Principle:Apache Kafka Coordinator State Loading
| Knowledge Sources | |
|---|---|
| Domains | Distributed_Systems, State_Management |
| Last Updated | 2026-02-09 12:00 GMT |
Overview
A log replay mechanism that reconstructs coordinator state by reading and deserializing all records from a topic-partition.
Description
Coordinator State Loading reads all records from a coordinator's topic-partition log and replays them through a CoordinatorPlayback interface to reconstruct the coordinator's in-memory state. The loader handles pagination through records in configurable batch sizes, periodically commits progress to enable snapshotting, and produces a LoadSummary with statistics about the loading process.
Usage
Use this principle to understand how coordinator state is recovered after leadership changes or broker restarts. Loading is the mechanism that provides durability for coordinator state.
Theoretical Basis
- Sequential Replay: Records are read from the partition log starting from the earliest offset and replayed in order.
- Batched Reading: Records are read in configurable batches (loadBufferSize) for efficiency.
- Periodic Commit: The loader commits progress every commitIntervalOffsets (default 16384) to enable snapshot creation.
- Completion: Loading completes when all records up to the log end offset have been replayed, transitioning the coordinator to ACTIVE.
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