[infinispan-issues] [JBoss JIRA] (ISPN-7749) A node leaving during rebalance causes extra segment transfers

A node leaving during rebalance causes extra segment transfers -------------------------------------------------------------- Key: ISPN-7749 URL: https://issues.jboss.org/browse/ISPN-7749 Project: Infinispan Issue Type: Bug Components: Core, State Transfer Affects Versions: 9.0.0.Final Reporter: Dan Berindei Assignee: Dan Berindei Fix For: 9.2.0.Final If a node leaves during a rebalance, the only change is that other nodes will no longer request segments from that node. Otherwise the rebalance proceeds as usual, and at the end a node may delete its copy of a segment even if that leaves less than {{numOwners}} copies in the cluster. When the leaver is the joiner, a 2nd rebalance is very likely to return to the initial CH, but only after transferring some segments twice: {noformat} Rebalance starts: current_owners(s) = AB, pending_owners(s) = AC C leaves: current_owners(s) = AB, pending_owners(s) = A Rebalance finishes: current_owners(s) = A, pending_owners(s) = A 2nd rebalance starts: current_owners(s) = A, pending_owners(s) = AB {noformat} Even if the leaver is one of the old owners and the 2 segment transfers are necessary, the cluster stays for too long with less than {{numOwners}} copies of the segment: {noformat} Rebalance starts: current_owners(s) = AB, pending_owners(s) = AC A leaves: current_owners(s) = B, pending_owners(s) = C C transfers segment s from B Rebalance finishes: current_owners(s) = C, pending_owners(s) = C 2nd rebalance starts: current_owners(s) = C, pending_owners(s) = DC {noformat} We can fix this by making the pending CH a union of the current and pending CH whenever a node leavers, and only removing extra segment copies after the 2nd rebalance.