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 |
---|---|
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.
|
public static final DefaultRetryPolicy INSTANCE
public RetryPolicy.RetryDecision onReadTimeout(Statement statement, ConsistencyLevel cl, int requiredResponses, int receivedResponses, boolean dataRetrieved, int nbRetry)
Note that this method may be called even if requiredResponses >= receivedResponses
if dataPresent
is false
(see ReadTimeoutException.wasDataRetrieved()
).
This implementation 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 RetryPolicy
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.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)
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).
This implementation 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 RetryPolicy
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.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 implementation does the following:
nbRetry == 0
), it triggers a retry on the next host
in the query plan with the same consistency level (RetryDecision#tryNextHost(null)
.
The rationale is that the first coordinator might have been network-isolated from all
other nodes (thinking they're down), but still able to communicate with the client; in
that case, retrying on the same host has almost no chance of success, but moving to the
next host might solve the issue.
onUnavailable
in interface RetryPolicy
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.RetryDecision.RETHROW
is returned, an UnavailableException
will be thrown for the operation.public RetryPolicy.RetryDecision onRequestError(Statement statement, ConsistencyLevel cl, DriverException e, int nbRetry)
This method might be invoked in the following situations:
SocketOptions.getReadTimeoutMillis()
);
OVERLOADED
error, SERVER_ERROR
,
READ_FAILURE
or WRITE_FAILURE
.
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).
onRequestError
in interface RetryPolicy
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.RetryDecision.RETHROW
is returned, the DriverException
passed to this method will be thrown for the operation.public void init(Cluster cluster)
RetryPolicy
init
in interface RetryPolicy
cluster
- the cluster that this policy is associated with.public void close()
RetryPolicy
This gives the policy the opportunity to perform some cleanup, for instance stop threads that it might have started.
close
in interface RetryPolicy
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