Oh thanks, now I see. For some reason I thought the streamCodec is used to get the partitionId when data is taken out of buffer server, but the partitionId is determined when data is put into buffer server. In which case Pramod is right :).
Tim On Thu, Feb 11, 2016 at 7:17 PM, Amol Kekre <[email protected]> wrote: > Tim, > Data for window 20-40 is already in bufferserver. It is post partition > decision? > > Thks > Amol > > On Thu, Feb 11, 2016 at 7:14 PM, Timothy Farkas <[email protected]> > wrote: > > > Hey Pramod, > > > > I thought APEX-339 would cause everyone to get restarted to a common > > checkpoint if P1 failed. But I think I misunderstood. > > Based on what you just said, how do you guarantee that P1 will receive > the > > same data as before? Will Stream Codecs only apply to windows higher > than a > > certain id? > > > > Building off of Gaurav's example. Let's say we have the following > > situation: > > > > 1. we are using Stream Codec A, > > 2. then on Window 30 we start using Stream Code B. > > 3. Window 40 P1 fails and comes back to window 20. > > 4. P2 never failed and continues running this whole time. > > > > Will Stream Codec A still apply to the data P1 gets for window 20 - 30 > and > > Stream Codec B will be used for windows 30 and above? If it is not, some > > data could be > > lost or duplicated. > > > > Thanks, > > Tim > > > > On Thu, Feb 11, 2016 at 6:58 PM, Pramod Immaneni <[email protected] > > > > wrote: > > > > > So P1 and P2 have an upstream operator sending data, when P1 restarts > it > > > will receive same data as before already present in buffer server. If > the > > > upstream operator has to restart all downstream will be reset to same > > > checkpoint. > > > > > > On Thu, Feb 11, 2016 at 6:03 PM, Gaurav Gupta < > [email protected]> > > > wrote: > > > > > > > How will it work in following scenario > > > > > > > > Say Operator O has two partitions P1 and P2. P1 was processing faster > > > than > > > > P2 and streamcodec decided to send more data to P1. P1 process some > > > windows > > > > and then P1 crashes and it came back to previous checkpoint. Now P1 > > comes > > > > on a node which is slow and it processes slowly. So the streamcodec > > > decides > > > > to send less data to P1. In this case will application not loose data > > > some > > > > windows? > > > > > > > > Similarly in a reverse scenario, I think there will be duplicate of > > data. > > > > > > > > > > > > > > > > On Thu, Feb 11, 2016 at 5:46 PM, Pramod Immaneni < > > [email protected] > > > > > > > > wrote: > > > > > > > > > Inline > > > > > > > > > > On Thu, Feb 11, 2016 at 4:32 PM, Timothy Farkas < > [email protected] > > > > > > > > wrote: > > > > > > > > > > > Comments inline > > > > > > > > > > > > +1 Overall as well provided Apex-339 is implemented first and it > is > > > > > > documented that the mechanism should not be used with some > stateful > > > > > > operators. > > > > > > > > > > > > On Thu, Feb 11, 2016 at 4:20 PM, Pramod Immaneni < > > > > [email protected] > > > > > > > > > > > > wrote: > > > > > > > > > > > > > Comments inline > > > > > > > > > > > > > > On Thu, Feb 11, 2016 at 4:13 PM, Timothy Farkas < > > > [email protected] > > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > Hey Pramod, > > > > > > > > > > > > > > > > I agree if APEX-339 is in place then it would work without > > > > > redeploying > > > > > > > > containers for operators that are Stateless, or a subset of > > > > Stateful > > > > > > > > operators. > > > > > > > > > > > > > > > > Addressing your previous questions. > > > > > > > > > > > > > > > > - The StatsListener can be used to see how far behind > operators > > > > are. > > > > > > You > > > > > > > > could determine what window the operator is on, or the number > > of > > > > > tuples > > > > > > > > it's processed so far, or how long > > > > > > > > it takes it to complete a window. > > > > > > > > > > > > > > > > > > > > > > What if tuples are different sizes and number of tuples > processed > > > > > doesn't > > > > > > > reflect how far ahead or behind a downstream partition is? How > is > > > the > > > > > > > information