CASSANDRA-12126 addresses one correctness issue of Light Weight Transactions. Unfortunately, the current patch developed by Sylvain and Benedict requires an extra round trip between the coordinator and the replicas for SERIAL and LOCAL_SERIAL reads. After some experimentations, Benedict discovered that this extra round trip could lead to a significant increase in timeouts for read-heavy workloads.
Users for which this behavior is a problem will be able to switch back to the old behavior using a system property, therefore choosing performance versus correctness. On the side, Benedict has worked on another approach that does not suffer from that performance problem and also addresses some LWT correctness issues that can happen when adding or removing nodes. He initially intended to deliver that improvement in 4.X but can try to incorporate it into 4.0. Regarding CASSANDRA-12126 and 4.0 we are facing several options and Benedict, Sylvain and I wanted to get the community feedback on them. We can: 1. Try to use Benedict proposal for 4.0 if the community has the appetite for it. The main issue there is some potential extra delay for 4.0 2. Do nothing for 4.0. Meaning do not commit the current patch. We have lived a long time with that issue and we can probably wait a bit more for a proper solution. 3. Commit the patch as such, fixing the correctness but introducing potentially some performance issue until we release a better solution. 4. Changing the patch to default to the current behavior but allowing people to enable the new one if the correctness is a problem for them. Thanks in advance for your feedback.
