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<mailto:bened...@apache.org> <bened...@apache.org<mailto: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 wrote: I am strongly in favour of deprecating python dtests in all cases where they are currently superseded by in-jvm dtests.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<mailto:jmcken...@apache.org>> Date: Monday, 14 March 2022 at 12:11 To: dev@cassandra.apache.org<mailto:dev@cassandra.apache.org> <dev@cassandra.apache.org<mailto: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?
