One thing that we can add to docs is for people how to update the in-jvm framework and test their patches before asking for in-jvm api release. The assumption is those won’t be many updates needed I think, but it is good to be documented.
On Tue, 29 Mar 2022 at 13:51, David Capwell <dcapw...@apple.com> wrote: > They use a separate implementation of instance initialization and thus > they test the test server rather than the real node. > > > I think we can get rid of this by extending CassandraDaemon, just need to > add a few hooks to mock out gossip/internode/client (for cases where the > mocks are desired), and when mocks are not desired just run the real logic. > > Too many times I have had to make the 2 more in-line, and this is hard to > maintain… we should fix this and feel this is 100% fixable > > we shouldn't neglect that there is a significant learning curve associated > with it for new contributors which IMO is much lower for pyhton dtests > > > I am curious about this comment. When I first joined I learned jvm-dtest > within an hour and started walking Repair code in a debugger (and this was > way before the improvements that let us do things like nodetool)… python > dtest took weeks to get working correctly (still having issues with the > MBean library we use… so have to comment out error handling to get some > tests to pass)…. > > Maybe we could have some example docs showing how to do the same in both > tools? Honestly Cluster.build(3).withConfig(c -> > c.with(Feature.values())).start() matches 95% of python dtest tests (the > withConfig logic is a bit cryptic), so don’t think the docs would be too > much work > > > On Mar 29, 2022, at 5:48 AM, Josh McKenzie <jmcken...@apache.org> wrote: > > we should at least write extensive documentation on how to use/modify > in-jvm dtest framework before deprecating python dtests. > > We should have this for all our testing frameworks period, in-jvm dtest, > python dtest, and ccm. They're woefully under-documented IMO. > > On Tue, Mar 29, 2022, at 6:11 AM, Paulo Motta wrote: > > To elaborate a bit on the steep learning curve point, when mentoring new > contributors on a couple of occasions I told them to "just write a python > dtest" because we had no idea on how to test that functionality on in-jvm > tests while the python dtest was fairly straightforward to implement (I > can't recall exactly what feature was it but I can dig if necessary). > > While we might be already familiar with the in-jvm dtest framework due to > our exposure to it, we shouldn't neglect that there is a significant > learning curve associated with it for new contributors which IMO is much > lower for pyhton dtests. So we should at least write extensive > documentation on how to use/modify in-jvm dtest framework before > deprecating python dtests. > > Em ter., 29 de mar. de 2022 às 06:58, Paulo Motta < > pauloricard...@gmail.com> escreveu: > > > They use a separate implementation of instance initialization and thus > they test the test server rather than the real node. > > I also have this concern. When adding a new service on CASSANDRA-16789 we > had to explicitly modify the in-jvm dtest server to match the behavior from > the actual server [1] (this is just a minor example but I remember having > to do something similar on other tickets). > > Besides having a steep learning curve since users need to be familiar with > the in-jvm dtest framework in order to add new functionality not supported > by it, this is potentially unsafe, since the implementations can diverge > without being caught by tests. > > Is there any way we could avoid duplicating functionality on the test > server and use the same initialization code on in-jvm dtests? > > [1] - > https://github.com/apache/cassandra/commit/ad249424814836bd00f47931258ad58bfefb24fd#diff-321b52220c5bd0aaadf275a845143eb208c889c2696ba0d48a5fc880551131d8R735 > > Em ter., 29 de mar. de 2022 às 04:22, Benjamin Lerer <ble...@apache.org> > escreveu: > > They use a separate implementation of instance initialization and thus > they test the test server rather than the real node. > > > This is actually my main concern. What is the real gap between the in-JVM > tests server instance and a server as run by python DTests? > > Le mar. 29 mars 2022 à 00:08, bened...@apache.org <bened...@apache.org> a > écrit : > > > Other than that, it can be problematic to test upgrades when the > starting version must run with a different Java version than the end release > > > > python upgrade tests seem to be particularly limited (from a quick skim, > primarily testing major upgrade points that are now long in the past), so > I’m not sure how much of a penalty this is today in practice - but it might > well become a problem. > > > > There’s several questions to answer, namely how many versions we want to: > > > > - test upgrades across > > - maintain backwards compatibility of the in-jvm dtest api across > > - support a given JVM for > > > > However, if we need to, we can probably use RMI to transparently support > multiple JVMs for tests that require it. Since we already use serialization > to cross the ClassLoader boundary it might not even be very difficult. > > > > > > *From: *Jacek Lewandowski <lewandowski.ja...@gmail.com> > *Date: *Monday, 28 March 2022 at 22:30 > *To: *dev@cassandra.apache.org <dev@cassandra.apache.org> > *Subject: *Re: [DISCUSS] Should we deprecate / freeze python dtests > > Although I like in-jvm DTests for many scenarios, I can see that they do > not test the production code as it is. They use a separate > implementation of instance initialization and thus they test the test > server rather than the real node. Other than that, it can be problematic to > test upgrades when the starting version must run with a different Java > version than the end release. One more thing I've been observing sometimes > is high consumption of metaspace, which does not seem to be cleaned after > individual test cases. Given each started instance uses a dedicated class > loader there is some amount of trash left and when there are a couple of > multi-node test cases in a single test class, it sometimes happens that the > test fail with out of memory in metaspace error. > > > > Thanks, > > Jacek > > > > On Mon, Mar 28, 2022 at 10:06 PM David Capwell <dcapw...