Hi, Artem, Thanks for the reply.
20. So for the dual-write recipe, we should always call InitProducerId(keepPreparedTxn=true) from the producer? Then, should we change the following in the example to use InitProducerId(true) instead? 1. InitProducerId(false); TC STATE: Empty, ProducerId=42, ProducerEpoch=MAX-1, PrevProducerId=-1, NextProducerId=-1, NextProducerEpoch=-1; RESPONSE ProducerId=42, Epoch=MAX-1, OngoingTxnProducerId=-1, OngoingTxnEpoch=-1. Also, could Flink just follow the dual-write recipe? It's simpler if there is one way to solve the 2pc issue. 21. Could a non 2pc user explicitly set the TransactionTimeoutMs to Integer.MAX_VALUE? 24. Hmm, In KIP-890, without 2pc, the coordinator expects the endTxn request to use the ongoing pid. With 2pc, the coordinator now expects the endTxn request to use the next pid. So, the flow is different, right? 25. "We send out markers using the original ongoing transaction ProducerId and ProducerEpoch" We should use ProducerEpoch + 1 in the marker, right? Jun On Fri, Jan 26, 2024 at 8:35 PM Artem Livshits <alivsh...@confluent.io.invalid> wrote: > Hi Jun, > > > 20. I am a bit confused by how we set keepPreparedTxn. ... > > keepPreparedTxn=true informs the transaction coordinator that it should > keep the ongoing transaction, if any. If the keepPreparedTxn=false, then > any ongoing transaction is aborted (this is exactly the current behavior). > enable2Pc is a separate argument that is controlled by the > *transaction.two.phase.commit.enable *setting on the client. > > To start 2PC, the client just needs to set > *transaction.two.phase.commit.enable*=true in the config. Then if the > client knows the status of the transaction upfront (in the case of Flink, > Flink keeps the knowledge if the transaction is prepared in its own store, > so it always knows upfront), it can set keepPreparedTxn accordingly, then > if the transaction was prepared, it'll be ready for the client to complete > the appropriate action; if the client doesn't have a knowledge that the > transaction is prepared, keepPreparedTxn is going to be false, in which > case we'll get to a clean state (the same way we do today). > > For the dual-write recipe, the client doesn't know upfront if the > transaction is prepared, this information is implicitly encoded > PreparedTxnState value that can be used to resolve the transaction state. > In that case, keepPreparedTxn should always be true, because we don't know > upfront and we don't want to accidentally abort a committed transaction. > > The forceTerminateTransaction call can just use keepPreparedTxn=false, it > actually doesn't matter if it sets Enable2Pc flag. > > > 21. TransactionLogValue: Do we need some field to identify whether this > is written for 2PC so that ongoing txn is never auto aborted? > > The TransactionTimeoutMs would be set to Integer.MAX_VALUE if 2PC was > enabled. I've added a note to the KIP about this. > > > 22 > > You're right it's a typo. I fixed it as well as step 9 (REQUEST: > ProducerId=73, ProducerEpoch=MAX). > > > 23. It's a bit weird that Enable2Pc is driven by a config while > KeepPreparedTxn is from an API param ... > > The intent to use 2PC doesn't change from transaction to transaction, but > the intent to keep prepared txn may change from transaction to > transaction. In dual-write recipes the distinction is not clear, but for > use cases where keepPreparedTxn value is known upfront (e.g. Flink) it's > more prominent. E.g. a Flink's Kafka sink operator could be deployed with > *transaction.two.phase.commit.enable*=true hardcoded in the image, but > keepPreparedTxn cannot be hardcoded in the image, because it depends on the > job manager's state. > > > 24 > > The flow is actually going to be the same way as it is now -- the "main" > producer id + epoch needs to be used in all operations to prevent fencing > (it's sort of a common "header" in all RPC calls that follow the same > rules). The ongoing txn info is just additional info for making a commit / > abort decision based on the PreparedTxnState from the DB. > > --Artem > > On Thu, Jan 25, 2024 at 11:05 AM Jun Rao <j...@confluent.io.invalid> wrote: > > > Hi, Artem, > > > > Thanks for the reply. A few more comments. > > > > 20. I am a bit confused by how we set keepPreparedTxn. From the KIP, I > got > > the following (1) to start 2pc, we call > > InitProducerId(keepPreparedTxn=false); (2) when the producer fails and > > needs to do recovery, it calls InitProducerId(keepPreparedTxn=true); (3) > > Admin.forceTerminateTransaction() calls > > InitProducerId(keepPreparedTxn=false). > > 20.1 In (1), when a producer calls InitProducerId(false) with 2pc > enabled, > > and there is an ongoing txn, should the server return an error to the > > InitProducerId request? If so, what would be the error code? > > 20.2 How do we distinguish between (1) and (3)? It's the same API call > but > > (1) doesn't abort ongoing txn and (2) does. > > 20.3 The usage in (1) seems unintuitive. 2pc implies keeping the ongoing > > txn. So, setting keepPreparedTxn to false to start 2pc seems counter > > intuitive. > > > > 21. TransactionLogValue: Do we need some field to identify whether this > is > > written for 2PC so that ongoing txn is never auto aborted? > > > > 22. "8. InitProducerId(true); TC STATE: Ongoing, ProducerId=42, > > ProducerEpoch=MAX-1, PrevProducerId=-1, NextProducerId=73, > > NextProducerEpoch=MAX; RESPONSE ProducerId=73, Epoch=MAX-1, > > OngoingTxnProducerId=42, OngoingTxnEpoch=MAX-1" > > It seems in the above example, Epoch in RESPONSE should be MAX to match > > NextProducerEpoch? > > > > 23. It's a bit weird that Enable2Pc is driven by a config > > while KeepPreparedTxn is from an API param. Should we make them more > > consistent since they seem related? > > > > 24. "9. Commit; REQUEST: ProducerId=73, ProducerEpoch=MAX-1; TC STATE: > > PrepareCommit, ProducerId=42, ProducerEpoch=MAX, PrevProducerId=73, > > NextProducerId=85, NextProducerEpoch=0; RESPONSE ProducerId=85, Epoch=0, > > When a commit request is sent, it uses the latest ProducerId and > > ProducerEpoch." > > The step where we use the next produceId to commit an old txn works, but > > can be confusing. It's going to be hard for people implementing this new > > client protocol to figure out when to use the current or the new > producerId > > in the EndTxnRequest. One potential way to improve this is to extend > > EndTxnRequest with a new field like expectedNextProducerId. Then we can > > always use the old produceId in the existing field, but set > > expectedNextProducerId to bypass the fencing logic when needed. > > > > Thanks, > > > > Jun > > > > > > > > On Mon, Dec 18, 2023 at 2:06 PM Artem Livshits > > <alivsh...