The term multitenancy, 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. 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 multitenant data, that we will focus on.
There are three main approaches to isolating information in these multitenant systems which go hand-in-hand with different database schema definitions and JDBC setups.
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Note
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Each multitenancy strategy has pros and cons as well as specific techniques and considerations. Such topics are beyond the scope of this documentation. |
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.
Each tenant’s data is kept in a distinct database schema on a single database instance. There are two different ways to define JDBC Connections here:
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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.
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.
Using Hibernate with multitenant 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.
SessionFactorylink:../../../../../../../hibernate-core/src/test/java/org/hibernate/orm/test/multitenancy/AbstractMultiTenancyTest.java[role=include]For the partitioned data approach, each entity representing partitioned data must declare a field
annotated @TenantId.
@TenantId usage example@Entity
public class Account {
@Id @GeneratedValue Long id;
@TenantId String tenantId;
...
}The @TenantId field is automatically populated by Hibernate when an instance is made
persistent.
When using either the separate database or separate schema approach, Hibernate needs to be able to obtain connections in a tenant-specific manner.
That is the role of the MultiTenantConnectionProvider contract.
Application developers will need to provide an implementation of this contract.
Most of its methods are extremely self-explanatory.
The only ones which might not be are getAnyConnection and releaseAnyConnection.
It is important to note also that these methods do not accept the tenant identifier.
Hibernate uses these methods during startup to perform various configuration, mainly via the java.sql.DatabaseMetaData object.
The MultiTenantConnectionProvider to use can be specified in a number of ways:
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Use the
hibernate.multi_tenant_connection_providersetting. It could name aMultiTenantConnectionProviderinstance, aMultiTenantConnectionProviderimplementation class reference or aMultiTenantConnectionProviderimplementation class name. -
Provided by the configured
BeanContainer. -
Passed directly to the
org.hibernate.boot.registry.StandardServiceRegistryBuilder. -
If none of the above options match, but the settings do specify a
hibernate.connection.datasourcevalue, Hibernate will assume it should use the specificDataSourceBasedMultiTenantConnectionProviderImplimplementation which works on a number of pretty reasonable assumptions when running inside of an app server and using onejavax.sql.DataSourceper tenant. See its Javadocs for more details.
The following example portrays a MultiTenantConnectionProvider implementation that handles multiple ConnectionProviders.
MultiTenantConnectionProvider implementationlink:../../../../../../../hibernate-core/src/test/java/org/hibernate/orm/test/multitenancy/ConfigurableMultiTenantConnectionProvider.java[role=include]The ConfigurableMultiTenantConnectionProvider can be set up as follows:
MultiTenantConnectionProvider usage examplelink:../../../../../../../hibernate-core/src/test/java/org/hibernate/orm/test/multitenancy/AbstractMultiTenancyTest.java[role=include]When using multitenancy, it’s possible to save an entity with the same identifier across different tenants:
link:../../../../../../../hibernate-core/src/test/java/org/hibernate/orm/test/multitenancy/AbstractMultiTenancyTest.java[role=include]org.hibernate.context.spi.CurrentTenantIdentifierResolver is a contract for Hibernate to be able to resolve what the application considers the current tenant identifier.
The implementation to use can be either passed directly to Configuration via its setCurrentTenantIdentifierResolver method,
or be specified via the hibernate.tenant_identifier_resolver setting, or be provided by the configured BeanContainer.
There are two situations where CurrentTenantIdentifierResolver is used:
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The first situation is when the application is using the
org.hibernate.context.spi.CurrentSessionContextfeature in conjunction with multitenancy. In the case of the current-session feature, Hibernate will need to open a session if it cannot find an existing one in scope. However, when a session is opened in a multitenant environment, the tenant identifier has to be specified. This is where theCurrentTenantIdentifierResolvercomes into play; Hibernate will consult the implementation you provide to determine the tenant identifier to use when opening the session. In this case, it is required that aCurrentTenantIdentifierResolveris supplied. -
The other situation is when you do not want to explicitly specify the tenant identifier all the time. If a
CurrentTenantIdentifierResolverhas been specified, Hibernate will use it to determine the default tenant identifier to use when opening the session.
Additionally, if the CurrentTenantIdentifierResolver implementation returns true for its validateExistingCurrentSessions method, Hibernate will make sure any existing sessions that are found in scope have a matching tenant identifier.
This capability is only pertinent when the CurrentTenantIdentifierResolver is used in current-session settings.
Multitenancy support in Hibernate works seamlessly with the Hibernate second level cache. The key used to cache data encodes the tenant identifier.
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Note
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Currently, schema export will not really work with multitenancy. |
When using multitenancy, you might want to configure each tenant-specific Session differently.
For instance, each tenant could specify a different time zone configuration.
link:../../../../../../../hibernate-core/src/test/java/org/hibernate/orm/test/multitenancy/DatabaseTimeZoneMultiTenancyTest.java[role=include]The registerConnectionProvider method is used to define the tenant-specific context.
registerConnectionProvider method used for defining the tenant-specific contextlink:../../../../../../../hibernate-core/src/test/java/org/hibernate/orm/test/multitenancy/DatabaseTimeZoneMultiTenancyTest.java[role=include]For our example, the tenant-specific context is held in the connectionProviderMap and timeZoneTenantMap.
link:../../../../../../../hibernate-core/src/test/java/org/hibernate/orm/test/multitenancy/DatabaseTimeZoneMultiTenancyTest.java[role=include]Now, when building the Hibernate Session, aside from passing the tenant identifier,
we could also configure the Session to use the tenant-specific time zone.
Session can be configured using the tenant-specific contextlink:../../../../../../../hibernate-core/src/test/java/org/hibernate/orm/test/multitenancy/DatabaseTimeZoneMultiTenancyTest.java[role=include]So, if we set the useTenantTimeZone parameter to true, Hibernate will persist the Timestamp properties using the
tenant-specific time zone. As you can see in the following example, the Timestamp is successfully retrieved
even if the currently running JVM uses a different time zone.
useTenantTimeZone allows you to persist a Timestamp in the provided time zonelink:../../../../../../../hibernate-core/src/test/java/org/hibernate/orm/test/multitenancy/DatabaseTimeZoneMultiTenancyTest.java[role=include]However, behind the scenes, we can see that Hibernate has saved the created_on property in the tenant-specific time zone.
The following example shows you that the Timestamp was saved in the UTC time zone, hence the offset displayed in the
test output.
useTenantTimeZone property set to false, the Timestamp is fetched in the tenant-specific time zonelink:../../../../../../../hibernate-core/src/test/java/org/hibernate/orm/test/multitenancy/DatabaseTimeZoneMultiTenancyTest.java[role=include]link:extras/multitenacy-hibernate-not-applying-timezone-configuration-example.sql[role=include]Notice that for the Eastern European Time time zone, the time zone offset was 2 hours when the test was executed.