com.google.cloud.spanner

Interface TransactionRunner

public interface TransactionRunner

An interface for executing a body of work in the context of a read-write transaction, with retries for transaction aborts. See TransactionContext for a description of transaction semantics. TransactionRunner instances are obtained by calling DatabaseClient.readWriteTransaction().

A TransactionRunner instance can only be used for a single invocation of run(TransactionCallable).

Nested Class Summary

Nested Classes

Modifier and Type	Interface and Description
static interface	TransactionRunner.TransactionCallable<T> A unit of work to be performed in the context of a transaction.

Method Summary

Modifier and Type	Method and Description
TransactionRunner	allowNestedTransaction() Allows overriding the default behaviour of blocking nested transactions.
com.google.cloud.Timestamp	getCommitTimestamp() Returns the timestamp at which the transaction committed.
<T> T	run(TransactionRunner.TransactionCallable<T> callable) Executes a read-write transaction, with retries as necessary.

Method Detail

run

@Nullable
<T> T run(TransactionRunner.TransactionCallable<T> callable)

Executes a read-write transaction, with retries as necessary. The work to perform in each transaction attempt is defined by callable, which may return an object as the result of the work. callable will be retried if a transaction attempt aborts; implementations must be prepared to be called more than once. Any writes buffered by callable will only be applied if the transaction commits successfully. Similarly, the value produced by callable will only be returned by this method if the transaction commits successfully.

callable is allowed to raise an unchecked exception. Typically this prevents further attempts to execute callable, and the exception will propagate from this method call. However, if a read or query in callable detected that the transaction aborted, callable will be retried even if it raised an exception.

getCommitTimestamp

com.google.cloud.Timestamp getCommitTimestamp()

Returns the timestamp at which the transaction committed. This method may only be called once run(TransactionCallable) has returned normally.

allowNestedTransaction

TransactionRunner allowNestedTransaction()

Allows overriding the default behaviour of blocking nested transactions.

Note that the client library does not maintain any information regarding the nesting structure. If an outer transaction fails and an inner transaction succeeds, upon retry of the outer transaction, the inner transaction will be re-executed.

Use with care when certain that the inner transaction is idempotent. Avoid doing this when accessing the same db. There might be legitimate uses where access need to be made across DBs for instance.

E.g. of nesting that is discouraged, see nestedReadWriteTxnThrows nestedReadOnlyTxnThrows, nestedBatchTxnThrows, nestedSingleUseReadTxnThrows

Returns:

this object