@confluent.io.invalid> wrote: > > > > > Hi Jun, > > > > > > Thank you for the comments. > > > > > > > 10. For the two new fields in Enable2Pc and KeepPreparedTxn ... > > > > > > I added a note that all combinations are valid. Enable2Pc=false & > > > KeepPreparedTxn=true could be potentially useful for backward > > compatibility > > > with Flink, when the new version of Flink that implements KIP-319 tries > > to > > > work with a cluster that doesn't authorize 2PC. > > > > > > > 11. InitProducerIdResponse: If there is no ongoing txn, what will > > > OngoingTxnProducerId and OngoingTxnEpoch be set? > > > > > > I added a note that they will be set to -1. The client then will know > > that > > > there is no ongoing txn and .completeTransaction becomes a no-op (but > > still > > > required before .send is enabled). > > > > > > > 12. ListTransactionsRequest related changes: It seems those are > already > > > covered by KIP-994? > > > > > > Removed from this KIP. > > > > > > > 13. TransactionalLogValue ... > > > > > > This is now updated to work on top of KIP-890. > > > > > > > 14. "Note that the (producerId, epoch) pair that corresponds to the > > > ongoing transaction ... > > > > > > This is now updated to work on top of KIP-890. > > > > > > > 15. active-transaction-total-time-max : ... > > > > > > Updated. > > > > > > > 16. "transaction.two.phase.commit.enable The default would be > ‘false’. > > > If it’s ‘false’, 2PC functionality is disabled even if the ACL is set > ... > > > > > > Disabling 2PC effectively removes all authorization to use it, hence I > > > thought TRANSACTIONAL_ID_AUTHORIZATION_FAILED would be appropriate. > > > > > > Do you suggest using a different error code for 2PC authorization vs > some > > > other authorization (e.g. TRANSACTIONAL_ID_2PC_AUTHORIZATION_FAILED) > or a > > > different code for disabled vs. unauthorised (e.g. > > > TWO_PHASE_COMMIT_DISABLED) or both? > > > > > > > 17. completeTransaction(). We expect this to be only used during > > > recovery. > > > > > > It can also be used if, say, a commit to the database fails and the > > result > > > is inconclusive, e.g. > > > > > > 1. Begin DB transaction > > > 2. Begin Kafka transaction > > > 3. Prepare Kafka transaction > > > 4. Commit DB transaction > > > 5. The DB commit fails, figure out the state of the transaction by > > reading > > > the PreparedTxnState from DB > > > 6. Complete Kafka transaction with the PreparedTxnState. > > > > > > > 18. "either prepareTransaction was called or initTransaction(true) > was > > > called": "either" should be "neither"? > > > > > > Updated. > > > > > > > 19. Since InitProducerId always bumps up the epoch, it creates a > > > situation ... > > > > > > InitProducerId only bumps the producer epoch, the ongoing transaction > > epoch > > > stays the same, no matter how many times the InitProducerId is called > > > before the transaction is completed. Eventually the epoch may > overflow, > > > and then a new producer id would be allocated, but the ongoing > > transaction > > > producer id would stay the same. > > > > > > I've added a couple examples in the KIP ( > > > > > > > > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-939%3A+Support+Participation+in+2PC#KIP939:SupportParticipationin2PC-PersistedDataFormatChanges > > > ) > > > that walk through some scenarios and show how the state is changed. > > > > > > -Artem > > > > > > On Fri, Dec 8, 2023 at 6:04 PM Jun Rao <j...@confluent.io.invalid> > wrote: > > > > > > > Hi, Artem, > > > > > > > > Thanks for the KIP. A few comments below. > > > > > > > > 10. For the two new fields in Enable2Pc and KeepPreparedTxn in > > > > InitProducerId, it would be useful to document a bit more detail on > > what > > > > values are set under what cases. For example, are all four > combinations > > > > valid? > > > > > > > > 11. InitProducerIdResponse: If there is no ongoing txn, what will > > > > OngoingTxnProducerId and OngoingTxnEpoch be set? > > > > > > > > 12. ListTransactionsRequest related changes: It seems those are > already > > > > covered by KIP-994? > > > > > > > > 13. TransactionalLogValue: Could we name TransactionProducerId and > > > > ProducerId better? It's not clear from the name which is for which. > > > > > > > > 14. "Note that the (producerId, epoch) pair that corresponds to the > > > ongoing > > > > transaction is going to be written instead of the existing ProducerId > > and > > > > ProducerEpoch fields (which are renamed to reflect the semantics) to > > > > support downgrade.": I am a bit confused on that. Are we writing > > > different > > > > values to the existing fields? Then, we can't downgrade, right? > > > > > > > > 15. active-transaction-total-time-max : Would > > > > active-transaction-open-time-max be more intuitive? Also, could we > > > include > > > > the full name (group, tags, etc)? > > > > > > > > 16. "transaction.two.phase.commit.enable The default would be > ‘false’. > > > If > > > > it’s ‘false’, 2PC functionality is disabled even if the ACL is set, > > > clients > > > > that attempt to use this functionality would receive > > > > TRANSACTIONAL_ID_AUTHORIZATION_FAILED error." > > > > TRANSACTIONAL_ID_AUTHORIZATION_FAILED seems unintuitive for the > client > > to > > > > understand what the actual cause is. > > > > > > > > 17. completeTransaction(). We expect this to be only used during > > > recovery. > > > > Could we document this clearly? Could we prevent it from being used > > > > incorrectly (e.g. throw an exception if the producer has called other > > > > methods like send())? > > > > > > > > 18. "either prepareTransaction was called or initTransaction(true) > was > > > > called": "either" should be "neither"? > > > > > > > > 19. Since InitProducerId always bumps up the epoch, it creates a > > > situation > > > > where there could be multiple outstanding txns. The following is an > > > example > > > > of a potential problem during recovery. > > > > The last txn epoch in the external store is 41 when the app dies. > > > > Instance1 is created for recovery. > > > > 1. (instance1) InitProducerId(keepPreparedTxn=true), epoch=42, > > > > ongoingEpoch=41 > > > > 2. (instance1) dies before completeTxn(41) can be called. > > > > Instance2 is created for recovery. > > > > 3. (instance2) InitProducerId(keepPreparedTxn=true), epoch=43, > > > > ongoingEpoch=42 > > > > 4. (instance2) completeTxn(41) => abort > > > > The first problem is that 41 now is aborted when it should be > > > committed. > > > > The second one is that it's not clear who could abort epoch 42, which > > is > > > > still open. > > > > > > > > Jun > > > > > > > > > > > > On Thu, Dec 7, 2023 at 2:43 PM Justine Olshan > > > <jols...@confluent.io.invalid > > > > > > > > > wrote: > > > > > > > > > Hey Artem, > > > > > > > > > > Thanks for the updates. I think what you say makes sense. I just > > > updated > > > > my > > > > > KIP so I want to reconcile some of the changes we made especially > > with > > > > > respect to the TransactionLogValue. > > > > > > > > > > Firstly, I believe tagged fields require a default value so that if > > > they > > > > > are not filled, we return the default (and know that they were > > empty). > > > > For > > > > > my KIP, I proposed the default for producer ID tagged fields should > > be > > > > -1. > > > > > I was wondering if we could update the KIP to include the default > > > values > > > > > for producer ID and epoch. > > > > > > > > > > Next, I noticed we decided to rename the fields. I guess that the > > field > > > > > "NextProducerId" in my KIP correlates to "ProducerId" in this KIP. > Is > > > > that > > > > > correct? So we would have "TransactionProducerId" for the > non-tagged > > > > field > > > > > and have "ProducerId" (NextProducerId) and "PrevProducerId" as > tagged > > > > > fields the final version after KIP-890 and KIP-936 are implemented. > > Is > > > > this > > > > > correct? I think the tags will need updating, but that is trivial. > > > > > > > > > > The final question I had was with respect to storing the new epoch. > > In > > > > > KIP-890 part 2 (epoch bumps) I think we concluded that we don't > need > > to > > > > > store the epoch since we can interpret the previous epoch based on > > the > > > > > producer ID. But here we could call the InitProducerId multiple > times > > > and > > > > > we only want the producer with the correct epoch to be able to > commit > > > the > > > > > transaction. Is that the correct reasoning for why we need epoch > here > > > but > > > > > not the Prepare/Commit state. > > > > > > > > > > Thanks, > > > > > Justine > > > > > > > > > > On Wed, Nov 22, 2023 at 9:48 AM Artem Livshits > > > > > <alivsh...@confluent.io.invalid> wrote: > > > > > > > > > > > Hi Justine, > > > > > > > > > > > > After thinking a bit about supporting atomic dual writes for > Kafka > > + > > > > > NoSQL > > > > > > database, I came to a conclusion that we do need to bump the > epoch > > > even > > > > > > with InitProducerId(keepPreparedTxn=true). As I described in my > > > > previous > > > > > > email, we wouldn't need to bump the epoch to protect from zombies > > so > > > > that > > > > > > reasoning is still true. But we cannot protect from split-brain > > > > > scenarios > > > > > > when two or more instances of a producer with the same > > transactional > > > id > > > > > try > > > > > > to produce at the same time. The dual-write example for SQL > > > databases > > > > ( > > > > > > https://github.com/apache/kafka/pull/14231/files) doesn't have a > > > > > > split-brain problem because execution is protected by the update > > lock > > > > on > > > > > > the transaction state record; however NoSQL databases may not > have > > > this > > > > > > protection (I'll write an example for NoSQL database dual-write > > > soon). > > > > > > > > > > > > In a nutshell, here is an example of a split-brain scenario: > > > > > > > > > > > > 1. (instance1) InitProducerId(keepPreparedTxn=true), got > > epoch=42 > > > > > > 2. (instance2) InitProducerId(keepPreparedTxn=true), got > > epoch=42 > > > > > > 3. (instance1) CommitTxn, epoch bumped to 43 > > > > > > 4. (instance2) CommitTxn, this is considered a retry, so it > got > > > > epoch > > > > > 43 > > > > > > as well > > > > > > 5. (instance1) Produce messageA w/sequence 1 > > > > > > 6. (instance2) Produce messageB w/sequence 1, this is > > considered a > > > > > > duplicate > > > > > > 7. (instance2) Produce messageC w/sequence 2 > > > > > > 8. (instance1) Produce messageD w/sequence 2, this is > > considered a > > > > > > duplicate > > > > > > > > > > > > Now if either of those commit the transaction, it would have a > mix > > of > > > > > > messages from the two instances (messageA and messageC). With > the > > > > proper > > > > > > epoch bump, instance1 would get fenced at step 3. > > > > > > > > > > > > In order to update epoch in InitProducerId(keepPreparedTxn=true) > we > > > > need > > > > > to > > > > > > preserve the ongoing transaction's epoch (and producerId, if the > > > epoch > > > > > > overflows), because we'd need to make a correct decision when we > > > > compare > > > > > > the PreparedTxnState that we read from the database with the > > > > (producerId, > > > > > > epoch) of the ongoing transaction. > > > > > > > > > > > > I've updated the KIP with the following: > > > > > > > > > > > > - Ongoing transaction now has 2 (producerId, epoch) pairs -- > one > > > > pair > > > > > > describes the ongoing transaction, the other pair describes > > > expected > > > > > > epoch > > > > > > for operations on this transactional id > > > > > > - InitProducerIdResponse now returns 2 (producerId, epoch) > pairs > > > > > > - TransactionalLogValue now has 2 (producerId, epoch) pairs, > the > > > new > > > > > > values added as tagged fields, so it's easy to downgrade > > > > > > - Added a note about downgrade in the Compatibility section > > > > > > - Added a rejected alternative > > > > > > > > > > > > -Artem > > > > > > > > > > > > On Fri, Oct 6, 2023 at 5:16 PM Artem Livshits < > > > alivsh...