Hi, Here's something potentially useful.
1) Before: https://apps.sematext.com/spm-reports/s/eQ9WhLegW9 - the "flat Lag situation" 2) I restarted the consumer whose lag is shown in the above graph 3) After restart: https://apps.sematext.com/spm-reports/s/4YGkcUP9ms - NO lag at all!? So that 81560 Lag value that was stuck in JMX is gone. Went down to 0. Kind of makes sense - the whole consumer was restarted, consumer/java process was restarted, everything that was in JMX got reset, and if there is truly no consumer lag it makes sense that the values in JMX are 0. HOWEVER, is the Lag *really* always *exactly* 0? No way. Look what Offset Checker shows for this one consumer: af_servers spm_cluster_topic-new-cdh 18 220551962 220586078 34116 af_servers_spm-afs-6.prod.sematext-1433447997963-c40182c8-0 af_servers spm_cluster_topic-new-cdh 19 161936440 161960377 23937 af_servers_spm-afs-6.prod.sematext-1433447997963-c40182c8-0 af_servers spm_cluster_topic-new-cdh 20 248308642 248340350 31708 af_servers_spm-afs-6.prod.sematext-1433447997963-c40182c8-0 af_servers spm_cluster_topic-new-cdh 21 259901355 259934911 33556 af_servers_spm-afs-6.prod.sematext-1433447997963-c40182c8-0 af_servers spm_cluster_topic-new-cdh 22 205274547 205296950 22403 af_servers_spm-afs-6.prod.sematext-1433447997963-c40182c8-0 af_servers spm_cluster_topic-new-cdh 23 167756654 167780028 23374 af_servers_spm-afs-6.prod.sematext-1433447997963-c40182c8-0 af_servers spm_cluster_topic-new-cdh 24 357517989 357574627 56638 af_servers_spm-afs-6.prod.sematext-1433447997963-c40182c8-0 af_servers spm_cluster_topic-new-cdh 25 194313232 194338154 24922 af_servers_spm-afs-6.prod.sematext-1433447997963-c40182c8-0 You can see Lag is NOT == 0 for any of the partitions! And yet, look what JMX is showing now -- all Lag for all partitions is supposedly 0. Always: kafka.server:type=FetcherLagMetrics,name=ConsumerLag,clientId=af_servers,topic=spm_cluster_free_system_topic-new-cdh,partition=17 Value java.lang.Object = 0 kafka.server:type=FetcherLagMetrics,name=ConsumerLag,clientId=af_servers,topic=spm_cluster_free_system_topic-new-cdh,partition=18 Value java.lang.Object = 0 kafka.server:type=FetcherLagMetrics,name=ConsumerLag,clientId=af_servers,topic=spm_cluster_topic-2-new-cdh,partition=18 Value java.lang.Object = 0 kafka.server:type=FetcherLagMetrics,name=ConsumerLag,clientId=af_servers,topic=spm_cluster_topic-3-new-cdh,partition=18 Value java.lang.Object = 0 kafka.server:type=FetcherLagMetrics,name=ConsumerLag,clientId=af_servers,topic=spm_cluster_topic-new-cdh,partition=18 Value java.lang.Object = 0 kafka.server:type=FetcherLagMetrics,name=ConsumerLag,clientId=af_servers,topic=spm_cluster_free_system_topic-new-cdh,partition=19 Value java.lang.Object = 0 kafka.server:type=FetcherLagMetrics,name=ConsumerLag,clientId=af_servers,topic=spm_cluster_topic-2-new-cdh,partition=19 Value java.lang.Object = 0 kafka.server:type=FetcherLagMetrics,name=ConsumerLag,clientId=af_servers,topic=spm_cluster_topic-3-new-cdh,partition=19 Value java.lang.Object = 0 kafka.server:type=FetcherLagMetrics,name=ConsumerLag,clientId=af_servers,topic=spm_cluster_topic-new-cdh,partition=19 Value java.lang.Object = 0 kafka.server:type=FetcherLagMetrics,name=ConsumerLag,clientId=af_servers,topic=spm_cluster_free_system_topic-new-cdh,partition=20 Value java.lang.Object = 0 kafka.server:type=FetcherLagMetrics,name=ConsumerLag,clientId=af_servers,topic=spm_cluster_topic-2-new-cdh,partition=20 Value java.lang.Object = 0 kafka.server:type=FetcherLagMetrics,name=ConsumerLag,clientId=af_servers,topic=spm_cluster_topic-3-new-cdh,partition=20 