redpanda/migrator: avoid O(N²) schema registry fan-out in translate_ids sync #4734
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| // Copyright 2026 Redpanda Data, Inc. | ||
| // | ||
| // Licensed under the Apache License, Version 2.0 (the "License"); | ||
| // you may not use this file except in compliance with the License. | ||
| // You may obtain a copy of the License at | ||
| // | ||
| // http://www.apache.org/licenses/LICENSE-2.0 | ||
| // | ||
| // Unless required by applicable law or agreed to in writing, software | ||
| // distributed under the License is distributed on an "AS IS" BASIS, | ||
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| // See the License for the specific language governing permissions and | ||
| // limitations under the License. | ||
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| package migrator_test | ||
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| import ( | ||
| "context" | ||
| "fmt" | ||
| "net/http" | ||
| "net/http/httptest" | ||
| "net/http/httputil" | ||
| "net/url" | ||
| "regexp" | ||
| "sync/atomic" | ||
| "testing" | ||
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| "github.com/stretchr/testify/assert" | ||
| "github.com/stretchr/testify/require" | ||
| "github.com/twmb/franz-go/pkg/sr" | ||
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| "github.com/redpanda-data/benthos/v4/public/service/integration" | ||
| "github.com/redpanda-data/connect/v4/internal/impl/redpanda/migrator" | ||
| ) | ||
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| // countingProxy is a reverse proxy in front of the destination Schema | ||
| // Registry that records request counts and peak concurrent in-flight | ||
| // requests. | ||
| type countingProxy struct { | ||
| server *httptest.Server | ||
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| total atomic.Int64 // all requests | ||
|
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| registers atomic.Int64 // POST /subjects/{s}/versions | ||
| idGets atomic.Int64 // GET /schemas/ids/{id}/versions (usage listing) | ||
| versionGets atomic.Int64 // GET /subjects/{s}/versions/{v} (usage fan-out) | ||
| inFlight atomic.Int64 | ||
| maxInFlight atomic.Int64 | ||
| } | ||
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| var ( | ||
| reVersionGet = regexp.MustCompile(`^/subjects/[^/]+/versions/[^/]+$`) | ||
| reIDGet = regexp.MustCompile(`^/schemas/ids/\d+/versions$`) | ||
| reRegister = regexp.MustCompile(`^/subjects/[^/]+/versions$`) | ||
| ) | ||
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| func newCountingProxy(t *testing.T, targetURL string) *countingProxy { | ||
| t.Helper() | ||
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| target, err := url.Parse(targetURL) | ||
| require.NoError(t, err) | ||
| rp := httputil.NewSingleHostReverseProxy(target) | ||
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| p := &countingProxy{} | ||
| p.server = httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { | ||
| cur := p.inFlight.Add(1) | ||
| defer p.inFlight.Add(-1) | ||
| for { | ||
| maxSeen := p.maxInFlight.Load() | ||
| if cur <= maxSeen || p.maxInFlight.CompareAndSwap(maxSeen, cur) { | ||
| break | ||
| } | ||
| } | ||
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| p.total.Add(1) | ||
| switch { | ||
| case r.Method == "GET" && reVersionGet.MatchString(r.URL.Path): | ||
| p.versionGets.Add(1) | ||
| case r.Method == "GET" && reIDGet.MatchString(r.URL.Path): | ||
| p.idGets.Add(1) | ||
| case r.Method == "POST" && reRegister.MatchString(r.URL.Path): | ||
| p.registers.Add(1) | ||
| } | ||
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| rp.ServeHTTP(w, r) | ||
| })) | ||
| t.Cleanup(p.server.Close) | ||
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| return p | ||
| } | ||
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| // TestIntegrationSchemaRegistryMigratorSyncSharedSchemaFanout guards against | ||
| // O(N^2) destination-registry traffic when syncing subjects that share | ||
| // identical schema bodies, in both ID-translation modes. | ||
| // | ||
| // Identical schema bodies deduplicate to a single destination schema ID. | ||
| // Registering via franz-go's CreateSchema/CreateSchemaWithIDAndVersion | ||
| // resolves the returned ID through SchemaUsagesByID, which fetches every | ||
| // subject-version sharing that ID using one unbounded goroutine per usage: N | ||
| // such subjects cost ~N(N+1)/2 requests, none of them bounded by | ||
| // max_parallel_http_requests. The sync must instead cost one registration per | ||
| // subject with no usage fan-out, and respect the configured concurrency | ||
| // limit. | ||
| func TestIntegrationSchemaRegistryMigratorSyncSharedSchemaFanout(t *testing.T) { | ||
| integration.CheckSkip(t) | ||
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| // Number of source subjects sharing one identical schema body. Large | ||
| // enough to make quadratic growth unambiguous while keeping runtime low. | ||
