Although collecting all configuration keys into a single file is definitely an anti-pattern I’m not sure the same is true of package or Maven module level aggregation classes marked LP(CONFIG).Somewhat like DFSConfigKeys but geared toward our API/release auditing.
This would seem virtuous for a couple of reasons. Relevant configuration key constants for the package or module would be grouped in a well known place for users and developers alike. The LP(CONFIG) designation would require developers to think about deprecation cycle if contemplating a change, thus providing some back pressure against snap decisions. Or, if not then, then at release candidate evaluation time, user configuration breaking changes could be caught be a release automation tool that diffs LP(CONFIG) annotated classes. Something like this would improve the state of configuration key management quite dramatically, because currently it’s ad hoc. > On Mar 16, 2022, at 10:46 AM, Bryan Beaudreault > <[email protected]> wrote: > > Thanks for your detailed response, Nick! > >> I think that none of my comments address your intended topic: how do we > publish our configuration points as an API that can be consumed by user > applications? (Do I have that correct?) > > This is a good summary, and I appreciate the other thoughts/clarifications > as well. I also realize this is probably hard to get perfect and any choice > must be weighed against the effort necessary to change/maintain. > > One example I know is Hadoop/HDFS, and I bet some on this list have much > more knowledge of that project's history than I do. For HDFS they have > DFSConfigKeys which in my experience does seem to include most configs. I > believe they even have unit tests which verify that all configs in the > various site.xml files are represented in code. In more recent versions > they have split that class up into smaller groupings, for example > DfsClientConf and the various inner classes there. > > In a vacuum, from a code design perspective, I'm not commenting on whether > that's a good or bad pattern. I also don't know of the politics of the > project or what sorts of pain points they've discovered in that pattern > over the years. But from *user's perspective*, this is a handy way to > handle things in my opinion. > > At my company, in general we try to avoid "magic strings" [1] and instead > always try to use constants. We can and do define our own constants to try > to mirror some of the "private" magic strings in the hbase client. This is > better than nothing but even better would be to use hbase-provided > constants so that we can build more defensive applications, using the > compiler to verify that the configs we reference still do anything. > > I unfortunately can't speak to the original issues with HConstants that > turned it into an anti-pattern. What I do notice is there are definitely > examples in the hbase codebase of duplicated config strings, one of which > is called out in one of the jiras I linked in my original email. These are > just bugs waiting to happen in my opinion, either for hbase itself or for > users which may reference them. > > [1] https://deviq.com/antipatterns/magic-strings >> On Wed, Mar 16, 2022 at 10:52 AM Nick Dimiduk <[email protected]> wrote: >> >> Hi Bryan, >> >> Thanks for bringing this up. >> >> I agree with Duo (and I think we have this settled as project-wide >> consensus) that HConstants is/was an anti-pattern, that we are actively >> against adding new fields there, and opportunistically removing fields when >> we can. Further, the documented meaning of the >> HBaseInterfaceAudience.CONFIG field is "Denotes class names that appear in >> user facing configuration files", so this isn't really appropriate for >> marking a field that exposes a configuration key to user applications. I >> will also note that there appears to be two categories of tunable >> parameters -- configuration points that we expect users to tweak are >> catalogued and documented in the book [0] and everything else is left to >> the obscurity of code-grep. >> >> While we are actively squashing use of fields in HConstants, I don't know >> that we have proposed some alternative to the user community. For my part, >> when I write and review code that involves configuration keys, I generally >> implement the key constant string as a private field in an appropriate >> class, and the unit test coverage for that configuration key replicates the >> string in the test. My reasoning being that the string is a part of our >> public API and making a change to the public API should be detected from >> the unit test. I also have (on occasion) gone out of my way to write about >> the configuration keys in the package or class-level javadoc. >> >> I think that none of my comments address your intended topic: how do we >> publish our configuration points as an API that can be consumed by user >> applications? (Do I have that correct?) >> >> I am of the mind that we don't need/want an API of configurations ; we want >> a catalogue, i.e., what has been started in our book. Perhaps accompanied >> by/generated from an authoritative hbase-defaults.xml file. In fact, we >> already do generate from hbase-default.xml, the result is [1] ; I don't >> believe it is authoritative. >> >> If we did have an AP thoughI, what would be better than the HConstants >> approach of key-strings as public fields ? What if we had a >> ConfigurationBuilder type of class, which had methods tied to configuration >> keys? I would think that such a globally applicable class would have the >> same maintenance issues as HConstants. But what if we had some kind of >> ConfigurationSetter class, perhaps per package, that performed this >> function? That might be maintainable for us and useful for users. >> >> I'm keen to hear what other ideas are out there, or better, examples and >> counter-examples from other projects. >> >> Thanks, >> Nick >> >> [0]: https://hbase.apache.org/book.html#important_configurations >> <https://hbase.apache.org/book.html#important_configurations> >> [1]: https://hbase.apache.org/book.html#hbase_default_configurations >> <https://hbase.apache.org/book.html#hbase_default_configurations> >> >> On Tue, Mar 15, 2022 at 4:28 PM Bryan Beaudreault >> <[email protected]> wrote: >> >>> Hi devs, >>> >>> As a major user of hbase, my company has thousands of clients deployed >>> which use the hbase client to connect to a variety of hbase clusters. We >>> have a common library which handles configuring all clients by setting up >>> the Configuration object prior to creating a Connection. Our library sets >>> configurations using the various configs in HConstants, but there are >> also >>> a bunch of configs which don't exist in HConstants. For these we have >>> hardcoded config strings in our client. >>> >>> We're now working on an hbase upgrade and need to go through our client >>> library and check how the configs may have changed in the new version. >> This >>> is relatively easy to do for those HConstants cases -- configs may be >>> marked @Deprecated which will show up in one's editor, they may be >> removed >>> entirely which would show up is a compile error, and otherwise one can >>> easily click through or bring up the javadoc. For the others that don't >>> exist in HConstants, we need to go manually search the hbase codebase for >>> those strings. >>> >>> Without doing this painstaking manual process, we would potentially >> deploy >>> the upgraded client with configs which are no longer used or deprecated >> by >>> the hbase client. For those using HConstants, this is immediately obvious >>> because the HConstant field may have been removed. This is a clear >>> indication of needing to investigate the config. In this case it's >>> preferred to face the compile failure because it's clearer than having >>> something silently disappear or change. >>> >>> I opened 3 jiras to move some fields to HConstants, but got some >> reasonable >>> pushback from Duo: >>> >>> https://issues.apache.org/jira/browse/HBASE-26845 >> <https://issues.apache.org/jira/browse/HBASE-26845> >>> https://issues.apache.org/jira/browse/HBASE-26846 >> <https://issues.apache.org/jira/browse/HBASE-26846> >>> https://issues.apache.org/jira/browse/HBASE-26847 >> <https://issues.apache.org/jira/browse/HBASE-26847> >>> >>> Duo's pushback is that HConstants is an anti-pattern and these configs >> are >>> not part of our public API. I can agree that a catch-all constants class >>> might be an anti-pattern, but would argue that consolidating configs >> there >>> is very useful for end-users. I can also potentially agree that exposing >>> these as part of our public API might limit the flexibility of >> development >>> due to compatibility constraints about IA.Public. >>> >>> To me it seems odd to add a configuration, whose whole point is to make >>> something tuneable, but then bury it in a private class despite having >> real >>> implications for how the application runs. If a configuration is not >> meant >>> to be tuned, it shouldn't be a configuration at all. Otherwise it should >> be >>> exposed for reference. >>> >>> I'm wondering if there is some compromise we can achieve which makes it >>> easier for end-users to integrate with tunable configs. >>> >>> One can imagine a large project to clean up all of our configs under some >>> new class with maybe IA.LimitedPrivate(CONFIG), but I fear making perfect >>> (needing to migrate all configs) the enemy of good. >>> >>> A better option might be to make those classes which expose configs >>> LimitedPrivate(CONFIG) -- for example AsyncProcess and >>> ConnectionImplementation. That might be the most incremental change we >>> could make. We could handle this on a case-by-case basis. >>> >>> Does anyone have any thoughts? >>> >>
