fix(GODT-2933): Add index to message flags

Should improve performance in join operation and general lookups.

internal/db_impl/sqlite3/migrations.go

@@ -11,6 +11,7 @@ import (
 	v0 "github.com/ProtonMail/gluon/internal/db_impl/sqlite3/v0"
 	v1 "github.com/ProtonMail/gluon/internal/db_impl/sqlite3/v1"
 	v2 "github.com/ProtonMail/gluon/internal/db_impl/sqlite3/v2"
+	v3 "github.com/ProtonMail/gluon/internal/db_impl/sqlite3/v3"
 	"github.com/sirupsen/logrus"
 )
 
@@ -22,6 +23,7 @@ var migrationList = []Migration{
 	&v0.Migration{},
 	&v1.Migration{},
 	&v2.Migration{},
+	&v3.Migration{},
 }
 
 func RunMigrations(ctx context.Context, tx utils.QueryWrapper, generator imap.UIDValidityGenerator) error {

internal/db_impl/sqlite3/v3/migration.go

@@ -0,0 +1,26 @@
+package v3
+
+import (
+	"context"
+	"fmt"
+	v1 "github.com/ProtonMail/gluon/internal/db_impl/sqlite3/v1"
+
+	"github.com/ProtonMail/gluon/imap"
+	"github.com/ProtonMail/gluon/internal/db_impl/sqlite3/utils"
+)
+
+type Migration struct{}
+
+func (m Migration) Run(ctx context.Context, tx utils.QueryWrapper, _ imap.UIDValidityGenerator) error {
+	// Create an index on message id field to speed up lookup queries for message flags.
+	query := fmt.Sprintf("create index message_flags_message_id_index on %v (%v)",
+		v1.MessageFlagsTableName,
+		v1.MessageFlagsFieldMessageID,
+	)
+
+	if _, err := utils.ExecQuery(ctx, tx, query); err != nil {
+		return fmt.Errorf("failed to create connector settings table: %w", err)
+	}
+
+	return nil
+}