Data Multi-tenancy

Multi-tenancy

The term multi-tenancy in general is applied to software development to indicate an architecture in which a single running instance of an application simultaneously serves multiple clients (tenants). This is highly common in SaaS solutions.

Data Multi-tenancy

Isolating information (data, customizations, etc) pertaining to the various tenants is a particular challenge in these systems. This includes the data owned by each tenant stored in the database. It is this last piece, sometimes called multi-tenant data, on which we will focus.

Multi-tenant data approaches

There are 3 main approaches to isolating information in these multi-tenant systems which goes hand-in-hand with different database schema definitions and JDBC setups. Each approach has pros and cons as well as specific techniques and considerations. Multi-TenantData Architecture does a great job of covering these topics.

Separate database

Each tenant's data is kept in a physically separate database instance. JDBC Connections would point specifically to each database, so any pooling would be per-tenant. A general application approach here would be to define a JDBC Connection pool per-tenant and to select the pool to use based on the“tenant identifier” associated with the currently logged in user.

Separate schema

Each tenant's data is kept in a distinct database schema on a single database instance. There are 2 different ways to define JDBC Connections here:

• Connections could point specifically to each schema, as we saw with the Separate databaseapproach. This is an option provided that the driver supports naming the default schema in the connection URL or if the pooling mechanism supports naming a schema to use for its Connections. Using this approach, we would have a distinct JDBC Connection pool per-tenant where the pool to use would be selected based on the “tenant identifier” associated with the currently logged in user.
• Connections could point to the database itself (using some default schema) but the Connections would be altered using the SQL SET SCHEMA (or similar) command. Using this approach, we would have a single JDBC Connection pool for use to service all tenants, but before using the Connection it would be altered to reference the schema named by the “tenant identifier” associated with the currently logged in user.

Partitioned (discriminator) data

All data is kept in a single database schema. The data for each tenant is partitioned by the use of partition value or discriminator. The complexity of this discriminator might range from a simple column value to a complex SQL formula. Again, this approach would use a single Connection pool to service all tenants. However, in this approach the application needs to alter each and every SQL statement sent to the database to reference the “tenant identifier” discriminator.

Data Multi-tenancy in Hibernate

Using Hibernate with multi-tenant data comes down to both an API and then integration piece(s). As usual Hibernate strives to keep the API simple and isolated from any underlying integration complexities. The API is really just defined by passing the tenant identifier as part of opening any session.

Example 16.1. Specifying tenant identifier from SessionFactory

Session session = sessionFactory.withOptions()

        .tenantIdentifier( yourTenantIdentifier )

        ...

        .openSession();

Additionally, when specifying configuration, a org.hibernate.MultiTenancyStrategy should be named using the hibernate.multiTenancy setting. Hibernate will perform validations based on the type of strategy you specify. The strategy here correlates to the isolation approach discussed above.

NONE

(the default) No multi-tenancy is expected. In fact, it is considered an error if a tenant identifier is specified when opening a session using this strategy

            

 SCHEMA

Correlates to the separate schema approach. It is an error to attempt to open a session without a tenant identifier using this strategy. Additionally, aorg.hibernate.service.jdbc.connections.spi.MultiTenantConnectionProvider must be specified.

DATABASE

Correlates to the separate database approach. It is an error to attempt to open a session without a tenant identifier using this strategy. Additionally, aorg.hibernate.service.jdbc.connections.spi.MultiTenantConnectionProvider must be specified.

DISCRIMINATOR

Correlates to the partitioned (discriminator) approach. It is an error to attempt to open a session without a tenant identifier using this strategy. This strategy is not yet implemented in Hibernate as of 4.0 and 4.1. Its support is planned for 5.0.

 Google doc link