from StatsListener made available to the upstream > > > > partition > > > > > > > codecs. > > > > > > > > > > > > > What is the information Buffer Server can provide that the > > > > StatsListener > > > > > > cannot? > > > > > > > > > > > > > > > > The stats information would have to be relayed down to the upstream > > > > > operators. It's possible. > > > > > > > > > > > > > > > > > > > > > > The StatsListener can trigger a repartition. The information in > the > > > > > > StatsListener can be shared > > > > > > with the partitioner by setting the same object for both in > > populate > > > > Dag. > > > > > > The partitioner can then > > > > > > compute the new Stream Codec. The mechanism by which the upstream > > > would > > > > > be > > > > > > updated with the new > > > > > > Stream Codec would have to be implemented as it's currently not > > > there. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > - Some examples of Stateful operators that require > > repartitioning > > > > of > > > > > > > state > > > > > > > > are the following: > > > > > > > > - Deduper > > > > > > > > In this case after updating the stream codec the > > > > operator > > > > > > may > > > > > > > > allow a previously seen value to pass because the partition > > > didn't > > > > > > > receive > > > > > > > > that value with the previous stream codec. > > > > > > > > - A key value store that holds aggregations for each > key. > > > > > > > > In this case multiple partitions would hold > partial > > > > > > > aggregations > > > > > > > > for a key, when they are expecting to hold the complete > > > > aggregation. > > > > > > > > > > > > > > > > > > > > > > Agreed for deduper. For the second case a unifier is a better > > > > approach > > > > > so > > > > > > > that you are not affected by key skew in general. > > > > > > > > > > > > > This is not always possible. We can discuss this offline, since > it > > > > won't > > > > > > add much to the discussion here to go into the details. > > > > > > > > > > > > > > > > > Yes not always. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Tim > > > > > > > > > > > > > > > > On Thu, Feb 11, 2016 at 4:04 PM, Pramod Immaneni < > > > > > > [email protected] > > > > > > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > Additionally it can be treated as a non-idempotent stream > for > > > > > > recovery. > > > > > > > > > Look at APEXCORE-339. In cases where the downstream > > partitions > > > > > > require > > > > > > > > some > > > > > > > > > key based partitioning, what you are suggesting would be a > > good > > > > > > > approach > > > > > > > > > but it will require more complex logic in the StreamCodec > to > > > both > > > > > key > > > > > > > and > > > > > > > > > load based partitioning. > > > > > > > > > > > > > > > > > > On Thu, Feb 11, 2016 at 3:49 PM, Pramod Immaneni < > > > > > > > [email protected] > > > > > > > > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > How would you know how far behind partitions are without > > > > > > interacting > > > > > > > > with > > > > > > > > > > BufferServer like you were mentioning in the earlier > email. > > > > > > Secondly > > > > > > > > why > > > > > > > > > > would changing where the data is sent to based mandate > > > > > > > re-partitioning > > > > > > > > if > > > > > > > > > > the downstream partitions can handle data with different > > > keys. > > > > > > > > > > > > > > > > > > > > On Thu, Feb 11, 2016 at 3:43 PM, Timothy Farkas < > > > > > > [email protected] > > > > > > > > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > >> Hey Pramod, > > > > > > > > > >> > > > > > > > > > >> I think in general and for recovery the existing > > > Partitioning > > > > > > > > machinery > > > > > > > > > >> can > > > > > > > > > >> be reused to update the Stream Codec. > > > > > > > > > >> The reason why is because If the operator is Stateful > and > > > > > changes > > > > > > > are > > > > > > > > > made > > > > > > > > > >> to the Stream Codec, the state of the partitions will > also > > > > have > > > > > to > > > > > > > be > > > > > > > > > >> repartitioned. > > > > > > > > > >> In