@confluent.io> > > > > > > wrote: > > > > > > > > > > > > > Hi Justine, > > > > > > > > > > > > > > Thank you for the questions. Currently (pre-KIP-939) we always > > > bump > > > > > the > > > > > > > epoch on InitProducerId and abort an ongoing transaction (if > > > any). I > > > > > > > expect this behavior will continue with KIP-890 as well. > > > > > > > > > > > > > > With KIP-939 we need to support the case when the ongoing > > > transaction > > > > > > > needs to be preserved when keepPreparedTxn=true. Bumping epoch > > > > without > > > > > > > aborting or committing a transaction is tricky because epoch > is a > > > > short > > > > > > > value and it's easy to overflow. Currently, the overflow case > is > > > > > handled > > > > > > > by aborting the ongoing transaction, which would send out > > > transaction > > > > > > > markers with epoch=Short.MAX_VALUE to the partition leaders, > > which > > > > > would > > > > > > > fence off any messages with the producer id that started the > > > > > transaction > > > > > > > (they would have epoch that is less than Short.MAX_VALUE). > Then > > it > > > > is > > > > > > safe > > > > > > > to allocate a new producer id and use it in new transactions. > > > > > > > > > > > > > > We could say that maybe when keepPreparedTxn=true we bump epoch > > > > unless > > > > > it > > > > > > > leads to overflow, and don't bump epoch in the overflow case. > I > > > > don't > > > > > > > think it's a good solution because if it's not safe to keep the > > > same > > > > > > epoch > > > > > > > when keepPreparedTxn=true, then we must handle the epoch > overflow > > > > case > > > > > as > > > > > > > well. So either we should convince ourselves that it's safe to > > > keep > > > > > the > > > > > > > epoch and do it in the general case, or we always bump the > epoch > > > and > > > > > > handle > > > > > > > the overflow. > > > > > > > > > > > > > > With KIP-890, we bump the epoch on every transaction commit / > > > abort. > > > > > > This > > > > > > > guarantees that even if InitProducerId(keepPreparedTxn=true) > > > doesn't > > > > > > > increment epoch on the ongoing transaction, the client will > have > > to > > > > > call > > > > > > > commit or abort to finish the transaction and will increment > the > > > > epoch > > > > > > (and > > > > > > > handle epoch overflow, if needed). If the ongoing transaction > > was > > > > in a > > > > > > bad > > > > > > > state and had some zombies waiting to arrive, the abort > operation > > > > would > > > > > > > fence them because with KIP-890 every abort would bump the > epoch. > > > > > > > > > > > > > > We could also look at this from the following perspective. > With > > > > > KIP-890, > > > > > > > zombies won't be able to cross transaction boundaries; each > > > > transaction > > > > > > > completion creates a boundary and any activity in the past gets > > > > > confined > > > > > > in > > > > > > > the boundary. Then data in any partition would look like this: > > > > > > > > > > > > > > 1. message1, epoch=42 > > > > > > > 2. message2, epoch=42 > > > > > > > 3. message3, epoch=42 > > > > > > > 4. marker (commit or abort), epoch=43 > > > > > > > > > > > > > > Now if we inject steps 3a and 3b like this: > > > > > > > > > > > > > > 1. message1, epoch=42 > > > > > > > 2. message2, epoch=42 > > > > > > > 3. message3, epoch=42 > > > > > > > 3a. crash > > > > > > > 3b. InitProducerId(keepPreparedTxn=true) > > > > > > > 4. marker (commit or abort), epoch=43 > > > > > > > > > > > > > > The invariant still holds even with steps 3a and 3b -- whatever > > > > > activity > > > > > > > was in the past will get confined in the past with mandatory > > abort > > > / > > > > > > commit > > > > > > > that must follow InitProducerId(keepPreparedTxn=true). > > > > > > > > > > > > > > So KIP-890 provides the proper isolation between transactions, > so > > > > > > > injecting crash + InitProducerId(keepPreparedTxn=true) into the > > > > > > > transaction sequence is safe from the zombie protection > > > perspective. > > > > > > > > > > > > > > That said, I'm still thinking about it and looking for cases > that > > > > might > > > > > > > break because we don't bump epoch when > > > > > > > InitProducerId(keepPreparedTxn=true), if such cases exist, > we'll > > > need > > > > > to > > > > > > > develop the logic to handle epoch overflow for ongoing > > > transactions. > > > > > > > > > > > > > > -Artem > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Tue, Oct 3, 2023 at 10:15 AM Justine Olshan > > > > > > > <jols...@confluent.io.invalid> wrote: > > > > > > > > > > > > > >> Hey Artem, > > > > > > >> > > > > > > >> Thanks for the KIP. I had a question about epoch bumping. > > > > > > >> > > > > > > >> Previously when we send an InitProducerId request on Producer > > > > startup, > > > > > > we > > > > > > >> bump the epoch and abort the transaction. Is it correct to > > assume > > > > that > > > > > > we > > > > > > >> will still bump the epoch, but just not abort the transaction? > > > > > > >> If we still bump the epoch in this case, how does this > interact > > > with > > > > > > >> KIP-890 where we also bump the epoch on every transaction. (I > > > think > > > > > this > > > > > > >> means that we may skip epochs and the data itself will all > have > > > the > > > > > same > > > > > > >> epoch) > > > > > > >> > > > > > > >> I may have follow ups depending on the answer to this. :) > > > > > > >> > > > > > > >> Thanks, > > > > > > >> Justine > > > > > > >> > > > > > > >> On Thu, Sep 7, 2023 at 9:51 PM Artem Livshits > > > > > > >> <alivsh...