MCInspector is a lightweight tool to get a summary of objects or dump the keys from a running Memcache server process without interrupting it.

The tool is designed to work on Linux only. The no_inline_ascii_resp option should not be specified on the Memcached process. It requires the kernel > 3.2 and the glibc > 2.15 to compile.

$ git clone https://github.com/quora/mcinspector.git
$ cd mcinspector
$ make

This tool has been tested on Memcached-1.4.14, Memcached-1.4.22 and Memcached-1.4.36. It also works on Memcached-1.5.2 but only if the Memcached is started with -o inline_ascii_resp option.

Below examples can be done in one pass by using all processors together. The examples also assume it uses the default ':' char as keyspace delimiter. Full list of arguments can be seen by running the binaries with no argument.

$ printf "stats\nstats slabs\nstats items\nstats settings\n" | \
      netcat 127.0.0.1 11211 > /tmp/mc_stat_file
$ sudo ./mcinspector --stats-file=/tmp/mc_stat_file --processor=item-aggregator

Though recent Memcached versions have built-in feature of cleaning up expired objects, this is an alternative way and can be useful if you are running an old version of Memcached.

$ printf "stats\nstats slabs\nstats items\nstats settings\n" | \
       netcat 127.0.0.1 11211 > /tmp/mc_stat_file
$ sudo ./mcinspector \
      --stats-file=/tmp/mc_stat_file \
      --processor=expired-dumper \
      --expired-dump-file=/tmp/mc_expired_list
$ ./mccleaner \
      --expired-keys-file=/tmp/mc_expired_list \
      --mc-port=11211 \
      --clean-batch=200 \
      --sleep-interval=10

The example is to dump keys in 'user_info' category which has size less than 200 bytes.

$ printf "stats\nstats slabs\nstats items\nstats settings\n" | \
       netcat 127.0.0.1 11211 > /tmp/mc_stat_file
$ sudo ./mcinspector \
      --stats-file=/tmp/mc_stat_file \
      --processor=item-dumper \
      --category-to-dump=user_info \
      --category-dump-file=./keylist_of_user_info.txt \
      --dump-size-max=200

In our production machines, which run on Intel Xeon E5-2670 CPUs, it is able to detect 130 million objects from a 23GB Memcached process in 85 seconds using a single core. The number of detected keys is about 99.9% of the number shown in Memcached's 'STATS' output.

MCInspector is released under the Apache 2.0 Licence.