public class DefaultRetryPolicy extends Object implements RetryPolicy
This policy retries queries in only two cases:
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.
RetryPolicy.RetryDecision| Modifier and Type | Field and Description |
|---|---|
static DefaultRetryPolicy |
INSTANCE |
| Modifier and Type | Method and Description |
|---|---|
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 |
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.
|
public static final DefaultRetryPolicy INSTANCE
public RetryPolicy.RetryDecision onReadTimeout(Statement statement, ConsistencyLevel cl, int requiredResponses, int receivedResponses, boolean dataRetrieved, int nbRetry)
This method triggers a maximum of one retry, and only if enough replicas 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 chance of success.
onReadTimeout in interface RetryPolicystatement - the original query that timed out.cl - the original consistency level of the read that timed out.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 retries already performed for this operation.RetryDecision.retry(cl) if no retry attempt has yet been tried and
receivedResponses >= requiredResponses && !dataRetrieved, RetryDecision.rethrow() otherwise.public RetryPolicy.RetryDecision onWriteTimeout(Statement statement, ConsistencyLevel cl, WriteType writeType, int requiredAcks, int receivedAcks, int nbRetry)
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 nodes 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 chance of success.
onWriteTimeout in interface RetryPolicystatement - the original query that timed out.cl - the original consistency level of the write that timed out.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.RetryDecision.retry(cl) if no retry attempt has yet been tried and
writeType == WriteType.BATCH_LOG, RetryDecision.rethrow() otherwise.public RetryPolicy.RetryDecision onUnavailable(Statement statement, ConsistencyLevel cl, int requiredReplica, int aliveReplica, int nbRetry)
This method triggers a retry iff no retry has been executed before
(nbRetry == 0), with
RetryDecision.tryNextHost(cl),
otherwise it throws an exception. The retry will be processed on the next host
in the query plan according to the current Load Balancing Policy.
Where retrying on the same host in the event of an Unavailable exception
has almost no chance of success, if the first replica tried happens to
be "network" isolated from all the other nodes but can still answer to
the client, it makes sense to retry the query on another node.
onUnavailable in interface RetryPolicystatement - the original query for which the consistency level cannot
be achieved.cl - the original consistency level for the operation.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.RetryDecision.rethrow().Copyright © 2012–2015. All rights reserved.