Offset Management
An offset records how far a consumer group has read in each partition. RobustMQ persists offsets in the meta layer and provides the full Kafka offset-management surface: commit, fetch, reset, delete, and lag computation. This page covers the relevant APIs and the kafka-consumer-groups.sh commands.
Commit and Fetch
| API | Purpose | Notes |
|---|---|---|
OffsetCommit | Commit offsets | A group writes a partition's consumption progress to meta (commitSync is a synchronous commit) |
OffsetFetch | Fetch committed offsets | v8+ supports querying multiple groups in one batched request |
Offsets are persisted in the meta layer, so a group can resume from its committed offset after a restart or membership change (see Consumer Group).
Reset Offsets
kafka-consumer-groups.sh --reset-offsets moves a group's offsets to a chosen position:
| Target | Meaning |
|---|---|
--to-earliest | Reset to the earliest available offset |
--to-latest | Reset to the latest offset |
--to-offset <n> | Reset to a specific offset |
--shift-by <n> | Move the current offset forward/back by n (negative to rewind) |
Execution modes:
| Mode | Behavior |
|---|---|
--dry-run | Preview the intended changes only, nothing is persisted |
--execute | Actually commit the changes |
Delete Offsets
kafka-consumer-groups.sh --delete-offsets deletes a group's committed offsets for a given topic/partition. Afterward the partition has no committed offset, and the next consumption starts per auto.offset.reset (see Consumer).
Lag
kafka-consumer-groups.sh --describe shows per-partition progress:
| Column | Meaning |
|---|---|
CURRENT-OFFSET | The group's committed offset |
LOG-END-OFFSET | The partition's latest offset (its end) |
LAG | The lag = LOG-END-OFFSET − CURRENT-OFFSET |
A larger lag means consumption is further behind production.
Persistence
All offsets are persisted in the Raft-based meta-service, managed in the same layer as cluster dynamic config and ACL/SCRAM/quotas (see System Architecture). The coordinator (Raft leader) handles offset reads and writes.