Value java.lang.Object = 0 kafka.server:type=FetcherLagMetrics,name=ConsumerLag,clientId=af_servers,topic=spm_cluster_topic-new-cdh,partition=20 Value java.lang.Object = 0 kafka.server:type=FetcherLagMetrics,name=ConsumerLag,clientId=af_servers,topic=spm_cluster_free_system_topic-new-cdh,partition=21 Value java.lang.Object = 0 kafka.server:type=FetcherLagMetrics,name=ConsumerLag,clientId=af_servers,topic=spm_cluster_topic-2-new-cdh,partition=21 Value java.lang.Object = 0 kafka.server:type=FetcherLagMetrics,name=ConsumerLag,clientId=af_servers,topic=spm_cluster_topic-3-new-cdh,partition=21 Value java.lang.Object = 0 kafka.server:type=FetcherLagMetrics,name=ConsumerLag,clientId=af_servers,topic=spm_cluster_topic-new-cdh,partition=21 Value java.lang.Object = 0 kafka.server:type=FetcherLagMetrics,name=ConsumerLag,clientId=af_servers,topic=spm_cluster_free_system_topic-new-cdh,partition=22 Value java.lang.Object = 0 kafka.server:type=FetcherLagMetrics,name=ConsumerLag,clientId=af_servers,topic=spm_cluster_topic-2-new-cdh,partition=22 Value java.lang.Object = 0 kafka.server:type=FetcherLagMetrics,name=ConsumerLag,clientId=af_servers,topic=spm_cluster_topic-3-new-cdh,partition=22 Value java.lang.Object = 0 kafka.server:type=FetcherLagMetrics,name=ConsumerLag,clientId=af_servers,topic=spm_cluster_topic-new-cdh,partition=22 Value java.lang.Object = 0 kafka.server:type=FetcherLagMetrics,name=ConsumerLag,clientId=af_servers,topic=spm_cluster_free_system_topic-new-cdh,partition=23 Value java.lang.Object = 0 kafka.server:type=FetcherLagMetrics,name=ConsumerLag,clientId=af_servers,topic=spm_cluster_topic-2-new-cdh,partition=23 Value java.lang.Object = 0 kafka.server:type=FetcherLagMetrics,name=ConsumerLag,clientId=af_servers,topic=spm_cluster_topic-3-new-cdh,partition=23 Value java.lang.Object = 0 kafka.server:type=FetcherLagMetrics,name=ConsumerLag,clientId=af_servers,topic=spm_cluster_topic-new-cdh,partition=23 Value java.lang.Object = 0 kafka.server:type=FetcherLagMetrics,name=ConsumerLag,clientId=af_servers,topic=spm_cluster_free_system_topic-new-cdh,partition=24 Value java.lang.Object = 0 kafka.server:type=FetcherLagMetrics,name=ConsumerLag,clientId=af_servers,topic=spm_cluster_topic-2-new-cdh,partition=24 Value java.lang.Object = 0 kafka.server:type=FetcherLagMetrics,name=ConsumerLag,clientId=af_servers,topic=spm_cluster_topic-3-new-cdh,partition=24 Value java.lang.Object = 0 kafka.server:type=FetcherLagMetrics,name=ConsumerLag,clientId=af_servers,topic=spm_cluster_topic-new-cdh,partition=24 Value java.lang.Object = 0 kafka.server:type=FetcherLagMetrics,name=ConsumerLag,clientId=af_servers,topic=spm_cluster_topic-2-new-cdh,partition=25 Value java.lang.Object = 0 kafka.server:type=FetcherLagMetrics,name=ConsumerLag,clientId=af_servers,topic=spm_cluster_topic-3-new-cdh,partition=25 Value java.lang.Object = 0 kafka.server:type=FetcherLagMetrics,name=ConsumerLag,clientId=af_servers,topic=spm_cluster_topic-new-cdh,partition=25 Value java.lang.Object = 0 Somebody's lying here. :) Any ideas? Thanks, Otis -- Monitoring * Alerting * Anomaly Detection * Centralized Log Management Solr & Elasticsearch Support * http://sematext.com/ On Thu, Jun 4, 2015 at 3:54 PM, Otis Gospodnetic <otis.gospodne...@gmail.com > wrote: > Hi Jason, > > (note: Kafka 0.8.2. GA) > Got some new info below! Could be a Kafka metrics bug.... > > On Thu, Jun 4, 2015 at 2:11 PM, Jason Rosenberg <j...