A multi-tenant system, comprises a main storage system including: a monolithic database storing global records associated with global objects, each global object including global fields common for all tenants; a monolithic application configured to process a particular global record storage request by instructing the monolithic database to store particular global field values of the particular global record for a particular tenant, and to process a particular global record fetch request by instructing the monolithic database to retrieve the one or more particular global field values; a custom object storage system including: a custom object database configured to store custom records associated with one or more custom objects, each custom object including one or more custom fields for a tenant; a custom object record service configured to process a particular custom record storage request by instructing the custom object database to store one or more particular custom field values for the tenant, and to process a particular custom record fetch request by instructing the custom object database to retrieve the one or more particular custom field values; and a query engine configured to receive a query, fetch relevant global records from the monolithic database, fetch relevant custom records from the custom object database, and generate a query response.