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Merge pull request #429 from bootjp/feature/refactor
fix: address critical data safety, consistency, and performance issues
2 parents 1eab525 + 8ea3ba9 commit efec2bc

22 files changed

Lines changed: 2583 additions & 170 deletions

adapter/internal.go

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Original file line numberDiff line numberDiff line change
@@ -38,6 +38,9 @@ func (i *Internal) Forward(_ context.Context, req *pb.ForwardRequest) (*pb.Forwa
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if i.raft.State() != raft.Leader {
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return nil, errors.WithStack(ErrNotLeader)
4040
}
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if err := i.raft.VerifyLeader().Error(); err != nil {
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return nil, errors.WithStack(ErrNotLeader)
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}
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if err := i.stampTimestamps(req); err != nil {
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return &pb.ForwardResponse{

docs/review_todo.md

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# Review TODO
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Critical and high-severity issues found during a comprehensive code review.
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Items are ordered by priority within each section.
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---
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## 1. Data Loss
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### ~~1.1 [Critical] `saveLastCommitTS` uses `pebble.NoSync` — timestamp rollback after crash~~ DONE
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- **Status:** Fixed. Durable `lastCommitTS` is now guaranteed by the synced `ApplyMutations` `WriteBatch`; `saveLastCommitTS` remains a best-effort hint written with `pebble.NoSync`.
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### 1.2 [Low — downgraded] Batch Apply in FSM allows partial application without rollback
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- **File:** `kv/fsm.go:44-69`
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- **Problem:** When a `RaftCommand` contains multiple requests, each is applied individually. If request N fails, requests 1..N-1 are already persisted with no rollback.
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- **Analysis:** Downgraded from Critical. Batch items are independent raw writes from different clients. `applyRawBatch` returns per-item errors via `fsmApplyResponse`, so each caller receives their correct result. Partial success is by design for the raw batching optimization.
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- **Remaining concern:** If a future code path batches requests that must be atomic, this would need revisiting.
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### ~~1.3 [High] `pebbleStore.Compact()` is unimplemented — unbounded version accumulation~~ DONE
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- **Status:** Fixed. Implemented MVCC GC for pebbleStore and `RetentionController` interface (`MinRetainedTS`/`SetMinRetainedTS`).
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### ~~1.4 [High] Secondary commit is best-effort — lock residue on failure~~ DONE
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- **Status:** Fixed. Added `LockResolver` background worker (`kv/lock_resolver.go`) that runs every 10s on each leader, scans `!txn|lock|` keys for expired locks, checks primary transaction status, and resolves (commit/abort) orphaned locks.
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### ~~1.5 [High] `abortPreparedTxn` silently ignores errors~~ DONE
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- **Status:** Fixed. Errors are now logged with full context (gid, primary_key, start_ts, abort_ts).
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### ~~1.6 [High] MVCC compaction does not distinguish transaction internal keys~~ DONE
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- **Status:** Fixed. Both mvccStore and pebbleStore compaction now skip keys with `!txn|` prefix.
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---
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## 2. Concurrency / Distributed Failures
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### ~~2.1 [Critical] TOCTOU in `pebbleStore.ApplyMutations`~~ DONE
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- **Status:** Fixed. `ApplyMutations` now holds `mtx.Lock()` from conflict check through batch commit.
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### ~~2.2 [High] Leader proxy forward loop risk~~ DONE
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- **Status:** Fixed. Added `forwardWithRetry` with `maxForwardRetries=3`. Each retry re-fetches leader address via `LeaderWithID()`. Returns immediately on `ErrLeaderNotFound`.
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### ~~2.3 [High] Secondary commit failure leaves locks indefinitely~~ DONE
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- **Status:** Fixed. (Same as 1.4) Background `LockResolver` worker resolves expired orphaned locks.
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### ~~2.4 [Medium] `redirect` in Coordinate has no timeout~~ DONE
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- **Status:** Fixed. Added 5s `context.WithTimeout` to redirect gRPC forward call.
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### ~~2.5 [Medium] Proxy gRPC calls (`proxyRawGet` etc.) have no timeout~~ DONE
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- **Status:** Fixed. Added 5s `context.WithTimeout` to `proxyRawGet`, `proxyRawScanAt`, and `proxyLatestCommitTS`.
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### 2.6 [Low — downgraded] `GRPCConnCache` allows ConnFor after Close
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- **File:** `kv/grpc_conn_cache.go`
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- **Analysis:** Downgraded. `Close` properly closes all existing connections. Subsequent `ConnFor` lazily re-inits and creates fresh connections — this is by design and tested.
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### ~~2.7 [Medium] `Forward` handler skips `VerifyLeader`~~ DONE
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- **Status:** Fixed. Added `raft.VerifyLeader()` quorum check to `Forward` handler.
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---
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## 3. Performance
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### ~~3.1 [Critical] `mvccStore.ScanAt` scans the entire treemap~~ DONE
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- **Status:** Fixed. Replaced `tree.Each()` with `Iterator()` loop that breaks on limit and seeks via `Ceiling(start)`.
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### ~~3.2 [Critical] PebbleStore uses unbounded iterators in `GetAt` / `LatestCommitTS`~~ DONE
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- **Status:** Fixed. Both methods now use bounded `IterOptions` scoped to the target key.
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### ~~3.3 [High] FSM double-deserialization for single requests~~ DONE
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- **Status:** Fixed. Added prefix byte (`0x00` single, `0x01` batch) to `marshalRaftCommand` and `decodeRaftRequests` with legacy fallback.
