Status
Current state: Voting
Discussion thread: here
JIRA: here
Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).
Motivation
In KAFKA-4879, we first noticed that KafkaConsumer will hang forever when deleting a topic. However, after looking closer, we have found that in general the position(TopicPartition topicPartition)
,commitSync()
, committed()
, and poll()
(since pollOnce()
calls updateFetchPositions()
which blocks through a series of callbacks) method will continue to block indefinitely unless the offsets are retrieved for the provided TopicPartition
. To avoid this scenario from occurring:
- A secondary method will be added, but with an extra parameter
timeout
,as well as a variable giving the TimeUnit, which bounds the amount of time spent. - A
TimeoutException
will be thrown once the amount of time spent exceedstimeout.
Public Interfaces
A TimeoutException
will be thrown when the time spent exceeds requestTimeoutMs
:
/** * Get the offset of the <i>next record</i> that will be fetched (if a record with that offset exists). * This method may issue a remote call to the server if there is no current position for the given partition. * <p> * This call will block until either the position could be determined or an unrecoverable error is * encountered (in which case it is thrown to the caller). * * @param partition The partition to get the position for + * @param timeout The maximum duration of the method + * @param timeunit The time unit to which timeout refers to * @return The current position of the consumer (that is, the offset of the next record to be fetched) * @throws IllegalArgumentException if the provided TopicPartition is not assigned to this consumer * @throws org.apache.kafka.clients.consumer.InvalidOffsetException if no offset is currently defined for * the partition * @throws org.apache.kafka.common.errors.WakeupException if {@link #wakeup()} is called before or while this * function is called * @throws org.apache.kafka.common.errors.InterruptException if the calling thread is interrupted before or while * this function is called + * @throws org.apache.kafka.common.errors.TimeoutException if time spent blocking for offsets exceed requestTimeoutMs * @throws org.apache.kafka.common.errors.AuthenticationException if authentication fails. See the exception for more details * @throws org.apache.kafka.common.errors.AuthorizationException if not authorized to the topic or to the * configured groupId. See the exception for more details * @throws org.apache.kafka.common.KafkaException for any other unrecoverable errors */ + public long position(TopicPartition partition, long timeout, TimeUnit unit);
Similarily, this will also be applied to other methods in KafkaConsumer that blocks indefinitely.
/** * Get the last committed offset for the given partition (whether the commit happened by this process or * another). This offset will be used as the position for the consumer in the event of a failure. * <p> * This call will block to do a remote call to get the latest committed offsets from the server. * * @param partition The partition to check + * @param timeout The maximum duration of the method + * @param timeunit The unit of time timeout refers to * @return The last committed offset and metadata or null if there was no prior commit * @throws org.apache.kafka.common.errors.WakeupException if {@link #wakeup()} is called before or while this * function is called * @throws org.apache.kafka.common.errors.InterruptException if the calling thread is interrupted before or while * this function is called * @throws org.apache.kafka.common.errors.AuthenticationException if authentication fails. See the exception for more details * @throws org.apache.kafka.common.errors.AuthorizationException if not authorized to the topic or to the * configured groupId. See the exception for more details * @throws org.apache.kafka.common.KafkaException for any other unrecoverable errors + * @throws TimeoutException if method exceeds maximum given time */ @Override public OffsetAndMetadata committed(TopicPartition partition, final long timeout, final Timeunit timeunit) { acquireAndEnsureOpen(); final long totalWaitTime = determineWaitTimeInMilliseconds(timeout, timeunit); try { Map<TopicPartition, OffsetAndMetadata> offsets = coordinator.fetchCommittedOffsets(Collections.singleton(partition), totalWaitTime); return offsets.get(partition); } finally { release(); } } /** * Commit the specified offsets for the specified list of topics and partitions. * <p> * This commits offsets to Kafka. The offsets committed using this API will be used on the first fetch after every * rebalance and also on startup. As such, if you need to store offsets in anything other than Kafka, this API * should not be used. The committed offset should be the next message your application will consume, * i.e. lastProcessedMessageOffset + 1. * <p> * This is a synchronous commits and will block until either the commit succeeds or an unrecoverable error is * encountered (in which case it is thrown to the caller). * <p> * Note that asynchronous offset commits sent previously with the {@link #commitAsync(OffsetCommitCallback)} * (or similar) are guaranteed to have their callbacks invoked prior to completion of this method. * * @param offsets A map of offsets by partition with associated metadata + * @param timeout Maximum duration of methof + * @param timeunit The unit of time which timeout refers to * @throws org.apache.kafka.clients.consumer.CommitFailedException if the commit failed and cannot be retried. * This can only occur if you are using automatic group management with {@link #subscribe(Collection)}, * or if there is an active group with the same groupId which is using group management. * @throws org.apache.kafka.common.errors.WakeupException if {@link #wakeup()} is called before or while this * function is called * @throws org.apache.kafka.common.errors.InterruptException if the calling thread is interrupted before or while * this function is called * @throws org.apache.kafka.common.errors.AuthenticationException if authentication fails. See the exception for more details * @throws org.apache.kafka.common.errors.AuthorizationException if not authorized to the topic or to the * configured groupId. See the exception for more details * @throws java.lang.IllegalArgumentException if the committed offset is negative * @throws org.apache.kafka.common.KafkaException for any other unrecoverable errors (e.g. if offset metadata * is too large or if the topic does not exist). */ @Override public void commitSync(final Map<TopicPartition, OffsetAndMetadata> offsets, final long timeout, final Timeunit timeunit) { final long totalWaitTime = determineWaitTimeInMilliseconds(timeout, timeunit); acquireAndEnsureOpen(); try { coordinator.commitOffsetsSync(new HashMap<>(offsets), totalWaitTime); } finally { release(); } }
Another change shall be made to KafkaConsumer#poll()
, due to its call to updateFetchPositions()
which blocks indefinitely. To combat this, poll() will automatically return
if the time limit is hit.
Proposed Changes
A TimeoutException will be thrown if time spent of position()
method exceeds requestTimeoutMs
.
Compatibility, Deprecation, and Migration Plan
Since old methods will not be modified, preexisting data frameworks will not be affected. However, these methods might be deprecated in favor of methods which are bound by a specific time limit.
Rejected Alternatives
One alternative was to add a timeout
parameter to position()
and other methods. However, the changes made by the user will be much more extensive then basing the time constraint on requestTimeoutMs
because the method signature has been changed.
Another possibility was the usage of requestTimeoutMs
to bound position()
, however, this would make the method highly inflexible, especially since requestTimeoutMs
is already being used by multiple other methods.