Since you didn't specify a compaction strategy I'm guessing you're using STCS. Your TTL'ed data is becoming a tombstone. TWCS is a better strategy for this type of workload. On Sat, Jan 28, 2017 at 8:30 AM John Sanda <john.sa...@gmail.com> wrote:
> I have a time series data model that is basically: > > CREATE TABLE metrics ( > id text, > time timeuuid, > value double, > PRIMARY KEY (id, time) > ) WITH CLUSTERING ORDER BY (time DESC); > > I do append-only writes, no deletes, and use a TTL of seven days. Data > points are written every seconds. The UI queries data for the past hour, > two hours, day, or week. The UI refreshes and executes queries every 30 > seconds. In one test environment I am seeing lots of tombstone threshold > warnings and Cassandra has even OOME'd. Since I am storing data in > descending order and always query for recent data, I do not understand why > I am running into this problem. > > I know that it is recommended to do some date partitioning in part to > ensure partitions do not grow too large. I already have some changes in > place to partition by day.. Before I make those changes I want to > understand why I am scanning so many tombstones so that I can be more > confident that the date partitioning changes will help. > > Thanks > > - John >
