RE: A keyspace with RF=3, Cluster with 3 RACS, CL=LQ: No Data on FirstAttempt, but 1 Row Aftwards

[Fd Habash <fm...@gmail.com>]

Any ideas, please? 

----------------
Thank you

From: Fd Habash
Sent: Tuesday, April 23, 2019 10:38 AM
To: user@cassandra.apache.org
Subject: A keyspace with RF=3, Cluster with 3 RACS, CL=LQ: No Data on FirstAttempt, but 1 Row Aftwards

Cluster setup …
- C* 2.2.8
- Three RACs, one DC
- Keyspace with RF=3
- RS = Network topology 

At CL=LQ …

I get zero rows on first attempt, and one row on the second or third. Once found, I always get the row afterwards. 

Trying to understand this behavior …

First attempt, my read request hits a RAC that simply does not have the data. Subsequent attempts hit another RAC that has it which triggers a read repair causing the row to be returned consistently afterwards. Is this correct?

If a coordinator picks a node in the same RAC and the node does not have the data on disk, is it going to stop there and return nothing even though the row does exist on another RAC?

If anti-entropy repair has completed successfully on the entire cluster ‘repair -pr’, why is this still happening? 


----------------
Thank you