Question

How are people coping with changes to redis object schemas – adding or removing properties from objects?

Answer 1

Sharing from my own experience (one year old project with thousands of user requests per second).

Usually, there were two scenarios for me:

1. Add new information to existing structures (like, “email” field to a user)
2. Remove or change existing values in existing structures (like, change format of some field)
3. Drop stuff from the database

For 1 I keep following simple strategy: degrade gracefully, e.g. if user doesn’t have email record – treat it as empty email. Worked all the time.

For 2 and 3 it depends, whether data can be changed/calculated/fixed before releasing or after. I run a job on database that does all the work for me, for few millions of keys it takes considerable time (minutes). If that job can be run only after I release the new code – then degrading gracefully helps a lot, I simply release and then run the job.

PS: If you affect a lot of keys in redis then it is very important to use http://redis.io/topics/pipelining Saves a lot of time.

1. Take a list of all affected (i.e. you want to fix them in any way) keys or records in pipeline
2. Do whatever you want on them. If it’s possible try to queue writing operations into pipeline too
3. Send queued operations to redis.

It is also very important for you to make indexes of your structures. I keep sets with ids. Then I simply iterate over SMEMBERS(set_with_ids).
It is much, much better than iterating over KEYS command.