Hi Luke, I assume that unclean leader election exists as a static config in kafka kraft, but is still unavailable dynamically? Or is it unavailable in general?
Thanks! ttyl Dima On Wed, Aug 28, 2024 at 3:45 AM Luke Chen <show...@gmail.com> wrote: > Hi all, > > In v3.9.0, we're planning to support the `unclean.leader.election.enable` > config in KRaft. Currently, the implementation PR > <https://github.com/apache/kafka/pull/16866> is under review now. But I'd > like to raise the discussion to let you know there will be one behavior > change when enabling `unclean.leader.election.enable` config dynamically in > KRaft. > > scenario: > 1. broker [0, 1] config are all set `unclean.leader.election.enable=false`. > 2. topic A is created with 1 partition, 2 replication factors and > `unclean.leader.election.enable=false`. Leader of the partition 0 is 0. ISR > is [0]. > 3. broker 0 is down, which leaves ISR to empty [ ], and leader none. > 4. dynamically alter config using admin API to set > `unclean.leader.election.enable=true`, no matter it changes to the topic A, > or to broker 1, or default broker. > > In ZK mode, with this scenario, it'll trigger unclean leader election > immediately, and broker 1 will be elected as the leader, which brings the > availability of the partition back. > In KRaft mode, with this scenario, the unclean leader election will be > triggered in an unclean election thread, which is scheduled every 5 mins by > default. That is, this partition might still be unavailable even if it > enables `unclean.leader.election.enable`. If users want to elect a leader > for this partition, run `kafka-leader-election.sh` with `unclean` option to > trigger the unclean leader election immediately. > > The main reason we didn't implement what ZK did is because of this > complication > <https://github.com/apache/kafka/pull/16284#discussion_r1635410206> we > faced. > > Other behaviors keep the same. Ex: When the topic config, or broker config, > or default broker config set `unclean.leader.election.enable=true`, and > later, a partition has leader down with empty ISR [ ], and having some > alive non-ISR replicas, in this case, the unclean leader election will be > triggered, as long as the config was set earlier. > > But since the PR is still under review, any comments or thoughts are > welcomed. > > Thank you. > Luke > -- ddbrod...@gmail.com "The price of reliability is the pursuit of the utmost simplicity. It is a price which the very rich find the most hard to pay." (Sir Antony Hoare, 1980)