@confluent.io.invalid> wrote: > > > > > > >> > > > > > > >> > Hi Alex, > > > > > > >> > > > > > > > >> > Thank you for your questions. > > > > > > >> > > > > > > > >> > > the purpose of having broker-level > > > > > > transaction.two.phase.commit.enable > > > > > > >> > > > > > > > >> > The thinking is that 2PC is a bit of an advanced construct > so > > > > > enabling > > > > > > >> 2PC > > > > > > >> > in a Kafka cluster should be an explicit decision. If it is > > set > > > > to > > > > > > >> 'false' > > > > > > >> > InitiProducerId (and initTransactions) would > > > > > > >> > return TRANSACTIONAL_ID_AUTHORIZATION_FAILED. > > > > > > >> > > > > > > > >> > > WDYT about adding an AdminClient method that returns the > > state > > > > of > > > > > > >> > transaction.two.phase.commit.enable > > > > > > >> > > > > > > > >> > I wonder if the client could just try to use 2PC and then > > handle > > > > the > > > > > > >> error > > > > > > >> > (e.g. if it needs to fall back to ordinary transactions). > > This > > > > way > > > > > it > > > > > > >> > could uniformly handle cases when Kafka cluster doesn't > > support > > > > 2PC > > > > > > >> > completely and cases when 2PC is restricted to certain > users. > > > We > > > > > > could > > > > > > >> > also expose this config in describeConfigs, if the fallback > > > > approach > > > > > > >> > doesn't work for some scenarios. > > > > > > >> > > > > > > > >> > -Artem > > > > > > >> > > > > > > > >> > > > > > > > >> > On Tue, Sep 5, 2023 at 12:45 PM Alexander Sorokoumov > > > > > > >> > <asorokou...@confluent.io.invalid> wrote: > > > > > > >> > > > > > > > >> > > Hi Artem, > > > > > > >> > > > > > > > > >> > > Thanks for publishing this KIP! > > > > > > >> > > > > > > > > >> > > Can you please clarify the purpose of having broker-level > > > > > > >> > > transaction.two.phase.commit.enable config in addition to > > the > > > > new > > > > > > >> ACL? If > > > > > > >> > > the brokers are configured with > > > > > > >> > transaction.two.phase.commit.enable=false, > > > > > > >> > > at what point will a client configured with > > > > > > >> > > transaction.two.phase.commit.enable=true fail? Will it > > happen > > > at > > > > > > >> > > KafkaProducer#initTransactions? > > > > > > >> > > > > > > > > >> > > WDYT about adding an AdminClient method that returns the > > state > > > > of > > > > > t > > > > > > >> > > ransaction.two.phase.commit.enable? This way, clients > would > > > know > > > > > in > > > > > > >> > advance > > > > > > >> > > if 2PC is enabled on the brokers. > > > > > > >> > > > > > > > > >> > > Best, > > > > > > >> > > Alex > > > > > > >> > > > > > > > > >> > > On Fri, Aug 25, 2023 at 9:40 AM Roger Hoover < > > > > > > roger.hoo...@gmail.com> > > > > > > >> > > wrote: > > > > > > >> > > > > > > > > >> > > > Other than supporting multiplexing transactional streams > > on > > > a > > > > > > single > > > > > > >> > > > producer, I don't see how to improve it. > > > > > > >> > > > > > > > > > >> > > > On Thu, Aug 24, 2023 at 12:12 PM Artem Livshits > > > > > > >> > > > <alivsh...@confluent.io.invalid> wrote: > > > > > > >> > > > > > > > > > >> > > > > Hi Roger, > > > > > > >> > > > > > > > > > > >> > > > > Thank you for summarizing the cons. I agree and I'm > > > curious > > > > > > what > > > > > > >> > would > > > > > > >> > > > be > > > > > > >> > > > > the alternatives to solve these problems better and if > > > they > > > > > can > > > > > > be > > > > > > >> > > > > incorporated into this proposal (or built > independently > > in > > > > > > >> addition > > > > > > >> > to > > > > > > >> > > or > > > > > > >> > > > > on top of this proposal). E.g. one potential > extension > > we > > > > > > >> discussed > > > > > > >> > > > > earlier in the thread could be multiplexing logical > > > > > > transactional > > > > > > >> > > > "streams" > > > > > > >> > > > > with a single producer. > > > > > > >> > > > > > > > > > > >> > > > > -Artem > > > > > > >> > > > > > > > > > > >> > > > > On Wed, Aug 23, 2023 at 4:50 PM Roger Hoover < > > > > > > >> roger.hoo...@gmail.com > > > > > > >> > > > > > > > > >> > > > > wrote: > > > > > > >> > > > > > > > > > > >> > > > > > Thanks. I like that you're moving Kafka toward > > > supporting > > > > > > this > > > > > > >> > > > > dual-write > > > > > > >> > > > > > pattern. Each use case needs to consider the > > tradeoffs. > > > > > You > > > > > > >> > already > > > > > > >> > > > > > summarized the pros very well in the KIP. I would > > > > summarize > > > > > > the > > > > > > >> > cons > > > > > > >> > > > > > as follows: > > > > > > >> > > > > > > > > > > > >> > > > > > - you sacrifice availability - each write requires > > both > > > DB > > > > > and > > > > > > >> > Kafka > > > > > > >> > > to > > > > > > >> > > > > be > > > > > > >> > > > > > available so I think your overall application > > > availability > > > > > is > > > > > > 1 > > > > > > >> - > > > > > > >> > > p(DB > > > > > > >> > > > is > > > > > > >> > > > > > unavailable)*p(Kafka is unavailable). > > > > > > >> > > > > > - latency will be higher and throughput lower - each > > > write > > > > > > >> requires > > > > > > >> > > > both > > > > > > >> > > > > > writes to DB and Kafka while holding an exclusive > lock > > > in > > > > > DB. > > > > > > >> > > > > > - you need to create a producer per unit of > > concurrency > > > in > > > > > > your > > > > > > >> app > > > > > > >> > > > which > > > > > > >> > > > > > has some overhead in the app and Kafka side (number > of > > > > > > >> connections, > > > > > > >> > > > poor > > > > > > >> > > > > > batching). I assume the producers would need to be > > > > > configured > > > > > > >> for > > > > > > >> > > low > > > > > > >> > > > > > latency (linger.ms=0) > > > > > > >> > > > > > - there's some complexity in managing stable > > > transactional > > > > > ids > > > > > > >> for > > > > > > >> > > each > > > > > > >> > > > > > producer/concurrency unit in your application. With > > k8s > > > > > > >> > deployment, > > > > > > >> > > > you > > > > > > >> > > > > > may need to switch to something like a StatefulSet > > that > > > > > gives > > > > > > >> each > > > > > > >> > > pod > > > > > > >> > > > a > > > > > > >> > > > > > stable identity across restarts. On top of that pod > > > > > identity > > > > > > >> which > > > > > > >> > > you > > > > > > >> > > > > can > > > > > > >> > > > > > use as a prefix, you then assign unique > transactional > > > ids > > > > to > > > > > > >> each > > > > > > >> > > > > > concurrency unit (thread/goroutine). > > > > > > >> > > > > > > > > > > > >> > > > > > On Wed, Aug 23, 2023 at 12:53 PM Artem Livshits > > > > > > >> > > > > > <alivsh...