graph/db+sqldb: use batch validation for closed SCID migration

diff --git a/graph/db/sql_migration.go b/graph/db/sql_migration.go
index d62fe74..467f543 100644
--- a/graph/db/sql_migration.go
+++ b/graph/db/sql_migration.go
@@ -67,7 +67,7 @@ func MigrateGraphToSQL(ctx context.Context, cfg *SQLStoreConfig,
 	}
 
 	// 5) Migrate the closed SCID index.
-	err = migrateClosedSCIDIndex(ctx, kvBackend, sqlDB)
+	err = migrateClosedSCIDIndex(ctx, cfg.QueryCfg, kvBackend, sqlDB)
 	if err != nil {
 		return fmt.Errorf("could not migrate closed SCID index: %w",
 			err)
@@ -992,12 +992,11 @@ func forEachPruneLogEntry(db kvdb.Backend, cb func(height uint32,
 }
 
 // migrateClosedSCIDIndex migrates the closed SCID index from the KV backend to
-// the SQL database. It iterates over each closed SCID in the KV store, inserts
-// it into the SQL database, and then verifies that the SCID was inserted
-// correctly by checking if the channel with the given SCID is seen as closed in
-// the SQL database.
-func migrateClosedSCIDIndex(ctx context.Context, kvBackend kvdb.Backend,
-	sqlDB SQLQueries) error {
+// the SQL database. It collects SCIDs in batches, inserts them individually,
+// and then validates them in batches using GetClosedChannelsSCIDs for better
+// performance.
+func migrateClosedSCIDIndex(ctx context.Context, cfg *sqldb.QueryConfig,
+	kvBackend kvdb.Backend, sqlDB SQLQueries) error {
 
 	var (
 		count uint64
@@ -1008,6 +1007,43 @@ func migrateClosedSCIDIndex(ctx context.Context, kvBackend kvdb.Backend,
 			Interval: 10 * time.Second,
 		}
 	)
+
+	batch := make([][]byte, 0, cfg.MaxBatchSize)
+
+	// validateBatch validates a batch of closed SCIDs using batch query.
+	validateBatch := func() error {
+		if len(batch) == 0 {
+			return nil
+		}
+
+		// Batch fetch all closed SCIDs from the database.
+		dbSCIDs, err := sqlDB.GetClosedChannelsSCIDs(ctx, batch)
+		if err != nil {
+			return fmt.Errorf("could not batch get closed "+
+				"SCIDs: %w", err)
+		}
+
+		// Create set of SCIDs that exist in the database for quick
+		// lookup.
+		dbSCIDSet := make(map[string]struct{})
+		for _, scid := range dbSCIDs {
+			dbSCIDSet[string(scid)] = struct{}{}
+		}
+
+		// Validate each SCID in the batch.
+		for _, expectedSCID := range batch {
+			if _, found := dbSCIDSet[string(expectedSCID)]; !found {
+				return fmt.Errorf("closed SCID %x not found "+
+					"in database", expectedSCID)
+			}
+		}
+
+		// Reset the batch for the next iteration.
+		batch = make([][]byte, 0, cfg.MaxBatchSize)
+
+		return nil
+	}
+
 	migrateSingleClosedSCID := func(scid lnwire.ShortChannelID) error {
 		count++
 		chunk++
@@ -1019,17 +1055,16 @@ func migrateClosedSCIDIndex(ctx context.Context, kvBackend kvdb.Backend,
 				"with SCID %s: %w", scid, err)
 		}
 
-		// Now, verify that the channel with the given SCID is
-		// seen as closed.
-		isClosed, err := sqlDB.IsClosedChannel(ctx, chanIDB)
-		if err != nil {
-			return fmt.Errorf("could not check if channel %s "+
-				"is closed: %w", scid, err)
-		}
+		// Add to validation batch.
+		batch = append(batch, chanIDB)
 
-		if !isClosed {
-			return fmt.Errorf("channel %s should be closed, "+
-				"but is not", scid)
+		// Validate batch when full.
+		if len(batch) >= cfg.MaxBatchSize {
+			err := validateBatch()
+			if err != nil {
+				return fmt.Errorf("batch validation failed: %w",
+					err)
+			}
 		}
 
 		s.Do(func() {
@@ -1051,6 +1086,15 @@ func migrateClosedSCIDIndex(ctx context.Context, kvBackend kvdb.Backend,
 			err)
 	}
 
