On Mon, Feb 10, 2020 at 3:38 AM Andor Molnar <an...@apache.org> wrote:
> Hi, > > Answers inline. > > > > In my experience when you are close to a release it is better to to > > make big changes. (I am among the approvers of that patch, so I am > > responsible for this change) > > > > Although this statement is acceptable for me, I don’t feel this patch > should not have been merged into 3.6.0. Submission has been preceded by a > long argument with MAPR folks who originally wanted to be merged into 3.4 > branch (considering the pace how ZooKeeper community is moving forward) and > we reached an agreement that release it with 3.6.0. > > Make a long story short, this patch has been outstanding for ages without > much attention from the community and contributors made a lot of effort to > get it done before the release. > > > > I would like to ear from people that have been in the community for > > long time, then I am ready to complete the release process for > > 3.6.0rc2. > > > Me too. > > I tend to accept the way rolling restart works now - as you described > Enrico - and given that situation was pretty much the same between 3.4 and > 3.5, I don’t feel we have to make additional changes. > > On the other hand, the fix that Mate suggested sounds quite cool, I’m also > happy to work on getting it in. > > Fyi, Release Management page says the following: > https://cwiki.apache.org/confluence/display/ZOOKEEPER/ReleaseManagement > > "major.minor release of ZooKeeper must be backwards compatible with the > previous minor release, major.(minor-1)" > > Our users, direct and indirect, value the ability to migrate to newer versions - esp as we drop support for older. Frictions such as this can be a reason to go elsewhere. I'm "pro" b/w compact - esp given our published guidelines. Patrick > Andor > > > > > > On 2020. Feb 10., at 11:32, Enrico Olivelli <eolive...@gmail.com> wrote: > > > > Thank you Mate for checking and explaining this story. > > > > I find it very interesting that the cause is ZOOKEEPER-3188 as: > > - it is the last "big patch" committed to 3.6 before starting the > > release process > > - it is the cause of the failure of the first RC > > > > In my experience when you are close to a release it is better to to > > make big changes. (I am among the approvers of that patch, so I am > > responsible for this change) > > > > This is a pointer to the change to whom who wants to understand better > > the context > > > https://github.com/apache/zookeeper/pull/1048/files#diff-7a209d890686bcba351d758b64b22a7dR11 > > > > IIUC even for the upgrade from 3.4 to 3.5 the story was the same and > > if this statement holds then I feel we can continue > > with this release. > > > > - Reverting ZOOKEEPER-3188 is not an option for me, it is too complex. > > - Making 3.5 and 3.6 "compatible" can be very tricky and we do not > > have tools to certify this compatibility (at least not in the short > > term) > > > > I would like to ear from people that have been in the community for > > long time, then I am ready to complete the release process for > > 3.6.0rc2. > > > > I will update the website and the release notes with a specific > > warning about the upgrade, we should also update the Wiki > > > > Enrico > > > > > > Il giorno lun 10 feb 2020 alle ore 11:17 Szalay-Bekő Máté > > <szalay.beko.m...@gmail.com> ha scritto: > >> > >> Hi Enrico! > >> > >> This is caused by the different PROTOCOL_VERSION in the > QuorumCnxManager. > >> The Protocol version was changed last time in ZOOKEEPER-2186 released > >> first in 3.4.7 and 3.5.1 to avoid some crashing / fix some bugs. Later I > >> also changed the protocol version when the format of the initial message > >> changed in ZOOKEEPER-3188. So actually the quorum protocol is not > >> compatible in this case and is the 'expected' behavior if you upgrade > e.g > >> from 3.4.6 to 3.4.7, or 3.4.6 to 3.5.5 or e.g from 3.5.6 to 3.6.0. > >> > >> We had some discussion in the PR of ZOOKEEPER-3188 back then and got to > the > >> conclusion that it is not that bad, as there will be no data loss as you > >> wrote. The tricky thing is that during rolling upgrade we should ensure > >> both backward and forward compatibility to make sure that the old and > the > >> new part of the quorum can