL instance. For more information about managing security groups, see Controlling access with security groups.

You turn off the memcached support for an instance by modifying the instance and specifying the default option group for your MySQL version. For more information about modifying a DB instance, see Modifying an Amazon RDS DB instance.

MySQL memcached security considerations

The memcached protocol does not support user authentication. For more information about MySQL memcached security considerations, see Security Considerations for the InnoDB memcached Plugin in the MySQL documentation.

You can take the following actions to help increase the security of the memcached interface:

• Specify a different port than the default of 11211 when adding the MEMCACHED option to the option group.

• Ensure that you associate the memcached interface with a VPC security group that limits access to known, trusted client addresses and EC2 instances. For more information about managing security groups, see Controlling access with security groups.

MySQL memcached connection information

To access the memcached interface, an application must specify both the DNS name of the Amazon RDS instance and the memcached port number. For example, if an instance has a DNS name of my-cache-instance.cg034hpkmmjt.region.rds.amazonaws.com and the memcached interface is using port 11212, the connection information specified in PHP would be:

<?php

$cache = new Memcache;
$cache->connect('my-cache-instance.cg034hpkmmjt.region.rds.amazonaws.com',11212);
?> 

To find the DNS name and memcached port of a MySQL DB instance

1. Sign in to the AWS Management Console and open the Amazon RDS console at https://console.aws.amazon.com/rds/.

2. In the top right corner of the AWS Management Console, select the region that contains the DB instance.

3. In the navigation pane, choose Databases.

4. Choose the MySQL DB instance name to display its details.

5. In the Connect section, note the value of the Endpoint field. The DNS name is the same as the endpoint. Also, note that the port in the Connect section is not used to access the memcached interface.

6. In the Details section, note the name listed in the Option Group field.

7. In the navigation pane, choose Option groups.

8. Choose the name of the option group used by the MySQL DB instance to show the option group details. In the Options section, note the value of the Port setting for the MEMCACHED option.

MySQL memcached option settings

Amazon RDS exposes the MySQL memcached parameters as option settings in the Amazon RDS MEMCACHED option.

MySQL memcached parameters

• DAEMON_MEMCACHED_R_BATCH_SIZE – an integer that specifies how many memcached read operations (get) to perform before doing a COMMIT to start a new transaction. The allowed values are 1 to 4294967295; the default is 1. The option does not take effect until the instance is restarted.

• DAEMON_MEMCACHED_W_BATCH_SIZE – an integer that specifies how many memcached write operations, such as add, set, or incr, to perform before doing a COMMIT to start a new transaction. The allowed values are 1 to 4294967295; the default is 1. The option does not take effect until the instance is restarted.

• INNODB_API_BK_COMMIT_INTERVAL – an integer that specifies how often to auto-commit idle connections that use the InnoDB memcached interface. The allowed values are 1 to 1073741824; the default is 5. The option takes effect immediately, without requiring that you restart the instance.

• INNODB_API_DISABLE_ROWLOCK – a Boolean that disables (1 (true)) or enables (0 (false)) the use of row locks when using the InnoDB memcached interface. The default is 0 (false). The option does not take effect until the instance is restarted.

• INNODB_API_ENABLE_MDL – a Boolean that when set to 0 (false) locks the table used by the InnoDB memcached plugin, so that it cannot be dropped or altered by DDL through the SQL interface. The default is 0 (false). The option does not take effect until the instance is restarted.

• INNODB_API_TRX_LEVEL – an integer that specifies the transaction isolation level for queries processed by the memcached interface. The allowed values are 0 to 3. The default is 0. The option does not take effect until the instance is restarted.

Amazon RDS configures these MySQL memcached parameters, and they cannot be modified: DAEMON_MEMCACHED_LIB_NAME, DAEMON_MEMCACHED_LIB_PATH, and INNODB_API_ENABLE_BINLOG. The parameters that MySQL administrators set by using daemon_memcached_options are available as individual MEMCACHED option settings in Amazon RDS.

MySQL daemon_memcached_options parameters

• BINDING_PROTOCOL – a string that specifies the binding protocol to use. The allowed values are auto, ascii, or binary. The default is auto, which means the server automatically negotiates the protocol with the client. The option does not take effect until the instance is restarted.

• BACKLOG_QUEUE_LIMIT – an integer that specifies how many network connections can be waiting to be processed by memcached. Increasing this limit may reduce errors received by a client that is not able to connect to the memcached instance, but does not improve the performance of the server. The allowed values are 1 to 2048; the default is 1024. The option does not take effect until the instance is restarted.

• CAS_DISABLED – a Boolean that enables (1 (true)) or disables (0 (false)) the use of compare and swap (CAS), which reduces the per-item size by 8 bytes. The default is 0 (false). The option does not take effect until the instance is restarted.

• CHUNK_SIZE – an integer that specifies the minimum chunk size, in bytes, to allocate for the smallest item's key, value, and flags. The allowed values are 1 to 48. The default is 48 and you can significantly improve memory efficiency with a lower value. The option does not take effect until the instance is restarted.

• CHUNK_SIZE_GROWTH_FACTOR – a float that controls the size of new chunks. The size of a new chunk is the size of the previous chunk times CHUNK_SIZE_GROWTH_FACTOR. The allowed values are 1 to 2; the default is 1.25. The option does not take effect until the instance is restarted.

• ERROR_ON_MEMORY_EXHAUSTED – a Boolean that when set to 1 (true) specifies that memcached will return an error rather than evicting items when there is no more memory to store items. If set to 0 (false), memcached will evict items if there is no more memory. The default is 0 (false). The option does not take effect until the instance is restarted.

• MAX_SIMULTANEOUS_CONNECTIONS – an integer that specifies the maximum number of concurrent connections. Setting this value to anything under 10 prevents MySQL from starting. The allowed values are 10 to 1024; the default is 1024. The option does not take effect until the instance is restarted.

• VERBOSITY – a string that specifies the level of information logged in the MySQL error log by the memcached service. The default is v. The option does not take effect until the instance is restarted. The allowed values are:

  • v – Logs errors and warnings while running the main event loop.

  • vv – In addition to the information logged by v, also logs each client command and the response.

  • vvv – In addition to the information logged by vv, also logs internal state transitions.

Amazon RDS configures these MySQL DAEMON_MEMCACHED_OPTIONS parameters, they cannot be modified: DAEMON_PROCESS, LARGE_MEMORY_PAGES, MAXIMUM_CORE_FILE_LIMIT, MAX_ITEM_SIZE, LOCK_DOWN_PAGE_MEMORY, MASK, IDFILE, REQUESTS_PER_EVENT, SOCKET, and USER.