There's a small discrepancy, in the old spout we track the offset the next batch should start at, while in storm-kafka-client we track the last emitted offset. So for example if offset 0, 1, 2 were emitted, the old spout would store offset = 0, nextOffset = 3. The new spout would store firstOffset = 0, lastOffset = 2. I think it should be lastOffset = nextOffset - 1. Other than that I agree with your mapping.
2018-01-12 3:43 GMT+01:00 Nasron Cheong <nas...@gmail.com>: > Hi Stig, > > That's great! Thanks for all the info. Looking through the code, one small > detail is the difference between storm-kafka-client's format and > storm-kafka. The former uses 'firstOffset' and 'lastOffset' and the latter > uses 'offset' and 'nextOffset'. > > So, can I map with > > firstOffset = offset > > and > > lastOffset = nextOffset+1 ? > > Looking through the code it seems to be that nextOffset is placed after > the last consumed message, but I'm not sure. > > Thanks > > - Nasron > > On Thu, Jan 11, 2018 at 5:43 PM, Stig Rohde Døssing <s...@apache.org> > wrote: > >> Nasron, >> >> Okay, migrating a Trident spout is a very different thing. Trident spouts >> store their state in Storm's zookeeper (unless you decide otherwise by >> setting transactional.zookeeper.servers in storm.yaml). This also >> applies to the storm-kafka-client Trident spout, so we won't need to move >> offsets into Kafka. >> >> The idea of stopping all the producers and starting at LATEST (or >> UNCOMMITTED_LATEST) is decent, but as you note there's a (small) risk of >> skipping tuples. In order to get Trident to commit something, you have to >> deploy the new topology with LATEST and start the producers again, wait >> until at least one commit happens, and then take the topology back down and >> redeploy with whatever your first poll strategy normally is. If the worker >> crashes before the spout manages to commit something, you will skip tuples. >> >> If you don't want to do that, here's my notes on storm-kafka -> >> storm-kafka-client for Trident: >> >> The storage formats and zk paths for the two spouts are a little >> different. Both spouts store their state as JSON maps, but some of the keys >> are different. I use ${} below to indicate variable substitution. >> >> The root path (in the following: zkRoot) for your spouts data is >> /${transactional.zookeeper.root from storm.yaml}/${txId you set with >> TopologyBuilder.newStream}/user. >> >> For the storm-kafka spout the offsets are stored in one of the following >> two paths: >> ${zkRoot}/${topicName}partition_${partition} if you are using wildcard >> topic subscriptions >> ${zkRoot}/partition_${partition} otherwise >> >> The storage format for storm-kafka is as follows: >> { "${topicName}partition_${partition}': {"offset": 0, "nextOffset": 2 } >> } if you are using wildcard topic subscriptions >> { "${topicName}partition_${partition}': {"offset": 0, "nextOffset": 2 } >> } otherwise (I left out some irrelevant properties) >> >> For storm-kafka-client the zk path is >> ${zkRoot}/${topicName}@${partition} >> >> and the storage format is >> { "${topicName}@${partition}': {"firstOffset": 0, "nextOffset": 2 } } >> >> In order to migrate from storm-kafka to storm-kafka-client, we need to >> stop the topology and run a script that moves the offsets from the old >> location/format to the new location/format. There's no way to tell Trident >> to read from one path/format and write to another, so it has to be done >> offline. Once the offsets are migrated, the spout can be replaced in the >> topology and the topology can be redeployed. >> >> I might look at writing an application that can do this at some point, >> but it might take me a while. If you'd like to look at it yourself, here's >> some pointers where to start: >> * This is where the offset are written to Zookeeper, assuming you use an >> opaque spout https://github.com/apache/storm/blob/master/storm-client/src >> /jvm/org/apache/storm/trident/spout/OpaquePartitionedTrident >> SpoutExecutor.java#L184. You