Transactions

A transaction is a set of operations on one or more entities. Each transaction is guaranteed to be atomic, meaning that transactions are never partially applied. Either all of the operations in the transaction are applied, or none of them are applied.

Using transactions

Transactions expire after 270 seconds or if idle for 60 seconds.

An operation may fail when:

• Too many concurrent modifications are attempted on the same entity.
• The transaction exceeds a resource limit.
• The Datastore mode database encounters an internal error.

In all these cases, the Datastore API returns an error.

Transactions are an optional feature. You're not required to use transactions to perform database operations.

An application can execute a set of statements and operations in a single transaction, such that if any statement or operation raises an exception, none of the database operations in the set are applied. The application defines the actions to perform in the transaction.

The following snippet shows how to perform a transaction. It transfers money from one account to another.

private void TransferFunds(Key fromKey, Key toKey, long amount)
{
    using (var transaction = _db.BeginTransaction())
    {
        var entities = transaction.Lookup(fromKey, toKey);
        entities