You are right, the checkpoints should contain all offsets. I created a Ticket for this: https://issues.apache.org/jira/browse/FLINK-3440
On Thu, Feb 18, 2016 at 10:15 AM, agaoglu <erdem.agao...@gmail.com> wrote: > Hi, > > On a related and a more exaggerated setup, our kafka-producer (flume) seems > to send data to a single partition at a time and switches it every few > minutes. So when i run my flink datastream program for the first time, it > starts on the *largest* offsets and shows something like this: > > . Fetched the following start offsets [FetchPartition {partition=7, > offset=15118832832}] > . Fetched the following start offsets [FetchPartition {partition=1, > offset=15203613236}] > . Fetched the following start offsets [FetchPartition {partition=2, > offset=15366811664}] > . Fetched the following start offsets [FetchPartition {partition=0, > offset=15393999709}] > . Fetched the following start offsets [FetchPartition {partition=8, > offset=15319475583}] > . Fetched the following start offsets [FetchPartition {partition=5, > offset=15482889767}] > . Fetched the following start offsets [FetchPartition {partition=6, > offset=15113885928}] > . Fetched the following start offsets [FetchPartition {partition=3, > offset=15182701991}] > . Fetched the following start offsets [FetchPartition {partition=4, > offset=15186569356}] > > For that instance flume happens to be sending data to partition-6 only, so > other consumers sit idly. Working with default paralellism 4, only one of > the 4 threads is able to source data and checkpointing logs reflect that: > > Committing offsets [-915623761776, -915623761776, -915623761776, > -915623761776, -915623761776, -915623761776, -915623761776, -915623761776, > -915623761776] to offset store: FLINK_ZOOKEEPER > Committing offsets [-915623761776, -915623761776, -915623761776, > -915623761776, -915623761776, -915623761776, 15114275927, -915623761776, > -915623761776] to offset store: FLINK_ZOOKEEPER > Committing offsets [-915623761776, -915623761776, -915623761776, > -915623761776, -915623761776, -915623761776, -915623761776, -915623761776, > -915623761776] to offset store: FLINK_ZOOKEEPER > Committing offsets [-915623761776, -915623761776, -915623761776, > -915623761776, -915623761776, -915623761776, -915623761776, -915623761776, > -915623761776] to offset store: FLINK_ZOOKEEPER > > This also means checkpoint will only contain the offset for partition-6. So > if program is stopped and restarted at a later time, it restores the offset > for partition-6 only and other partitions are started at the largest > offset. > So it's able to process unseen data in partition-6 but not others. Say if > flume produces data to partition-3 when flink program is stopped, they're > lost, while the data in partition-6 is not. This generally causes multiple > (late-)windows to be fired after restart, because we now generate > watermarks > off partition-3 which says the windows of the unseen data in partition-6 > are > already complete. > > This also has a side effect of windows not triggering unless some > rebalancing is done beforehand. Since only 1 of the 4 threads will source > data and generate watermarks, window triggers won't get watermarks from > other 3 sources and wait long past the watermarks generated from the single > source. > > I know producers shouldn't work like that, but consumers shouldn't care. I > think it may also create some edge cases even if things were not as extreme > as ours. If checkpoints could contain offsets of all of the partitions > regardless of their contents, probably storing start offsets in first run, > i > guess that would solve the problems around restarting. > > > > -- > View this message in context: > http://apache-flink-user-mailing-list-archive.2336050.n4.nabble.com/Kafka-partition-alignment-for-event-time-tp4782p4998.html > Sent from the Apache Flink User Mailing List archive. mailing list archive > at Nabble.com. >