REP-6743 Ignore MongoDB-internal databases (#180)

MongoDB will soon designate `__mdb_internal` as a prefix for MongoDB-internal services. This changeset teaches Migration Verifier to ignore databases with that prefix.

Author: FGasper

internal/verifier/change_stream.go

@@ -87,7 +87,7 @@ func (csr *ChangeStreamReader) GetChangeStreamFilter() (pipeline mongo.Pipeline)
 			{{"$match", util.ExcludePrefixesQuery(
 				"ns.db",
 				append(
-					slices.Clone(MongosyncMetaDBPrefixes),
+					slices.Clone(ExcludedDBPrefixes),
 					csr.metaDB.Name(),
 				),
 			)}},

internal/verifier/list_namespaces.go

@@ -12,20 +12,26 @@ import (
 	"go.mongodb.org/mongo-driver/v2/mongo/options"
 )
 
+const (
+	// ExcludedSystemCollPrefix is the prefix of system collections,
+	// which we ignore.
+	ExcludedSystemCollPrefix = "system."
+
+	// MongoDBInternalDBPrefix is the prefix for MongoDB-internal databases.
+	// (e.g., Atlas’s availability canary)
+	MongoDBInternalDBPrefix = "__mdb_internal"
+)
+
 var (
-	MongosyncMetaDBPrefixes = mslices.Of(
+	ExcludedDBPrefixes = mslices.Of(
+		// mongosync metadata:
 		"mongosync_internal_",
 		"mongosync_reserved_",
+		MongoDBInternalDBPrefix,
 	)
-)
 
-var (
 	// ExcludedSystemDBs are system databases that are excluded from verification.
 	ExcludedSystemDBs = []string{"admin", "config", "local"}
-
-	// ExcludedSystemCollPrefix is the prefix of system collections,
-	// which we ignore.
-	ExcludedSystemCollPrefix = "system."
 )
 
 // ListAllUserNamespaces lists all the user collections on a cluster,
@@ -52,7 +58,7 @@ func ListAllUserNamespaces(
 	dbNames, err := client.ListDatabaseNames(ctx, bson.D{
 		{"$and", []bson.D{
 			{{"name", bson.D{{"$nin", excluded}}}},
-			util.ExcludePrefixesQuery("name", MongosyncMetaDBPrefixes),
+			util.ExcludePrefixesQuery("name", ExcludedDBPrefixes),
 		}},
 	})
 

internal/verifier/migration_verifier_test.go

@@ -2240,6 +2240,48 @@ func (suite *IntegrationTestSuite) TestGenerationalRechecking() {
 	suite.Require().NoError(runner.Await())
 }
 
+func (suite *IntegrationTestSuite) TestMongoDBInternalDB() {
+	ctx := suite.Context()
+
+	dbName := MongoDBInternalDBPrefix + "internalDBTest"
+
+	_, err := suite.srcMongoClient.
+		Database(dbName).
+		Collection("foo").
+		InsertOne(ctx, bson.D{})
+	suite.Require().NoError(err)
+
+	verifier := suite.BuildVerifier()
+	runner := RunVerifierCheck(ctx, suite.T(), verifier)
+
+	// Dry run generation 0 to make sure change stream reader is started.
+	suite.Require().NoError(runner.AwaitGenerationEnd())
+
+	status, err := verifier.GetVerificationStatus(ctx)
+	suite.Require().NoError(err)
+
+	suite.Assert().Zero(status.FailedTasks, "gen0 should have no failed tasks: %+v", status)
+
+	_, err = suite.srcMongoClient.
+		Database(dbName).
+		Collection("foo").
+		InsertOne(ctx, bson.D{})
+	suite.Require().NoError(err)
+
+	suite.Require().NoError(runner.StartNextGeneration())
+	suite.Require().NoError(runner.AwaitGenerationEnd())
+	status, err = verifier.GetVerificationStatus(ctx)
+	suite.Require().NoError(err)
+	suite.Assert().Zero(status.FailedTasks, "gen1 should have no failed tasks: %+v", status)
+
+	suite.Require().NoError(verifier.WritesOff(ctx))
+	suite.Require().NoError(runner.Await())
+
+	status, err = verifier.GetVerificationStatus(ctx)
+	suite.Require().NoError(err)
+	suite.Assert().Zero(status.FailedTasks, "end should have no failed tasks: %+v", status)
+}
+
 func (suite *IntegrationTestSuite) TestVerifierWithFilter() {
 	zerolog.SetGlobalLevel(zerolog.DebugLevel)