com.datastax.driver.core.policies

Interface RetryPolicy

All Known Implementing Classes:

DefaultRetryPolicy, DowngradingConsistencyRetryPolicy, FallthroughRetryPolicy, IdempotenceAwareRetryPolicy, LoggingRetryPolicy

public interface RetryPolicy

A policy that defines a default behavior to adopt when a request fails.

Such policy allows to centralize the handling of query retries, allowing to minimize the need for exception catching/handling in business code.

Nested Class Summary

Nested Classes

Modifier and Type	Interface and Description
static class	RetryPolicy.RetryDecision A retry decision to adopt on a Cassandra exception (read/write timeout or unavailable exception).

Method Summary

Modifier and Type	Method and Description
void	close() Gets invoked at cluster shutdown.
void	init(Cluster cluster) Gets invoked at cluster startup.
RetryPolicy.RetryDecision	onReadTimeout(Statement statement, ConsistencyLevel cl, int requiredResponses, int receivedResponses, boolean dataRetrieved, int nbRetry) Defines whether to retry and at which consistency level on a read timeout.
RetryPolicy.RetryDecision	onRequestError(Statement statement, ConsistencyLevel cl, DriverException e, int nbRetry) Defines whether to retry and at which consistency level on an unexpected error.
RetryPolicy.RetryDecision	onUnavailable(Statement statement, ConsistencyLevel cl, int requiredReplica, int aliveReplica, int nbRetry) Defines whether to retry and at which consistency level on an unavailable exception.
RetryPolicy.RetryDecision	onWriteTimeout(Statement statement, ConsistencyLevel cl, WriteType writeType, int requiredAcks, int receivedAcks, int nbRetry) Defines whether to retry and at which consistency level on a write timeout.

Method Detail

onReadTimeout

RetryPolicy.RetryDecision onReadTimeout(Statement statement,
                                        ConsistencyLevel cl,
                                        int requiredResponses,
                                        int receivedResponses,
                                        boolean dataRetrieved,
                                        int nbRetry)

Defines whether to retry and at which consistency level on a read timeout.

Note that this method may be called even if requiredResponses >= receivedResponses if dataPresent is false (see ReadTimeoutException.wasDataRetrieved()).

Parameters:

statement - the original query that timed out.

cl - the requested consistency level of the read that timed out. Note that this can never be a serial consistency level.

requiredResponses - the number of responses that were required to achieve the requested consistency level.

receivedResponses - the number of responses that had been received by the time the timeout exception was raised.

dataRetrieved - whether actual data (by opposition to data checksum) was present in the received responses.

nbRetry - the number of retry already performed for this operation.

Returns:

the retry decision. If RetryDecision.RETHROW is returned, a ReadTimeoutException will be thrown for the operation.

onWriteTimeout

RetryPolicy.RetryDecision onWriteTimeout(Statement statement,
                                         ConsistencyLevel cl,
                                         WriteType writeType,
                                         int requiredAcks,
                                         int receivedAcks,
                                         int nbRetry)

Defines whether to retry and at which consistency level on a write timeout.

Note that if a statement is not idempotent, the driver will never retry it on a write timeout (this method won't even be called).

Parameters:

statement - the original query that timed out.

cl - the requested consistency level of the write that timed out. If the timeout occurred at the "paxos" phase of a Lightweight transaction, then cl will actually be the requested serial consistency level. Beware that serial consistency levels should never be passed to a RetryDecision as this would invariably trigger an InvalidQueryException. Also, when cl is serial, then writeType is always CAS.

writeType - the type of the write that timed out.

requiredAcks - the number of acknowledgments that were required to achieve the requested consistency level.

receivedAcks - the number of acknowledgments that had been received by the time the timeout exception was raised.

nbRetry - the number of retry already performed for this operation.

Returns:

the retry decision. If RetryDecision.RETHROW is returned, a WriteTimeoutException will be thrown for the operation.

onUnavailable

RetryPolicy.RetryDecision onUnavailable(Statement statement,
                                        ConsistencyLevel cl,
                                        int requiredReplica,
                                        int aliveReplica,
                                        int nbRetry)

Defines whether to retry and at which consistency level on an unavailable exception.

Parameters:

statement - the original query for which the consistency level cannot be achieved.

cl - the requested consistency level for the operation. If the operation failed at the "paxos" phase of a Lightweight transaction, then cl will actually be the requested serial consistency level. Beware that serial consistency levels should never be passed to a RetryDecision as this would invariably trigger an InvalidQueryException.

requiredReplica - the number of replica that should have been (known) alive for the operation to be attempted.

aliveReplica - the number of replica that were know to be alive by the coordinator of the operation.

nbRetry - the number of retry already performed for this operation.

Returns:

the retry decision. If RetryDecision.RETHROW is returned, an UnavailableException will be thrown for the operation.

onRequestError

RetryPolicy.RetryDecision onRequestError(Statement statement,
                                         ConsistencyLevel cl,
                                         DriverException e,
                                         int nbRetry)

Defines whether to retry and at which consistency level on an unexpected error.

This method might be invoked in the following situations:

1. On a client timeout, while waiting for the server response (see SocketOptions.getReadTimeoutMillis());
2. On a connection error (socket closed, etc.);
3. When the contacted host replies with an OVERLOADED error or a SERVER_ERROR.

Note that when such an error occurs, there is no guarantee that the mutation has been applied server-side or not. Therefore, if a statement is not idempotent, the driver will never retry it (this method won't even be called).

Parameters:

statement - the original query that failed.

cl - the requested consistency level for the operation. Note that this is not necessarily the achieved consistency level (if any), and it is never a serial one.

e - the exception that caused this request to fail.

nbRetry - the number of retries already performed for this operation.

Returns:

the retry decision. If RetryDecision.RETHROW is returned, the DriverException passed to this method will be thrown for the operation.

init

void init(Cluster cluster)

Gets invoked at cluster startup.

Parameters:

cluster - the cluster that this policy is associated with.

close

void close()

Gets invoked at cluster shutdown.

This gives the policy the opportunity to perform some cleanup, for instance stop threads that it might have started.