In non-tx caches, write operations may not be atomic during rebalance --------------------------------------------------------------------- Key: ISPN-3422 URL: https://issues.jboss.org/browse/ISPN-3422 Project: Infinispan Issue Type: Bug Reporter: Dan Berindei Assignee: Dan Berindei Priority: Critical Labels: 620, nbst Fix For: 6.1.0.Final If the cache topology changes while a write command is running and before it has actually committed the entry to the data container, we retry the command (see ISPN-3366 and ISPN-3357). But before we detect the topology change, one or more of the backup owners may have already applied the modification. Retrying the command re-acquires the key lock on the primary owner (even if the primary owner didn't change). That means another command could have modified the same key in the meantime, but the retried command is going to ignore any changes and is going to return the value before the first attempt. Obviously, the command is not retried if the first attempt is not successful, but scenarios like this are possible: {code} thread 1: putIfAbsent(k, v1) -> null thread 2: putIfAbsent(k, v2) -> null {code}