Memcached statistics (stats command)

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Memcached is a great tool for speeding up your database access. A "stats" command returns usage statistics but few documentation is available on what's returned.

The official Memcached Wiki shows a bounce of stats commandsbut doesn't explain their meaning. I collected some information from various Internet sites.

Perl's Cache::Memcached module has a ->stats call for getting the data, Cache::Memcached::Fast lacks this call (but I don't understand why). Here is a sample from a real life multi user development environment:

perl -MCache::Memcached -MData::Dumper=Dumper -le  'print Dumper(Cache::Memcached->new(  servers => ["memcache-01:11211", "memcache-02:11211"])->stats);'

$VAR1 = { 'hosts' => { 'memcache-02:11211' => { 'misc' => { 'cas_hits' => '0', 'conn_yields' => '1', 'cmd_set' => '584479', 'bytes_written' => '1029238847', 'curr_items' => '28088', 'pid' => '31690', 'uptime' => '538844', 'rusage_system' => '54.690000', 'reclaimed' => '3738', 'get_hits' => '153312', 'incr_misses' => '0', 'total_connections' => '12780', 'delete_misses' => '19082', 'decr_misses' => '0', 'get_misses' => '537174', 'bytes' => '6479905', 'curr_connections' => '32', 'time' => '1323007700', 'pointer_size' => '64', 'connection_structures' => '34', 'total_items' => '84110', 'decr_hits' => '0', 'evictions' => '0', 'auth_cmds' => '0', 'accepting_conns' => '1', 'limit_maxbytes' => '1073741824', 'rusage_user' => '24.910000', 'delete_hits' => '37031', 'cmd_get' => '690486', 'incr_hits' => '0', 'version' => '1.4.5', 'cas_badval' => '0', 'bytes_read' => '329112270', 'threads' => '4', 'cas_misses' => '0', 'auth_errors' => '0', 'cmd_flush' => '0', 'listen_disabled_num' => '0' }, 'sizes' => { '8448' => '1', '384' => '4', '2016' => '1', '9984' => '1', '1376' => '1', [...] } }, 'memcache-01:11211' => { 'misc' => { 'cas_hits' => '0', 'conn_yields' => '1', 'cmd_set' => '2279779', 'bytes_written' => '3607288198', 'curr_items' => '30345', 'pid' => '24040', 'uptime' => '1145391', 'rusage_system' => '310.020000', 'reclaimed' => '14740', 'get_hits' => '391278', 'incr_misses' => '0', 'total_connections' => '27373', 'delete_misses' => '107095', 'decr_misses' => '0', 'get_misses' => '1235540', 'bytes' => '6775829', 'curr_connections' => '34', 'time' => '1323007699', 'pointer_size' => '64', 'connection_structures' => '42', 'total_items' => '323610', 'decr_hits' => '0', 'evictions' => '0', 'auth_cmds' => '0', 'accepting_conns' => '1', 'limit_maxbytes' => '1073741824', 'rusage_user' => '103.220000', 'delete_hits' => '138702', 'cmd_get' => '1626818', 'incr_hits' => '0', 'version' => '1.4.5', 'cas_badval' => '0', 'bytes_read' => '880394652', 'threads' => '4', 'cas_misses' => '0', 'auth_errors' => '0', 'cmd_flush' => '0', 'listen_disabled_num' => '0' }, 'sizes' => { '8448' => '1', '384' => '4', '2016' => '1', '9984' => '1', '1376' => '1', [...] } } }, 'self' => {}, 'total' => { 'cmd_get' => 2317304, 'bytes' => 13255734, 'get_hits' => 544590, 'connection_structures' => 76, 'total_items' => 407720, 'bytes_read' => 1209506922, 'total_connections' => 40153, 'cmd_set' => 2864258, 'bytes_written' => 4636527045, 'curr_items' => 58433, 'get_misses' => 1772714 } };

Huge amount of data, isn't it? The same data is available via telnet:

telnet memcache-01 11211Trying 192.168.3.5...Connected to memcache-01.Escape character is '^]'.statsSTAT pid 24040STAT uptime 1145873STAT time 1323008181STAT version 1.4.5STAT pointer_size 64STAT rusage_user 103.230000STAT rusage_system 310.030000STAT curr_connections 34STAT total_connections 27384STAT connection_structures 42STAT cmd_get 1626823STAT cmd_set 2279784STAT cmd_flush 0STAT get_hits 391283STAT get_misses 1235540STAT delete_misses 107095STAT delete_hits 138707STAT incr_misses 0STAT incr_hits 0STAT decr_misses 0STAT decr_hits 0STAT cas_misses 0STAT cas_hits 0STAT cas_badval 0STAT auth_cmds 0STAT auth_errors 0STAT bytes_read 880545081STAT bytes_written 3607442137STAT limit_maxbytes 1073741824STAT accepting_conns 1STAT listen_disabled_num 0STAT threads 4STAT conn_yields 1STAT bytes 6775829STAT curr_items 30345STAT total_items 323615STAT evictions 0STAT reclaimed 14740ENDquitConnection closed by foreign host.

(Other types of stats may be requested using the commands from the Memcached wiki.)

What do all these values mean?

The ->stat method of Cache::Memcached returns all data ("misc" key) for all currently connected servers plus the number of items per item size ("sizes" key). Another "total" key is calculated for some of the most important statistics keys.

Descriptions for most but not all keys are shown in the Memcached repository, let's see if this list is being updated in the future.