If our goal is to make the default experience closer to production while removing TreeMap, then JDBC with H2 seems like a more natural choice. It exercises the same persistence layer, schema management, and configuration that users will encounter in production, while still keeping setup lightweight.
Yufei Yufei On Thu, Jul 2, 2026 at 3:46 AM Alexandre Dutra <[email protected]> wrote: > > Hi Russell, > > The existing default metastore shouldn't be viewed merely as a > "relatively simple, self-contained implementation": it has unique > quirks, such as returning result types that no other metastore does. > > Choosing the status quo simply to avoid making changes is imho the > worst solution. > > Transitioning to the NoSQL metastore as the default remains a net > benefit, even if it is only used by 30% of the user base. > > However, I agree with keeping the test suite on JDBC + H2 by default > if that ensures a higher level of confidence in our tests ability to > reproduce real production setups. > > Thanks, > Alex > > On Wed, Jul 1, 2026 at 12:23 AM Russell Spitzer > <[email protected]> wrote: > > > > I agree TreeMap and its associated transactional stack should be deprecated. > > It’s test-only, confusing, and not used by JDBC production paths. > > > > I’m less convinced that NoSQL + InMemory is a clearly superior replacement > > for TreeMap in tests. At the storage layer it’s essentially the same class > > of > > thing: an in-memory, non-durable backend. The difference is that it > > exercises > > a completely different MetaStoreManager/persistence stack > > (NoSqlMetaStoreManager > > vs TransactionalMetaStoreManagerImpl), not the JDBC path most deployments > > use. It > > replaces a relatively simple, self-contained implementation with something > > that is > > part of a much more complicated persistence stack, while remaining > > non-durable > > and test-only at the storage layer. > > > > For the problems originally raised (test-grade defaults, dead production > > path, developer confusion), > > JDBC + H2 seems like an actual fix. > > > > > > On Mon, Jun 29, 2026 at 2:06 PM Dmitri Bourlatchkov <[email protected]> > > wrote: > > > > > Hi Alex, > > > > > > I tend to agree that the DataSource discussion related to H2 became a bit > > > convoluted, and it's a lot simpler to use the NoSQL in-memory persistence > > > instead. > > > > > > Cheers, > > > Dmitri. > > > > > > On Mon, Jun 29, 2026 at 1:57 PM Alexandre Dutra <[email protected]> wrote: > > > > > > > Hi all, > > > > > > > > Some updates on this: > > > > > > > > I recently started a separate discussion regarding dynamic datasource > > > > activation at runtime [1]. This was intended as a prerequisite for > > > > adopting H2 as the default JDBC driver, as suggested on this thread. > > > > > > > > However, that proposal may end up being rejected. > > > > > > > > Given this situation, we should reconsider our options. If the > > > > PostgreSQL + H2 approach is no longer a viable replacement to the > > > > TreeMapMetaStore, I propose an alternative: let's use the NoSQL > > > > metastore with an InMemory backend. > > > > > > > > My reasoning is as follows: > > > > > > > > 1. It remains a production-ready metastore, so strictly superior to > > > > TreeMapMetaStore. > > > > > > > > 2. The metastore state update logic is the same regardless of the > > > > backend, so we're still close to a real production setup (same as with > > > > an in-memory JDBC driver). > > > > > > > > 3. It doesn't require any external dependencies (no bundled driver). > > > > > > > > I'd also note that while the NoSQL metastore is already included > > > > today, it is not actionable because no backend is available. This goes > > > > against the onboarding UX that we're trying to achieve, as users > > > > interested in Polaris with the NoSQL metastore cannot test this setup > > > > with the official image. > > > > > > > > Therefore, I think NoSQL + InMemory would serve as a more appropriate > > > > default setup for the official Polaris image. > > > > > > > > From what I see, it would boil down to adding one line to > > > > polaris-server or polaris-service: > > > > > > > > runtimeOnly(project(":polaris-persistence-nosql-db-inmemory")) > > > > > > > > What