Dave, You mean implementing the transactions in pulsar function?
- Sijie On Sun, Mar 3, 2019 at 1:52 AM Dave Fisher <dave2w...@comcast.net> wrote: > Hi - > > Is this a case where a Pulsar function base class for transactions would > help? > > Regards, > Dave > > Sent from my iPhone > > > On Mar 2, 2019, at 2:39 AM, Sijie Guo <guosi...@gmail.com> wrote: > > > > Pravega's model is a better model than Kafka - it addressed the > > interleaving problems. However Pravega's model is based on a giant > > replicated log and rewrite the data to a second tiered storage for > > persistence, which basically re-implemented bookkeeper's logic in > broker. A > > fundamental drawback of Pravega is write amplifications. The > amplifications > > of both network and IO bandwidth are huge. If you use bookkeeper both for > > its first-and-second tier storage and assume the bookkeeper replication > > factor is 3, pravega requires 6x network bandwidth and 12x IO bandwidth. > > For a given message, it needs to write 3 times into the journal, and 3 > > times for persistent. The amplifications hugely limit the throughput at > > pravega "brokers". > > > > - Sijie > > > > > > > >> On Sat, Mar 2, 2019 at 6:13 PM Ali Ahmed <ahmal...@gmail.com> wrote: > >> > >> I agree we many want to review pravega's past efforts in this area also. > >> > >> > >> > https://github.com/pravega/pravega/blob/master/documentation/src/docs/transactions.md > >> > >> > https://github.com/pravega/pravega/blob/master/client/src/main/java/io/pravega/client/stream/Transaction.java > >> > >> -Ali > >> > >>> On Sat, Mar 2, 2019 at 1:56 AM Sijie Guo <guosi...@gmail.com> wrote: > >>> > >>> Kafka's implementation is interleaving committed messages with > >> uncommitted > >>> messages at storage. Personally I think it is a very ugly design and > >>> implementation. > >>> > >>> Pulsar is a segment centric system, where we have a shared segment > >> storage > >>> - bookkeeper. I think a better direction is to leverage the segments > (aka > >>> ledgers) > >>> for buffering uncommitted messages and commit the whole segment when > the > >>> whole transaction is committed. > >>> > >>> A rough idea would be: > >>> > >>> 1) for any transaction, write the messages to a separate ledger (or > >>> multiple separate ledger). > >>> 2) during the transaction, accumulates the messages in those ledgers. > >>> 3) when commit, merge the txn ledgers back to the main data ledger. the > >>> merge can be done either adding a meta message where data is stored in > >> the > >>> txn ledger or actually copying the data to data ledger (depending on > the > >>> size of data accumulate in the transaction). > >>> 4) when abort, delete the txn ledger. No other additional work to be > >> done. > >>> > >>> This would be producing a much clear design than Kafka. > >>> > >>> On Ivan's comments: > >>> > >>>> Transactional acknowledgement also needs to be taken into account > >>> > >>> I don't think we have to treat `transactional acknowledgement` as a > >> special > >>> case. currently `acknowledgment` are actually "append" operations into > >>> cursor ledgers. > >>> So the problem set can be reduced as `atomic append` to both data > ledgers > >>> and cursor ledgers. in that way, we can use one solution for handling > >>> appending data and updating cursors. > >>> > >>> Additionally, I think a related topic about transactions would be > >>> supporting large sized message (e.g. >= 5MB). If we take the approach I > >>> described above using a separated ledger for accumulating messages for > a > >>> transaction, that we are easy to model a large size message as a > >>> transaction of chunked messages. > >>> > >>> @Richard, @Ivan let me know what do you think. If you guys think the > >>> direction I raised is a good one to go down, I am happy to write them > >> down > >>> into details, and drive the design and coordinate the implementations > in > >>> the community. > >>> > >>> - Sijie > >>> > >>> On Sat, Mar 2, 2019 at 9:45 AM Richard Yu <yohan.richard...@gmail.com> > >>> wrote: > >>> > >>>> Hi all, > >>>> > >>>> We might be able to get some ideas on implementing this from Kafka: > >>>> > >>>> > >>> > >> > https://cwiki.apache.org/confluence/display/KAFKA/Transactional+Messaging+in+Kafka > >>>> > >>>> Obviously, there is some differences in Kafka and Pulsar internals but > >> at > >>>> some level, the implementation would be similar. > >>>> It should help. > >>>> > >>>> > >>>> > >>>> On Thu, Feb 28, 2019 at 4:29 PM Richard Yu < > yohan.richard...