GAE Multitenancy and Transaction - Go

Question

If I use multitenancy feature on GAE Datastore, will a datastore transaction lock be applied per tenant as well? Or if a tenant is using a datastore transaction, all of the other tenants will have to wait until the tenant's transaction is finished?

Answer 1

Two things to note:

1. Namespace is part of the key of the entity, so transaction will work only for entities that are part of your transaction. Entities of other namespaces will not be affected even if they have same IDs.

2. Transactions on GAE do not do locking, instead they use optimistic concurrency control. So transactions are never blocking, just when two transactions operate on same entities the second will fail and then go runtime will try to repeat it up to three times. This auto-retry is the reason why your transactions should be idempotent (= running the code multiple times should produce same end result).

Answer 2

The scope of transactions is limited to entity groups. Namespaces (multi tenancy) don't define an entity group on their own. You need the key (plus potential ancestor).

The only clash will be with multiple requests writing to the same entity group. With namespaces in use that could not happen between tenants.

https://developers.google.com/appengine/docs/go/datastore/entities#Go_Ancestor_paths