still speak to each other. The current > solution > >> (simply failing if the protocol versions mismatch) is more simple and > still > >> working just fine: as the servers are restarted one-by-one, the nodes > with > >> the old protocol version and the nodes with the new protocol version > will > >> form two partitions, but any given time only one partition will have the > >> quorum. > >> > >> Still, thinking it trough, as a side effect in these cases there will > be a > >> short time when none of the partitions will have quorums (when we have N > >> servers with the old protocol version, N servers with the new protocol > >> version, and there is one server just being restarted). I am not sure > if we > >> can accept this. > >> > >> For ZOOKEEPER-3188 we can add a small patch to make it possible to parse > >> the initial message of the old protocol version with the new code. But > I am > >> not sure if it would be enough (as the old code will not be able to > parse > >> the new initial message). > >> > >> One option can be to make a patch also for 3.5 to have a version which > >> supports both protocol versions. (let's say in 3.5.8) Then we can write > to > >> the release note, that if you need rolling upgrade from any versions > since > >> 3.4.7, then you have to first upgrade from 3.5.8 before upgrading to > 3.6.0. > >> We can even make the same thing on the 3.4 branch. > >> > >> But I am also new to the community... It would be great to hear the > opinion > >> of more experienced people. > >> Whatever the decision will be, I am happy to make the changes. > >> > >> And sorry for breaking the RC (if we decide that this needs to be > >> changed...). ZOOKEEPER-3188 was a complex patch. > >> > >> Kind regards, > >> Mate > >> > >> On Mon, Feb 10, 2020 at 9:47 AM Enrico Olivelli <eolive...@gmail.com> > wrote: > >> > >>> Hi, > >>> even if we had enough binding +1 on 3.6.0rc2 before closing the VOTE > >>> of 3.6.0 I wanted to finish my tests and I am coming to an apparent > >>> blocker. > >>> > >>> I am trying to upgrade a 3.5.6 cluster to 3.6.0, but it looks like > >>> peers are not able to talk to each other. > >>> I have a cluster of 3, server1, server2 and server3. > >>> When I upgrade server1 to 3.6.0rc2 I see this kind of errors on 3.5 > nodes: > >>> > >>> 2020-02-10 09:35:07,745 [myid:3] - INFO > >>> [localhost/127.0.0.1:3334:QuorumCnxManager$Listener@918] - Received > >>> connection request 127.0.0.1:62591 > >>> 2020-02-10 09:35:07,746 [myid:3] - ERROR > >>> [localhost/127.0.0.1:3334:QuorumCnxManager@527] - > >>> > >>> > org.apache.zookeeper.server.quorum.QuorumCnxManager$InitialMessage$InitialMessageException: > >>> Got unrecognized protocol version -65535 > >>> > >>> Once I upgrade all of the peers the system is up and running, without > >>> apparently no data loss. > >>> > >>> During the upgrade as soon as I upgrade the first node, say, server1, > >>> server1 is not able to accept connections (error "Close of session 0x0 > >>> java.io.IOException: ZooKeeperServer not running") from clients, this > >>> is expected, because as far as it cannot talk with the other peers it > >>> is practically partitioned away from the cluster. > >>> > >>> My questions are: > >>> 1) is this expected ? I can't remember protocol changes from 3.5 to > >>> 3.6, but actually 3.6 diverged from 3.5 branch so long ago, and I was > >>> not in the community as dev so I cannot tell > >>> 2) is this a viable option for users ? to have some temporary glitch > >>> during the upgrade and hope that the upgrade completes without > >>> troubles ? > >>> > >>> In theory as long as two servers are running the same major version > >>> (3.5 or 3.6) we have a quorum and the system is able to make progress > >>> and to server clients. > >>> I feel that this is quite dangerous, but I don't have enough context > >>> to understand how this problem is possible and when we decided to > >>> break compatibility. > >>> > >>> The other option is that I am wrong in my test and I am messing up :-) > >>> > >>> The other upgrade path I would like to see working like a charm is the > >>> upgrade from 3.4 to 3.6, as I see that as soon as we release 3.6 we > >>> should encourage users to move to 3.6 and not to 3.5. > >>> > >>> Regards > >>> Enrico > >>> > >
