Yes, my issue is with handling concurrent requests. I'm not sure how your logic will work with eventual consistency. I'm going to have the same issue in the "tracker" CF too, no?
On Jan 6, 2012, at 10:38 AM, Mohit Anchlia wrote: > On Fri, Jan 6, 2012 at 10:03 AM, Drew Kutcharian <d...@venarc.com> wrote: >> Hi Everyone, >> >> What's the best way to reliably have unique constraints like functionality >> with Cassandra? I have the following (which I think should be very common) >> use case. >> >> User CF >> Row Key: user email >> Columns: userId: UUID, etc... >> >> UserAttribute1 CF: >> Row Key: userId (which is the uuid that's mapped to user email) >> Columns: ... >> >> UserAttribute2 CF: >> Row Key: userId (which is the uuid that's mapped to user email) >> Columns: ... >> >> The issue is we need to guarantee that no two people register with the same >> email address. In addition, without locking, potentially a malicious user >> can "hijack" another user's account by registering using the user's email >> address. > > It could be as simple as reading before writing to make sure that > email doesn't exist. But I think you are looking at how to handle 2 > concurrent requests for same email? Only way I can think of is: > > 1) Create new CF say tracker > 2) write email and time uuid to CF tracker > 3) read from CF tracker > 4) if you find a row other than yours then wait and read again from > tracker after few ms > 5) read from USER CF > 6) write if no rows in USER CF > 7) delete from tracker > > Please note you might have to modify this logic a little bit, but this > should give you some ideas of how to approach this problem without > locking. > > Regarding hijacking accounts, can you elaborate little more? >> >> I know that this can be done using a lock manager such as ZooKeeper or >> HazelCast, but the issue with using either of them is that if ZooKeeper or >> HazelCast is down, then you can't be sure about the reliability of the lock. >> So this potentially, in the very rare instance where the lock manager is >> down and two users are registering with the same email, can cause major >> issues. >> >> In addition, I know this can be done with other tools such as Redis (use >> Redis for this use case, and Cassandra for everything else), but I'm >> interested in hearing if anyone has solved this issue using Cassandra only. >> >> Thanks, >> >> Drew
