I do store a lot of statistical data in Redis, storing information on what users do and behave every day, week, month and so on... But storing a huge amount of data in memory has a little drawback: memory is cheap and fast, but is finite.
From time to time (e.g: cron job) I need to clean up the house because there is too much memory filled that is no longer interesting to keep it. Maybe you are thinking now, why this guy is not setting an EXPIRATION date? Well, I do.
Problem is that with early versions of Redis after the expiration time a KEY won't be really deleted from memory until the next access to the key, which never might happen. There is also a random process that deletes keys and there was a change of behaviour regarding expiration in Redis 2.2, read more on expiration here.
In my case, I do store keys using human-readable dates as part of the key name, which I need to delete by pattern. To make it more graphical with a similar example, imagine you are storing user behavior in keys named like:
Decomposing the elements:
- ub: user-behavior alias
- 2011-08-18: Stores all the events for August 18th
- id-tracked-page: Name or code of the page I want to track (e.g: home)
- ... more constraints could be added
Then, I am not interested in last month's data (July) regarding user behaviour so I can trigger in the terminal the following command:
redis-cli -n 0 KEYS ub:2011-07-* | xargs redis-cli -n 0 DEL
This deletes all the redis keys based on this pattern.
The output would produce something like:
$ redis-cli -n 0 KEYS ub:2011-07-* | xargs redis-cli -n 0 DEL (integer) 188 (integer) 175 (integer) 191 (integer) 186 (integer) 153
You should notice that there is a -n 0 in the command indicating to trigger the command in the DATABASE 0. Since I do have many databases in a single server (multiple database support will be removed soon) I do always specify it. If you use a single database, just drop the "-n 0".
Also, you might need to surround by quotes the pattern part if contains spaces or other unfriendly chars.
Hope this helps