Interface TransactionRunner
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public interface TransactionRunner
An interface for executing a body of work in the context of a read-write transaction, with retries for transaction aborts. SeeTransactionContext
for a description of transaction semantics.TransactionRunner
instances are obtained by callingSession#readWriteTransaction()
.A
TransactionRunner
instance can only be used for a single invocation ofrun(TransactionCallable)
.
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Nested Class Summary
Nested Classes Modifier and Type Interface Description static interface
TransactionRunner.TransactionCallable<T>
A unit of work to be performed in the context of a transaction.
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Method Summary
All Methods Instance Methods Abstract Methods Modifier and Type Method Description TransactionRunner
allowNestedTransaction()
Allows overriding the default behaviour of blocking nested transactions.CommitResponse
getCommitResponse()
Returns theCommitResponse
of this transaction.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.
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Method Detail
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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 bycallable
, 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 bycallable
will only be applied if the transaction commits successfully. Similarly, the value produced bycallable
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 executecallable
, and the exception will propagate from this method call. However, if a read or query incallable
detected that the transaction aborted,callable
will be retried even if it raised an exception.
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getCommitTimestamp
com.google.cloud.Timestamp getCommitTimestamp()
Returns the timestamp at which the transaction committed. This method may only be called oncerun(TransactionCallable)
has returned normally.
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getCommitResponse
CommitResponse getCommitResponse()
Returns theCommitResponse
of this transaction.
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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
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