[keycloak-dev] Potential performance regression between 3.4.3.Final and 4.3.0.Final

Hello Keycloak team, has anyone encountered some performance issues after upgrading 3.4.3 to 4.x (4.3.0)? Today I noticed a performance regression while preparing an upgrade from Keycloak 3.4.3.Final to 4.3.0.Final in our staging environment. In our test environment, we have around ~100k test users stored in a postgres-backed database. When we started the server with the new Keycloak version, the migration went through, and everything looked fine at first, but when we tried to browse the list of users via the admin-console, we noticed that the CPU and memory consumption of the server increased significantly, up to a point where Keycloak crashed with an OOME. All previous Keycloak versions including 3.4.3 were very modest with their memory requirements and quite happy with ~1g heap. However, that seems to have changed in Keycloak 4.3.0 - there we needed at least 4g to prevent Keycloak from crashing with an OOME. Furthermore, we noticed that the response times for browsing the paginated user view increased significantly as well: In Keycloak 3.4.3 the average time to load a user page is ~80ms. In Keycloak 4.3.0 (and older versions >= 4.0.0.Beta1) the same operation takes ~7 seconds for a test realm with just 10k users. In the test realm with 100k users, the time to load a single page in the users listing was 66 seconds for version 4.3.0, on average - compared to quite stable 80ms in 3.4.3. The database query that is executed by Keycloak 4.3.0 runs in ~1.5 seconds for 100k users, so I assume the processing logic in Keycloak is the culprit. The problem of long load-times can be reproduced with the Keycloak docker images and the in-memory database. I also created a small example project that creates some users with just a few attributes in a docker based 3.4.3 and 4.3.0 Keycloak environment with a Postgres database to reproduce the problem. https://github.com/thomasdarimont/kc-user-regression-tester Cheers, Thomas