+	// Validate any remaining SCIDs in the batch.
+	if len(batch) > 0 {
+		err := validateBatch()
+		if err != nil {
+			return fmt.Errorf("final batch validation failed: %w",
+				err)
+		}
+	}
+
 	log.Infof("Migrated %d closed SCIDs from KV to SQL", count)
 
 	return nil
diff --git a/graph/db/sql_store.go b/graph/db/sql_store.go
index 1de5016..fbfee84 100644
--- a/graph/db/sql_store.go
+++ b/graph/db/sql_store.go
@@ -151,6 +151,7 @@ type SQLQueries interface {
 	*/
 	InsertClosedChannel(ctx context.Context, scid []byte) error
 	IsClosedChannel(ctx context.Context, scid []byte) (bool, error)
+	GetClosedChannelsSCIDs(ctx context.Context, scids [][]byte) ([][]byte, error)
 }
 
 // BatchedSQLQueries is a version of SQLQueries that's capable of batched
diff --git a/sqldb/sqlc/graph.sql.go b/sqldb/sqlc/graph.sql.go
index 5718f25..7b9e472 100644
--- a/sqldb/sqlc/graph.sql.go
+++ b/sqldb/sqlc/graph.sql.go
@@ -1602,6 +1602,45 @@ func (q *Queries) GetChannelsBySCIDs(ctx context.Context, arg GetChannelsBySCIDs
 	return items, nil
 }
 
+const getClosedChannelsSCIDs = `-- name: GetClosedChannelsSCIDs :many
+SELECT scid
+FROM graph_closed_scids
+WHERE scid IN (/*SLICE:scids*/?)
+`
+
+func (q *Queries) GetClosedChannelsSCIDs(ctx context.Context, scids [][]byte) ([][]byte, error) {
+	query := getClosedChannelsSCIDs
+	var queryParams []interface{}
+	if len(scids) > 0 {
+		for _, v := range scids {
+			queryParams = append(queryParams, v)
+		}
+		query = strings.Replace(query, "/*SLICE:scids*/?", makeQueryParams(len(queryParams), len(scids)), 1)
+	} else {
+		query = strings.Replace(query, "/*SLICE:scids*/?", "NULL", 1)
+	}
+	rows, err := q.db.QueryContext(ctx, query, queryParams...)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var items [][]byte
+	for rows.Next() {
+		var scid []byte
+		if err := rows.Scan(&scid); err != nil {
+			return nil, err
+		}
+		items = append(items, scid)
+	}
+	if err := rows.Close(); err != nil {
+		return nil, err
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
+}
+
 const getExtraNodeTypes = `-- name: GetExtraNodeTypes :many
 SELECT node_id, type, value
 FROM graph_node_extra_types
diff --git a/sqldb/sqlc/querier.go b/sqldb/sqlc/querier.go
index e7b4f3f..b3c0857 100644
--- a/sqldb/sqlc/querier.go
+++ b/sqldb/sqlc/querier.go
@@ -48,6 +48,7 @@ type Querier interface {
 	GetChannelsBySCIDRange(ctx context.Context, arg GetChannelsBySCIDRangeParams) ([]GetChannelsBySCIDRangeRow, error)
 	GetChannelsBySCIDWithPolicies(ctx context.Context, arg GetChannelsBySCIDWithPoliciesParams) ([]GetChannelsBySCIDWithPoliciesRow, error)
 	GetChannelsBySCIDs(ctx context.Context, arg GetChannelsBySCIDsParams) ([]GraphChannel, error)
+	GetClosedChannelsSCIDs(ctx context.Context, scids [][]byte) ([][]byte, error)
 	GetDatabaseVersion(ctx context.Context) (int32, error)
 	GetExtraNodeTypes(ctx context.Context, nodeID int64) ([]GraphNodeExtraType, error)
 	// This method may return more than one invoice if filter using multiple fields
diff --git a/sqldb/sqlc/queries/graph.sql b/sqldb/sqlc/queries/graph.sql
index ed0eb8c..f77e504 100644
--- a/sqldb/sqlc/queries/graph.sql
+++ b/sqldb/sqlc/queries/graph.sql
@@ -984,3 +984,8 @@ SELECT EXISTS (
     FROM graph_closed_scids
     WHERE scid = $1
 );
+
+-- name: GetClosedChannelsSCIDs :many
+SELECT scid
+FROM graph_closed_scids
+WHERE scid IN (sqlc.slice('scids')/*SLICE:scids*/);