Hi Weike, thanks for getting back to us with your findings. Looking at the `TaskManagerLocation`, we are actually calling `InetAddress.getCanonicalHostName` twice for every creation of a `TaskManagerLocation` instance. This does not look right.
I think it should be fine to make the look up configurable. Moreover, one could think about only doing a lazy look up if the canonical hostname is really needed (as far as I can see it is only really needed input split assignments and for the LocationPreferenceSlotSelectionStrategy to calculate how many TMs run on the same machine). Do you want to fix this issue? Cheers, Till On Thu, Oct 15, 2020 at 11:38 AM DONG, Weike <kyled...@connect.hku.hk> wrote: > Hi Till and community, > > By the way, initially I resolved the IPs several times but results > returned rather quickly (less than 1ms, possibly due to DNS cache on the > server), so I thought it might not be the DNS issue. > > However, after debugging and logging, it is found that the lookup time > exhibited high variance, i. e. normally it completes fast but occasionally > some slow results would block the thread. So an unstable DNS server might > have a great impact on the performance of Flink job startup. > > Best, > Weike > > On Thu, Oct 15, 2020 at 5:19 PM DONG, Weike <kyled...@connect.hku.hk> > wrote: > >> Hi Till and community, >> >> Increasing `kubernetes.jobmanager.cpu` in the configuration makes this >> issue alleviated but not disappeared. >> >> After adding DEBUG logs to the internals of *flink-runtime*, we have >> found the culprit is >> >> inetAddress.getCanonicalHostName() >> >> in *org.apache.flink.runtime.taskmanager.TaskManagerLocation#getHostName* >> and >> *org.apache.flink.runtime.taskmanager.TaskManagerLocation#getFqdnHostName*, >> which could take ~ 6 seconds to complete, thus Akka dispatcher(s) >> are severely blocked by that. >> >> By commenting out the two methods, this issue seems to be solved >> immediately, so I wonder if Flink could provide a configuration parameter >> to turn off the DNS reverse lookup process, as it seems that Flink jobs >> could run happily without it. >> >> Sincerely, >> Weike >> >> >> On Tue, Oct 13, 2020 at 6:52 PM Till Rohrmann <trohrm...@apache.org> >> wrote: >> >>> Hi Weike, >>> >>> could you try setting kubernetes.jobmanager.cpu: 4 in your >>> flink-conf.yaml? I fear that a single CPU is too low for the JobManager >>> component. >>> >>> Cheers, >>> Till >>> >>> On Tue, Oct 13, 2020 at 11:33 AM Till Rohrmann <trohrm...@apache.org> >>> wrote: >>> >>>> Hi Weike, >>>> >>>> thanks for posting the logs. I will take a look at them. My suspicion >>>> would be that there is some operation blocking the JobMaster's main thread >>>> which causes the registrations from the TMs to time out. Maybe the logs >>>> allow me to validate/falsify this suspicion. >>>> >>>> Cheers, >>>> Till >>>> >>>> On Mon, Oct 12, 2020 at 10:43 AM DONG, Weike <kyled...@connect.hku.hk> >>>> wrote: >>>> >>>>> Hi community, >>>>> >>>>> I have uploaded the log files of JobManager and TaskManager-1-1 (one >>>>> of the 50 TaskManagers) with DEBUG log level and default Flink >>>>> configuration, and it clearly shows that TaskManager failed to register >>>>> with JobManager after 10 attempts. >>>>> >>>>> Here is the link: >>>>> >>>>> JobManager: >>>>> https://gist.github.com/kylemeow/740c470d9b5a1ab3552376193920adce >>>>> >>>>> TaskManager-1-1: >>>>> https://gist.github.com/kylemeow/41b9a8fe91975875c40afaf58276c2fe >>>>> >>>>> Thanks : ) >>>>> >>>>> Best regards, >>>>> Weike >>>>> >>>>> >>>>> On Mon, Oct 12, 2020 at 4:14 PM DONG, Weike <kyled...