Now, since we have memcached installed, let's see what kind of commands memcached daemon supports and how simple the memcached protocol is.
We will be using a plain simple TELNET tool to connect to the memcached daemon.
Remember that memcached has no persistent storage whatsoever, so it's totally memory-based and once we terminate the daemon everything we have stored is simply gone!
You will need to have telnet client installed on your machine, in most cases you will find it already installed but in case you didn't find it you can install it on your Ubuntu box using
sudo apt-get install telnet
You also must make sure that the memcached daemon is actually running.
Connect to the running memcached daemon with telnet on port 11211.
telnet localhost 11211
You should see something like the following:
Trying 127.0.0.1... Connected to localhost. Escape character is '^]'.
So, let's play with some basic storage commands to understand the main concepts behind memcached. We believe that this way is the best way to understand the features of the service and to truly realize its design simplicity and power.
Memcached supports a plain ASCII (text) protocol, you can find the protocol definition and specifications in the document in this link https://github.com/memcached/memcached/blob/master/doc/protocol.txt
The first command is
statswhere you request some basic information about the running service:stats STAT pid 8141 STAT uptime 1926 STAT time 1380294691 STAT version 1.4.13 STAT libevent 2.0.16-stable STAT pointer_size 64 STAT rusage_user 0.108006 –
So, let's now use it for settings:
stats settings STAT maxbytes 67108864 STAT maxconns 1024 STAT tcpport 11211 STAT udpport 11211 STAT inter 127.0.0.1 STAT verbosity 0 STAT oldest 849 STAT evictions on STAT domain_socket NULL STAT umask 700 STAT growth_factor 1.25 STAT chunk_size 48 STAT num_threads 4 STAT num_threads_per_udp 4 STAT stat_key_prefix : STAT detail_enabled no STAT reqs_per_event 20 STAT cas_enabled yes STAT tcp_backlog 1024 STAT binding_protocol auto-negotiate STAT auth_enabled_sasl no STAT item_size_max 1048576 STAT maxconns_fast no STAT hashpower_init 0 STAT slab_reassign no STAT slab_automove no END
Now, let's store some value for a given key:
set mykey 0 300 5 16 I Love Memcached
After you hit the return key, you will see the
STOREDmessage. So the whole listing is as follows:set mykey 0 300 16 I Love Memcached STORED
Now, let's read this key by using the
getcommand:get mykey VALUE mykey 0 16 I Love Memcached END
This recipe gives you a glimpse of the kind of commands you can send to your memcached daemon using a simple tool like telnet.
We started by connecting to the memcached daemon on the default port 11211 using telenet. Then we used the stats command which asks the daemon to send us some useful statistics from the service such as the uptime, how many get requests actually returned data get_hits, and how many get requests resulted in a miss hit get_misses.
Then, we used stats settings which prints out the settings and configuration of the current running daemon, you will be able to see things such as tcpport which points to the port it is listening to and something such as maxbytes which is the maximum number of bytes allowed in this cache server.
Then, we moved to the storage commands set and get. Storage commands have the following format:
<command name> <key> <flags> <exptime> <bytes>
The <command name> field can be set, add, replace, append, or prepend.
The <key> field is the name of the key you are storing, in our case that was mykey.
The <flags> field is an arbitrary 16-bit unsigned number that the server stores along with the key and is returned when the client requests to get the value. It's opaque to the server, so it doesn't give any special meaning to the server itself but the client can use this number to add some special meaning to this key if needed. In our case, we just passed 0 for this field.
The <exptime> field indicates the expiration time, if it's 0, the item never expires (although it might get deleted when the server needs to free up place for another key to be stored). If it's non-zero (either Unix time or offset in seconds from the current time), it is guaranteed that clients will not be able to retrieve this item after the expiration time arrives (measured by the server time).
The <bytes> field indicates the length of the value to be stored, in our case that was 16, which is the length of the words I Love Memcached.
After hitting your return (Enter) key, you are supposed to feed the server with the value to be stored along with the key. Then, after hitting another return, you receive a STORED message indicating that the key-value pair has been stored.
Then, we moved to get, it's very simple, you get a <key> field and the value returns along with the <flags> field and the length of the value, then the value is printed before the END sentinel.
VALUE mykey 0 16 I Love Memcached END