Class DefaultRetryPolicy

The default retry policy.

This policy retries queries in only two cases:

On a read timeout, if enough replica replied but data was not retrieved.
On a write timeout, if we timeout while writting the distributed log used by batch statements.

This retry policy is conservative in that it will never retry with a different consistency level than the one of the initial operation.

In some cases, it may be convenient to use a more aggressive retry policy like DowngradingConsistencyRetryPolicy.

Inheritance

object

DefaultRetryPolicy

Implements

IExtendedRetryPolicy

IRetryPolicy

Inherited Members

object.Equals(object)

object.Equals(object, object)

object.GetHashCode()

object.GetType()

object.MemberwiseClone()

object.ReferenceEquals(object, object)

object.ToString()

Namespace: Cassandra

Assembly: Cassandra.dll

Syntax

public class DefaultRetryPolicy : IExtendedRetryPolicy, IRetryPolicy

Methods

OnReadTimeout(IStatement, ConsistencyLevel, int, int, bool, int)

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

This method triggers a maximum of one retry, and only if enough replica had responded to the read request but data was not retrieved amongst those. Indeed, that case usually means that enough replica are alive to satisfy the consistency but the coordinator picked a dead one for data retrieval, not having detected that replica as dead yet. The reasoning for retrying then is that by the time we get the timeout the dead replica will likely have been detected as dead and the retry has a high change of success.

Declaration

public RetryDecision OnReadTimeout(IStatement query, ConsistencyLevel cl, int requiredResponses, int receivedResponses, bool dataRetrieved, int nbRetry)

Parameters

Type	Name	Description
IStatement	query	the original query that timed out.
ConsistencyLevel	cl	the original consistency level of the read that timed out.
int	requiredResponses	the number of responses that were required to achieve the requested consistency level.
int	receivedResponses	the number of responses that had been received by the time the timeout exception was raised.
bool	dataRetrieved	whether actual data (by opposition to data checksum) was present in the received responses.
int	nbRetry	the number of retry already performed for this operation.

Returns

Type	Description
RetryDecision	`RetryDecision.Retry(cl)` if no retry attempt has yet been tried and `receivedResponses >= requiredResponses && !dataRetrieved`, `RetryDecision.Rethrow()` otherwise.

OnRequestError(IStatement, Configuration, Exception, int)

The default implementation triggers a retry on the next host in the query plan with the same consistency level, regardless of the statement's idempotence, for historical reasons.

Declaration

public RetryDecision OnRequestError(IStatement statement, Configuration config, Exception ex, int nbRetry)

Parameters

Type	Name	Description
IStatement	statement
Configuration	config
Exception	ex
int	nbRetry

Returns

Type	Description
RetryDecision

OnUnavailable(IStatement, ConsistencyLevel, int, int, int)

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

This method never retries as a retry on an unavailable exception using the same consistency level has almost no change of success.

Declaration

public RetryDecision OnUnavailable(IStatement query, ConsistencyLevel cl, int requiredReplica, int aliveReplica, int nbRetry)

Parameters

Type	Name	Description
IStatement	query	the original query for which the consistency level cannot be achieved.
ConsistencyLevel	cl	the original consistency level for the operation.
int	requiredReplica	the number of replica that should have been (known) alive for the operation to be attempted.
int	aliveReplica	the number of replica that were know to be alive by the coordinator of the operation.
int	nbRetry	the number of retry already performed for this operation.

Returns

Type	Description
RetryDecision	`RetryDecision.rethrow()`.

OnWriteTimeout(IStatement, ConsistencyLevel, string, int, int, int)

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

This method triggers a maximum of one retry, and only in the case of a WriteType.BATCH_LOG write. The reasoning for the retry in that case is that write to the distributed batch log is tried by the coordinator of the write against a small subset of all the node alive in the local datacenter. Hence, a timeout usually means that none of the nodes in that subset were alive but the coordinator hasn't' detected them as dead. By the time we get the timeout the dead nodes will likely have been detected as dead and the retry has thus a high change of success.

Declaration

public RetryDecision OnWriteTimeout(IStatement query, ConsistencyLevel cl, string writeType, int requiredAcks, int receivedAcks, int nbRetry)

Parameters

Type	Name	Description
IStatement	query	the original query that timeouted.
ConsistencyLevel	cl	the original consistency level of the write that timeouted.
string	writeType	the type of the write that timeouted.
int	requiredAcks	the number of acknowledgments that were required to achieve the requested consistency level.
int	receivedAcks	the number of acknowledgments that had been received by the time the timeout exception was raised.
int	nbRetry	the number of retry already performed for this operation.

Returns

Type	Description
RetryDecision	`RetryDecision.retry(cl)` if no retry attempt has yet been tried and `writeType == WriteType.BATCH_LOG`, `RetryDecision.rethrow()` otherwise.

Implements

IExtendedRetryPolicy

IRetryPolicy