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List local memcached keys using Ruby
#!/usr/bin/env ruby
# List all keys stored in memcache.
# Credit to Graham King at for the original article on how to get the data from memcache in the first place.
require 'net/telnet'
headings = %w(id expires bytes cache_key)
rows = []
localhost = Net::Telnet::new("Host" => "localhost", "Port" => 11211, "Timeout" => 3)
matches = localhost.cmd("String" => "stats items", "Match" => /^END/).scan(/STAT items:(\d+):number (\d+)/)
slabs = matches.inject([]) { |items, item| items << Hash[*['id','items'].zip(item).flatten]; items }
longest_key_len = 0
slabs.each do |slab|
localhost.cmd("String" => "stats cachedump #{slab['id']} #{slab['items']}", "Match" => /^END/) do |c|
matches = c.scan(/^ITEM (.+?) \[(\d+) b; (\d+) s\]$/).each do |key_data|
cache_key, bytes, expires_time = key_data
rows << [slab['id'],, bytes, cache_key]
longest_key_len = [longest_key_len,cache_key.length].max
row_format = %Q(|%8s | %28s | %12s | %-#{longest_key_len}s |)
puts row_format%headings
rows.each{|row| puts row_format%row}
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Any help on doing this in a remote server would be great!

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bkimble commented Apr 16, 2014

To do this on a remote server, you'd have a few options. Either deploy this script to your memcache servers and run it there, or just change

localhost = Net::Telnet::new("Host" => "localhost", "Port" => 11211, "Timeout" => 3)

to be the actual host/port of your memcache server. Keep in mind that firewall rules on your server could limit access to memcache in this manner and you may wind up having to put the script on the server anyway.

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gfa commented May 27, 2014

does it list all the keys or most of them?

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saxxi commented Jan 5, 2015

As I didn't know about this snippet I created a similar one based on the same source. Please have a look if you find it useful.

require 'net/telnet'
memcached = Net::Telnet::new("Host" => "localhost", "Port" => 11211)
memcached.puts 'stats items'
slab_ids = memcached.waitfor(/./).split("\n").map { |line| x = line[/([^\:]+)\d+/, 0].to_i ; x > 0 ? x : nil }.uniq.compact
slab_ids.inject([]) do |items, slab_id|
  memcached.puts "stats cachedump #{slab_id} 100"
  items << memcached.waitfor(/./).split("\n")[0].split(' ', 3)[1]

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saxxi commented Jan 5, 2015

@gfa from the first couple of lines of the source in
"In the general case, there is no way to list all the keys that a memcached instance is storing. You can, however, list something like the first 1Meg of keys, which is usually enough during development."

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ginjo commented Jan 30, 2015

@bkimble thanks for this!

Here's yet another fork of your original gist:

This revision adds a couple of features for working with cache item rows as ruby objects.

  • Isolates the cache item query and enumeration into a method that yields to an optional block (passing all elements of cache item. You can do anything with the block - print rows, return rows as an array of hashes, return a single 'matching' row, etc..
  • Accepts a list of servers and runs the above enumerator for all items found on every server.

I've included a method that mimics your original formatted printing, plus a method that returns all found cache items as an array of hashes.

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Unfortunately it does not work when the server has several 100 thousand keys...

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excellent, thanks a lot!

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rbalman commented Aug 18, 2017

Nice 😮 . I have customized this script for dump and restore using dalli gem.

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jsqu99 commented Sep 5, 2017

I'm fairly certain this does not work on memcachier.

I successfully telneted in to our production servers and tried issues the stats cachedump command and got:

CLIENT_ERROR unsupported stats command

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bingo! 👍

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ralphjay24 commented Apr 13, 2018

Thank you! This help me to solve problem of infinite caching(no expiration).

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archan937 commented Oct 16, 2019

Hello, @bkimble. I have adjusted your Gist a bit, see:

The logic is in a method called keys and you can pass your memcached host (or a list of hosts) and an optional pattern to filter on keys.
Also, prints the slab IDs with all of its keys.

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Unfortunately it does not work when the server has several 100 thousand keys...

Same here. Does not work with 60k keys.

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The require statement at the top needs to be updated because telnet was removed from the standard library at some point and made a separate gem. Otherwise script works as expected. Thanks @bkimble 👍

- require 'net/telnet'
+ gem 'net-telnet'

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