Connections leak on subscription cancellation

[stefannegele]

Bug Report

Versions

• Driver: r2dbc-postgresql-0.8.10.RELEASE
• Database: PostgreSQL
• Java: 14
• OS: macOS

Current Behavior

When a subscriber sends a cancellation signal upstream, connections might not get closed. This produces connections leaks which lead to non-responding applications in the long term.

Table schema

Input Code

```sql create extension if not exists "uuid-ossp"; create table if not exists test_entity ( id uuid default public.uuid_generate_v4(), name text not null, primary key (id) ); ```

Steps to reproduce

Input Code

```kotlin private val logger = LoggerFactory.getLogger("StressTest") fun main(args: Array) { runStressTest() } private fun runStressTest() { val pool = connectionPool() val client = DatabaseClient.create(pool) val threads = (1..5).map { runStressTestRequestThread(it, client) } threads.forEach { it.join() } Thread.sleep(20_000) // connection should be evicted after 10 seconds assert(pool.metrics.get().allocatedSize() == 0) // this fails } private fun runStressTestRequestThread(num: Int, databaseClient: DatabaseClient): Thread = thread(name = "stress-test-$num") { for (i in (1..1_000)) { runCatching { databaseClient.sql("select id, name from test_entity") .then() .timeout(Duration.ofMillis(15)) // cancel before answer .block() }.onFailure { logger.debug(it.message, it) } } logger.info("done") } private fun connectionPool(): ConnectionPool = ConnectionPoolConfiguration .builder(connectionFactory()) .maxSize(1) .initialSize(0) .maxIdleTime(Duration.ofSeconds(1)) .maxLifeTime(Duration.ofSeconds(1)) .backgroundEvictionInterval(Duration.ofSeconds(1)) .build() .let { ConnectionPool(it) } private fun connectionFactory(): ConnectionFactory = ConnectionFactories.get( ConnectionFactoryOptions.parse("r2dbc:postgresql://localhost:5432/test?schema=test") .mutate() .option(ConnectionFactoryOptions.USER, "postgres") .option(ConnectionFactoryOptions.PASSWORD, "pass") .build() ) ```

I also created a demo where this occurs in combination with a netty based spring webflux setup here, that's how i found out about this. This example uses spring boot r2dbc. https://github.com/stefannegele/connection-leak-demo

Expected behavior/code

Connection does not leak.

[mp911de]

We fixed the issue in R2DBC pool just yesterday with #140. There are a few potential leaks in Spring Framework so I'd ask you to file your ticket at https://github.com/spring-projects/spring-framework/issues.

[stefannegele]

Sorry for the duplicate. Did not catch the other issue, because it was raised while i was still investigating. I will now wait for a new release of the pool and run my tests with the new version again. Thanks a lot!