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Memcache Commands

Commands Cheat-Sheet

The supported commands (the official ones and some unofficial) are documented in the doc/protocol.txt document.
Sadly the syntax description isn’t really clear and a simple help command listing the existing commands would be much better. Here is an overview of the commands you can find in the source (as of 19.08.2016):
Command
Description
Example
get
Reads a value
get mykey
set
Set a key unconditionally
set mykey <flags> <ttl> <size> <p>Ensure to use \r\n als line breaks when using Unix CLI tools. For example</p> printf "set mykey 0 60 4\r\ndata\r\n"
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 all items immediately
flush_all
flush_all
Invalidate all items in n seconds
flush_all 900
stats
Prints general statistics
stats
​
Prints memory statistics
stats slabs
​
Print higher level allocation statistics
stats malloc
​
Print info on items
stats items
​
​
stats detail
​
​
stats sizes
​
Resets statistics counters
stats reset
lru_crawler metadump
Dump (most of) the metadata for (all of) the items in the cache
lru_crawler metadump all
version
Prints server version.
version
verbosity
Increases log level
verbosity
quit
Terminate session
quit

Traffic Statistics

You can query the current traffic statistics using the command
stats
You will get a listing which serves the number of connections, bytes in/out and much 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

You can query the current memory statistics using
stats slabs
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
If you are unsure if you have enough memory for your memcached instance always look out for the “evictions” counters given by the “stats” command. If you have enough memory for the instance the “evictions” counter should be 0 or at least not increasing.

Which Keys Are Used?

There is no builtin function to directly determine the current set of keys. However you can use the
stats items
command to determine how many keys do exist.
stats items
STAT items:1:number 220
STAT items:1:age 83095
STAT items:2:number 7
STAT items:2:age 1405
[...]
END
This at least helps to see if any keys are used. To dump the key names from a PHP script that already does the memcache access you can use the PHP code from 100days.de.