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https://issues.apache.org/jira/browse/FLINK-4280?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15697189#comment-15697189
]
ASF GitHub Bot commented on FLINK-4280:
---------------------------------------
Github user tzulitai commented on a diff in the pull request:
https://github.com/apache/flink/pull/2509#discussion_r89664876
--- Diff:
flink-streaming-connectors/flink-connector-kafka-0.9/src/main/java/org/apache/flink/streaming/connectors/kafka/internal/Kafka09Fetcher.java
---
@@ -218,26 +221,57 @@ public void run() {
}
}
- // seek the consumer to the initial offsets
+ List<KafkaTopicPartition> partitionsWithNoOffset = new
ArrayList<>();
for (KafkaTopicPartitionState<TopicPartition> partition
: subscribedPartitions()) {
if (partition.isOffsetDefined()) {
LOG.info("Partition {} has restored
initial offsets {} from checkpoint / savepoint; seeking the consumer " +
"to position {}",
partition.getKafkaPartitionHandle(), partition.getOffset(),
partition.getOffset() + 1);
consumer.seek(partition.getKafkaPartitionHandle(), partition.getOffset() + 1);
} else {
- // for partitions that do not have
offsets restored from a checkpoint/savepoint,
- // we need to define our internal
offset state for them using the initial offsets retrieved from Kafka
- // by the KafkaConsumer, so that they
are correctly checkpointed and committed on the next checkpoint
+
partitionsWithNoOffset.add(partition.getKafkaTopicPartition());
+ }
+ }
- long fetchedOffset =
consumer.position(partition.getKafkaPartitionHandle());
+ if (partitionsWithNoOffset.size() ==
subscribedPartitions().length) {
+ // if all partitions have no initial offsets,
that means we're starting fresh
+ switch (startupMode) {
+ case EARLIEST:
+ LOG.info("Setting starting
point as earliest offset for partitions {}", partitionsWithNoOffset);
+
+
seekPartitionsToBeginning(consumer,
convertKafkaPartitions(subscribedPartitions()));
--- End diff --
The problem with this one is that the `seekToBeginning` method broke
compatibility from 0.8 to 0.9+.
In 0.8, it's `seekToBeginning(TopicPartition...)` while in 0.9+ it's
`seekToBeginning(Collection<TopicPartition>)`.
I'll integrate these seek methods into the `KafkaConsumerCallBridge`
introduced in a recent PR. I'll be inevitable that we must redundantly do the
Array -> List conversion because our `subscribedPartitions` is an Array, while
0.9+ methods take an API. For the 0.8 methods, instead of converting the list
back to an array, I'll just iterate over the list and call
`seekPartitionsToBeginning` for each one.
> New Flink-specific option to set starting position of Kafka consumer without
> respecting external offsets in ZK / Broker
> -----------------------------------------------------------------------------------------------------------------------
>
> Key: FLINK-4280
> URL: https://issues.apache.org/jira/browse/FLINK-4280
> Project: Flink
> Issue Type: New Feature
> Components: Kafka Connector
> Reporter: Tzu-Li (Gordon) Tai
> Assignee: Tzu-Li (Gordon) Tai
> Fix For: 1.2.0
>
>
> Currently, to start reading from the "earliest" and "latest" position in
> topics for the Flink Kafka consumer, users set the Kafka config
> {{auto.offset.reset}} in the provided properties configuration.
> However, the way this config actually works might be a bit misleading if
> users were trying to find a way to "read topics from a starting position".
> The way the {{auto.offset.reset}} config works in the Flink Kafka consumer
> resembles Kafka's original intent for the setting: first, existing external
> offsets committed to the ZK / brokers will be checked; if none exists, then
> will {{auto.offset.reset}} be respected.
> I propose to add Flink-specific ways to define the starting position, without
> taking into account the external offsets. The original behaviour (reference
> external offsets first) can be changed to be a user option, so that the
> behaviour can be retained for frequent Kafka users that may need some
> collaboration with existing non-Flink Kafka consumer applications.
> How users will interact with the Flink Kafka consumer after this is added,
> with a newly introduced {{flink.starting-position}} config:
> {code}
> Properties props = new Properties();
> props.setProperty("flink.starting-position", "earliest/latest");
> props.setProperty("auto.offset.reset", "..."); // this will be ignored (log a
> warning)
> props.setProperty("group.id", "...") // this won't have effect on the
> starting position anymore (may still be used in external offset committing)
> ...
> {code}
> Or, reference external offsets in ZK / broker:
> {code}
> Properties props = new Properties();
> props.setProperty("flink.starting-position", "external-offsets");
> props.setProperty("auto.offset.reset", "earliest/latest"); // default will be
> latest
> props.setProperty("group.id", "..."); // will be used to lookup external
> offsets in ZK / broker on startup
> ...
> {code}
> A thing we would need to decide on is what would the default value be for
> {{flink.starting-position}}.
> Two merits I see in adding this:
> 1. This compensates the way users generally interpret "read from a starting
> position". As the Flink Kafka connector is somewhat essentially a
> "high-level" Kafka consumer for Flink users, I think it is reasonable to add
> Flink-specific functionality that users will find useful, although it wasn't
> supported in Kafka's original consumer designs.
> 2. By adding this, the idea that "the Kafka offset store (ZK / brokers) is
> used only to expose progress to the outside world, and not used to manipulate
> how Kafka topics are read in Flink (unless users opt to do so)" is even more
> definite and solid. There was some discussion in this PR
> (https://github.com/apache/flink/pull/1690, FLINK-3398) on this aspect. I
> think adding this "decouples" more Flink's internal offset checkpointing from
> the external Kafka's offset store.
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