Thanks Felix. One question still remains. Why SimpleConsumer? Why not high level Consumer? If i change the code to high level consumer, will it create any challenges?
Navneet On Tue, Jan 15, 2013 at 11:46 PM, Felix GV <fe...@mate1inc.com> wrote: > Please read the Kafka design paper <http://kafka.apache.org/design.html>. > > It may look a little long, but it's as short as it can be. Kafka differs > from other messaging system in a couple of ways, and it's important to > understand the fundamental design choices that were made in order to > understand the way Kafka works. > > I believe my previous email already answers both your offset tracking and > retention questions, but if my explanation are not clear enough, then the > next best thing is probably to read the design paper :) > > -- > Felix > > > On Tue, Jan 15, 2013 at 12:01 PM, navneet sharma < > navneetsharma0...@gmail.com> wrote: > > > Thanks Felix for sharing your work. Contrib hadoop-consumer looks like > the > > same way. > > > > I think i need to really understand this offset stuff. So far i have used > > only high level consumer.When consumer is done reading all the messages, > i > > used to kill the process(because it won't on its own). > > > > Again i used Producer to pump more messages and Consumer to read the new > > messages(which is a new process as i killed the last consumer). > > > > But i never saw messages getting duplicating. > > > > Now its not very clear for me that how offsets is tracked specifically > when > > i am re-launching the consumer? > > And why retention policy is not working when used with SimpleConsumer? > For > > my experiment i made it 4 hours. > > > > Please help me understand. > > > > Thanks, > > Navneet > > > > > > On Tue, Jan 15, 2013 at 4:12 AM, Felix GV <fe...@mate1inc.com> wrote: > > > > > I think you may be misunderstanding the way Kafka works. > > > > > > A kafka broker is never supposed to clear messages just because a > > consumer > > > read them. > > > > > > The kafka broker will instead clear messages after their retention > period > > > ends, though it will not delete the messages at the exact time when > they > > > expire. Instead, a background process will periodically delete a batch > of > > > expired messages. The retention policies guarantee a minimum retention > > > time, not an exact retention time. > > > > > > It is the responsibility of each consumer to keep track of which > messages > > > they have consumed already (by recording an offset for each consumed > > > partition). The high-level consumer stores these offsets in ZK. The > > simple > > > consumer has no built-in capability to store and manage offsets, so it > is > > > the developer's responsibility to do so. In the case of the hadoop > > consumer > > > in the contrib package, these offsets are stored in offset files within > > > HDFS. > > > > > > I wrote a blog post a while ago that explains how to use the offset > files > > > generated by the contrib consumer to do incremental consumption (so > that > > > you don't get duplicated messages by re-consuming everything in > > subsequent > > > runs). > > > > > > > > > > > > http://felixgv.com/post/69/automating-incremental-imports-with-the-kafka-hadoop-consumer/ > > > > > > I'm not sure how up to date this is, regarding the current Kafka > > versions, > > > but it may still give you some useful pointers... > > > > > > -- > > > Felix > > > > > > -- > > > Felix > > > > > > > > > On Mon, Jan 14, 2013 at 1:34 PM, navneet sharma < > > > navneetsharma0...@gmail.com > > > > wrote: > > > > > > > Hi, > > > > > > > > I am trying to use the code supplied in hadoop-consumer package. I am > > > > running into following issues: > > > > > > > > 1) This code is using SimpleConsumer which is actually contacting > Kafka > > > > Broker without Zookeeper. Because of which messages are not getting > > > cleared > > > > from broker. > > > > And i am getting duplicate messages in each run. > > > > > > > > 2) The retention policy specified as log.retention.hours in > > > > server.properties is not working. Not sure if its due to > > SimpleConsumer. > > > > > > > > Is it expected behaviour. Is there any code using high level consumer > > for > > > > same work? > > > > > > > > Thanks, > > > > Navneet Sharma > > > > > > > > > >
