device/telemetry: lower batch size to be within transaction size limit

controlplane/telemetry/internal/telemetry/submitter_test.go

@@ -424,8 +424,11 @@ func TestAgentTelemetry_Submitter(t *testing.T) {
 		mu.Lock()
 		defer mu.Unlock()
 
-		require.Equal(t, 3, calls, "expected 3 submission calls for 5500 samples with max 2560 per call")
-		assert.Equal(t, []int{sdktelemetry.MaxSamplesPerBatch, sdktelemetry.MaxSamplesPerBatch, 380}, samplesPerCall, "each call should contain at most 2560 samples")
+		require.Equal(t, 23, calls, "expected 23 submission calls for 5500 samples with max 245 per call")
+		for i := range 22 {
+			assert.Equal(t, sdktelemetry.MaxSamplesPerBatch, samplesPerCall[i])
+		}
+		assert.Equal(t, 110, samplesPerCall[22], "last call should contain 110 samples")
 	})
 
 	t.Run("negative_rtts_are_submitted_as_one", func(t *testing.T) {

e2e/sdk_telemetry_test.go

@@ -266,6 +266,7 @@ func TestE2E_SDK_Telemetry(t *testing.T) {
 		900000,
 		1000000,
 	}
+
 	t.Run("write second device latency samples", func(t *testing.T) {
 		ctx, cancel := context.WithDeadline(t.Context(), time.Now().Add(30*time.Second))
 		defer cancel()
@@ -309,6 +310,44 @@ func TestE2E_SDK_Telemetry(t *testing.T) {
 		require.Equal(t, uint32(len(combinedSamples)), deviceLatencySamples.NextSampleIndex)
 		require.Equal(t, combinedSamples, deviceLatencySamples.Samples)
 	})
+
+	t.Run("write largest possible batch of samples per transaction", func(t *testing.T) {
+		ctx, cancel := context.WithDeadline(t.Context(), time.Now().Add(30*time.Second))
+		defer cancel()
+		start := time.Now()
+		log.Info("==> Writing largest possible batch of samples per transaction")
+		sig, res, err := la2AgentTelemetryClient.WriteDeviceLatencySamples(ctx, telemetry.WriteDeviceLatencySamplesInstructionConfig{
+			AgentPK:                    la2DeviceAgentPrivateKey.PublicKey(),
+			OriginDevicePK:             la2DevicePK,
+			TargetDevicePK:             ny5DevicePK,
+			LinkPK:                     la2ToNy5LinkPK,
+			Epoch:                      epoch,
+			StartTimestampMicroseconds: secondStartTimestampMicroseconds,
+			Samples:                    make([]uint32, telemetry.MaxSamplesPerBatch),
+		})
+		require.NoError(t, err)
+		for _, msg := range res.Meta.LogMessages {
+			log.Debug("solana log message", "msg", msg)
+		}
+		require.Nil(t, res.Meta.Err, "transaction failed: %+v", res.Meta.Err)
+		log.Info("==> Wrote largest possible batch of samples per transaction", "sig", sig, "tx", res, "duration", time.Since(start))
+	})
+
+	t.Run("write largest possible batch of samples per transaction +1 (should fail)", func(t *testing.T) {
+		ctx, cancel := context.WithDeadline(t.Context(), time.Now().Add(30*time.Second))
+		defer cancel()
+		log.Info("==> Writing largest possible batch of samples per transaction +1 (should fail)")
+		_, _, err := la2AgentTelemetryClient.WriteDeviceLatencySamples(ctx, telemetry.WriteDeviceLatencySamplesInstructionConfig{
+			AgentPK:                    la2DeviceAgentPrivateKey.PublicKey(),
+			OriginDevicePK:             la2DevicePK,
+			TargetDevicePK:             ny5DevicePK,
+			LinkPK:                     la2ToNy5LinkPK,
+			Epoch:                      epoch,
+			StartTimestampMicroseconds: secondStartTimestampMicroseconds,
+			Samples:                    make([]uint32, telemetry.MaxSamplesPerBatch+1),
+		})
+		require.ErrorIs(t, err, telemetry.ErrSamplesBatchTooLarge)
+	})
 }
 
 func airdropAndWait(ctx context.Context, client *solanarpc.Client, pubkey solana.PublicKey, lamports uint64) error {

smartcontract/sdk/go/telemetry/constants.go

@@ -13,13 +13,14 @@ const (
 	// when the given PDA does not exist.
 	InstructionErrorAccountDoesNotExist = 1011
 
-	// SolanaMaxPermittedDataIncrease is the maximum number of bytes a program may add to an
-	// account during a single realloc.
-	// This is the samples batch size limit in bytes.
-	SolanaMaxPermittedDataIncrease = 10_240
-
 	// MaxSamplesPerBatch is the maximum number of samples that can be written in a single batch.
-	MaxSamplesPerBatch = SolanaMaxPermittedDataIncrease / 4
+	//
+	// Messages transmitted to Solana validators must not exceed the IPv6 MTU size to ensure fast
+	// and reliable network transmission of cluster info over UDP. Solana's networking stack uses a
+	// conservative MTU size of 1280 bytes which, after accounting for headers, leaves 1232 bytes
+	// for packet data like serialized transactions.
+	// https://docs.anza.xyz/proposals/versioned-transactions#problem
+	MaxSamplesPerBatch = 245 // 980 bytes
 
 	// MaxSamples is the maximum number of samples that can be written to a single account.
 	MaxSamples = 35_000