Curious if you considered switching to a different connection pooling library. These days I usually use HikariCP which is fast an actively maintained. c3p0 hasn't had any activity for years, I'm not sure if it's still maintained.
Crucially, c3p0 will probably never see the `synchronized` blocks being replaced by reentrant locks. Since LTS offers exist for Java 21, many libraries might actually do that. But I actually hope that the ecosystem resists, which would force virtual thread users suffering from this problem to upgrade soon.
Perhaps we'll give HikariCP a chance. However, please keep in mind that the goal of the YDB team is to enhance database performance. We needed virtual threads to make TPC-C efficient enough to generate a reasonable load on a modest amount of hardware.
Virtual threads aren't necessarily faster, you still have just as many sockets and network connections as before. You can easily spawn 5000 platform threads, and if that's not enough, there are quite a few user-space implementations of fibers/coroutines/async etc on the JVM that can deal with many outlying requests (Cats/ZIO in Scala, Kotlin coroutines, the Play framework, concurrent.Future, etc.)
Been ages since I’ve touched it but back in 2017-2018 I had some fun integrating HikariCP in place of c3p0 in some Clojure projects and it was more performant.
