Memcached High-Performance Distributed Object Cache System

Memcached is a high-performance distributed memory object Cache System for dynamic web applications to reduce database load. It caches data and objects in the memory to reduce the number of reads to the database, thus improving the speed of dynamic and database-driven websites. Memcached is based on a hashmap that stores key/value pairs. Its daemon is written in C, but the client can write it in any language and communicate with the daemon through memcached protocol.

For memcached Server Client Communication, simple text line-based protocols are used instead of complex XML and other formats.

Therefore, you can use Telnet to save and retrieve data on memcached. The following is an example.

$ Telnet local host 11211

Trying 127.0.0.1...

Connected to localhost. localdomain (127.0.0.1 ).

Escape Character is '^]'.

Set Foo 0 0 3 (save command)

Bar (data)

Stored (result)

Get Foo (GET command)

Value Foo 0 3 (data)

Bar (data)

Event Processing

Libevent is a library that encapsulates the epoll, kqueue, and other event processing functions of Linux operating systems into a unified interface. O (1) performance can be used even if the number of connections to the server increases. Memcached uses this libevent library to achieve high performance in Linux, BSD, Solaris, and other operating systems. For more information about event processing, see the c10k problem of Dan keel.

Storage Method

To improve performance, data stored in memcached is stored in the memory storage space built in memcached. Because the data only exists in the memory, restarting memcached and the operating system will cause all data to disappear. In addition, when the content capacity reaches the specified value, the unused cache is automatically deleted based on the LRU (least recently used) algorithm. Memcached itself is a server designed for caching, so it does not take the permanent data into consideration.

Distributed Communication

Although memcached is a "distributed" cache server, the server does not have distributed functions. Memcached does not communicate with each other to share information. So, how to implement distributed? This depends entirely on the implementation of the client. This article also introduces the distributed memcached.

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A visual memcached management system written in PHP

Memadmin is a visualized memcached management and monitoring tool. It is developed using PHP and is small in size and easy to operate.

Main functions:

Server parameter monitoring: Real-Time refresh of stats, settings, items, slabs, and sizes

Server performance monitoring: real-time monitoring of hit rates of common operations such as get, delete, incr, decr, and CAS

Supports data traversal to facilitate monitoring of stored content

Supports conditional queries to filter out keys or values that meet the conditions.

Array, JSON, and other Serialized character deserialization display

Other services compatible with the memcache protocol, such as Tokyo tyrant (excluding traversal)

Supports server connection pools, facilitating and simplifying multi-server management Switching

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In many languages, clients connected to memcached are implemented, including Perl and PHP. List only on memcached website

The language

· Perl

· PHP

· Python

· Ruby

· C #

· C/C ++

· Lua

And so on.

How to Use memcached-Server

Run on the server:

#./Memcached-D-M 2048-l 10.0.0.40-P 11211

This starts a process that occupies 2 GB of memory and opens port 11211 to receive requests. Because the 32-bit system can only handle 4G memory addressing, 2-3 processes can be run on 32-bit servers with 4G memory and monitored on different ports.

How to Use memcached-Client

After the application end contains a class used to describe the client, it can be used directly, which is very simple.

PHP example:

$ Options ["servers"] = array ("192.168.1.41: 11211", "192.168.1.42: 11212 ");

$ Options ["debug"] = false;

$ MEMC = new memcachedclient ($ options );

$ Myarr = array ("one", "two", 3 );

$ MEMC-> set ("key_one", $ myarr );

$ Val = $ MEMC-> get ("key_one ");

Print $ Val [0]. "\ n"; // prints 'one'

Print $ Val [1]. "\ n"; // prints 'two'

Print $ Val [2]. "\ n"; // prints 3

Centos Installation

Install
Yum-y install memcached

Set to boot
Chkconfig -- level 2345 memcached on

Start and Stop
/Etc/init. d/memcached START | stop

Supplement: If the installation lacks other support, you can:

Yum groupinstall "development tools"

1. To install memcached, install libevent first.

Install libevent using Yum-y install.

Then install memcached in Yum-y install

View installation status

[[Email protected] ~] # Telnet 127.0.0.1 11211

Trying 127.0.0.1...

Connected to 127.0.0.1.

Escape Character is]

Stats

Stat PID 1422

Statuptime 635

Stat time 1406012189

Stat version 1.4.4

Stat pointer_size 64

Stat rusage_user 0.000000

Stat rusage_system 0.032994

Stat curr_connections 10

Stat total_connections 13

Stat connection_structures 11

Stat performance_get 0

Stat performance_set 0

Stat 1__flush 0

Stat get_hits 0

Stat get_misses 0

Stat delete_misses 0

Stat delete_hits 0

Stat incr_misses 0

Stat incr_hits 0

Stat decr_misses 0

Stat decr_hits 0

Stat cas_misses 0

Stat cas_hits 0

Stat cas_badval 0

Stat auth_cmds 0

Stat auth_errors 0

Stat bytes_read 21

Stat bytes_written 1537

Stat limit_maxbytes 67108864

Stat accepting_conns 1

Stat listen_disabled_num 0

Stat threads 4

Stat conn_yields 0

Stat bytes 0

Stat curr_items 0

Stat total_items 0

Stat evictions 0

End

This article is from the "Anna -- Linux house" blog and is not reposted!

Memcached High-Performance Distributed Object Cache System