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### ~~3.4 [High] Excessive `pebble.Sync` on every write~~ DONE
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- **Status:** Fixed. `PutAt`, `DeleteAt`, `ExpireAt` changed to `pebble.NoSync`. `ApplyMutations` retains `pebble.Sync`.
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### 3.5 [High] `VerifyLeader` called on every read — network round-trip (deferred)
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- **File:** `kv/shard_store.go:53-58`
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- **Problem:** Each read triggers a quorum-based leader verification with network round-trip.
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- **Trade-off:** A lease-based cache improves latency but widens the stale-read TOCTOU window (see 4.3). The current approach is the safe default — linearizable reads at the cost of one quorum RTT per read. Implementing leader leases is a major architectural decision requiring careful analysis of acceptable staleness bounds.
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### ~~3.6 [High] `mvccStore.Compact` holds exclusive lock during full tree scan~~ DONE
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- **Status:** Fixed. Split into 2 phases: scan under RLock, then apply updates in batched Lock/Unlock cycles (batch size 500).
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### ~~3.7 [High] `isTxnInternalKey` allocates `[]byte` on every call (5x)~~ DONE
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- **Status:** Fixed. Added package-level `var` for all prefix byte slices and common prefix fast-path check.
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### ~~3.8 [Medium] txn codec `bytes.Buffer` allocation per encode~~ DONE
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- **Status:** Fixed. `EncodeTxnMeta`, `encodeTxnLock`, `encodeTxnIntent` now use direct `make([]byte, size)` + `binary.BigEndian.PutUint64`.
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### ~~3.9 [Medium] `decodeKey` copies key bytes on every iteration step~~ DONE
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- **Status:** Fixed. Added `decodeKeyUnsafe` returning a zero-copy slice reference. Used in all temporary comparison sites (`GetAt`, `ExistsAt`, `skipToNextUserKey`, `LatestCommitTS`, `Compact`, reverse scan seek). `decodeKey` (copying) retained for `nextScannableUserKey`/`prevScannableUserKey` whose results are stored in `KVPair`.
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---
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## 4. Data Consistency
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### ~~4.1 [High] pebbleStore key encoding ambiguity with meta keys~~ DONE
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- **Status:** Fixed. Meta key changed to `\x00_meta_last_commit_ts` prefix. Added `isMetaKey()` helper for both new and legacy keys. `findMaxCommitTS()` migrates legacy key on startup. All scan/compact functions use `isMetaKey()` to skip meta keys.
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### ~~4.2 [High] Write Skew not prevented in one-phase transactions~~ DONE
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- **Status:** Fixed. Documented as Snapshot Isolation in `handleOnePhaseTxnRequest` and `MVCCStore.ApplyMutations` interface. Write skew is a known limitation; SSI requires read-set tracking at a higher layer.
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### ~~4.3 [High] VerifyLeader-to-read TOCTOU allows stale reads~~ DONE (documented)
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- **Status:** Documented as known limitation. The TOCTOU window between quorum-verified `VerifyLeader` and the read is inherently small. Full fix requires Raft ReadIndex protocol which is a significant architectural change. Added doc comment to `leaderOKForKey` explaining the trade-off.
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### ~~4.4 [High] DynamoDB `ConditionCheck` does not prevent write skew~~ DONE
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- **Status:** Already addressed. `buildConditionCheckLockRequest` writes a dummy Put (re-writing the current value) or Del for the checked key. This includes the key in the transaction's write set, so write-write conflict detection covers it.
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### ~~4.5 [Medium] Cross-shard `ScanAt` does not guarantee a consistent snapshot~~ DONE
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- **Status:** Documented. Added doc comment to `ShardStore.ScanAt` explaining the limitation and recommending transactions or a snapshot fence for callers requiring cross-shard consistency.
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---
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## 5. Test Coverage
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Overall coverage: **60.5%****1,043 functions at 0%**.
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### ~~5.1 [Critical] FSM Abort path entirely untested~~ DONE
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- **Status:** Fixed. Added `kv/fsm_abort_test.go` with 10 tests: Prepare→Abort flow, commit rejection, lock/intent cleanup, rollback record verification, non-primary abort, timestamp validation, idempotent abort conflict, missing primary key, empty mutations.
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### ~~5.2 [Critical] PebbleStore transaction functions entirely untested~~ DONE
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- **Status:** Fixed. Added `store/lsm_store_txn_test.go` with 14 tests: ApplyMutations (put/delete/TTL/conflict/no-conflict/atomicity/lastCommitTS update), LatestCommitTS (single/multi/not-found), Compact (old version removal/newest retained/tombstone cleanup/meta key skip/txn internal key skip/multi-key).
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### ~~5.3 [Critical] `Coordinate.Dispatch` untested~~ DONE
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- **Status:** Fixed. Added `kv/coordinator_dispatch_test.go` with 6 tests: raw put, raw delete, one-phase txn, nil request, empty elems, startTS assignment.
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### ~~5.4 [High] ShardedCoordinator Abort rollback flow untested~~ DONE
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- **Status:** Fixed. Added `kv/sharded_coordinator_abort_test.go` testing that when Shard2 Prepare fails, Shard1's locks are cleaned up via Abort.
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### 5.5 [High] Jepsen tests are single-shard, single-workload only
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- **Current:** Append workload on one Raft group, 30s duration.
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- **Needed:** Multi-shard transactions, CAS workload, longer duration (5-10 min).
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### ~~5.6 [Medium] No concurrent access tests for ShardStore / ShardedCoordinator~~ DONE
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- **Status:** Fixed. Expanded `store/mvcc_store_concurrency_test.go` from 1 to 8 tests with race detection: concurrent PutAt (different/same keys), concurrent GetAt+PutAt, concurrent ApplyMutations (single/multi-key), concurrent ScanAt+PutAt, scan snapshot consistency.
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### 5.7 [Medium] No error-path tests (I/O failure, corrupt data, gRPC connection failure)

