memcache

由 datahunter 在五, 25/10/2013 - 16:11 發表

最後更新: 2019-09-09

介紹

memcache 是一個 distributed memory object caching system

in-memory key-value store for small chunks of arbitrary data (strings, objects)

安全問題:

clients may freely connect to any server ==> deployments of Memcached exist within trusted networks

(memcached is built for speed, not for security)

Wiki 上的 Example

get_foo 與 update_foo

 
// 沒有 memcache 的
 function get_foo(int userid) {
    data = db_select("SELECT * FROM users WHERE userid = ?", userid);
    return data;
 }
 
// 有 memcache 的
 function get_foo(int userid) {
    /* first try the cache */
    data = memcached_fetch("userrow:" + userid);
    if (!data) {
       /* not found : request database */
       data = db_select("SELECT * FROM users WHERE userid = ?", userid);
       /* then store in cache until next get */
       memcached_add("userrow:" + userid, data);
    }
    return data;
 }

 function update_foo(int userid, string dbUpdateString) {
   /* first update database */
    result = db_execute(dbUpdateString);
    if (result) {
       /* database update successful : fetch data to be stored in cache */
       data = db_select("SELECT * FROM users WHERE userid = ?", userid);
       /* the previous line could also look like data = createDataFromDBString(dbUpdateString); */
       /* then store in cache until next get */
       memcached_set("userrow:" + userid, data);
    }
 }

Debian 安裝 memcached

apt install memcached

Proccess

ps aux | grep memcache

/usr/bin/memcached -m 64 -p 11211 -u memcache -l 127.0.0.1 -P /var/run/memcached/memcached.pid

-m # -m, --memory-limit=N. Default: 64
-p PORT # Default: 11211
-u USER # Default: memcache
-l IP # Default to 127.0.0.1
-P FILE # path to pidfile

設定檔 - memcached.conf

/etc/memcached.conf

# Run memcached as a daemon.
-d

# Log memcached's output to /var/log/memcached
logfile /var/log/memcached.log

改用 unix socket

#-l 127.0.0.1
#-p 11211
-s /tmp/memcached.sock
-a 666

Test with telnet

Usage

telnet localhost 11211

Notes

使用 nc 會更方便

echo 'stats slabs' | nc localhost 11211

Command

version

VERSION 1.4.5

stats

STAT pid 10234
STAT uptime 1047218
STAT time 1575357582
STAT version 1.5.20
STAT libevent 2.0.21-stable
STAT pointer_size 64
STAT rusage_user 1186.735778
STAT rusage_system 1341.286057
STAT max_connections 1024
STAT curr_connections 73
STAT total_connections 4324
STAT rejected_connections 0
...

add <key> <flags> <exptime> <bytes>

add mykey 0 900 4

1234             # input 4 byte value, 按 'ENTER' 後 Save
STORED

flag

flag 是一個16位的無符號整數
屬於自定義標記
在緩存條目被 set 或者 get 的時一起返回

get <key>

get mykey

VALUE mykey 0 4
1234
END

set <key> <flags> <exptime> <bytes>

* SET is there to update the value, regardless of whether it already exists.

set mykey 0 900 4

test
STORED

delete key

delete mykey

DELETED

dump

stats slabs

# 沒有 data 時

STAT active_slabs 0
STAT total_malloced 0
END

# 當有 data 時

STAT 11:chunk_size 872
STAT 11:chunks_per_page 1202
STAT 11:total_pages 1
STAT 11:total_chunks 1202
STAT 11:used_chunks 1
STAT 11:free_chunks 1
STAT 11:free_chunks_end 1200
STAT 11:mem_requested 769
STAT 11:get_hits 4
STAT 11:cmd_set 3
STAT 11:delete_hits 0
STAT 11:incr_hits 0
STAT 11:decr_hits 0
STAT 11:cas_hits 0
STAT 11:cas_badval 0
STAT active_slabs 4
STAT total_malloced 4193280