@connect.hku.hk> >>>>> wrote: >>>>> >>>>>> Hi community, >>>>>> >>>>>> Recently we have noticed a strange behavior for Flink jobs on >>>>>> Kubernetes per-job mode: when the parallelism increases, the time it >>>>>> takes >>>>>> for the TaskManagers to register with *JobManager *becomes >>>>>> abnormally long (for a task with parallelism of 50, it could take 60 ~ >>>>>> 120 >>>>>> seconds or even longer for the registration attempt), and usually more >>>>>> than >>>>>> 10 attempts are needed to finish this registration. >>>>>> >>>>>> Because of this, we could not submit a job requiring more than 20 >>>>>> slots with the default configuration, as the TaskManager would say: >>>>>> >>>>>> >>>>>>> Registration at JobManager >>>>>>> (akka.tcp://flink@myjob-201076.default:6123/user/rpc/jobmanager_2) >>>>>>> attempt 9 timed out after 25600 ms >>>>>> >>>>>> Free slot with allocation id 60d5277e138a94fb73fc6691557001e0 >>>>>>> because: The slot 60d5277e138a94fb73fc6691557001e0 has timed out. >>>>>> >>>>>> Free slot TaskSlot(index:0, state:ALLOCATED, resource profile: >>>>>>> ResourceProfile{cpuCores=1.0000000000000000, taskHeapMemory=1.425gb >>>>>>> (1530082070 bytes), taskOffHeapMemory=0 bytes, managedMemory=1.340gb >>>>>>> (1438814063 bytes), networkMemory=343.040mb (359703515 bytes)}, >>>>>>> allocationId: 60d5277e138a94fb73fc6691557001e0, jobId: >>>>>>> 493cd86e389ccc8f2887e1222903b5ce). >>>>>>> java.lang.Exception: The slot 60d5277e138a94fb73fc6691557001e0 has >>>>>>> timed out. >>>>>> >>>>>> >>>>>> In order to cope with this issue, we have to change the below >>>>>> configuration parameters: >>>>>> >>>>>>> >>>>>>> # Prevent "Could not allocate the required slot within slot request >>>>>>> timeout. Please make sure that the cluster has enough resources. >>>>>>> Stopping >>>>>>> the JobMaster for job" >>>>>>> slot.request.timeout: 500000 >>>>>> >>>>>> # Increase max timeout in a single attempt >>>>>>> cluster.registration.max-timeout: 300000 >>>>>>> # Prevent "free slot (TaskSlot)" >>>>>>> akka.ask.timeout: 10 min >>>>>>> # Prevent "Heartbeat of TaskManager timed out." >>>>>>> heartbeat.timeout: 500000 >>>>>> >>>>>> >>>>>> However, we acknowledge that this is only a temporary dirty fix, >>>>>> which is not what we want. It could be seen that during TaskManager >>>>>> registration to JobManager, lots of warning messages come out in logs: >>>>>> >>>>>> No hostname could be resolved for the IP address 9.166.0.118, using >>>>>>> IP address as host name. Local input split assignment (such as for HDFS >>>>>>> files) may be impacted. >>>>>> >>>>>> >>>>>> Initially we thought this was probably the cause (reverse lookup of >>>>>> DNS might take up a long time), however we later found that the reverse >>>>>> lookup only took less than 1ms, so maybe not because of this. >>>>>> >>>>>> Also, we have checked the GC log of both TaskManagers and JobManager, >>>>>> and they seem to be perfectly normal, without any signs of pauses. And >>>>>> the >>>>>> heartbeats are processed as normal according to the logs. >>>>>> >>>>>> Moreover, TaskManagers register quickly with ResourceManager, but >>>>>> then extra slow with TaskManager, so this is not because of a slow >>>>>> network >>>>>> connection. >>>>>> >>>>>> Here we wonder what could be the cause for the slow registration >>>>>> between JobManager and TaskManager(s)? No other warning or error messages >>>>>> in the log (DEBUG level) other than the "No hostname could be resolved" >>>>>> messages, which is quite weird. >>>>>> >>>>>> Thanks for the reading, and hope to get some insights into this >>>>>> issues : ) >>>>>> >>>>>> Sincerely, >>>>>> Weike >>>>>> >>>>>> >>>>>> >>>>>