kv/coordinator.go

Lines changed: 6 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -3,12 +3,15 @@ package kv
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import (
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"bytes"
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"context"
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"time"
67

78
pb "github.com/bootjp/elastickv/proto"
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"github.com/cockroachdb/errors"
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"github.com/hashicorp/raft"
1011
)
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const redirectForwardTimeout = 5 * time.Second
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func NewCoordinator(txm Transactional, r *raft.Raft) *Coordinate {
1316
return &Coordinate{
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transactionManager: txm,
@@ -237,7 +240,9 @@ func (c *Coordinate) redirect(ctx context.Context, reqs *OperationGroup[OP]) (*C
237240
}
238241
}
239242

240-
r, err := cli.Forward(ctx, c.toForwardRequest(requests))
243+
fwdCtx, cancel := context.WithTimeout(ctx, redirectForwardTimeout)
244+
defer cancel()
245+
r, err := cli.Forward(fwdCtx, c.toForwardRequest(requests))
241246
if err != nil {
242247
return nil, errors.WithStack(err)
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}

kv/coordinator_dispatch_test.go

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package kv
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import (
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"context"
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"testing"
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"github.com/bootjp/elastickv/store"
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"github.com/stretchr/testify/require"
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)
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func TestCoordinateDispatch_RawPut(t *testing.T) {
12+
t.Parallel()
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st := store.NewMVCCStore()
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fsm := NewKvFSM(st)
16+
r, stop := newSingleRaft(t, "dispatch-raw-put", fsm)
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t.Cleanup(stop)
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tm := NewTransaction(r)
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c := NewCoordinator(tm, r)
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ctx := context.Background()
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resp, err := c.Dispatch(ctx, &OperationGroup[OP]{
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Elems: []*Elem[OP]{
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{Op: Put, Key: []byte("k1"), Value: []byte("v1")},
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},
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})
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require.NoError(t, err)
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require.NotNil(t, resp)
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// Verify the value was written.
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val, err := st.GetAt(ctx, []byte("k1"), ^uint64(0))
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require.NoError(t, err)
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require.Equal(t, []byte("v1"), val)
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}
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func TestCoordinateDispatch_RawDel(t *testing.T) {
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t.Parallel()
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st := store.NewMVCCStore()
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fsm := NewKvFSM(st)
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r, stop := newSingleRaft(t, "dispatch-raw-del", fsm)
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t.Cleanup(stop)
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tm := NewTransaction(r)
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c := NewCoordinator(tm, r)
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ctx := context.Background()