@confluent.io.invalid> wrote: > > > > > > >> > > > > > > > > > > > >> > > > > > > Hi Roger, > > > > > > >> > > > > > > > > > > > > >> > > > > > > Thank you for the feedback. You make a very good > > > point > > > > > that > > > > > > >> we > > > > > > >> > > also > > > > > > >> > > > > > > discussed internally. Adding support for multiple > > > > > > concurrent > > > > > > >> > > > > > > transactions in one producer could be valuable but > > it > > > > > seems > > > > > > to > > > > > > >> > be a > > > > > > >> > > > > > fairly > > > > > > >> > > > > > > large and independent change that would deserve a > > > > separate > > > > > > >> KIP. > > > > > > >> > If > > > > > > >> > > > > such > > > > > > >> > > > > > > support is added we could modify 2PC functionality > > to > > > > > > >> incorporate > > > > > > >> > > > that. > > > > > > >> > > > > > > > > > > > > >> > > > > > > > Maybe not too bad but a bit of pain to manage > > these > > > > ids > > > > > > >> inside > > > > > > >> > > each > > > > > > >> > > > > > > process and across all application processes. > > > > > > >> > > > > > > > > > > > > >> > > > > > > I'm not sure if supporting multiple transactions > in > > > one > > > > > > >> producer > > > > > > >> > > > would > > > > > > >> > > > > > make > > > > > > >> > > > > > > id management simpler: we'd need to store a piece > of > > > > data > > > > > > per > > > > > > >> > > > > > transaction, > > > > > > >> > > > > > > so whether it's N producers with a single > > transaction > > > > or N > > > > > > >> > > > transactions > > > > > > >> > > > > > > with a single producer, it's still roughly the > same > > > > amount > > > > > > of > > > > > > >> > data > > > > > > >> > > to > > > > > > >> > > > > > > manage. In fact, managing transactional ids > > (current > > > > > > >> proposal) > > > > > > >> > > might > > > > > > >> > > > > be > > > > > > >> > > > > > > easier, because the id is controlled by the > > > application > > > > > and > > > > > > it > > > > > > >> > > knows > > > > > > >> > > > > how > > > > > > >> > > > > > to > > > > > > >> > > > > > > complete the transaction after crash / restart; > > while > > > a > > > > > TID > > > > > > >> would > > > > > > >> > > be > > > > > > >> > > > > > > generated by Kafka and that would create a > question > > of > > > > > > >> starting > > > > > > >> > > Kafka > > > > > > >> > > > > > > transaction, but not saving its TID and then > > crashing, > > > > > then > > > > > > >> > > figuring > > > > > > >> > > > > out > > > > > > >> > > > > > > which transactions to abort and etc. > > > > > > >> > > > > > > > > > > > > >> > > > > > > > 2) creating a separate producer for each > > concurrency > > > > > slot > > > > > > in > > > > > > >> > the > > > > > > >> > > > > > > application > > > > > > >> > > > > > > > > > > > > >> > > > > > > This is a very valid concern. Maybe we'd need to > > have > > > > > some > > > > > > >> > > > > multiplexing > > > > > > >> > > > > > of > > > > > > >> > > > > > > transactional logical "streams" over the same > > > > connection. > > > > > > >> Seems > > > > > > >> > > > like a > > > > > > >> > > > > > > separate KIP, though. > > > > > > >> > > > > > > > > > > > > >> > > > > > > > Otherwise, it seems you're left with > > single-threaded > > > > > model > > > > > > >> per > > > > > > >> > > > > > > application process? > > > > > > >> > > > > > > > > > > > > >> > > > > > > That's a fair assessment. Not necessarily exactly > > > > > > >> > single-threaded > > > > > > >> > > > per > > > > > > >> > > > > > > application, but a single producer per thread > model > > > > (i.e. > > > > > an > > > > > > >> > > > > application > > > > > > >> > > > > > > could have a pool of threads + producers to > increase > > > > > > >> > concurrency). > > > > > > >> > > > > > > > > > > > > >> > > > > > > -Artem > > > > > > >> > > > > > > > > > > > > >> > > > > > > On Tue, Aug 22, 2023 at 7:22 PM Roger Hoover < > > > > > > >> > > roger.hoo...@gmail.com > > > > > > >> > > > > > > > > > > >> > > > > > > wrote: > > > > > > >> > > > > > > > > > > > > >> > > > > > > > Artem, > > > > > > >> > > > > > > > > > > > > > >> > > > > > > > Thanks for the reply. > > > > > > >> > > > > > > > > > > > > > >> > > > > > > > If I understand correctly, Kafka does not > support > > > > > > concurrent > > > > > > >> > > > > > transactions > > > > > > >> > > > > > > > from the same producer (transactional id). I > > think > > > > this > > > > > > >> means > > > > > > >> > > that > > > > > > >> > > > > > > > applications that want to support in-process > > > > concurrency > > > > > > >> (say > > > > > > >> > > > > > > thread-level > > > > > > >> > > > > > > > concurrency with row-level DB locking) would > need > > to > > > > > > manage > > > > > > >> > > > separate > > > > > > >> > > > > > > > transactional ids and producers per thread and > > then > > > > > store > > > > > > >> txn > > > > > > >> > > state > > > > > > >> > > > > > > > accordingly. The potential usability > downsides I > > > see > > > > > are > > > > > > >> > > > > > > > 1) managing a set of transactional ids for each > > > > > > application > > > > > > >> > > process > > > > > > >> > > > > > that > > > > > > >> > > > > > > > scales up to it's max concurrency. Maybe not > too > > > bad > > > > > but > > > > > > a > > > > > > >> bit > > > > > > >> > > of > > > > > > >> > > > > pain > > > > > > >> > > > > > > to > > > > > > >> > > > > > > > manage these ids inside each process and across > > all > > > > > > >> application > > > > > > >> > > > > > > processes. > > > > > > >> > > > > > > > 2) creating a separate producer for each > > concurrency > > > > > slot > > > > > > in > > > > > > >> > the > > > > > > >> > > > > > > > application - this could create a lot more > > producers > > > > and > > > > > > >> > > resultant > > > > > > >> > > > > > > > connections to Kafka than the typical model of a > > > > single > > > > > > >> > producer > > > > > > >> > > > per > > > > > > >> > > > > > > > process. > > > > > > >> > > > > > > > > > > > > > >> > > > > > > > Otherwise, it seems you're left with > > single-threaded > > > > > model > > > > > > >> per > > > > > > >> > > > > > > application > > > > > > >> > > > > > > > process? > > > > > > >> > > > > > > > > > > > > > >> > > > > > > > Thanks, > > > > > > >> > > > > > > > > > > > > > >> > > > > > > > Roger > > > > > > >> > > > > > > > > > > > > > >> > > > > > > > On Tue, Aug 22, 2023 at 5:11 PM Artem Livshits > > > > > > >> > > > > > > > <alivsh...