@gmail.com > >>> > >>>> wrote: > >>>> > >>>>> Hi, > >>>>> > >>>>> Per request, I've created a doc so we could get some more input in an > >>>>> organized manner: > >>>>> > >>>>> > >>>> > >>> > >> > https://docs.google.com/document/d/1mSUsJvPgThnWizeQqljKU5244BMEiYHabA6OP6QEHmQ/edit?usp=sharing > >>>>> > >>>>> And for Ivan's questions, I would answer accordingly. > >>>>> > >>>>>> By "set the message to unknown", do you mean the broker will cache > >> the > >>>>>> message, not writing it to any log? > >>>>> > >>>>> We wouldn't cache the message from my interpretation of the steps. > >> What > >>>>> the producer is first sending is a pre-processing message, not the > >> real > >>>>> message itself. This step basically notifies the broker that the > >>> message > >>>> is > >>>>> on its way. So all we have to do is store the message id and its > >>>>> corresponding status in a map, and depending on the producer's > >>> response, > >>>>> the status will change accordingly. > >>>>> > >>>>>> In designs we've discussed previously, this was handled > >>>>>> by a component called the transaction coordinator, which is a > >> logical > >>>>>> component which each broker knows how to talk to. For a transaction > >>>>>> the commit message is sent to the coordinator, which writes it to > >> its > >>>>>> own log, and then goes through each topic in the commit and marks > >> the > >>>>>> transaction as completed. > >>>>> > >>>>> I wasn't aware of previous discussions on this topic, but it seems > >>> pretty > >>>>> good to me. It's certainly better than what I would come up with. > >>>>> If there's any more things we need to talk about, I suppose we could > >>> move > >>>>> it to the google doc to play around with. > >>>>> > >>>>> Hope we can get this PIP rolling. > >>>>> > >>>>> > >>>>> On Thu, Feb 28, 2019 at 2:53 AM Sijie Guo <guosi...@gmail.com> > >> wrote: > >>>>> > >>>>>> Richard, > >>>>>> > >>>>>> Thank you for putting this put and pushing the discussion forward. > >>>>>> > >>>>>> I think this is a very large feature. It might be worth creating a > >>>> google > >>>>>> doc for it (which is better for collaboration). And I believe Ivan > >> has > >>>>>> some > >>>>>> thoughts as well. If you can put up a google doc (make it > >>>> world-editable), > >>>>>> Ivan can probably dump his thoughts there and we can finalize the > >>>>>> discussion and break down into tasks. So the whole community can > >>>> actually > >>>>>> work together at collaborating this. > >>>>>> > >>>>>> Thanks, > >>>>>> Sijie > >>>>>> > >>>>>> On Thu, Feb 28, 2019 at 1:08 PM Richard Yu < > >>> yohan.richard...@gmail.com> > >>>>>> wrote: > >>>>>> > >>>>>>> Hi all, > >>>>>>> > >>>>>>> I would like to create a PIP for issue #2664 on Github. The > >> details > >>> of > >>>>>> the > >>>>>>> PIP are below. > >>>>>>> I hope we could discuss this thoroughly. > >>>>>>> > >>>>>>> Cheers, > >>>>>>> Richard > >>>>>>> > >>>>>>> PIP-31: Add support for transactional messaging > >>>>>>> > >>>>>>> Motivation: Pulsar currently could improve upon their system of > >>>> sending > >>>>>>> packets of data by implementing transactional messaging. This > >> system > >>>>>>> enforces eventual consistency within the system, and allows > >>> operations > >>>>>> to > >>>>>>> be performed atomically. > >>>>>>> > >>>>>>> Proposal: > >>>>>>> > >>>>>>> As described in the issue, we would implement the following policy > >>> in > >>>>>>> Producer and Pulsar Broker: > >>>>>>> 1. The producer produces the pre-processing transaction message. > >> At > >>>> this > >>>>>>> point, the broker will set the status of this message to unknown. > >>>>>>> 2. After the local transaction is successfully executed, the > >> commit > >>>>>> message > >>>>>>> is sent, otherwise the rollback message is sent. > >>>>>>> 3. The broker receives the message. If it is a commit message, it > >>>>>> modifies > >>>>>>> the transaction status to commit, and then sends an actual message > >>> to > >>>>>> the > >>>>>>> consumer queue. At this time, the consumer can consume the > >> message. > >>>>>>> Otherwise, the transaction status is modified to rollback. The > >>> message > >>>>>> will > >>>>>>> be discarded. > >>>>>>> 4. If at step 2, the producer is down or abnormal, at this time, > >> the > >>>>>> broker > >>>>>>> will periodically ask the specific producer for the status of the > >>>>>> message, > >>>>>>> and update the status according to the producer's response, and > >>>> process > >>>>>> it > >>>>>>> according to step 3, the action that comes down. > >>>>>>> > >>>>>>> Specific concerns: > >>>>>>> There are a number of things we will improve upon or add: > >>>>>>> - A configuration called ```maxMessageUnknownTime```. Consider > >> this > >>>>>>> scenario: the pre-processing transaction message is sent, but the > >>>>>> commit or > >>>>>>> rollback message is never received, which could mean that the > >> status > >>>> of > >>>>>> a > >>>>>>> message would be permanently unknown. To avoid this from > >> happening, > >>> we > >>>>>>> would need a config which limits the amount of time the status of > >> a > >>>>>> message > >>>>>>> could be unknown (i.e. ```maxMessageUnknownTime```) After that, > >> the > >>>>>> message > >>>>>>> would be discarded. > >>>>>>> - Logging would be updated to log the status of a message i.e. > >>>> UNKNOWN, > >>>>>>> ROLLBACK, or COMMITTED. This would allow the user to know whether > >> or > >>>>>> not a > >>>>>>> message had failed or fallen through. > >>>>>>> > >>>>>>> Possible Additional API: > >>>>>>> - We would add a method which allows the user to query the state > >> of > >>>> the > >>>>>>> message i.e. ```getStateOfMessage(long id)``` > >>>>>>> > >>>>>> > >>>>> > >>>> > >>> > >> > >> > >> -- > >> -Ali > >> > >