說明

一共有 "4" 個 slab, 而 "11" 是其中一個 slab 的 ID

stats cachedump slab_id limit_num_of_key

# first digit is the numeric ID for the slab and the second digit is how many items you want to retrieve.

# limit_num_of_key=0 means all items

stats cachedump 1 10

ITEM mytest1 [4 b; 1383214507 s]
ITEM mytest2 [1 b; 1383214507 s]
END

stats items

#       slab id
#          |
#         \/
STAT items:1:number 2
STAT items:1:age 1772
STAT items:1:evicted 0
STAT items:1:evicted_nonzero 0
STAT items:1:evicted_time 0
STAT items:1:outofmemory 0
STAT items:1:tailrepairs 0
STAT items:1:reclaimed 0
END

flags: 32-bit unsigned integer that the server store with the data

exptime: seconds, 0 = 不過期

+ / - 數

# 把 mykey + 3

incr mykey 3

當 mykey 不是數字時

CLIENT_ERROR cannot increment or decrement non-numeric value

# 把 mykey - 3

decr mykey 3

Flush Contents

# It does not free up or flush memory at all, it just causes all items to expire.

flush_all [sec]

OK

memcached-tool

Usage: memcached-tool <host[:port]> [mode]

memcached-tool 127.0.0.1 [display] # shows slabs (default)

  #  Item_Size  Max_age   Pages   Count   Full?  Evicted Evict_Time OOM
  2     104B     58991s       1       1      no        0        0    0
  4     176B     58991s       1       1      no        0        0    0

memcached-tool 127.0.0.1 stats # shows general stats

#127.0.0.1:11211   Field       Value
         accepting_conns           1
               auth_cmds           0
             auth_errors           0
                   bytes         694
              bytes_read       17657
           bytes_written       18230
              cas_badval           0
                cas_hits           0
              cas_misses           0
               cmd_flush           0
                 cmd_get         109
                 cmd_set         193
             conn_yields           0
   connection_structures          20
        curr_connections          18
              curr_items           6
               decr_hits           0
             decr_misses           0
             delete_hits           0
           delete_misses           0
               evictions           0
                get_hits         102
              get_misses           7
               incr_hits          38
             incr_misses          27
          limit_maxbytes    67108864
     listen_disabled_num           0
                     pid       23536
            pointer_size          32
           rusage_system    3.145521
             rusage_user    0.625904
                 threads           4
                    time  1435203879
       total_connections          71
             total_items         155
                  uptime       60670
                 version       1.4.4

memcached-tool 127.0.0.1 dump # dumps keys and values

Dumping memcache contents
  Number of buckets: 0
  Number of items  :

libmemcached-tools

Commandline tools for talking to memcached via libmemcached

安裝

apt-get install libmemcached-tools

/usr/bin/memccapable
/usr/bin/memccat
/usr/bin/memccp
/usr/bin/memcdump
/usr/bin/memcerror
/usr/bin/memcexist
/usr/bin/memcflush
/usr/bin/memcparse
/usr/bin/memcpingr
/usr/bin/memcrm
/usr/bin/memcslap
/usr/bin/memcstat
/usr/bin/memctouch

# ping

memcping --servers 192.168.200.1

Failed to ping 192.168.200.1:11211 SYSTEM ERROR

# operating status of memcached servers

memcstat --servers=localhost

Server: localhost (11211)
         pid: 42590
         uptime: 175
         time: 1717660870
         version: 1.6.14
         ...

# dumps a list of "keys"

e.g.

memcdump --server localhost

231:IMAP:mailboxes.05c7329682137ecdb00f5e396343c575
231:IMAP:messagecount

# outputs keys stored in a memcached(1) server

memcat [options] key

e.g.

memccat --server localhost 231:IMAP:messagecount

Centos 7 - memcached

安裝 memcached

yum install memcached

memcached 設定

# /etc/sysconfig/memcached

TCP

PORT="11211"
USER="memcached"

# max simultaneous connections; the default is 1024
MAXCONN="1024"

# the default is 64 megabytes
CACHESIZE="128"

OPTIONS="-l 127.0.0.1"

UNIX Socket

#PORT="11211"
OPTIONS="-a 666 -s /tmp/memcached.sock"

Other Useful Setting

-L # Try to use large memory pages (if available).

-b <num> # Set the backlog queue limit to <num> connections. The default is 1024.

Enable service

systemctl start memcached

systemctl enable memcached

Checking

netstat -ntlp | grep memcached

tcp        0      0 127.0.0.1:11211         0.0.0.0:*               LISTEN      31179/memcached

telnet 127.0.0.1 11211