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[server] Register external KV snapshots and restore replicas - #4242
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Copilot review overview
🟡 Changes recommended
Critical snapshot integrity and manifest validation are missing, and metadata versions are not validated.
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Review effort: Lite
Findings: 2
Open (3)
What changed in this PR
Adds external KV snapshot registration, retention, and replica restoration support.
Changes:
- Adds portable snapshot metadata serialization.
- Registers external snapshots in ZooKeeper with retry and retention handling.
- Restores replicas from external snapshots and initializes log tails.
- Adds recovery, registration, retention, and compatibility tests.
| File | Summary |
|---|---|
fluss-server/src/test/java/org/apache/fluss/server/replica/ReplicaTest.java |
Tests replica recovery behavior. |
fluss-server/src/test/java/org/apache/fluss/server/log/LogTabletTest.java |
Tests log-tail initialization. |
fluss-server/src/test/java/org/apache/fluss/server/kv/snapshot/TestCompletedSnapshotHandleStore.java |
Updates test snapshot-store implementation. |
fluss-server/src/test/java/org/apache/fluss/server/coordinator/ExternalKvSnapshotITCase.java |
Tests external snapshot recovery end to end. |
fluss-server/src/test/java/org/apache/fluss/server/coordinator/CoordinatorServiceOrphanRpcsITCase.java |
Updates test-store fixtures. |
fluss-server/src/test/java/org/apache/fluss/server/coordinator/CompletedSnapshotStoreManagerTest.java |
Tests registration and retention scenarios. |
fluss-server/src/main/java/org/apache/fluss/server/zk/ZooKeeperClient.java |
Adds idempotent external snapshot registration. |
fluss-server/src/main/java/org/apache/fluss/server/replica/Replica.java |
Integrates snapshot-based KV recovery. |
fluss-server/src/main/java/org/apache/fluss/server/log/LogTablet.java |
Supports empty log-tail initialization. |
fluss-server/src/main/java/org/apache/fluss/server/log/LogManager.java |
Persists initialized log tails. |
fluss-server/src/main/java/org/apache/fluss/server/kv/snapshot/ZooKeeperCompletedSnapshotHandleStore.java |
Implements ZooKeeper-backed external registration. |
fluss-server/src/main/java/org/apache/fluss/server/kv/snapshot/CompletedSnapshotStore.java |
Integrates external snapshots with retention. |
fluss-server/src/main/java/org/apache/fluss/server/kv/snapshot/CompletedSnapshotJsonSerde.java |
Adapts server snapshots to portable metadata. |
fluss-server/src/main/java/org/apache/fluss/server/kv/snapshot/CompletedSnapshotHandleStore.java |
Extends the snapshot handle-store contract. |
fluss-server/src/main/java/org/apache/fluss/server/coordinator/CompletedSnapshotStoreManager.java |
Registers and tracks external snapshots. |
fluss-common/src/test/java/org/apache/fluss/metadata/KvSnapshotFileMetadataJsonSerdeTest.java |
Tests metadata serialization compatibility. |
fluss-common/src/main/java/org/apache/fluss/metadata/KvSnapshotFileMetadataJsonSerde.java |
Serializes and deserializes portable metadata. |
fluss-common/src/main/java/org/apache/fluss/metadata/KvSnapshotFileMetadata.java |
Defines portable snapshot metadata. |
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Share KV snapshot file metadata across modules and register externally produced target-bucket snapshots with coordinator fencing and idempotent retries. Adopt confirmed snapshots into retention and protect persistent references when registration responses are lost. Initialize the local log boundary from snapshot-only history through ordinary replica role notifications. Cover external snapshot production, registration, recovery, repeated notifications, online writes, failover and subsequent snapshot retention.
Use the selected KV snapshot to initialize an empty local log after its files have been loaded, and capture the leader log boundary after recovery. Reject conflicting log initialization and propagate snapshot lookup errors. Release partially recovered KV state before retrying, and publish leader identity only after recovery succeeds so failed elections can be retried. Cover snapshot lookup and download failures, metadata retry after loading, and protection of existing local log records.
Keep the existing leader and follower transition behavior while coordinating KV snapshot recovery with local log initialization. Test snapshot lookup failures independently of role transition retries, and recover from a failed download under a subsequent leader epoch.
Serialize external snapshot identity and ordering checks, persistent handle confirmation and retention updates in CompletedSnapshotStore. Delegate coordinator fencing and idempotent persistence to the handle store while preserving ordinary snapshot writes and cleanup behavior. Describe the snapshot counter check as an allocation bound; reserving the ID remains the caller's responsibility.
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Resolve the recovery snapshot and log prerequisites before changing role state or discarding the current KV. Reuse that selection for the first recovery attempt while preserving retries through older healthy snapshots. Avoid remote manifest lookups when the local log already covers the snapshot. Cover metadata lookup failures with a live KV and recovery after metadata becomes available. Clarify that obsolete snapshot cleanup may be deferred.
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Wait for KV replicas before bounded snapshot split enumeration. Keep synthetic orphan-cleanup snapshot metadata from participating in leader recovery, and let replica readiness checks retry while the leader or tablet server is temporarily unavailable.
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Addressing the three Copilot review comments:
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Purpose
Linked issue: close #4223
Brief change log
Tests
API and Format
Documentation