Nikolay Izhikov created IGNITE-19369:
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Summary: metadata topic offset must be stored only after commit
Key: IGNITE-19369
URL: https://issues.apache.org/jira/browse/IGNITE-19369
Project: Ignite
Issue Type: Improvement
Components: extensions
Reporter: Ilya Shishkov
Assignee: Ilya Shishkov
Currently, when CDC through Kafka is used there are possible delays in
replication between clusters when {{KafkaToIgniteCdcStreamerApplier}} tries to
update binary metadata and marshaller mappings.
Delays caused by calls of {{KafkaConsumer#poll}} in
{{KafkaToIgniteMetadataUpdater#updateMetadata}} , when meta topic is empty:
# When first {{KafkaToIgniteCdcStreamerApplier}} meets {{META_UPDATE_MARKER}}
it calls {{KafkaToIgniteMetadataUpdater#updateMetadata}} which in turn calls
{{KafkaConsumer#poll}}, which returns immediately [1] when data is present in
metadata topic. If there are few binary types and mappings to update, first
{{KafkaToIgniteCdcStreamerApplier}} will consume all entries from metadata
topic.
# {{KafkaToIgniteCdcStreamerApplier}} consequently call
{{KafkaToIgniteMetadataUpdater#updateMetadata}} for each partition with meta
update marker. All further consequent calls will wait for {{kafkaReqTimeout}}.
# Also there is a bottleneck, when multiple applier threads tries to update
metadata and call synchronized method
{{KafkaToIgniteMetadataUpdater#updateMetadata}}, because
{{KafkaToIgniteMetadataUpdater}} is shared between applier threads.
# Because {{META_UPDATE_MARKER}} is sent twice to each Kafka partition of event
topic from every node: firstly, in case of type mappings updates, secondly, in
case of binary types update there are possible delays up to {{clusterSize x
(topicPartitions x 2 - 1) x kafkaReqTimeout}}.
# Data updates are blocked for Kafka partitions with unprocessed update markers.
# For example for default timeout and 16 Kafka partitions _last partition will
be consumed after 1.5 minutes_ in case of two one-node clusters.
Links:
#
[https://kafka.apache.org/27/javadoc/org/apache/kafka/clients/consumer/KafkaConsumer.html#poll-java.time.Duration-]
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