Understanding Memcached stats cachedump command

This is an undocumented feature, meaning this command is not supported by the Memcached team, it still exists in 1.4.5 but can possibly be removed in any version.

stats cachedump command

Telnet command : stats cachedump <slabs_id> <limit>\r\n

Parameters :

• <slabs_id> : slab id from where you want to retreive the keys
  
• <limit> : result limit, 0 mean no limit
  

Be aware that this function return is limited to 1MB (or maybe 2MB, this is not clear actually)

Example :

stats cachedump 4 0

ITEM key_7abc8b445c35d211046a856f946dde96a8b48bf8 [172 b; 1293184017 s]
ITEM key_da39a3ee5e6b4b0d3255bfef95601890afd80709 [173 b; 1293183894 s]
ITEM key_b858a87c07b04c4568f51b0dce655f78d73c02b3 [178 b; 1289314215 s]
ITEM key_eadcd9bd2a09c75aef04954e6799e50278ee124a [173 b; 1293186833 s]
ITEM key_fa3a0c6f483fb9e1cf9b5d7e4aa224c541dcf618 [167 b; 1289314215 s]
END

stats cachedump command return

It return items with the template
ITEM <item_key> [<item_size> b; <expiration_timestamp> s]

Parameters :

• <item_key> : The item key
  
• <item_size> : Item size (including key) in bytes
  
• <expiration_timestamp> : Expiration timestamp in second

To understand the timestamp, we need to make a stats command on the server

stats

stats
STAT pid 1879
STAT uptime 4222347
STAT time 1293536562
STAT version 1.4.5
[...]

If the timestamp is equal to stats(time - uptime) then the item have got an infinite expiration else the item will expire when the timestamp is reached.

In our example, 1293536562 - 4222347 = 1289314215, two items have an infinite expiration

Other Memcached Resources

You can find a lot of Memcached resources on this Memcached resources page.