Hi Bruno, John and Sophie, thank you very much for quick responses, you are the best. After thinking about it a little bit more, it seems fishy.
>From logs, I see that it is not happening when application is running normally. I have checked timestamps (windowStartTimestamp) - connecting local instance in debug mode to Kafka cluster. And they are mixed up. Not always, there can be a day with good sequence and then a time interval with mixed up timestamps, like these (store retention is 20.6 minutes): StreamThread-1.task.1_57, 2020-02-07T13:05:46.550Z StreamThread-1.task.1_57, 2020-02-07T13:12:07.870Z StreamThread-1.task.1_57, 2020-02-07T13:10:49.980Z StreamThread-1.task.1_57, 2020-02-07T13:12:55.909Z StreamThread-1.task.1_57, 2020-02-07T13:09:02.662Z StreamThread-1.task.1_57, 2020-02-07T13:13:08.651Z StreamThread-1.task.1_57, 2020-02-07T13:06:53.946Z StreamThread-1.task.1_57, 2020-02-07T13:11:58.188Z StreamThread-1.task.1_57, 2020-02-07T12:59:42.884Z StreamThread-1.task.1_57, 2020-02-07T13:07:30.412Z StreamThread-1.task.1_57, 2020-02-07T12:55:53.328Z StreamThread-1.task.1_57, 2020-02-07T12:44:51.912Z StreamThread-1.task.1_57, 2020-02-07T12:59:27.364Z StreamThread-1.task.1_57, 2020-02-07T13:01:34.313Z StreamThread-1.task.1_57, 2020-02-07T13:07:56.379Z StreamThread-1.task.1_57, 2020-02-07T12:45:32.984Z StreamThread-1.task.1_57, 2020-02-07T12:45:44.232Z StreamThread-1.task.1_57, 2020-02-07T12:45:59.594Z StreamThread-1.task.1_57, 2020-02-07T12:46:02.860Z StreamThread-1.task.1_57, 2020-02-07T13:02:17.658Z StreamThread-1.task.1_57, 2020-02-07T12:46:25.125Z StreamThread-1.task.1_57, 2020-02-07T12:46:44.864Z StreamThread-1.task.1_57, 2020-02-07T12:44:44.074Z StreamThread-1.task.1_57, 2020-02-07T13:03:36.221Z StreamThread-1.task.1_57, 2020-02-07T13:12:16.691Z StreamThread-1.task.1_57, 2020-02-07T12:56:55.214Z Picking a few of these, the stack trace was like: put:134, InMemoryWindowStore (org.apache.kafka.streams.state.internals) lambda$init$0:112, InMemoryWindowStore (org.apache.kafka.streams.state.internals) restore:-1, 69348804 (org.apache.kafka.streams.state.internals.InMemoryWindowStore$$Lambda$270) lambda$adapt$1:47, StateRestoreCallbackAdapter (org.apache.kafka.streams.processor.internals) restoreBatch:-1, 791473363 (org.apache.kafka.streams.processor.internals.StateRestoreCallbackAdapter$$Lambda$269) restoreBatch:89, CompositeRestoreListener (org.apache.kafka.streams.processor.internals) restore:92, StateRestorer (org.apache.kafka.streams.processor.internals) processNext:349, StoreChangelogReader (org.apache.kafka.streams.processor.internals) restore:93, StoreChangelogReader (org.apache.kafka.streams.processor.internals) updateNewAndRestoringTasks:389, TaskManager (org.apache.kafka.streams.processor.internals) runOnce:769, StreamThread (org.apache.kafka.streams.processor.internals) runLoop:698, StreamThread (org.apache.kafka.streams.processor.internals) run:671, StreamThread (org.apache.kafka.streams.processor.internals) So I believe it happens on stream restoration phase. And it's restoring state from internal changelog topic. It's all task.1_57 so I expect that it is a single partition. Thinking about it, I don't understand how such a case can even theoretically happen. I expect that a window, in order to be written to the changelog topic, first needs to go through "put"; so even if it's mixed on the input side, it should be skipped if expired at the moment of "put" (relatively to observedStreamTime) and on restoration everything should be fine. As the next step, I would like to list/inspect records and their timestamps from given partition of the changelog topic via a command line tool (or in some other way) - to confirm if they are really stored this way. If you have a tip on how to do it, please let me know. That is all I have for now. I would like to resolve it. I will post it here if I come up with something new. Thank you Jiri On Mon, Feb 10, 2020 at 10:14 PM John Roesler <vvcep...