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// Write a value first.
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_, err := c.Dispatch(ctx, &OperationGroup[OP]{
51+
Elems: []*Elem[OP]{
52+
{Op: Put, Key: []byte("k1"), Value: []byte("v1")},
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},
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})
55+
require.NoError(t, err)
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// Delete the value.
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_, err = c.Dispatch(ctx, &OperationGroup[OP]{
59+
Elems: []*Elem[OP]{
60+
{Op: Del, Key: []byte("k1")},
61+
},
62+
})
63+
require.NoError(t, err)
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// Verify the key is gone.
66+
_, err = st.GetAt(ctx, []byte("k1"), ^uint64(0))
67+
require.ErrorIs(t, err, store.ErrKeyNotFound)
68+
}
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70+
func TestCoordinateDispatch_TxnOnePhase(t *testing.T) {
71+
t.Parallel()
72+
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st := store.NewMVCCStore()
74+
fsm := NewKvFSM(st)
75+
r, stop := newSingleRaft(t, "dispatch-txn", fsm)
76+
t.Cleanup(stop)
77+
78+
tm := NewTransaction(r)
79+
c := NewCoordinator(tm, r)
80+
ctx := context.Background()
81+
82+
startTS := c.clock.Next()
83+
resp, err := c.Dispatch(ctx, &OperationGroup[OP]{
84+
IsTxn: true,
85+
StartTS: startTS,
86+
Elems: []*Elem[OP]{
87+
{Op: Put, Key: []byte("a"), Value: []byte("1")},
88+
{Op: Put, Key: []byte("b"), Value: []byte("2")},
89+
},
90+
})
91+
require.NoError(t, err)
92+
require.NotNil(t, resp)
93+
94+
// Both keys should be readable.
95+
v1, err := st.GetAt(ctx, []byte("a"), ^uint64(0))
96+
require.NoError(t, err)
97+
require.Equal(t, []byte("1"), v1)
98+
99+
v2, err := st.GetAt(ctx, []byte("b"), ^uint64(0))
100+
require.NoError(t, err)
101+
require.Equal(t, []byte("2"), v2)
102+
}
103+
104+
func TestCoordinateDispatch_NilRequest(t *testing.T) {
105+
t.Parallel()
106+
107+
c := &Coordinate{
108+
clock: NewHLC(),
109+
}
110+
111+
_, err := c.Dispatch(context.Background(), nil)
112+
require.ErrorIs(t, err, ErrInvalidRequest)
113+
}
114+
115+
func TestCoordinateDispatch_EmptyElems(t *testing.T) {
116+
t.Parallel()
117+
118+
c := &Coordinate{
119+
clock: NewHLC(),
120+
}
121+
122+
_, err := c.Dispatch(context.Background(), &OperationGroup[OP]{})
123+
require.ErrorIs(t, err, ErrInvalidRequest)
124+
}
125+
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func TestCoordinateDispatch_TxnAssignsStartTS(t *testing.T) {
127+
t.Parallel()
128+
129+
tx := &stubTransactional{}
130+
st := store.NewMVCCStore()
131+
fsm := NewKvFSM(st)
132+
r, stop := newSingleRaft(t, "dispatch-ts-assign", fsm)
133+
t.Cleanup(stop)
134+
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c := &Coordinate{
136+
transactionManager: tx,
137+
raft: r,
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clock: NewHLC(),
139+
}
140+
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// When StartTS is 0 for a txn, Dispatch should assign one.
142+
resp, err := c.Dispatch(context.Background(), &OperationGroup[OP]{
143+
IsTxn: true,
144+
Elems: []*Elem[OP]{
145+
{Op: Put, Key: []byte("k"), Value: []byte("v")},
146+
},
147+
})
148+
require.NoError(t, err)
149+
require.NotNil(t, resp)
150+
require.Equal(t, 1, tx.commits)
151+
152+
// The request should have a non-zero startTS.
153+
require.Len(t, tx.reqs, 1)
154+
require.Len(t, tx.reqs[0], 1)
155+
require.Greater(t, tx.reqs[0][0].Ts, uint64(0))
156+
}
157+
158+
func TestCoordinateDispatchRaw_CallsTransactionManager(t *testing.T) {
159+
t.Parallel()
160+
161+
tx := &stubTransactional{}
162+
st := store.NewMVCCStore()
163+
fsm := NewKvFSM(st)
164+
r, stop := newSingleRaft(t, "dispatch-raw-tm", fsm)
165+
t.Cleanup(stop)
166+
167+
c := &Coordinate{
168+
transactionManager: tx,
169+
raft: r,
170+
clock: NewHLC(),
171+
}
172+
173+
resp, err := c.Dispatch(context.Background(), &OperationGroup[OP]{
174+
Elems: []*Elem[OP]{
175+
{Op: Put, Key: []byte("k"), Value: []byte("v")},
176+
},
177+
})
178+
require.NoError(t, err)
179+
require.NotNil(t, resp)
180+
require.Equal(t, 1, tx.commits)
181+
}

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