@confluent.io.invalid> wrote: > > > > > > >> > > > > > > > > > > > > > >> > > > > > > > > Hi Roger, Arjun, > > > > > > >> > > > > > > > > > > > > > > >> > > > > > > > > Thank you for the questions. > > > > > > >> > > > > > > > > > It looks like the application must have > stable > > > > > > >> > transactional > > > > > > >> > > > ids > > > > > > >> > > > > > over > > > > > > >> > > > > > > > > time? > > > > > > >> > > > > > > > > > > > > > > >> > > > > > > > > The transactional id should uniquely identify > a > > > > > producer > > > > > > >> > > instance > > > > > > >> > > > > and > > > > > > >> > > > > > > > needs > > > > > > >> > > > > > > > > to be stable across the restarts. If the > > > > > transactional > > > > > > >> id is > > > > > > >> > > not > > > > > > >> > > > > > > stable > > > > > > >> > > > > > > > > across restarts, then zombie messages from a > > > > previous > > > > > > >> > > incarnation > > > > > > >> > > > > of > > > > > > >> > > > > > > the > > > > > > >> > > > > > > > > producer may violate atomicity. If there are > 2 > > > > > producer > > > > > > >> > > > instances > > > > > > >> > > > > > > > > concurrently producing data with the same > > > > > transactional > > > > > > >> id, > > > > > > >> > > they > > > > > > >> > > > > are > > > > > > >> > > > > > > > going > > > > > > >> > > > > > > > > to constantly fence each other and most likely > > > make > > > > > > >> little or > > > > > > >> > > no > > > > > > >> > > > > > > > progress. > > > > > > >> > > > > > > > > > > > > > > >> > > > > > > > > The name might be a little bit confusing as it > > may > > > > be > > > > > > >> > mistaken > > > > > > >> > > > for > > > > > > >> > > > > a > > > > > > >> > > > > > > > > transaction id / TID that uniquely identifies > > > every > > > > > > >> > > transaction. > > > > > > >> > > > > The > > > > > > >> > > > > > > > name > > > > > > >> > > > > > > > > and the semantics were defined in the original > > > > > > >> > > > > exactly-once-semantics > > > > > > >> > > > > > > > (EoS) > > > > > > >> > > > > > > > > proposal ( > > > > > > >> > > > > > > > > > > > > > > >> > > > > > > > > > > > > > > >> > > > > > > > > > > > > > >> > > > > > > > > > > > > >> > > > > > > > > > > > >> > > > > > > > > > > >> > > > > > > > > > >> > > > > > > > > >> > > > > > > > >> > > > > > > > > > > > > > > > > > > > > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-98+-+Exactly+Once+Delivery+and+Transactional+Messaging > > > > > > >> > > > > > > > > ) > > > > > > >> > > > > > > > > and KIP-939 just build on top of that. > > > > > > >> > > > > > > > > > > > > > > >> > > > > > > > > > I'm curious to understand what happens if > the > > > > > producer > > > > > > >> > dies, > > > > > > >> > > > and > > > > > > >> > > > > > does > > > > > > >> > > > > > > > not > > > > > > >> > > > > > > > > come up and recover the pending transaction > > within > > > > the > > > > > > >> > > > transaction > > > > > > >> > > > > > > > timeout > > > > > > >> > > > > > > > > interval. > > > > > > >> > > > > > > > > > > > > > > >> > > > > > > > > If the producer / application never comes > back, > > > the > > > > > > >> > transaction > > > > > > >> > > > > will > > > > > > >> > > > > > > > remain > > > > > > >> > > > > > > > > in prepared (a.k.a. "in-doubt") state until an > > > > > operator > > > > > > >> > > > forcefully > > > > > > >> > > > > > > > > terminates the transaction. That's why there > > is a > > > > new > > > > > > >> ACL is > > > > > > >> > > > > defined > > > > > > >> > > > > > > in > > > > > > >> > > > > > > > > this proposal -- this functionality should > only > > > > > provided > > > > > > >> to > > > > > > >> > > > > > > applications > > > > > > >> > > > > > > > > that implement proper recovery logic. > > > > > > >> > > > > > > > > > > > > > > >> > > > > > > > > -Artem > > > > > > >> > > > > > > > > > > > > > > >> > > > > > > > > On Tue, Aug 22, 2023 at 12:52 AM Arjun Satish > < > > > > > > >> > > > > > arjun.sat...@gmail.com> > > > > > > >> > > > > > > > > wrote: > > > > > > >> > > > > > > > > > > > > > > >> > > > > > > > > > Hello Artem, > > > > > > >> > > > > > > > > > > > > > > > >> > > > > > > > > > Thanks for the KIP. > > > > > > >> > > > > > > > > > > > > > > > >> > > > > > > > > > I have the same question as Roger on > > concurrent > > > > > > writes, > > > > > > >> and > > > > > > >> > > an > > > > > > >> > > > > > > > additional > > > > > > >> > > > > > > > > > one on consumer behavior. Typically, > > > transactions > > > > > will > > > > > > >> > > timeout > > > > > > >> > > > if > > > > > > >> > > > > > not > > > > > > >> > > > > > > > > > committed within some time interval. With > the > > > > > proposed > > > > > > >> > > changes > > > > > > >> > > > in > > > > > > >> > > > > > > this > > > > > > >> > > > > > > > > KIP, > > > > > > >> > > > > > > > > > consumers cannot consume past the ongoing > > > > > transaction. > > > > > > >> I'm > > > > > > >> > > > > curious > > > > > > >> > > > > > to > > > > > > >> > > > > > > > > > understand what happens if the producer > dies, > > > and > > > > > does > > > > > > >> not > > > > > > >> > > come > > > > > > >> > > > > up > > > > > > >> > > > > > > and > > > > > > >> > > > > > > > > > recover the pending transaction within the > > > > > transaction > > > > > > >> > > timeout > > > > > > >> > > > > > > > interval. > > > > > > >> > > > > > > > > Or > > > > > > >> > > > > > > > > > are we saying that when used in this 2PC > > > context, > > > > we > > > > > > >> should > > > > > > >> > > > > > configure > > > > > > >> > > > > > > > > these > > > > > > >> > > > > > > > > > transaction timeouts to very large > durations? > > > > > > >> > > > > > > > > > > > > > > > >> > > > > > > > > > Thanks in advance! > > > > > > >> > > > > > > > > > > > > > > > >> > > > > > > > > > Best, > > > > > > >> > > > > > > > > > Arjun > > > > > > >> > > > > > > > > > > > > > > > >> > > > > > > > > > > > > > > > >> > > > > > > > > > On Mon, Aug 21, 2023 at 1:06 PM Roger > Hoover < > > > > > > >> > > > > > roger.hoo...