| const numSubjects = 40 | ||
| const sharedSchema = `{"type":"record","name":"Shared","fields":[{"name":"a","type":"int"}]}` | ||
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| tests := []struct { | ||
| name string | ||
| translate bool | ||
| mode sr.Mode | ||
| }{ | ||
| {name: "translate_ids=true", translate: true, mode: sr.ModeReadWrite}, | ||
| {name: "translate_ids=false", translate: false, mode: sr.ModeImport}, | ||
| } | ||
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| for _, tc := range tests { | ||
| t.Run(tc.name, func(t *testing.T) { | ||
| t.Log("Given: source and destination Redpanda clusters with Schema Registry") | ||
| srcCluster, dstCluster := startRedpandaSourceAndDestination(t) | ||
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| srcSR, err := sr.NewClient(sr.URLs(srcCluster.SchemaRegistryURL)) | ||
| require.NoError(t, err) | ||
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| t.Log("And: a counting reverse proxy in front of the destination Schema Registry") | ||
| proxy := newCountingProxy(t, dstCluster.SchemaRegistryURL) | ||
| dstSR, err := sr.NewClient(sr.URLs(proxy.server.URL)) | ||
| require.NoError(t, err) | ||
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| t.Logf("And: destination is set to %s mode", tc.mode) | ||
| modeRes := dstSR.SetMode(t.Context(), tc.mode) | ||
| require.NoError(t, modeRes[0].Err) | ||
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| t.Logf("And: %d source subjects sharing one identical schema body", numSubjects) | ||
| const autoAssign = -1 | ||
| for i := range numSubjects { | ||
| // RegisterSchema: CreateSchema would perform the same usage | ||
| // fan-out this test guards against, against the source. | ||
| _, err := srcSR.RegisterSchema(t.Context(), | ||
| fmt.Sprintf("shared-%03d-value", i), | ||
| sr.Schema{Schema: sharedSchema}, autoAssign, autoAssign) | ||
| require.NoError(t, err) | ||
| } | ||
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| t.Logf("When: the schema migrator syncs with translate_ids=%v", tc.translate) | ||
| conf := migrator.SchemaRegistryMigratorConfig{ | ||
| Enabled: true, | ||
| Versions: migrator.VersionsAll, | ||
| TranslateIDs: tc.translate, | ||
| } | ||
| // NB: the testing constructor sets MaxParallelHTTPRequests to 2. | ||
| m := migrator.NewSchemaRegistryMigratorForTesting(t, conf, srcSR, dstSR) | ||
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| ctx, cancel := context.WithTimeout(t.Context(), redpandaTestWaitTimeout) | ||
| defer cancel() | ||
| require.NoError(t, m.Sync(ctx)) | ||
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| registers := proxy.registers.Load() | ||
| idGets := proxy.idGets.Load() | ||
| versionGets := proxy.versionGets.Load() | ||
| maxInFlight := proxy.maxInFlight.Load() | ||
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| t.Logf("Destination registry traffic for %d identical-body subjects:", numSubjects) | ||
| t.Logf(" total requests: %d", proxy.total.Load()) | ||
| t.Logf(" schema registrations (POST): %d", registers) | ||
| t.Logf(" usage listings (GET /schemas/ids/N/versions): %d", idGets) | ||
| t.Logf(" usage fan-out (GET /subjects/S/versions/V): %d (O(N^2) worst case: %d)", | ||
| versionGets, numSubjects*(numSubjects+1)/2) | ||
| t.Logf(" peak concurrent in-flight requests: %d (max_parallel_http_requests: 2)", maxInFlight) | ||
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| // Guard against a vacuous pass: the sync must actually have | ||
| // registered every subject at the destination. | ||
| assert.GreaterOrEqual(t, registers, int64(numSubjects), | ||
| "expected at least one registration per subject") | ||
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| // Registration must not resolve its result through the usage | ||
| // endpoints: any hit is the start of the O(N^2) fan-out. | ||
| assert.Zero(t, versionGets, | ||
| "schema registration must not fan out to the subject-versions sharing the destination schema ID") | ||
| assert.Zero(t, idGets, | ||
| "schema registration must not list usages of the destination schema ID") | ||
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| // Concurrency against the destination registry must respect | ||
| // max_parallel_http_requests (2 here). | ||
| assert.LessOrEqual(t, maxInFlight, int64(2), | ||
| "destination request concurrency exceeds max_parallel_http_requests") | ||
| }) | ||
| } | ||
| } | ||
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The
elsebranch below (translate_ids: false, the default) still callsCreateSchemaWithIDAndVersion, which performs the exact sameSchemaUsagesByIDfan-out this PR removes — so the O(N²) behaviour remains for the common configuration.The fix is even simpler there than here:
idandversionare inputs (ss.ID,ss.Version), soRegisterSchemaalone suffices andinfocan be built directly as{dstSubject, ss.Version, ss.ID}with no lookup at all. The new fan-out test only coverstranslate_ids: true, so this path is also untested.