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Chapter 1. Memcached Server
The Data Grid server distribution contains a server module that implements the Memcached text and binary protocols. This allows Memcached clients to connect with one or several Data Grid backed Memcached servers. These servers can be standalone like Memcached, where each server acts independently and does not communicate with others. They can also be clustered, where the servers replicate or distribute their contents to other Data Grid backed Memcached servers, providing clients with failover capabilities.
The Memcached endpoint is enabled by default on the single-port endpoint. Memcached client connections will automatically be detected and routed to the internal connector.
1.1. Client Encoding
The Memcached text protocol assumes data values read and written by clients are raw bytes.
It’s not possible for a Memcached client to negotiate the data type to obtain data from the server or send data in different formats. The server can optionally be configured to handle values encoded with a certain Media Type. By setting the client-encoding attribute in the memcached-connector element, the server will return content in this configured format, and clients can also send data in this format.
client-encoding is useful when a single cache is accessed from multiple remote endpoints such as Rest, HotRod, or Memcached. This also allows users to customize the response and request to Memcached text clients. For information about interoperability between endpoints, see the endpoint interoperability documentation.
1.2. Protocol detection
The Data Grid Memcached connector supports both manual and automatic protocol configuration by setting the protocol attribute in the memcached-connector element to one of TEXT, BINARY and AUTO. Automatic detection depends on whether the Memcached connector is on a dedicated socket binding or is part of a single port endpoint. Detection of text protocol clients in a single port endpoint requires authentication, in order to disambiguate the request from other protocols.
1.3. Security
The Data Grid Memcached connector supports authentication for both the text and binary protocols. Because the two variants implement authentication in a different way, the supported mechanisms depend on the protocol in use.
1.3.1. Text protocol
Authentication in the Memcached text protocol is performed by an initial set command where the key is ignored and the value is a concatenation of the username and the password separated by a space. This authentication scheme requires a security realm that supports plain-text.
1.3.2. Binary protocol
Authentication in the Memcached binary protocol is performed via dedicated operations which wrap the SASL challenge/response scheme. This authentication scheme works with all the Data Grid security realm implementations.
1.3.3. Flush All
Even in a clustered environment, the flush_all command clears only the Data Grid Memcached server where the call lands. There is no attempt to propagate this flush to other nodes in the cluster. This is done so that the flush_all with delay use case can be reproduced with the Data Grid Memcached server. The aim of passing a delay to flush_all is so that different Memcached servers can be flushed at different times, and hence avoid overloading the database with requests as a result of all Memcached servers being empty. For more information, see the Memcached text protocol section about flush_all .
1.4. Unsupported Features
This section details features of the Memcached text protocol that are currently not supported by the Data Grid based Memcached implementation.
1.4.1. Individual Statistics
There are differences between the original Memcached implementation, which is C/C++ based, and the Data Grid implementation, which is Java based. There are some general purpose statistics that are not supported. For these unsupported statistics, Data Grid Memcached server always returns 0.
Unsupported statistics
- pointer_size
- rusage_user
- rusage_system
- bytes
- curr_connections
- total_connections
- connection_structures
- auth_cmds
- auth_errors
- limit_maxbytes
- threads
- conn_yields
- reclaimed
Statistic settings
Statistics setting is not supported.
Settings with Arguments Parameter
Data Grid Memcached server does not support passing any arguments to the stats command. If any parameters are passed, the Data Grid Memcached server responds with CLIENT_ERROR .
Delete Hold Time Parameter
As Memcached no longer honors the optional hold time parameter for the delete command, the Data Grid based Memcached server does not implement the feature.
Verbosity Command
The verbosity command is not supported because Data Grid logging cannot be simplified to defining the logging level alone.
Meta protocol
The Memcached meta protocol, introduced in Memcached 1.6, is not supported.
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