might want to look at this class for a bit >> (particularly the emit function), because it's pretty useful for >> understanding how/where Trident stores metadata for spouts. >> * The return value of https://github.com/apache/stor >> m/blob/master/external/storm-kafka/src/jvm/org/apache/storm/ >> kafka/trident/TridentKafkaEmitter.java#L85 defines the format of what's >> being saved to Zookeeper for storm-kafka. It's being wrapped in a map so >> the full written value is { "${topicName}partition_${partition}': >> ${theReturnValue} } (see the storage format note above, it's different if >> you're not using wildcard subscriptions) >> * Similarly for storm-kafka-client the return value of >> https://github.com/apache/storm/blob/master/external/storm-k >> afka-client/src/main/java/org/apache/storm/kafka/spout/tride >> nt/KafkaTridentSpoutEmitter.java#L106 defines the format of what that >> spout saves to Zookeeper (and expects to find). >> * You should use zkCli (it's in your zookeeper/bin directory) to explore >> your Zookeeper filesystem. It should be pretty easy to find your offsets in >> there with that tool. >> >> Sorry about the wall of text, this turned out to have a lot of detail to >> cover. >> >> 2018-01-10 21:40 GMT+01:00 Nasron Cheong <nas...@gmail.com>: >> >>> Thanks Stig, >>> >>> So after some digging, I realized we are really migrating from the kafka >>> trident emitter in storm-kafka, to the trident emitter in >>> storm-kafka-client. >>> >>> As far as I can see, the offset information is still stored in zk, and >>> the offset info for storm-kafka is (https://github.com/apache/sto >>> rm/blob/master/external/storm-kafka/src/jvm/org/apache/storm >>> /kafka/trident/TridentKafkaEmitter.java#L140) >>> >>> However this seems quite different from storm-kafka-client, which uses >>> https://github.com/apache/storm/blob/master/external/st >>> orm-kafka-client/src/main/java/org/apache/storm/kafka/spout/ >>> trident/KafkaTridentSpoutBatchMetadata.java#L56 >>> >>> I'm not sure under which zknode this information is stored - and if the >>> zknode itself is different between the two implementations. >>> >>> Looks like I need a tool to copy the stored values in zk from old >>> storm-kafka to storm-kafka-client? >>> >>> Another option I suppose is to: >>> - stop topic producers >>> - run the old code until it drains all topics >>> - start new code with FirstPollOffsetStrategy.LATEST >>> >>> Although this seems risky. >>> >>> Thanks! >>> >>> - Nasron >>> >>> >>> On Thu, Dec 21, 2017 at 4:23 PM, Stig Rohde Døssing <s...@apache.org> >>> wrote: >>> >>>> Hi Nasron, >>>> >>>> I don't believe there's currently a tool to help you migrate. We did it >>>> manually by writing a small utility that looked up the commit offsets in >>>> Storm's Zookeeper, opened a KafkaConsumer with the new consumer group id >>>> and committed the offsets for the appropriate partitions. We stopped our >>>> topologies, used this utility and redeployed with the new spout. >>>> >>>> Assuming there isn't already a tool for migration floating around >>>> somewhere, I think we could probably build some migration support into the >>>> storm-kafka-client spout. If the path to the old offsets in Storm's >>>> Zookeeper is given, we might be able to extract them and start up the new >>>> spout from there. >>>> >>>> 2017-12-19 21:59 GMT+01:00 Nasron Cheong <nas...@gmail.com>: >>>> >>>>> Hi, >>>>> >>>>> I'm trying to determine steps for migration to the storm-kafka-client >>>>> in order to use the new kafka client. >>>>> >>>>> It's not quite clear to me how offsets are migrated - is there a >>>>> specific set of steps to ensure offsets are moved from the ZK based >>>>> offsets >>>>> into the kafka based offsets? >>>>> >>>>> Or is the original configuration respected, and storm-kafka-client can >>>>> mostly be a drop in replacement? >>>>> >>>>> I want to avoid having spouts reset to the beginning of topics after >>>>> deployment, due to this change. >>>>> >>>>> Thanks. >>>>> >>>>> - Nasron >>>>> >>>> >>>> >>> >> >