@apple.com> wrote: > > I am back and the work for trunk to support vnode is at the last stage of > review; I had not planned to backport the changes to other branches (aka, > older branches would only support single token), so if someone would like > to pick up this work it is rather LHF after 17332 goes in (see trunk patch GH > PR: trunk <https://github.com/apache/cassandra/pull/1432>). > > > > I am in favor of deprecating python dtests, and agree we should figure out > what the gaps are (once vnode support is merged) so we can either shrink > them or special case to unfreeze (such as startup changes being allowed). > > > On Mar 14, 2022, at 6:13 AM, Josh McKenzie <jmcken...@apache.org> wrote: > > > > vnode support for in-jvm dtests is in flight and fairly straightforward: > > > > https://issues.apache.org/jira/browse/CASSANDRA-17332 > > > > David's OOO right now but I suspect we can get this in in April some time. > > > > On Mon, Mar 14, 2022, at 8:36 AM, bened...@apache.org wrote: > > This is the limitation I mentioned. I think this is solely a question of > supplying an initial config that uses vnodes, i.e. that specifies multiple > tokens for each node. It is not really a limitation – I believe a dtest > could be written today using vnodes, by overriding the config’s tokens. It > does look like the token handling has been refactored since the initial > implementation to make this a little uglier than should be necessary. > > > > We should make this trivial, anyway, and perhaps offer a way to run all of > the dtests with vnodes (and suitably annotating those that cannot be run > with vnodes). This should be quite easy. > > > > > > *From: *Andrés de la Peña <adelap...@apache.org> > *Date: *Monday, 14 March 2022 at 12:28 > *To: *dev@cassandra.apache.org <dev@cassandra.apache.org> > *Subject: *Re: [DISCUSS] Should we deprecate / freeze python dtests > > Last time I checked there wasn't support for vnodes on in-jvm dtests, > which seems an important limitation. > > > > On Mon, 14 Mar 2022 at 12:24, bened...@apache.org <bened...@apache.org> > wrote: > > I am strongly in favour of deprecating python dtests in all cases where > they are currently superseded by in-jvm dtests. They are environmentally > more challenging to work with, causing many problems on local and remote > machines. They are harder to debug, slower, flakier, and mostly less > sophisticated. > > > > > all focus on getting the in-jvm framework robust enough to cover > edge-cases > > > > Would be great to collect gaps. I think it’s just vnodes, which is by no > means a fundamental limitation? There may also be some stuff to do > startup/shutdown and environmental scripts, that may be a niche we retain > something like python dtests for. > > > > > people aren’t familiar > > > > I would be interested to hear from these folk to understand their concerns > or problems using in-jvm dtests, if there is a cohort holding off for this > reason > > > > > This is going to require documentation work from some of the original > authors > > > > I think a collection of template-like tests we can point people to would > be a cheap initial effort. Cutting and pasting an existing test with the > required functionality, then editing to suit, should get most people off to > a quick start who aren’t familiar. > > > > > Labor and process around revving new releases of the in-jvm dtest API > > > > I think we need to revisit how we do this, as it is currently broken. We > should consider either using ASF snapshots until we cut new releases of C* > itself, or else using git subprojects. This will also become a problem for > Accord’s integration over time, and perhaps other subprojects in future, so > it is worth better solving this. > > > > I think this has been made worse than necessary by moving too many > implementation details to the shared API project – some should be retained > within the C* tree, with the API primarily serving as the shared API itself > to ensure cross-version compatibility. However, this is far from a complete > explanation of (or solution to) the problem. > > > > > > > > *From: *Josh McKenzie <jmcken...@apache.org> > *Date: *Monday, 14 March 2022 at 12:11 > *To: *dev@cassandra.apache.org <dev@cassandra.apache.org> > *Subject: *[DISCUSS] Should we deprecate / freeze python dtests > > I've been wrestling with the python dtests recently and that led to some > discussions with other contributors about whether we as a project should be > writing new tests in the python dtest framework or the in-jvm framework. > This discussion has come up tangentially on some other topics, including > the lack of documentation / expertise on the in-jvm framework > dis-incentivizing some folks from authoring new tests there vs. the > difficulty debugging and maintaining timer-based, sleep-based > non-deterministic python dtests, etc. > > > > I don't know of a place where we've formally discussed this and made a > project-wide call on where we expect new distributed tests to be written; > if I've missed an email about this someone please link on the thread here > (and stop reading! ;)) > > > > At this time we don't specify a preference for where you write new > multi-node distributed tests on our "development/testing" portion of the > site and documentation: > https://cassandra.apache.org/_/development/testing.html > > > > The primary tradeoffs as I understand them for moving from python-based > multi-node testing to jdk-based are: > > Pros: > > 1. Better debugging functionality (breakpoints, IDE integration, etc) > 2. Integration with simulator > 3. More deterministic runtime (anecdotally; python dtests _should_ be > deterministic but in practice they prove to be very prone to environmental > disruption) > 4. Test time visibility to internals of cassandra > > Cons: > > 1. The framework is not as mature as the python dtest framework (some > functionality missing) > 2. Labor and process around revving new releases of the in-jvm dtest > API > 3. People aren't familiar with it yet and there's a learning curve > > > > So my bid here: I personally think we as a project should freeze writing > new tests in the python dtest framework and all focus on getting the in-jvm > framework robust enough to cover edge-cases that might still be causing new > tests to be written in the python framework. This is going to require > documentation work from some of the original authors of the in-jvm > framework as well as folks currently familiar with it and effort from those > of us not yet intimately familiar with the API to get to know it, however I > believe the long-term benefits to the project will be well worth it. > > > > We could institute a pre-commit check that warns on a commit increasing > our raw count of python dtests to help provide process-based visibility to > this change in direction for the project's testing. > > > > So: what do we think? > > >
