A basic question. Maybe I'm just doing this wrong.
In my Redis DB I have a number of "prefix:" hashes.
Sometimes I want to purge them all atomically.
How to do this without using some distributed locking mechanism?
A:
Execute in bash:
redis-cli "KEYS prefix:*" | xargs redis-cli DEL
UPDATE
Ok, i understood. What about this way: store current additional incremental prefix and add it to all your keys. For example:
You have values like this:
prefix_prefix_actuall = 2
prefix:2:1 = 4
prefix:2:2 = 10
When you need to purge data, you change prefix_actuall first (for example set prefix_prefix_actuall = 3), so your application will write new data to keys prefix:3:1 and prefix:3:2. Then you can safely take old values from prefix:2:1 and prefix:2:2 and purge old keys.
Casey
2010-10-23 23:31:15
Sorry, but this is not atomic deletion. Someone may add new keys between KEYS and DEL. I do not want to delete those.
Alexander Gladysh
2010-10-24 00:03:18
Keys, that will be created after KEYS command will not be deleted.
Casey
2010-10-24 01:30:05
OK, you're right, sorry, wrong reason (5 AM here). The correct one: If the value changes between KEYS and DEL, I do not want to delete it. Furthermore, if value is changed between KEYS and DEL, I want the change to be of... "insert" kind, not "update" (if you get what I mean) -- important for hsets for example.
Alexander Gladysh
2010-10-24 02:16:09
Posted some new idea
Casey
2010-10-24 10:47:20
IMHO, it is better to post a new answer in such cases -- so old answer's "karma" would not harm new one.
Alexander Gladysh
2010-10-24 13:29:48
Anyway, a good solution, thanks. But it requires a single read for each write I do -- a bit of overhead. Is it possible to do what I want without that overhead?
Alexander Gladysh
2010-10-24 13:30:58
Thank you, i will create new answer next time. About your question - i think no. GET is extremely cheap operation in Redis, it will not be a bottleneck.
Casey
2010-10-24 21:03:46
+1
A:
I think what might help you is the MULTI/EXEC/DISCARD. While not 100% equivalent of transactions, you should be able to isolate the deletes from other updates.
alexpopescu
2010-10-24 08:51:05
But I can't figure out how to use them here. DEL is atomic by itself (or so I think). And I can't get values from KEYS until I do EXEC, so I can't use KEYS and DEL in the same MULTI.
Alexander Gladysh
2010-10-24 12:29:11