[
https://issues.apache.org/jira/browse/KAFKA-13289?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17464313#comment-17464313
]
Eugen Dück edited comment on KAFKA-13289 at 12/24/21, 3:16 AM:
---------------------------------------------------------------
As the "Skipping record for expired segment" log indicates the possibility of
message loss, and we have now confirmed message loss in an outer join (however
in a co-partitioned setting without re-partitioning) in a proper
production-like environment where we are seeing these messages, I assume that
is what is going on for us.
Both Matthew's test
[https://github.com/mattsheppard/ins14809/|https://github.com/mattsheppard/ins14809/blob/main/src/test/java/ins14809/Ins14809Test.java]
and my variation of it without re-partitioning
[https://github.com/EugenDueck/ins14809] seem to be losing messages, however
only in Matthew's test (when changing the log level to INFO) do the "Skipping
record for expired segment" logs show. So either that log is unrelated to the
message loss we are seeing, or there are 2 different reasons for the loss of
messages - or the test is flawed.
was (Author: eugendueck):
As the "Skipping record for expired segment" log indicates the possibility of
message loss, and we have now confirmed message loss in an outer join (however
in a co-partitioned setting without re-partitioning) in a proper
production-like environment where we are seeing these messages, I assume that
is what is going on for us.
Both Matthew's test
[https://github.com/mattsheppard/ins14809/|https://github.com/mattsheppard/ins14809/blob/main/src/test/java/ins14809/Ins14809Test.java]
and my variation of it without re-partitioning
[https://github.com/EugenDueck/ins14809] seem to be losing messages, however
only in Matthew's test (when changing the log level to INFO) do the "Skipping
record for expired segment" logs show. So either that log is unrelated to the
message loss we are seeing, or there are 2 different reasons for the loss of
messages.
> Bulk processing correctly ordered input data through a join with
> kafka-streams results in `Skipping record for expired segment`
> -------------------------------------------------------------------------------------------------------------------------------
>
> Key: KAFKA-13289
> URL: https://issues.apache.org/jira/browse/KAFKA-13289
> Project: Kafka
> Issue Type: Bug
> Components: streams
> Affects Versions: 2.8.0
> Reporter: Matthew Sheppard
> Priority: Minor
>
> When pushing bulk data through a kafka-steams app, I see it log the following
> message many times...
> {noformat}
> WARN
> org.apache.kafka.streams.state.internals.AbstractRocksDBSegmentedBytesStore -
> Skipping record for expired segment.
> {noformat}
> ...and data which I expect to have been joined through a leftJoin step
> appears to be lost.
> I've seen this in practice either when my application has been shut down for
> a while and then is brought back up, or when I've used something like the
> [app-reset-rool](https://docs.confluent.io/platform/current/streams/developer-guide/app-reset-tool.html)
> in an attempt to have the application reprocess past data.
> I was able to reproduce this behaviour in isolation by generating 1000
> messages to two topics spaced an hour apart (with the original timestamps in
> order), then having kafka streams select a key for them and try to leftJoin
> the two rekeyed streams.
> Self contained source code for that reproduction is available at
> https://github.com/mattsheppard/ins14809/blob/main/src/test/java/ins14809/Ins14809Test.java
> The actual kafka-streams topology in there looks like this.
> {code:java}
> final StreamsBuilder builder = new StreamsBuilder();
> final KStream<String, String> leftStream =
> builder.stream(leftTopic);
> final KStream<String, String> rightStream =
> builder.stream(rightTopic);
> final KStream<String, String> rekeyedLeftStream = leftStream
> .selectKey((k, v) -> v.substring(0, v.indexOf(":")));
> final KStream<String, String> rekeyedRightStream = rightStream
> .selectKey((k, v) -> v.substring(0, v.indexOf(":")));
> JoinWindows joinWindow = JoinWindows.of(Duration.ofSeconds(5));
> final KStream<String, String> joined = rekeyedLeftStream.leftJoin(
> rekeyedRightStream,
> (left, right) -> left + "/" + right,
> joinWindow
> );
> {code}
> ...and the eventual output I produce looks like this...
> {code}
> ...
> 523 [523,left/null]
> 524 [524,left/null, 524,left/524,right]
> 525 [525,left/525,right]
> 526 [526,left/null]
> 527 [527,left/null]
> 528 [528,left/528,right]
> 529 [529,left/null]
> 530 [530,left/null]
> 531 [531,left/null, 531,left/531,right]
> 532 [532,left/null]
> 533 [533,left/null]
> 534 [534,left/null, 534,left/534,right]
> 535 [535,left/null]
> 536 [536,left/null]
> 537 [537,left/null, 537,left/537,right]
> 538 [538,left/null]
> 539 [539,left/null]
> 540 [540,left/null]
> 541 [541,left/null]
> 542 [542,left/null]
> 543 [543,left/null]
> ...
> {code}
> ...where as, given the input data, I expect to see every row end with the two
> values joined, rather than the right value being null.
> Note that I understand it's expected that we initially get the left/null
> values for many values since that's the expected semantics of kafka-streams
> left join, at least until
> https://cwiki.apache.org/confluence/display/KAFKA/Kafka+Streams+Join+Semantics#KafkaStreamsJoinSemantics-ImprovedLeft/OuterStream-StreamJoin(v3.1.xandnewer)spurious
> I've noticed that if I set a very large grace value on the join window the
> problem is solved, but since the input I provide is not out of order I did
> not expect to need to do that, and I'm weary of the resource requirements
> doing so in practice on an application with a lot of volume.
> My suspicion is that something is happening such that when one partition is
> processed it causes the stream time to be pushed forward to the newest
> message in that partition, meaning when the next partition is then examined
> it is found to contain many records which are 'too old' compared to the
> stream time.
> I ran across this discussion thread which seems to cover the same issue
> http://mail-archives.apache.org/mod_mbox/kafka-users/202002.mbox/%3cCAB0tB9p_vijMS18jWXBqp7TQozL__ANoo3=h57q6z3y4hzt...@mail.gmail.com%3e
> and had a request from [~cadonna] for a reproduction case, so I'm hoping my
> example above might make the issue easier to tackle!
--
This message was sent by Atlassian Jira
(v8.20.1#820001)
