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20071026 Friday October 26, 2007

memcached hacks

I needed to clear a cache entry from a memcached cluster of 5 instances. Since I didn't know which one the client had put it in, I concocted a command line cache entry purger. netcat AKA nc(1) is my friend.

Let's say the cache key is "shard:7517" and the memcached instances are running on hosts ghcache01, ghcache02, ghcache03, ghcache04 and ghcache05 on port 11111 the incantation to spray them all with a delete command is 

$ for i in 1 2 3 4 5
> do echo $i && echo -e "delete shard:7517\r\nquit\r\n" | nc -i1 ghcache0$i 11111
> done
and the output looks like 
1
NOT_FOUND
2
DELETED
3
NOT_FOUND
4
NOT_FOUND
5
NOT_FOUND
which indicates that the memcached instance on ghcache02 had the key and deleted it (note the memcached protocol response: DELETED), the rest didn't have it and returned NOT_FOUND.

For more information on the memcached protocol, see the docs under source control.

     

( Oct 26 2007, 12:29:37 PM PDT ) Permalink