@gmail.com > > > > > > >> > > > > > > > > > > > > > >> > > > > > > > > > wrote: > > > > > > >> > > > > > > > > > > > > > > > >> > > > > > > > > > > Hi Artem, > > > > > > >> > > > > > > > > > > > > > > > > >> > > > > > > > > > > Thanks for writing this KIP. Can you > > clarify > > > > the > > > > > > >> > > > requirements > > > > > > >> > > > > a > > > > > > >> > > > > > > bit > > > > > > >> > > > > > > > > more > > > > > > >> > > > > > > > > > > for managing transaction state? It looks > > like > > > > the > > > > > > >> > > > application > > > > > > >> > > > > > must > > > > > > >> > > > > > > > > have > > > > > > >> > > > > > > > > > > stable transactional ids over time? What > > is > > > > the > > > > > > >> > > granularity > > > > > > >> > > > > of > > > > > > >> > > > > > > > those > > > > > > >> > > > > > > > > > ids > > > > > > >> > > > > > > > > > > and producers? Say the application is a > > > > > > >> multi-threaded > > > > > > >> > > Java > > > > > > >> > > > > web > > > > > > >> > > > > > > > > server, > > > > > > >> > > > > > > > > > > can/should all the concurrent threads > share > > a > > > > > > >> > transactional > > > > > > >> > > > id > > > > > > >> > > > > > and > > > > > > >> > > > > > > > > > > producer? That doesn't seem right to me > > > unless > > > > > the > > > > > > >> > > > application > > > > > > >> > > > > > is > > > > > > >> > > > > > > > > using > > > > > > >> > > > > > > > > > > global DB locks that serialize all > requests. > > > > > > >> Instead, if > > > > > > >> > > the > > > > > > >> > > > > > > > > application > > > > > > >> > > > > > > > > > > uses row-level DB locks, there could be > > > > multiple, > > > > > > >> > > concurrent, > > > > > > >> > > > > > > > > independent > > > > > > >> > > > > > > > > > > txns happening in the same JVM so it seems > > > like > > > > > the > > > > > > >> > > > granularity > > > > > > >> > > > > > > > > managing > > > > > > >> > > > > > > > > > > transactional ids and txn state needs to > > line > > > up > > > > > > with > > > > > > >> > > > > granularity > > > > > > >> > > > > > > of > > > > > > >> > > > > > > > > the > > > > > > >> > > > > > > > > > DB > > > > > > >> > > > > > > > > > > locking. > > > > > > >> > > > > > > > > > > > > > > > > >> > > > > > > > > > > Does that make sense or am I > > misunderstanding? > > > > > > >> > > > > > > > > > > > > > > > > >> > > > > > > > > > > Thanks, > > > > > > >> > > > > > > > > > > > > > > > > >> > > > > > > > > > > Roger > > > > > > >> > > > > > > > > > > > > > > > > >> > > > > > > > > > > On Wed, Aug 16, 2023 at 11:40 PM Artem > > > Livshits > > > > > > >> > > > > > > > > > > <alivsh...@confluent.io.invalid> wrote: > > > > > > >> > > > > > > > > > > > > > > > > >> > > > > > > > > > > > Hello, > > > > > > >> > > > > > > > > > > > > > > > > > >> > > > > > > > > > > > This is a discussion thread for > > > > > > >> > > > > > > > > > > > > > > > > > >> > > > > > > > > > > > > > > > > > >> > > > > > > > > > > > > > > > > >> > > > > > > > > > > > > > > > >> > > > > > > > > > > > > > > >> > > > > > > > > > > > > > >> > > > > > > > > > > > > >> > > > > > > > > > > > >> > > > > > > > > > > >> > > > > > > > > > >> > > > > > > > > >> > > > > > > > >> > > > > > > > > > > > > > > > > > > > > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-939%3A+Support+Participation+in+2PC > > > > > > >> > > > > > > > > > > > . > > > > > > >> > > > > > > > > > > > > > > > > > >> > > > > > > > > > > > The KIP proposes extending Kafka > > transaction > > > > > > support > > > > > > >> > > (that > > > > > > >> > > > > > > already > > > > > > >> > > > > > > > > uses > > > > > > >> > > > > > > > > > > 2PC > > > > > > >> > > > > > > > > > > > under the hood) to enable atomicity of > > dual > > > > > writes > > > > > > >> to > > > > > > >> > > Kafka > > > > > > >> > > > > and > > > > > > >> > > > > > > an > > > > > > >> > > > > > > > > > > external > > > > > > >> > > > > > > > > > > > database, and helps to fix a long > standing > > > > Flink > > > > > > >> issue. > > > > > > >> > > > > > > > > > > > > > > > > > >> > > > > > > > > > > > An example of code that uses the dual > > write > > > > > recipe > > > > > > >> with > > > > > > >> > > > JDBC > > > > > > >> > > > > > and > > > > > > >> > > > > > > > > should > > > > > > >> > > > > > > > > > > > work for most SQL databases is here > > > > > > >> > > > > > > > > > > > > > https://github.com/apache/kafka/pull/14231. > > > > > > >> > > > > > > > > > > > > > > > > > >> > > > > > > > > > > > The FLIP for the sister fix in Flink is > > here > > > > > > >> > > > > > > > > > > > > > > > > > >> > > > > > > > > > > > > > > > > >> > > > > > > > > > > > > > > > >> > > > > > > > > > > > > > > >> > > > > > > > > > > > > > >> > > > > > > > > > > > > >> > > > > > > > > > > > >> > > > > > > > > > > >> > > > > > > > > > >> > > > > > > > > >> > > > > > > > >> > > > > > > > > > > > > > > > > > > > > > https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=255071710 > > > > > > >> > > > > > > > > > > > > > > > > > >> > > > > > > > > > > > -Artem > > > > > > >> > > > > > > > > > > > > > > > > > >> > > > > > > > > > > > > > > > > >> > > > > > > > > > > > > > > > >> > > > > > > > > > > > > > > >> > > > > > > > > > > > > > >> > > > > > > > > > > > > >> > > > > > > > > > > > >> > > > > > > > > > > >> > > > > > > > > > >> > > > > > > > > >> > > > > > > > >> > > > > > > > > > > > > > > > > > > > > > > > > > > > >
