On Mon, Aug 31, 2020 at 12:28 PM Jason Gustafson <ja...@confluent.io> wrote:
> Hey Guozhang, > > Thanks for the detailed comments. Responses inline: > > > 1. I'd like to clarify how we can make "--abort" work with old brokers, > since without the additional field "Partitions" the tool needs to set the > coordinator epoch correctly instead of "-1"? Arguably that's still doable > but would require different call paths, and it's not clear whether that's > worth doing for old versions. > > That's a good question. What I had in mind was to write the marker using > the last coordinator epoch that was used by the respective ProducerId. I > realized that I left the coordinator epoch out of the `DescribeProducers` > response, so I have updated the KIP to include it. It is possible that > there is no coordinator epoch associated with a given ProducerId (e.g. if > it is the first transaction from that producer), but in this case we can > use 0. > > As for whether this is worth doing, I guess I would be more inclined to > leave it out if users had a reasonable alternative today to address this > problem. > > > 2. Why do we have to enforce "DescribeProducers" to be sent to only > leaders > while ListTransactions can be sent to any brokers? Or is it really > "ListTransactions to be sent to coordinators only"? From the workflow > you've described, based on the results back from DescribeProducers, we > should just immediately send ListTransactions to the > corresponding coordinators based on the collected producer ids, instead of > trying to send to any brokers right? > > I'm going to change `DescribeProducers` so that it can be handled by any > replica of a topic partition. This was suggested by Lucas in order to allow > this API to be used for replica consistency testing. As far as > `ListTransactions`, I was treating this similarly to `ListGroups`. Although > we know that the coordinators are the leaders of the __transaction_state > partitions, this is more of an implementation detail. From an API > perspective, we say that any broker could be a transaction coordinator. > > > 3. One thing I'm a bit hesitant about is that, is `Describe` permission > on > the associated topic sufficient to allow any users to get all producer > information writing to the specific topic-partitions including last > timestamp, txn-start-timestamp etc, which may be considered sensitive? > Should we require "ClusterAction" to only allow operators only? > > That's a fair point. Do you think `Read` permission would be reasonable? > This is all information that could be obtained by reading the topic. > > Yeah that makes sense. > > 4. From the example it seems "TxnStartOffset" should be included in the > DescribeTransaction response schema? Otherwise the user would not get it in > the following WriteTxnMarker request. > > The `DescribeTransaction` API is sent to the transaction coordinator, which > does not know the start offset of a transaction in each topic partition. > That is why we need `DescribeProducers`. > Hmm, but the "TxnStartOffset" is not included in the DescribeProducers response either? > > > 5. It is a bit easier for readers to highlight the added fields in the > existing WriteTxnMarkerRequest (btw I read is that we are only adding > "Partitions" with the starting offset, right?). Also as for its response it > seems we do not make any schema changes except adding one more potential > error code "INVALID_TXN_STATE" to it, right? If that's the case we can just > state that explicitly. > > I highlighted the new field in the request. For the response, the KIP > states the following: "There are no changes to the response schema, but it > will be bumped. Note that we are also enabling flexible version support." > > > 6. It is not clear to me for the overloaded function that the following > option classes are not specified, what should be the default options? > ... > > I was just trying to stick with existing conventions, but I will add some > more detail here. I think we should probably still include > `AbortTransactionOptions`. The `Options` classes are how users override > timeouts. > > > 7.1 Is "--broker" a required or optional (in that case I presume we would > just query all brokers iteratively) in "--find-hanging"? > > I think it should be required as a reasonable way to limit the scope of the > search. This is meant to be guided by metrics after all. If we do not limit > the scope to a single broker, then the behavior might get worse as the > cluster grows. I will clarify this. > > > 7.2 Seems "list-producers" is not exposed as a standalone feature in the > cmd but only used in the wrapping "--find-hanging", is that intentional? > Personally I feel exposing a "--list-producers" may be useful too: if we > believe the user has the right ACL, it is legitimate to return the producer > information to her anyways. But that is debatable in the meta point 3) > above. > > Yeah, I was planning to add this to support the use case that Lucas > mentioned. There is some awkwardness since it is a little difficult to > convey different sources of information through the same command. I guess > we can do `--list producers` and `--list transactions` and explain in the > documentation. Maybe that is good enough. > > > 7.3 "Describing Transactions": we should also explain how that would be > executed, e.g. at least we should clarify that we would first find the > coordinator based on the transactional.id and hence users do not need to > specify one. > > Sure, makes sense. > > > 7.4. In "Aborting Transactions", should we also specify the "--broker" > node > as a required option? Otherwise we would not know which broker to send to. > > The --topic and --partition arguments are required, so the target is always > the leader of that partition. > > > Thanks, > Jason > > > > On Fri, Aug 28, 2020 at 8:13 AM Robert Barrett <bob.barr...@confluent.io> > wrote: > > > Hi Jason, > > > > Thanks for this KIP, I think this will be a huge operational improvement > > and overall it looks great to me. > > > > I'm not sure how much value the MaxActiveTransactionDuration metric adds, > > given that we have the --find-hanging option in the tool. As you mention, > > instances of these transactions are expected to be rare, and a > > partition-level metric, which can generate a lot of data, seems very > > heavyweight for such a rare occurrence. I think "alert on > > PartitionsWithLateTransactionsCount" followed by "run kafka-transactions > > --find-hanging on the relevant broker" is a reasonable process for > cluster > > operators to follow. > > > > Thanks, > > Bob > > > > On Thu, Aug 27, 2020 at 9:23 PM Guozhang Wang <wangg...@gmail.com> > wrote: > > > > > Hi Jason, > > > > > > Thanks for the written KIP. I think this is going to be a very useful > > tool > > > for operational improvements since with eos in its current stage, we > > cannot > > > confidently assert that we are bug-free, and even in the future when we > > are > > > confident this is still going to be leveraged by older versioned > brokers. > > > Regarding the solution, I've also debated myself whether Kafka should > > > "self-heal" automatically when detected in such situations, or should > we > > > instead build into ecosystem tooling to let operators do it. And I've > > also > > > convinced myself that the latter should be a better solution to keep > > Kafka > > > software itself simpler. > > > > > > Regarding the KIP itself, I have a few meta comments below: > > > > > > 1. I'd like to clarify how we can make "--abort" work with old brokers, > > > since without the additional field "Partitions" the tool needs to set > the > > > coordinator epoch correctly instead of "-1"? Arguably that's still > doable > > > but would require different call paths, and it's not clear whether > that's > > > worth doing for old versions. > > > > > > 2. Why do we have to enforce "DescribeProducers" to be sent to only > > leaders > > > while ListTransactions can be sent to any brokers? Or is it really > > > "ListTransactions to be sent to coordinators only"? From the workflow > > > you've described, based on the results back from DescribeProducers, we > > > should just immediately send ListTransactions to the > > > corresponding coordinators based on the collected producer ids, instead > > of > > > trying to send to any brokers right? > > > > > > Also I'm a bit concerned if "ListTransactions" could potentially return > > too > > > much data with "StateFilters" set to all states, including completed > > ones. > > > Do we expect users ever want to know transactions that are not pending? > > On > > > the other hand, maybe we can just require users to specify the "pids[]" > > in > > > this request too to further filter those un-interested transactions. > This > > > also works well with the workflow: we know exactly from > > "DescribeProducers" > > > which pids are we diagnosing right now, so in the follow-up > > > "ListTransactions" we should also only care for those partitions only. > > > > > > 3. One thing I'm a bit hesitant about is that, is `Describe` permission > > on > > > the associated topic sufficient to allow any users to get all producer > > > information writing to the specific topic-partitions including last > > > timestamp, txn-start-timestamp etc, which may be considered sensitive? > > > Should we require "ClusterAction" to only allow operators only? > > > > > > Below are more detailed comments: > > > > > > 4. From the example it seems "TxnStartOffset" should be included in the > > > DescribeTransaction response schema? Otherwise the user would not get > it > > in > > > the following WriteTxnMarker request. > > > > > > 5. It is a bit easier for readers to highlight the added fields in the > > > existing WriteTxnMarkerRequest (btw I read is that we are only adding > > > "Partitions" with the starting offset, right?). Also as for its > response > > it > > > seems we do not make any schema changes except adding one more > potential > > > error code "INVALID_TXN_STATE" to it, right? If that's the case we can > > just > > > state that explicitly. > > > > > > 6. It is not clear to me for the overloaded function that the following > > > option classes are not specified, what should be the default options? > > > > > > * ListTransactionsOptions > > > * DescribeTransactionsOptions > > > * DescribeProducersOptions > > > > > > Also, it seems AbortTransactionOptions would just be empty? If yes do > we > > > really need this option class for now? > > > > > > 7. A couple questions from the cmd tool examples: > > > 7.1 Is "--broker" a required or optional (in that case I presume we > would > > > just query all brokers iteratively) in "--find-hanging"? > > > 7.2 Seems "list-producers" is not exposed as a standalone feature in > the > > > cmd but only used in the wrapping "--find-hanging", is that > intentional? > > > Personally I feel exposing a "--list-producers" may be useful too: if > we > > > believe the user has the right ACL, it is legitimate to return the > > producer > > > information to her anyways. But that is debatable in the meta point 3) > > > above. > > > 7.3 "Describing Transactions": we should also explain how that would be > > > executed, e.g. at least we should clarify that we would first find the > > > coordinator based on the transactional.id and hence users do not need > to > > > specify one. > > > 7.4. In "Aborting Transactions", should we also specify the "--broker" > > node > > > as a required option? Otherwise we would not know which broker to send > > to. > > > > > > > > > Overall, nice written one, thanks Jason. > > > > > > Guozhang > > > > > > > > > On Thu, Aug 27, 2020 at 11:44 AM Lucas Bradstreet <lu...@confluent.io> > > > wrote: > > > > > > > >> Would it be worth returning transactional.id.expiration.ms in the > > > > DescribeProducersResponse? > > > > > > > > > That's an interesting thought as well. Are you trying to avoid the > > need > > > > to > > > > specify it through the command line? The tool could also query the > > value > > > > with DescribeConfigs I suppose. > > > > > > > > Basically. I'm not sure how useful this will be in practice, though > it > > > > might help when debugging. > > > > > > > > Lucas > > > > > > > > On Thu, Aug 27, 2020 at 11:00 AM Jason Gustafson <ja...@confluent.io > > > > > > wrote: > > > > > > > > > Hey Lucas, > > > > > > > > > > Thanks for the comments. Responses below: > > > > > > > > > > > Given that it's possible for replica producer states to diverge > > from > > > > each > > > > > other, it would be very useful if > DescribeProducers(Request,Response) > > > and > > > > > tooling is able to query all partition replicas for their producers > > > > > > > > > > Yes, it makes sense to me to let DescribeProducers work on both > > > followers > > > > > and leaders. In fact, I'm encouraged that there are use cases for > > this > > > > work > > > > > other than detecting hanging transactions. That was indeed the > hope, > > > but > > > > I > > > > > didn't have anything specific in mind. I will update the proposal. > > > > > > > > > > > Would it be worth returning transactional.id.expiration.ms in > the > > > > > DescribeProducersResponse? > > > > > > > > > > That's an interesting thought as well. Are you trying to avoid the > > need > > > > to > > > > > specify it through the command line? The tool could also query the > > > value > > > > > with DescribeConfigs I suppose. > > > > > > > > > > Thanks, > > > > > Jason > > > > > > > > > > On Thu, Aug 27, 2020 at 10:48 AM Lucas Bradstreet < > > lu...