Hi Dave, Mattteo, and Sijie, Thanks for pitching in on the discussion! Sijie, it would be great if you could drive this PIP. To be frank, I don't know what the best direction is. Oh, and Ivan, if you have any other idea. Let us know. :)
If there is any changes that need to be made, edit the document On Sat, Mar 2, 2019 at 11:11 PM Sijie Guo <guosi...@gmail.com> wrote: > Matteo, Dave, > > I think you are talking about different things. My comments to both: > > > Once there's support for transactions in messaging API, there will be > > no need for a base class for functions. Rather a config option will > > allow to enable transactional mode. > > Matteo, If I understand your comment correctly, you are talking about > functions using transactions for processing semantics. If so, yes that > would be the end goal. > > > Yes, that way there is no additional broker overhead and whatever happens > when a commit happens is under the control of those making the transaction. > > Dave, this sounds an interesting idea and it is definitely do-able. Because > Pulsar is a multi-layered system and it is built on top of a reliable > storage, so a lot of components are just "stateless", "logical" and not > bound to any physical machines. so when we implement a component / > functionality, we basically implement a logical unit. How to run the logic > unit can be very flexible. It can run as a separated service, or as part of > broker, or in functions. > > - Sijie > > > On Sun, Mar 3, 2019 at 10:52 AM Dave Fisher <dave2w...@comcast.net> wrote: > > > Hi - > > > > > On Mar 2, 2019, at 6:39 PM, Sijie Guo <guosi...@gmail.com> wrote: > > > > > > Dave, > > > > > > You mean implementing the transactions in pulsar function? > > > > Yes, that way there is no additional broker overhead and whatever happens > > when a commit happens is under the control of those making the > transaction. > > > > I’m not sure if it would work, but it seems that functions, spouts, and > > connectors make sense as opposed to burdening the highly performant > brokers. > > > > Regards, > > Dave > > > > > > > > - 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 > > >>>> > > >> > > >> > > > > >
