CODEWITHSUNDEEP
cassandra
user2914577
user2914577

Reputation: 11

Storing list in cassandra

I want to save a friends list in Cassandra where a user may have few hundred of friends . Should i store the list of friends, which is an email id, as a list or set in Cassandra or should i create a separate table having the columns user_id and friends which will include all the user(millions of users) along with their friends .

If i create a separate table with user_id and friends column will there be degradation in performance while retrieving the entire friend list of the user/ one friend of the user as the table will contain many records/rows.

Upvotes: 0

Views: 600

Answers (1)

Russ Bradberry
Russ Bradberry

Reputation: 10865

It is important to note that lists and sets in Cassandra are not iterable. This means when you query for them, you get back the whole list or the whole set. If the collection has a high cardinality then this could pose issues in querying such as read timeouts or even a heap OOM error.

Since it sounds like there is no cap on the amount of friends one can have, one option could be to have a separate table that is partitioned on user and clustered on friend.

CREATE TABLE user_friends (
  owner_user_id int,
  friend_user_id int,
  PRIMARY KEY(owner_user_id, friend_user_id)
);

This will ensure that the friend_user_id is in order and will allow you to do client side paging if the number of friends is very large. It also allows for a quick way to check if a person is a friend of a user.

Upvotes: 2

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