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The memcached system has a built in statistics system that collects information about the data being stored into the cache, cache hit ratios, and detailed information on the memory usage and distribution of information through the slab allocation used to store individual items. Statistics are provided at both a basic level that provide the core statistics, and more specific statistics for specific areas of the memcached server.
This information can prove be very useful to ensure that you are getting the correct level of cache and memory usage, and that your slab allocation and configuration properties are set at an optimal level.
The stats interface is available through the standard memcached protocol, so the reports can be accessed by using telnet to connect to the memcached. The supplied memcached-tool includes support for obtaining the Section 14.5.4.2, “memcached Slabs Statistics” and Section 14.5.4.1, “memcached General Statistics” information. For more information, see Section 14.5.4.6, “Using memcached-tool”.
Alternatively, most of the language API interfaces provide a function for obtaining the statistics from the server.
For example, to get the basic stats using telnet:
shell> telnet localhost 11211 Trying ::1... Connected to localhost. Escape character is '^]'. stats STAT pid 23599 STAT uptime 675 STAT time 1211439587 STAT version 1.2.5 STAT pointer_size 32 STAT rusage_user 1.404992 STAT rusage_system 4.694685 STAT curr_items 32 STAT total_items 56361 STAT bytes 2642 STAT curr_connections 53 STAT total_connections 438 STAT connection_structures 55 STAT cmd_get 113482 STAT cmd_set 80519 STAT get_hits 78926 STAT get_misses 34556 STAT evictions 0 STAT bytes_read 6379783 STAT bytes_written 4860179 STAT limit_maxbytes 67108864 STAT threads 1 END
When using Perl and the Cache::Memcached
module, the stats()
function returns
information about all the servers currently configured in the
connection object, and total statistics for all the
memcached servers as a whole.
For example, the following Perl script will obtain the stats and dump the hash reference that is returned:
use Cache::Memcached; use Data::Dumper; my $memc = new Cache::Memcached; $memc->set_servers(\@ARGV); print Dumper($memc->stats());
When executed on the same memcached as used in the Telnet example above we get a hash reference with the host by host and total statistics:
$VAR1 = { 'hosts' => { 'localhost:11211' => { 'misc' => { 'bytes' => '2421', 'curr_connections' => '3', 'connection_structures' => '56', 'pointer_size' => '32', 'time' => '1211440166', 'total_items' => '410956', 'cmd_set' => '588167', 'bytes_written' => '35715151', 'evictions' => '0', 'curr_items' => '31', 'pid' => '23599', 'limit_maxbytes' => '67108864', 'uptime' => '1254', 'rusage_user' => '9.857805', 'cmd_get' => '838451', 'rusage_system' => '34.096988', 'version' => '1.2.5', 'get_hits' => '581511', 'bytes_read' => '46665716', 'threads' => '1', 'total_connections' => '3104', 'get_misses' => '256940' }, 'sizes' => { '128' => '16', '64' => '15' } } }, 'self' => {}, 'total' => { 'cmd_get' => 838451, 'bytes' => 2421, 'get_hits' => 581511, 'connection_structures' => 56, 'bytes_read' => 46665716, 'total_items' => 410956, 'total_connections' => 3104, 'cmd_set' => 588167, 'bytes_written' => 35715151, 'curr_items' => 31, 'get_misses' => 256940 } };
The statistics are divided up into a number of distinct sections,
and then can be requested by adding the type to the
stats
command. Each statistics output is
covered in more detail in the following sections.
General statistics, see Section 14.5.4.1, “memcached General Statistics”.
Slab statistics (slabs
), see
Section 14.5.4.2, “memcached Slabs Statistics”.
Item statistics (items
), see
Section 14.5.4.3, “memcached Item Statistics”.
Size statistics (sizes
), see
Section 14.5.4.4, “memcached Size Statistics”.
Detailed status (detail
), see
Section 14.5.4.5, “memcached
Detail Statistics”.
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