@confluent.io> > > > > > wrote: > > > > > > > > > > > Hi Jason, > > > > > > > > > > > > This looks like a very useful tool, thanks for writing it up. > > > > > > > > > > > > Given that it's possible for replica producer states to diverge > > from > > > > each > > > > > > other, it would be very useful if > > DescribeProducers(Request,Response) > > > > and > > > > > > tooling is able to query all partition replicas for their > > producers. > > > > One > > > > > > way I can see this being used immediately is in kafka's system > > tests, > > > > > > especially the ones that inject failures. At the end of the test > we > > > can > > > > > > query all replicas and make sure that their states have not > > > diverged. I > > > > > can > > > > > > also see it being useful when debugging production clusters too. > > > > > > > > > > > > Would it be worth returning transactional.id.expiration.ms in > the > > > > > > DescribeProducersResponse? > > > > > > > > > > > > Cheers, > > > > > > > > > > > > Lucas > > > > > > > > > > > > > > > > > > > > > > > > On Wed, Aug 26, 2020 at 12:12 PM Ron Dagostino < > rndg...@gmail.com> > > > > > wrote: > > > > > > > > > > > > > Yes, that definitely sounds reasonable. Thanks, Jason! > > > > > > > > > > > > > > Ron > > > > > > > > > > > > > > On Wed, Aug 26, 2020 at 3:03 PM Jason Gustafson < > > > ja...@confluent.io> > > > > > > > wrote: > > > > > > > > > > > > > > > Hey Ron, > > > > > > > > > > > > > > > > We do not typically backport new APIs to older versions. I > > think > > > we > > > > > can > > > > > > > > however make the --abort command compatible with older > > versions. > > > It > > > > > > would > > > > > > > > require a user to do some analysis on their own to identify a > > > > hanging > > > > > > > > transaction, but then they can use the tool from a new > release > > to > > > > > > > recover. > > > > > > > > For example, users could detect a hanging transaction through > > the > > > > > > > existing > > > > > > > > "LastStableOffsetLag" metric and then collect the needed > > > > information > > > > > > > from a > > > > > > > > dump of the log (or producer snapshot). It's more work, but > at > > > > least > > > > > > it's > > > > > > > > possible. Does that sound fair? > > > > > > > > > > > > > > > > Thanks, > > > > > > > > Jason > > > > > > > > > > > > > > > > On Wed, Aug 26, 2020 at 11:51 AM Ron Dagostino < > > > rndg...@gmail.com> > > > > > > > wrote: > > > > > > > > > > > > > > > > > Hi Jason. Thanks for the excellently-written KIP. > > > > > > > > > > > > > > > > > > Will the implementation be backported to prior Kafka > > versions? > > > > The > > > > > > > > reason > > > > > > > > > I ask is because if it is not backported and similar > > > > functionality > > > > > is > > > > > > > not > > > > > > > > > otherwise made available for older versions, then the only > > > > recourse > > > > > > > > (aside > > > > > > > > > from deleting and recreating the topic as you pointed out) > > may > > > be > > > > > to > > > > > > > > > upgrade to 2.7 (or whatever version ends up getting this > > > > > > > functionality). > > > > > > > > > Such an upgrade may not be desirable, especially if the > > number > > > of > > > > > > > > > intermediate versions is considerable. I understand the > > mantra > > > of > > > > > > > "never > > > > > > > > > fall too many versions behind" but the reality of it is > that > > it > > > > > isn't > > > > > > > > > always the case. Even if the version is relatively recent, > > an > > > > > > upgrade > > > > > > > > may > > > > > > > > > still not be possible for some time, and a quicker > resolution > > > may > > > > > be > > > > > > > > > necessary. > > > > > > > > > > > > > > > > > > Ron > > > > > > > > > > > > > > > > > > On Wed, Aug 26, 2020 at 2:33 PM Jason Gustafson < > > > > > ja...@confluent.io> > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > Hi All, > > > > > > > > > > > > > > > > > > > > I've added a proposal to handle the problem of hanging > > > > > > transactions: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-664%3A+Provide+tooling+to+detect+and+abort+hanging+transactions > > > > > > > > > > . > > > > > > > > > > In theory, this should never happen. In practice, we have > > hit > > > > one > > > > > > bug > > > > > > > > > where > > > > > > > > > > it was possible and there are few good options today to > > > > recover. > > > > > > > Take a > > > > > > > > > > look and let me know what you think. > > > > > > > > > > > > > > > > > > > > Thanks, > > > > > > > > > > Jason > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > -- > > > -- Guozhang > > > > > > -- -- Guozhang