@apache.org> wrote: > > Hey all, > > Sorry for the confusion. Bruno set me straight offline. > > Previously, we had metrics for each reason for skipping records, and the > rationale was that you would monitor the metrics and only turn to the logs > if you needed to *debug* unexpected record skipping. Note that skipping > records by itself isn't a cause for concern, since this is exactly what Streams > is designed to do in a number of situations. > > However, during the KIP-444 discussion, the decision was reversed, and we > decided to just log one "roll-up" metric for all skips and increase the log > messages to warning level for debuggability. This particularly makes sense > because you otherwise would have to restart the application to change the > log level if you needed to figure out why the single skipped-record metric > is non-zero. And then you may not even observe it again. > > I either missed the memo on that discussion, or participated in it and then > forgot it even happened. I'm not sure I want to look back at the thread to > find out. > > Anyway, I've closed the PR I opened to move it back to debug. We should > still try to help figure out the root cause of this particular email thread, > though. > > Thanks, > -John > > On Mon, Feb 10, 2020, at 12:20, Sophie Blee-Goldman wrote: > > While I agree that seems like it was probably a refactoring mistake, I'm > > not > > convinced it isn't the right thing to do. John, can you reiterate the > > argument > > for setting it to debug way back when? > > > > I would actually present this exact situation as an argument for keeping it > > as > > warn, since something indeed seems fishy here that was only surfaced > > through this warning. That said, maybe the metric is the more appropriate > > way to bring attention to this: not sure if it's info or debug level > > though, or > > how likely it is that anyone really pays attention to it? > > > > On Mon, Feb 10, 2020 at 9:53 AM John Roesler <j...@vvcephei.org> wrote: > > > > > Hi, > > > > > > I’m sorry for the trouble. It looks like it was a mistake during > > > > > > https://github.com/apache/kafka/pull/6521 > > > > > > Specifically, while addressing code review comments to change a bunch of > > > other logs from debugs to warnings, that one seems to have been included by > > > accident: > > > https://github.com/apache/kafka/commit/ac27e8578f69d60a56ba28232d7e96c76957f66c > > > > > > I’ll see if I can fix it today. > > > > > > Regarding Bruno's thoughts, there was a pretty old decision to capture the > > > "skipped records" as a metric for visibility and log it at the debug level > > > for debuggability. We decided that "warning" wasn't the right level because > > > Streams is operating completely as specified. > > > > > > However, I do agree that it doesn't seem right to see more skipped records > > > during start-up; I would expect to see exactly the same records skipped > > > during start-up as during regular processing, since the skipping logic is > > > completely deterministic and based on the sequence of timestamps your > > > records have in the topic. Maybe you just notice it more during startup? > > > I.e., if there are 1000 warning logs spread over a few months, then you > > > don't notice it, but when you see them all together at start-up, it's more > > > concerning? > > > > > > Thanks, > > > -John > > > > > > > > > On Mon, Feb 10, 2020, at 10:15, Bruno Cadonna wrote: > > > > Hi, > > > > > > > > I am pretty sure this was intentional. All skipped records log > > > > messages are on WARN level. > > > > > > > > If a lot of your records are skipped on app restart with this log > > > > message on WARN-level, they were also skipped with the log message on > > > > DEBUG-level. You simply did not know about it before. With an > > > > in-memory window store, this message is logged when a window with a > > > > start time older than the current stream time minus the retention > > > > period is put into the window store, i.e., the window is NOT inserted > > > > into the window stroe. If you get a lot of them on app restart, you > > > > should have a look at the timestamps of your records and the retention > > > > of your window store. If those values do not explain the behavior, > > > > please try to find a minimal example that shows the issue and post it > > > > here on the mailing list. > > > > > > > > On Mon, Feb 10, 2020 at 2:27 PM Samek, Jiří <sa...@avast.com.invalid > > > > wrote: > > > > > > > > > > Hi, > > > > > > > > > > in > > > > > > > > https://github.com/apache/kafka/commit/9f5a69a4c2d6ac812ab6134e64839602a0840b87#diff-a5cfe68a5931441eff5f00261653dd10R134 > > > > > > > > > > log level of "Skipping record for expired segment" was changed from > > > debug > > > > > to warn. Was it intentional change? Should it be somehow handled by > > > user? > > > > > How can user handle it? I am getting a lot of these on app restart. > > > > > > > > > -- Jiří Samek | Software Developer AVAST Software s.r.o. | Pikrtova 1737/1a | 140 00 Praha 4 M +420 734 524 549 | E sa...@avast.com | W www.avast.com