Hi, I think that’s unlikely to happen. As far as I know, the only way to actually unload the classes in JVM is when their class loader is garbage collected, which means all the references in the code to it must vanish. In other words, it should never happen that class is not found while anyone is still referencing it.
Most likely suspect is the standard java problem of some dependency convergence issue. Please check if you are not pulling in multiple Kafka versions into your class path. Especially your job shouldn’t pull any Kafka library except of the one that comes from flnk-connector-kafka-0.11 (which is 0.11.0.2). Please also consider upgrading your cluster at least to Kafka 0.11.0.2. Kafka 0.11.0.0 was pretty unstable release, and we do not support it. Our connector depend on Kafka 0.11.0.2 client and while I don’t assume that there is some incompatibility between 0.11.0.0 cluster and 0.11.0.2 client, it definitely wouldn’t hurt to upgrade the cluster. Piotrek > On 26 May 2018, at 17:58, Elias Levy <fearsome.lucid...@gmail.com> wrote: > > Piotr & Stephan, > > Thanks for the replies. Apologies for the late response. I've been > traveling for the past month. > > We've not observed this issue (spilling) again, but it is good to know that > 1.5 will use back-pressure based alignment. I think for now we'll leave > task.checkpoint.alignment.max-size as is and work towards moving to 1.5 once > we confirm it is stable. > > As for the java.lang.NoClassDefFoundError: > org/apache/kafka/clients/NetworkClient$1 error. We see that one constantly > when jobs are canceled/restarted/upgraded. We are using the > flink-connector-kafka-0.11 connector against a 0.11.0.0 cluster. The error > indicates to me that the Kafka threads are not being fully shutdown and they > are trying to reload the NetworkClient class but failing, maybe because the > code is no longer accessible via the class loader or some other reason. > > It looks like others are observing the same error. Alexander Smirnov > reported it here on the list last month as well. > > > On Thu, May 3, 2018 at 1:22 AM, Stephan Ewen <se...@apache.org > <mailto:se...@apache.org>> wrote: > Hi Elias! > > Concerning the spilling of alignment data to disk: > > - In 1.4.x , you can set an upper limit via " > task.checkpoint.alignment.max-size ". See [1]. > - In 1.5.x, the default is a back-pressure based alignment, which does not > spill any more. > > Best, > Stephan > > [1] > https://ci.apache.org/projects/flink/flink-docs-master/ops/config.html#task-checkpoint-alignment-max-size > > <https://ci.apache.org/projects/flink/flink-docs-master/ops/config.html#task-checkpoint-alignment-max-size> > > On Wed, May 2, 2018 at 1:37 PM, Piotr Nowojski <pi...@data-artisans.com > <mailto:pi...@data-artisans.com>> wrote: > Hi, > > It might be some Kafka issue. > > From what you described your reasoning seems sound. For some reason TM3 fails > and is unable to restart and process any data, thus forcing spilling on > checkpoint barriers on TM1 and TM2. > > I don’t know the reason behind java.lang.NoClassDefFoundError: > org/apache/kafka/clients/NetworkClient$1 errors, but it doesn’t seem to be > important in this case. > > 1. What Kafka version are you using? Have you looked for any known Kafka > issues with those symptoms? > 2. Maybe the easiest thing will be to reformat/reinstall/recreate TM3 AWS > image? It might be some system issue. > > Piotrek > >> On 28 Apr 2018, at 01:54, Elias Levy <fearsome.lucid...@gmail.com >> <mailto:fearsome.lucid...@gmail.com>> wrote: >> >> We had a job on a Flink 1.4.2 cluster with three TMs experience an odd >> failure the other day. It seems that it started as some sort of network >> event. >> >> It began with the 3rd TM starting to warn every 30 seconds about socket >> timeouts while sending metrics to DataDog. This latest for the whole outage. >> >> Twelve minutes later, all TMs reported at nearly the same time that they had >> marked the Kafka coordinator as deed ("Marking the coordinator XXX (id: >> 2147482640 rack: null) dead for group ZZZ"). The job terminated and the >> system attempted to recover it. Then things got into a weird state. >> >> The following related for six or seven times for a period of about 40 >> minutes: >> TM attempts to restart the job, but only the first and second TMs show signs >> of doing so. >> The disk begins to fill up on TMs 1 and 2. >> TMs 1 & 2 both report java.lang.NoClassDefFoundError: >> org/apache/kafka/clients/NetworkClient$1 errors. These were mentioned on >> this list earlier this month. It is unclear if the are benign. >> The job dies when the disks finally fills up on 1 and 2. >> >> Looking at the backtrace logged when the disk fills up, I gather that Flink >> is buffering data coming from Kafka into one of my operators as a result of >> a barrier. The job has a two input operator, with one input the primary >> data, and a secondary input for control commands. It would appear that for >> whatever reason the barrier for the control stream is not making it to the >> operator, thus leading to the buffering and full disks. Maybe Flink >> scheduled the operator source of the control stream on the 3rd TM which >> seems like it was not scheduling tasks? >> >> Finally the JM records that it 13 late messages for already expired >> checkpoints (could they be from the 3rd TM?), the job is restored one more >> time and it works. All TMs report nearly at the same time that they can now >> find the Kafka coordinator. >> >> >> Seems like the 3rd TM has some connectivity issue, but then all TMs seems to >> have a problem communicating with the Kafka coordinator at the same time and >> recovered at the same time. The TMs are hosted in AWS across AZs, so all of >> them having connectivity issues at the same time is suspect. The Kafka node >> in question was up and other clients in our infrastructure seems to be able >> to communicate with it without trouble. Also, the Flink job itself seemed >> to be talking to the Kafka cluster while restarting as it was spilling data >> to disk coming from Kafka. And the JM did not report any reduction on >> available task slots, which would indicate connectivity issues between the >> JM and the 3rd TM. Yet, the logs in the 3rd TM do not show any record of >> trying to restore the job during the intermediate attempts. >> >> What do folks make of it? >> >> >> And a question for Flink devs, is there some reason why Flink does not stop >> spilling messages to disk when the disk is going to fill up? Seems like >> there should be a configurable limit to how much data can be spilled before >> back-pressure is applied to slow down or stop the source. > > >