@squareup.com> wrote: > >> I assume you are looking at a 'MaxLag' metric, which reports the worst >> case >> lag over a set of partitions. > > > No, we're looking at MBeans that look like this one: > > > kafka.server:type=FetcherLagMetrics,name=ConsumerLag,clientId=af_servers,topic=spm_cluster_free_system_topic-new-cdh,partition=10 > Value java.lang.Object = 0 > > >> Are you consuming multiple partitions, and maybe one of them is stuck? >> > > Don't think so... Maybe what we are seeing is a Kafka bug. > > Here is what we just discovered: > > Dumped JMX on the consumer and we see this: > > > kafka.server:type=FetcherLagMetrics,name=ConsumerLag,clientId=af_servers,topic=spm_cluster_topic-new-cdh,partition=24 > Value java.lang.Object = 81560 > > This 81560 is also what we see in SPM - see the flat line here: > https://apps.sematext.com/spm-reports/s/eQ9WhLegW9 > (you can hover over a datapoint on that 81K line to see server name, > topic, and partition) > > This 81560 is just not going down. If I look at JMX in 5 minutes, it will > show the same value - the ConsumerLag of 81560! > > BUT, this gives different numbers: > > /usr/lib/kafka_2.8.0-0.8.1.1/bin/kafka-run-class.sh > kafka.tools.ConsumerOffsetChecker --zkconnect localhost:2181 --group > af_servers | grep spm_cluster_topic-new-cdh > > af_servers spm_cluster_topic-new-cdh 24 *355209634* > *355249858* 40224 > af_servers_spm-afs-6.prod.sematext-1433430424202-e366dfdf-0 > > The delta between the bolded numbers is NOT 81560. And if I run this > command N times the delta keeps going down, because the consumer is > catching up. Just like you'd expect. > > But the JMX number remains constant <== could this be a Kafka metrics/JMX > bug? > > Thanks, > Otis > -- > Monitoring * Alerting * Anomaly Detection * Centralized Log Management > Solr & Elasticsearch Support * http://sematext.com/ > > > >> >> On Tue, Jun 2, 2015 at 4:00 PM, Otis Gospodnetic < >> otis.gospodne...@gmail.com >> > wrote: >> >> > Hi, >> > >> > I've noticed that when we restart our Kafka consumers our consumer lag >> > metric sometimes looks "weird". >> > >> > Here's an example: https://apps.sematext.com/spm-reports/s/0Hq5zNb4hH >> > >> > You can see lag go up around 15:00, when some consumers were restarted. >> > The "weird" thing is that the lag remains flat! >> > How could it remain flat if consumers are running? (they have enough >> juice >> > to catch up!) >> > >> > What I think is happening is this: >> > 1) consumers are initially not really lagging >> > 2) consumers get stopped >> > 3) lag grows >> > 4) consumers get started again >> > 5) something shifts around...not sure what... >> > 6) consumers start consuming, and there is actually no lag, but the >> offsets >> > written to ZK sometime during 3) don't get updated because after restart >> > consumers are reading from somewhere else, not from partition(s) whose >> lag >> > and offset delta jumped during 3) >> > >> > Oh, and: >> > 7) Kafka JMX still exposes all offsets, event those for partitions that >> are >> > no longer being read, so the consumer lag metric remains constant/flat, >> > even though consumers are actually not lagging on partitions from which >> > they are now consuming. >> > >> > What bugs me is 7), because reading lag info from JMX looks like it's >> > "lying". >> > >> > Does this sound crazy or reasonable? >> > >> > If anyone has any comments/advice/suggestions for what one can do about >> > this, I'm all ears! >> > >> > Thanks, >> > Otis >> > -- >> > Monitoring * Alerting * Anomaly Detection * Centralized Log Management >> > Solr & Elasticsearch Support * http://sematext.com/ >> > >> > >