are your thoughts on this? > > > > > > > > Thanks, > > > > Alex > > > > > > > > [1]: https://lists.apache.org/thread/jy6wb186h94n9q86kv01shbn68ppr6gv > > > > > > > > > > > > On Fri, Jun 19, 2026 at 12:07 PM Alexandre Dutra <[email protected]> > > > > wrote: > > > > > > > > > > Hi all, > > > > > > > > > > I wanted to give an update on this topic: I have started working on > > > > > this, but I would like to have [4812] merged first, since that's a > > > > > prerequisite. > > > > > > > > > > Thanks, > > > > > Alex > > > > > > > > > > [4812]: https://github.com/apache/polaris/pull/4812 > > > > > > > > > > On Tue, Jun 16, 2026 at 5:15 PM Russell Spitzer > > > > > <[email protected]> wrote: > > > > > > > > > > > > I believe the original idea of TreeMapMetastore was that it looked > > > very > > > > > > similar to FoundationDB from an API perspective, so it served well > > > as > > > > a > > > > > > test system for the original backend being developed at SF. > > > > > > > > > > > > I agree that H2 + JDBC makes sense to me now for the project. > > > > > > > > > > > > On Tue, Jun 16, 2026 at 10:03 AM Alexandre Dutra <[email protected]> > > > > wrote: > > > > > > > > > > > > > Hi all, > > > > > > > > > > > > > > Thank you for your feedback. > > > > > > > > > > > > > > There seems to be a general agreement on the idea of deprecating > > > > > > > TreeMapMetaStore, coupled with the JDBC + H2 solution for tests. > > > > > > > > > > > > > > In most modules, the tests migration won't pose any serious > > > > > > > challenges, as replacing the metastore is generally just a matter > > > of > > > > > > > changing the configuration, and making sure the realm is properly > > > > > > > bootstrapped. > > > > > > > > > > > > > > There will be, however, a few tricky situations in polaris-core: a > > > > few > > > > > > > tests rely on the TreeMapMetaStore, mostly as a test convenience; > > > but > > > > > > > there is no obvious replacement for it in that module. I am > > > > > > > however > > > > > > > confident that we can find a solution for that, either based on > > > > mocks, > > > > > > > or by bringing in a real metastore. > > > > > > > > > > > > > > If no objections are raised, I am going to prepare a PR for this. > > > > > > > > > > > > > > Thanks, > > > > > > > Alex > > > > > > > > > > > > > > On Tue, Jun 16, 2026 at 3:28 PM Dmitri Bourlatchkov < > > > > [email protected]> > > > > > > > wrote: > > > > > > > > > > > > > > > > Hi Alex, > > > > > > > > > > > > > > > > Thanks for starting this thread. > > > > > > > > > > > > > > > > I also find the TransactionalMetaStoreManagerImpl and related > > > call > > > > paths > > > > > > > > conuising in Apache Polaris code. > > > > > > > > > > > > > > > > I support promoting H2 to the default (in memory) Persistence > > > > backend for > > > > > > > > getting started cases. This should also resolve the old H2 > > > > evolution > > > > > > > thread > > > > > > > > [1] by ensuring it is used regularly on the same code paths as > > > > > > > PostgreSQL. > > > > > > > > > > > > > > > > Deprecating TransactionalMetaStoreManagerImpl for removal also > > > > sounds > > > > > > > > reasonable to me. Existing downstream users > > > > > > > > of TransactionalMetaStoreManagerImpl will have time to migrate, > > > or > > > > even > > > > > > > > embed that code (per ASF license) into local builds, during the > > > > > > > deprecation > > > > > > > > phase. > > > > > > > > > > > > > > > > [1] > > > > https://lists.apache.org/thread/g1gg2w8hn9gvlmwrdh0x218whoh2wd39 > > > > > > > > > > > > > > > > Cheers, > > > > > > > > Dmitri. > > > > > > > > > > > > > > > > On Fri, Jun 12, 2026 at 11:24 AM Alexandre Dutra < > > > > [email protected]> > > > > > > > wrote: > > > > > > > > > > > > > > > > > Hi all, > > > > > > > > > > > > > > > > > > I am writing to ask the community whether it is OK to > > > > > > > > > deprecate > > > > > > > > > TreeMapMetaStore, as well as all the in-memory metastore > > > manager, > > > > > > > > > metastore manager factory, and persistence types that rely > > > > solely on > > > > > > > > > TreeMapMetaStore. > > > > > > > > > > > > > > > > > > As we know, these components are test-grade only, and not > > > > suitable for > > > > > > > > > production. They