Limiting the number of entries in a set

Shawn Debnath shawn at
Sat Jan 31 13:11:11 EST 2015

Good morning,

Wondering if there is a better way to do truncation of a set if entries exceed a certain threshold. I am trying to create a canonical timeline for every user in our system, set of UUID strings. We want the number of entries to be limited to about 1000 per timeline to keep the size of each KV object in check inside Riak and also not store unnecessary data. From looking around code and docs, there doesn’t seem to be a Redis style LTRIM<> option available. So is the only way to enforce this is to fetch the set, check count, trim it locally and then update?

My fear is that by using CRDTs, a set add wins over remove in the case of a conflict. If there were to be 1000 conflicting concurrent updates each trying to trim and add one entry to a set that already contains 1000 entries, I imagine the  final count of the set would be 2000. This can be greatly exasperated on a very “friendly” or popular person’s timeline and the code never being able to truncate the set back to 1000.

Any thoughts or suggestions appreciated.


freenode (sde)
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