Guest: Alexey Zatelepin
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Alexey Zatelepin is a Software Engineer at Redpanda Data interested in building reliable distributed systems. He works mostly on features involving interactions between several Redpanda nodes. And continuous balancing is one of them. A respected voice in the community, Alexey shared his expertise at the Redpanda Open House last year, receiving high praise and positive feedback from attendees for his clear and insightful presentation and demo.
Summary
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⦿ Rebalancing involves moving partitions between nodes to achieve even load distribution.
⦿ Redpanda uses a controller for managing metadata updates across the cluster.
⦿ The Controller Leader periodically assesses the cluster's state, plans rebalancing actions, and maintains a lease on partition-balancing duties.
⦿ The Controller Leader communicates with brokers to handle metadata updates, to manage partition rebalancing and ensures data distribution.
⦿ The Controller Leader ensures that only one process can perform the rebalancing task at a time.
⦿ Redpanda maintains a global partition map to track topic partitions and their replicas.
⦿ Information about brokers, partition replicas, disk usage, and node health is exchanged among nodes.
⦿ Rebalancing Mechanism:
» Rebalancing checks node liveness and disk usage periodically.
» Triggered by events like node decommissioning.
» Constraints on placement, e.g., avoiding certain nodes for partition moves.
» Rebalancing process submits commands to the controller log.
» All brokers update their partition map after rebalancing.
» Replicas move between nodes to reconcile the partition map.
⦿ Traffic Control during Replication:
» Replicas learning process.
» Learners are replicas that haven't yet learned the full log.
» Learners recover and become full-fledged replicas.
» Rate limits on replication traffic to avoid disruption.
⦿ Redpanda's data storage, including both system and user partitions, is organized into segment files.
⦿ The log data is replicated across replicas to ensure data durability and consistency.
⦿ There were also improvements made for the latest 23.2 release:
» Faster Rebalancing➡ Includes updates that result in faster rebalancing due to more aggressive scheduling of partition movements.
» Throttling Improvement➡ The throttling and rate limiting mechanisms have been enhanced, allowing individual partition movements to make more efficient use of available bandwidth.
» Smarter decision➡ Considering factors like node health and disk space capacity to ensure successful partition movement.
