Testing Memcached Using Telnet Commands
Troubleshooting memcached is not so transparent as some other technologies, but testing memcached using telnet commands can give us quite some insight on what’s happening under the hood.
The following tutorial on testing memcached with telnet from the command line is a short list of useful commands to inspect a running memcached instance.
How to find the IP address and port to connect
ps aux | grep memcached
The above will give us the process running memcached, with listening ip address and port. If this command does not yield any results, you’re likely not running the daemon and need to start it up first.
We can now connect using this info
telnet 127.0.0.1 11211 (replace your IP address and port)
Supported Commands
The following is a list of the most important memcached commands. For a more complete list of supported commands, check out the memcached wiki document.
| Command | Description | Example |
|---|---|---|
| get | Reads a value | get mykey |
| set | Set a key unconditionally | set mykey 0 60 5 |
| add | Add a new key | add newkey 0 60 5 |
| replace | Overwrite existing key | replace key 0 60 5 |
| append | Append data to existing key | append key 0 60 15 |
| prepend | Prepend data to existing key | prepend key 0 60 15 |
| incr | Increments numerical key value by given number | incr mykey 2 |
| decr | Decrements numerical key value by given number | decr mykey 5 |
| delete | Deletes an existing key | delete mykey |
| flush_all | Invalidate specific items immediately | flush_all |
| Invalidate all items in n seconds | flush_all 900 | |
| stats | Prints general statistics | stats |
| Prints memory statistics | stats slabs | |
| Prints memory statistics | stats malloc | |
| Print higher level allocation statistics | stats items | |
| stats detail | ||
| stats sizes | ||
| Resets statistics | stats reset | |
| version | Prints server version. | version |
| verbosity | Increases log level | verbosity |
| quit | Terminate telnet session | qui |
Traffic Statistics
$ stats
will give you general info on version, traffic, hits/misses, connections and more.
Example Output:
STAT pid 14868 STAT uptime 175931 STAT time 1220540125 STAT version 1.2.2 STAT pointer_size 32 STAT rusage_user 620.299700 STAT rusage_system 1545.703017 STAT curr_items 228 STAT total_items 779 STAT bytes 15525 STAT curr_connections 92 STAT total_connections 1740 STAT connection_structures 165 STAT cmd_get 7411 STAT cmd_set 28445156 STAT get_hits 5183 STAT get_misses 2228 STAT evictions 0 STAT bytes_read 2112768087 STAT bytes_written 1000038245 STAT limit_maxbytes 52428800 STAT threads 1 END
Memory Statistics:
$ stats slabs
gives you detailed memory statistics
Example Output:
STAT 1:chunk_size 80 STAT 1:chunks_per_page 13107 STAT 1:total_pages 1 STAT 1:total_chunks 13107 STAT 1:used_chunks 13106 STAT 1:free_chunks 1 STAT 1:free_chunks_end 12886 STAT 2:chunk_size 100 STAT 2:chunks_per_page 10485 STAT 2:total_pages 1 STAT 2:total_chunks 10485 STAT 2:used_chunks 10484 STAT 2:free_chunks 1 STAT 2:free_chunks_end 10477 [...] STAT active_slabs 3 STAT total_malloced 3145436 END
Items Statistics:
$ stats items
lets you know the item count and their age.
Example Output:
stats items STAT items:1:number 220 STAT items:1:age 83095 STAT items:2:number 7 STAT items:2:age 1405 [...] END
Using Telnet to get details about memcache is a nice way of looking under the hood or a running production system, where outputting variables in PHP or ASP .NET is not feasible. Zero values in hit/misses indicate that memcache in not used for some reason, connection errors may hint to a networking or permission issue. And with too many evictions you may need to increase the allocated amount of memory.
