test: add checking snapshot be sent in mix_version_test.

Signed-off-by: Siyuan Zhang <sizhang@google.com>

server/etcdmain/config.go

@@ -302,7 +302,7 @@ func newConfig() *config {
 	fs.BoolVar(&cfg.ec.ExperimentalMemoryMlock, "experimental-memory-mlock", cfg.ec.ExperimentalMemoryMlock, "Enable to enforce etcd pages (in particular bbolt) to stay in RAM.")
 	fs.BoolVar(&cfg.ec.ExperimentalTxnModeWriteWithSharedBuffer, "experimental-txn-mode-write-with-shared-buffer", true, "Enable the write transaction to use a shared buffer in its readonly check operations.")
 	fs.UintVar(&cfg.ec.ExperimentalBootstrapDefragThresholdMegabytes, "experimental-bootstrap-defrag-threshold-megabytes", 0, "Enable the defrag during etcd server bootstrap on condition that it will free at least the provided threshold of disk space. Needs to be set to non-zero value to take effect.")
-	fs.Uint64Var(&cfg.ec.SnapshotCatchUpEntries, "experimental-snapshot-catchup-entries", cfg.ec.SnapshotCatchUpEntries, "Number of entries for a slow follower to catch up after compacting the raft storage entries. (WARNING: only use this flag for tests.)")
+	fs.Uint64Var(&cfg.ec.SnapshotCatchUpEntries, "experimental-snapshot-catchup-entries", cfg.ec.SnapshotCatchUpEntries, "(WARNING: Use this flag with caution!) Number of entries for a slow follower to catch up after compacting the raft storage entries.")
 
 	// unsafe
 	fs.BoolVar(&cfg.ec.UnsafeNoFsync, "unsafe-no-fsync", false, "Disables fsync, unsafe, will cause data loss.")

tests/e2e/etcd_mix_versions_test.go

@@ -82,6 +82,7 @@ func mixVersionsSnapshotTestByAddingMember(t *testing.T, cfg e2e.EtcdProcessClus
 
 	t.Logf("Create an etcd cluster with %d member\n", cfg.ClusterSize)
 	cfg.SnapshotCount = 10
+	cfg.SnapshotCatchUpEntries = 10
 	cfg.BasePeerScheme = "unix" // to avoid port conflict
 
 	epc, err := e2e.NewEtcdProcessCluster(t, &cfg)
@@ -126,6 +127,7 @@ func mixVersionsSnapshotTestByMockPartition(t *testing.T, cfg e2e.EtcdProcessClu
 
 	t.Logf("Create an etcd cluster with %d member\n", cfg.ClusterSize)
 	cfg.SnapshotCount = 10
+	cfg.SnapshotCatchUpEntries = 10
 	cfg.BasePeerScheme = "unix" // to avoid port conflict
 
 	epc, err := e2e.NewEtcdProcessCluster(t, &cfg)
@@ -154,6 +156,12 @@ func mixVersionsSnapshotTestByMockPartition(t *testing.T, cfg e2e.EtcdProcessClu
 	require.NoError(t, err)
 
 	assertKVHash(t, epc)
+
+	leaderEPC = epc.Procs[epc.WaitLeader(t)]
+	if leaderEPC.Config().ExecPath == e2e.BinPath {
+		t.Log("Verify logs to check snapshot be sent from leader to follower")
+		e2e.AssertProcessLogs(t, leaderEPC, "sent database snapshot")
+	}
 }
 
 func writeKVs(t *testing.T, etcdctl *e2e.Etcdctl, startIdx, endIdx int) {

tests/framework/e2e/cluster.go

@@ -159,6 +159,7 @@ type EtcdProcessClusterConfig struct {
 	MetricsURLScheme string
 
 	SnapshotCount          int // default is 10000
+	SnapshotCatchUpEntries int // default is 5000
 
 	ClientTLS             ClientConnType
 	ClientCertAuthEnabled bool
@@ -402,6 +403,12 @@ func (cfg *EtcdProcessClusterConfig) EtcdServerProcessConfig(tb testing.TB, i in
 		panic(fmt.Sprintf("Unknown cluster version %v", cfg.Version))
 	}
 
+	// the "--experimental-snapshot-catchup-entries" flag is not available in 3.4.
+	// so it should not be set if the process execPath is not BinPath.
+	if cfg.SnapshotCatchUpEntries > 0 && execPath == BinPath {
+		args = append(args, "--experimental-snapshot-catchup-entries", fmt.Sprintf("%d", cfg.SnapshotCatchUpEntries))
+	}
+
 	return &EtcdServerProcessConfig{
 		lg:                  cfg.Logger,
 		ExecPath:            execPath,