With those consistency levels it’s already possible you don’t see your writes, so you’re already probably seeing some of what would happen if you went to RF=5 like that - just less common
If you did what you describe you’d have a 40% chance on each read of not seeing any data (or not seeing the most recent data) until repair runs. Alternatively: - you change the app to read at local quorum - you change RF from 3 to 4 - run repair - change RF from 4 to 5 - run repair - change the app to read local_one Then you’re back to status quo where you probably see most writes but it’s not strictly guaranteed > On May 22, 2020, at 8:51 AM, Leena Ghatpande <lghatpa...@hotmail.com> wrote: > > > We are on Cassandra 3.7 and have a 12 node cluster , 2DC, with 6 nodes in > each DC. RF=3 > We have around 150M rows across tables. > > We are planning to add more nodes to the cluster, and thinking of changing > the replication factor to 5 for each DC. > > Our application uses the below consistency level > read-level: LOCAL_ONE > write-level: LOCAL_QUORUM > > if we change the RF=5 on live cluster, and run full repairs, would we see > read/write errors while data is being replicated? > if so, This is not something that we can afford in production, so how would > we avoid this?