trigger a production readiness alert on > > > Polaris > > > > > > > > > startup. It's a considerable amount of code that is virtually > > > > dead in > > > > > > > > > production. > > > > > > > > > > > > > > > > > > It's also confusing for developers. E.g. the "transactional" > > > > metastore > > > > > > > > > is not transactional in the JDBC sense of the term, and thus > > > not > > > > used > > > > > > > > > by JDBC persistence. It also has its quirks: some return > > > > statuses are > > > > > > > > > only returned by that manager. > > > > > > > > > > > > > > > > > > However, these components are used in tests, and I agree that > > > > it's > > > > > > > > > useful to have an in-memory version of the persistence layer > > > for > > > > > > > > > tests. But we have today two alternatives that are imho > > > superior > > > > for > > > > > > > > > tests in polaris-runtime-service: > > > > > > > > > > > > > > > > > > - JDBC persistence with H2 backend. There are already a few > > > tests > > > > > > > > > using this setup. > > > > > > > > > - NoSQL persistence with InMemory backend. > > > > > > > > > > > > > > > > > > Both alternatives test real production-grade persistence code. > > > > > > > > > > > > > > > > > > And finally, TreeMapMetaStore is currently the default runtime > > > > > > > > > persistence in application.properties; and the Helm chart also > > > > > > > > > advertises it as the default. These are not sane defaults, > > > imho. > > > > It's > > > > > > > > > always tricky to provide a good default for datastores, but > > > > since JDBC > > > > > > > > > persistence is included by default in the server image, I > > > > > > > > > think > > > > that > > > > > > > > > including the H2 driver by default could give us a saner > > > default > > > > while > > > > > > > > > keeping the out-of-the-box experience intact (the license is > > > > Category > > > > > > > > > A). > > > > > > > > > > > > > > > > > > Concretely: > > > > > > > > > > > > > > > > > > On the MetaStoreManagerFactory hierarchy, the following > > > > > > > > > implementations are completely in-memory: > > > > > > > > > > > > > > > > > > - InMemoryPolarisMetaStoreManagerFactory: could be removed > > > > > > > > > > > > > > > > > > - InMemoryAtomicOperationMetaStoreManagerFactory: could be > > > > removed > > > > > > > > > > > > > > > > > > - LocalPolarisMetaStoreManagerFactory: is the base class of > > > > > > > > > the > > > > two > > > > > > > > > above; imho it can be removed, but since it's an abstract > > > class, > > > > it > > > > > > > > > may have been extended outside Polaris. But neither JDBC nor > > > > NoSQL use > > > > > > > > > it. > > > > > > > > > > > > > > > > > > On the PolarisMetaStoreManager hierarchy: > > > > > > > > > > > > > > > > > > - TransactionalMetaStoreManagerImpl: is only used by > > > > > > > > > LocalPolarisMetaStoreManagerFactory. JDBC and NoSQL do not use > > > > it. > > > > > > > > > Could be removed. > > > > > > > > > > > > > > > > > > - TransactionWorkspaceMetaStoreManager however is a different > > > > beast, > > > > > > > > > in spite of the similar name. It is in use today on the commit > > > > path, > > > > > > > > > so should not be removed. > > > > > > > > > > > > > > > > > > On the BasePersistence hierarchy: > > > > > > > > > > > > > > > > > > - TreeMapTransactionalPersistenceImpl and its TreeMapMetaStore > > > > are > > > > > > > > > only used by InMemoryPolarisMetaStoreManagerFactory, and could > > > be > > > > > > > > > removed; > > > > > > > > > > > > > > > > > > - TransactionalPersistence and > > > AbstractTransactionalPersistence: > > > > these > > > > > > > > > are supertypes of TreeMapTransactionalPersistenceImpl and thus > > > > only > > > > > > > > > used for in-memory. They imo can be removed, but they might > > > have > > > > been > > > > > > > > > extended or implemented outside Polaris. > > > > > > > > > > > > > > > > > > I think it's important to keep Polaris code tidy by removing > > > > unused, > > > > > > > > > unimplementable, or test-grade only components. > > > > > > > > > > > > > > > > > > What are your thoughts? > > > > > > > > > > > > > > > > > > Thanks, > > > > > > > > > Alex > > > > > > > > > > > > > > > > > > > > > > >
