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https://issues.apache.org/jira/browse/TWILL-199?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15685666#comment-15685666
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ASF GitHub Bot commented on TWILL-199:
--------------------------------------
Github user maochf commented on a diff in the pull request:
https://github.com/apache/twill/pull/16#discussion_r89042093
--- Diff:
twill-core/src/main/java/org/apache/twill/kafka/client/KafkaOffsetProvider.java
---
@@ -0,0 +1,36 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.twill.kafka.client;
+
+/**
+ * Define interface that could provide a method to check whether a message
meets a given condition. If the condition is
+ * not met, the method will return the next offset to continue searching
for the message meeting this condition.
+ */
+public interface KafkaOffsetProvider {
+
+ /**
+ * Check whether a message meets a given condition. If the condition is
not met, return the next offset to
+ * continue searching for the message meeting this condition.
+ * @param message {@link FetchedMessage} to check.
+ * @return A {@code long} larger than zero as the next offset to
continue searching for the message meeting the
+ * given condition if the current message doesn't meet the
condition. Return {code 0} if the current
+ * message meets the given condition. Return the earliest offset
{@code -2} if no message meeting the
+ * condition can be found.
+ */
+ public long getCandidateOffset(FetchedMessage message);
--- End diff --
I wanted to mean that the offset returned is the next message to be
checked, but it is not guaranteed to satisfy the given condition.
> Get next offset and handle offset error in KafkaConsumer.MessageCallback
> ------------------------------------------------------------------------
>
> Key: TWILL-199
> URL: https://issues.apache.org/jira/browse/TWILL-199
> Project: Apache Twill
> Issue Type: Improvement
> Reporter: Chengfeng Mao
>
> The method {{void onReceived(Iterator<FetchedMessage> messages)}} in
> {{KafkaConsumer.MessageCallback}} can be more flexible with the change to
> {{Long onReceived(Iterator<FetchedMessage> messages)}} so that it can provide
> additional functionalities:
> 1. To return the next offset to be fetched
> 2. To handle offset non-existence or offset mismatch error and take action on
> the error
> This method will return null for backward compatibility when it doesn't need
> to provide the next offset.
> In concrete implementation, a class of a new interface
> {{KafkaOffsetProvider}} can be added as a member in
> {{KafkaConsumer.MessageCallback}} to perform the offset error handling and
> provide the next offset. Besides, {{KafkaOffsetProvider}} also has methods to
> provide the following functionalities:
> 1. To fetch earliest/latest offset in Kafka
> 2. To find the offset of a message with timestamp equal to the given
> timestamp in Kafka
> For backward compatibility, if {{KafkaOffsetProvider}} instance is not
> provided, its default value will be null and none of its methods will be
> called.
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