this case the number of partitions will remain the > > same, > > > > just > > > > > > the > > > > > > > > > state > > > > > > > > > >> of the partitions is reshuffled. The implementation for > > this > > > > > state > > > > > > > > > >> reshuffling in a fault tolerant way is already handled > by > > > the > > > > > > > Dynamic > > > > > > > > > >> Partitioning logic, so it could be extended to update > the > > > > Stream > > > > > > > Codec > > > > > > > > > as > > > > > > > > > >> well. > > > > > > > > > >> > > > > > > > > > >> If the operator is Stateless, it may be possible to do > > > without > > > > > > > > > redeploying > > > > > > > > > >> any containers. But with the way I am envisioning it, I > > > think > > > > > > there > > > > > > > > > would > > > > > > > > > >> be a lot of difficult to handle corner cases for > recovery. > > > > > > > > > >> > > > > > > > > > >> Tim > > > > > > > > > >> > > > > > > > > > >> On Thu, Feb 11, 2016 at 3:07 PM, Pramod Immaneni < > > > > > > > > > [email protected]> > > > > > > > > > >> wrote: > > > > > > > > > >> > > > > > > > > > >> > Comment inline. > > > > > > > > > >> > > > > > > > > > > >> > On Thu, Feb 11, 2016 at 12:21 PM, Timothy Farkas < > > > > > > > > [email protected] > > > > > > > > > > > > > > > > > > > >> > wrote: > > > > > > > > > >> > > > > > > > > > > >> > > +1 for the idea. > > > > > > > > > >> > > > > > > > > > > > >> > > Gaurav, this could be done idempotently in the same > > way > > > > that > > > > > > > > dynamic > > > > > > > > > >> > > repartitioning is done idempotently. All the > > partitions > > > > are > > > > > > > rolled > > > > > > > > > >> back > > > > > > > > > >> > to > > > > > > > > > >> > > a common checkpoint and the new StreamCodec is > applied > > > > > > starting > > > > > > > > > then. > > > > > > > > > >> The > > > > > > > > > >> > > statistics that the Stream Codec are given are the > > > > > statistics > > > > > > > for > > > > > > > > > the > > > > > > > > > >> > > windows computed before the common checkpoint that > the > > > > > > > partitions > > > > > > > > > are > > > > > > > > > >> > > rolled back to. > > > > > > > > > >> > > > > > > > > > > > >> > > In fact I think this feature could be added easily > by > > > > > avoiding > > > > > > > > > buffer > > > > > > > > > >> > > server entirely and by allowing the Partitioner to > > > > redefine > > > > > > the > > > > > > > > > >> > StreamCodec > > > > > > > > > >> > > for the operator when define partitions is called. > > > > > > > > > >> > > > > > > > > > > > >> > > > > > > > > > > >> > Are you saying this in context of recovery or in > > general? > > > > > > > > > >> > > > > > > > > > > >> > > > > > > > > > > >> > > > > > > > > > > > >> > > Thanks, > > > > > > > > > >> > > Tim > > > > > > > > > >> > > > > > > > > > > > >> > > On Thu, Feb 11, 2016 at 12:07 PM, Amol Kekre < > > > > > > > > [email protected]> > > > > > > > > > >> > wrote: > > > > > > > > > >> > > > > > > > > > > > >> > > > Gaurav, > > > > > > > > > >> > > > It would not be idempotent per partition, but will > > be > > > > > across > > > > > > > all > > > > > > > > > >> > > partitions > > > > > > > > > >> > > > combined. In this case the user would have > > explicitly > > > > > asked > > > > > > > for > > > > > > > > > >> such a > > > > > > > > > >> > > > pattern. > > > > > > > > > >> > > > > > > > > > > > > >> > > > Thks, > > > > > > > > > >> > > > Amol > > > > > > > > > >> > > > > > > > > > > > > >> > > > > > > > > > > > > >> > > > On Thu, Feb 11, 2016 at 12:04 PM, Gaurav Gupta < > > > > > > > > > >> > [email protected] > > > > > > > > > >> > > > > > > > > > > > > >> > > > wrote: > > > > > > > > > >> > > > > > > > > > > > > >> > > > > Pramod, > > > > > > > > > >> > > > > > > > > > > > > > >> > > > > How would it work with recovery? There could be > > > cases > > > > > > where > > > > > > > a > > > > > > > > > >> tuple > > > > > > > > > >> > > went > > > > > > > > > >> > > > to > > > > > > > > > >> > > > > P1 and post recovery it can go to P2 > > > > > > > > > >> > > > > > > > > > > > > > >> > > > > Gaurav > > > > > > > > > >> > > > > > > > > > > > > > >> > > > > On Thu, Feb 11, 2016 at 11:56 AM, Pramod > Immaneni > > < > > > > > > > > > >> > > > [email protected]> > > > > > > > > > >> > > > > wrote: > > > > > > > > > >> > > > > > > > > > > > > > >> > > > > > Hi, > > > > > > > > > >> > > > > > > > > > > > > > > >> > > > > > There are scenarios where the downstream > > > partitions > > > > of > > > > > > an > > > > > > > > > >> upstream > > > > > > > > > >> > > > > operator > > > > > > > > > >> > > > > > are generally not performing uniformly > resulting > > > in > > > > an > > > > > > > > overall > > > > > > > > > >> > > > > sub-optimal > > > > > > > > > >> > > > > > performance dictated by the slowest > partitions. > > > The > > > > > > > reasons > > > > > > > > > >> could > > > > > > > > > >> > be > > > > > > > > > >> > > > data > > > > > > > > > >> > > > > > related such as some partitions are receiving > > more > > > > > data > > > > > > to > > > > > > > > > >> process > > > > > > > > > >> > > than > > > > > > > > > >> > > > > the > > > > > > > > > >> > > > > > others or could be environment related such as > > > some > > > > > > > > partitions > > > > > > > > > >> are > > > > > > > > > >> > > > > running > > > > > > > > > >> > > > > > slower than others because they are on heavily > > > > loaded > > > > > > > nodes. > > > > > > > > > >> > > > > > > > > > > > > > > >> > > > > > A solution based on currently available > > > > functionality > > > > > in > > > > > > > the > > > > > > > > > >> engine > > > > > > > > > >> > > > would > > > > > > > > > >> > > > > > be to write a StreamCodec implementation to > > > > distribute > > > > > > > data > > > > > > > > > >> among > > > > > > > > > >> > the > > > > > > > > > >> > > > > > partitions such that each partition is > receiving > > > > > similar > > > > > > > > > amount > > > > > > > > > >> of > > > > > > > > > >> > > data > > > > > > > > > >> > > > > to > > > > > > > > > >> > > > > > process. We should consider adding > StreamCodecs > > > like > > > > > > these > > > > > > > > to > > > > > > > > > >> the > > > > > > > > > >> > > > library > > > > > > > > > >> > > > > > but these however do not solve the problem > when > > it > > > > is > > > > > > > > > >> environment > > > > > > > > > >> > > > > related. > > > > > > > > > >> > > > > > > > > > > > > > > >> > > > > > For that a better and more comprehensive > > approach > > > > > would > > > > > > be > > > > > > > > > look > > > > > > > > > >> at > > > > > > > > > >> > > how > > > > > > > > > >> > > > > data > > > > > > > > > >> > > > > > is being consumed by the downstream partitions > > > from > > > > > the > > > > > > > > > >> > BufferServer > > > > > > > > > >> > > > and > > > > > > > > > >> > > > > > use that information to make decisions on how > to > > > > send > > > > > > > future > > > > > > > > > >> data. > > > > > > > > > >> > If > > > > > > > > > >> > > > > some > > > > > > > > > >> > > > > > partitions are behind others in consuming data > > > then > > > > > data > > > > > > > can > > > > > > > > > be > > > > > > > > > >> > > > directed > > > > > > > > > >> > > > > to > > > > > > > > > >> > > > > > the other partitions. One way to do this would > > be > > > to > > > > > > relay > > > > > > > > > this > > > > > > > > > >> > type > > > > > > > > > >> > > of > > > > > > > > > >> > > > > > statistical and positional information from > > > > > BufferServer > > > > > > > to > > > > > > > > > the > > > > > > > > > >> > > > upstream > > > > > > > > > >> > > > > > publishers. The publishers can use this > > > information > > > > in > > > > > > > ways > > > > > > > > > >> such as > > > > > > > > > >> > > > > making > > > > > > > > > >> > > > > > it available to StreamCodecs to affect > > destination > > > > of > > > > > > > future > > > > > > > > > >> data. > > > > > > > > > >> > > > > > > > > > > > > > > >> > > > > > What do you think. > > > > > > > > > >> > > > > > > > > > > > > > > >> > > > > > Thanks > > > > > > > > > >> > > > > > > > > > > > > > > >> > > > > > > > > > > > > > >> > > > > > > > > > > > > >> > > > > > > > > > > > >> > > > > > > > > > > >> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >
