Hello, I saw #82 which was marked to be resolved. I'm using r2dbc-pool 0.8.3 and but I'am still facing the similar issue.

Version

spring-data-r2dbc 1.1.2.RELEASE

r2dbc-pool 0.8.3.RELEASE

r2dbc-mysql 0.8.2-RELEASE

Case

I saw that if connections are closed on the server side, without any incoming requests, they're closed normally as expected with WARN log saying Connection has been closed by peer and new connection will be established on the next incoming request. However, when a request gets a connection and the server closes the connection before the it's executed, It prints logs like below and the pool hangs forever.

Configuration

MySQL wait_timeout: 8h

spring:
  r2dbc:
    pool:
      initial-size: 10
      max-size: 30
      max-idle-time: 15s
      validation-query: SELECT 1
    properties:
      connect-timeout: 10
      ssl: false
      max-create-connection-time: 3
      max-acquire-time: 5
      max-life-time: 15

Logs

Here's the log for it. My request arrived right before MySQL server closed the connection. After MySQL server close the connection after wait_timeout, as you can see, 7 of 10 connections are closed normally, but exception occured while closing the next one (which has been acquired by the incoming request). After this, any request through MySQL hangs and the number of connections is maintained to be 7, which should be 10 in normal case.

2020-10-24 05:40:00.833  INFO 1 --- [or-http-epoll-3] c.l.l.my.package.controller.MyController   : Request comes in
2020-10-24 05:40:00.837  WARN 1 --- [tor-tcp-epoll-2] d.m.r.mysql.client.MessageDuplexCodec    : Connection has been closed by peer
2020-10-24 05:40:00.838  WARN 1 --- [tor-tcp-epoll-2] d.m.r.mysql.client.MessageDuplexCodec    : Connection has been closed by peer
2020-10-24 05:40:00.839  WARN 1 --- [tor-tcp-epoll-2] d.m.r.mysql.client.MessageDuplexCodec    : Connection has been closed by peer
2020-10-24 05:40:00.840  WARN 1 --- [tor-tcp-epoll-2] d.m.r.mysql.client.MessageDuplexCodec    : Connection has been closed by peer
2020-10-24 05:40:00.841  WARN 1 --- [tor-tcp-epoll-2] d.m.r.mysql.client.MessageDuplexCodec    : Connection has been closed by peer
2020-10-24 05:40:00.841  WARN 1 --- [tor-tcp-epoll-2] d.m.r.mysql.client.MessageDuplexCodec    : Connection has been closed by peer
2020-10-24 05:40:00.841  WARN 1 --- [tor-tcp-epoll-2] d.m.r.mysql.client.MessageDuplexCodec    : Connection has been closed by peer
2020-10-24 05:40:00.844 ERROR 1 --- [or-http-epoll-3] reactor.core.publisher.Operators         : Operator called default onErrorDropped
dev.miku.r2dbc.mysql.client.MySqlConnectionException: null
        at dev.miku.r2dbc.mysql.client.ClientExceptions.wrap(ClientExceptions.java:47)
        at dev.miku.r2dbc.mysql.client.ReactorNettyClient.resumeError(ReactorNettyClient.java:214)
        at reactor.core.publisher.FluxOnErrorResume$ResumeSubscriber.onError(FluxOnErrorResume.java:88)
        at reactor.core.publisher.FluxConcatMap$ConcatMapImmediate.innerError(FluxConcatMap.java:301)
        at reactor.core.publisher.FluxConcatMap$ConcatMapInner.onError(FluxConcatMap.java:863)
        at reactor.core.publisher.Operators.error(Operators.java:196)
        at reactor.core.publisher.MonoError.subscribe(MonoError.java:52)
        at reactor.core.publisher.Mono.subscribe(Mono.java:4213)
        at reactor.netty.NettyOutbound.subscribe(NettyOutbound.java:331)
        at reactor.core.publisher.FluxConcatMap$ConcatMapImmediate.drain(FluxConcatMap.java:441)
        at reactor.core.publisher.FluxConcatMap$ConcatMapImmediate.onNext(FluxConcatMap.java:243)
        at reactor.core.publisher.EmitterProcessor.drain(EmitterProcessor.java:426)
        at reactor.core.publisher.EmitterProcessor.onNext(EmitterProcessor.java:268)
        at dev.miku.r2dbc.mysql.client.ReactorNettyClient.lambda$null$12(ReactorNettyClient.java:205)
        at reactor.core.publisher.MonoRunnable.call(MonoRunnable.java:73)
        at reactor.core.publisher.MonoRunnable.call(MonoRunnable.java:32)
        at reactor.core.publisher.MonoFlatMap$FlatMapMain.onNext(MonoFlatMap.java:132)
        at reactor.core.publisher.MonoCreate$DefaultMonoSink.success(MonoCreate.java:156)
        at dev.miku.r2dbc.mysql.client.RequestTask.run(RequestTask.java:46)
        at dev.miku.r2dbc.mysql.client.RequestQueue.submit(RequestQueue.java:93)
        at dev.miku.r2dbc.mysql.client.ReactorNettyClient.lambda$close$13(ReactorNettyClient.java:205)
        at reactor.core.publisher.MonoCreate.subscribe(MonoCreate.java:57)
        at reactor.core.publisher.Mono.subscribe(Mono.java:4213)
        at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.drain(MonoIgnoreThen.java:172)
        at reactor.core.publisher.MonoIgnoreThen.subscribe(MonoIgnoreThen.java:56)
        at reactor.core.publisher.Mono.subscribe(Mono.java:4213)
        at reactor.core.publisher.Mono.subscribeWith(Mono.java:4324)
        at reactor.core.publisher.Mono.subscribe(Mono.java:4184)
        at reactor.core.publisher.Mono.subscribe(Mono.java:4120)
        at reactor.pool.SimplePool.drainLoop(SimplePool.java:283)
        at reactor.pool.SimplePool.drain(SimplePool.java:187)
        at reactor.pool.SimplePool.doAcquire(SimplePool.java:136)
        at reactor.pool.AbstractPool$Borrower.request(AbstractPool.java:363)
        at reactor.core.publisher.FluxPeek$PeekSubscriber.request(FluxPeek.java:130)
        at reactor.core.publisher.MonoFlatMap$FlatMapMain.onSubscribe(MonoFlatMap.java:103)
        at reactor.core.publisher.FluxPeek$PeekSubscriber.onSubscribe(FluxPeek.java:163)
        at reactor.pool.SimplePool$QueueBorrowerMono.subscribe(SimplePool.java:381)
        at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:64)
        at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)
        at reactor.core.publisher.FluxRetry$RetrySubscriber.resubscribe(FluxRetry.java:110)
        at reactor.core.publisher.MonoRetry.subscribeOrReturn(MonoRetry.java:49)
        at reactor.core.publisher.Mono.subscribe(Mono.java:4198)
        at reactor.core.publisher.FluxOnErrorResume$ResumeSubscriber.onError(FluxOnErrorResume.java:97)
        at reactor.core.publisher.MonoFlatMap$FlatMapMain.onError(MonoFlatMap.java:165)
        at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.onError(FluxMapFuseable.java:134)
        at reactor.core.publisher.FluxHandleFuseable$HandleFuseableSubscriber.onNext(FluxHandleFuseable.java:185)
        at reactor.core.publisher.Operators$ScalarSubscription.request(Operators.java:2344)
        at reactor.core.publisher.FluxHandleFuseable$HandleFuseableSubscriber.request(FluxHandleFuseable.java:243)
        at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.request(FluxMapFuseable.java:162)
        at reactor.core.publisher.MonoFlatMap$FlatMapMain.onSubscribe(MonoFlatMap.java:103)
        at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.onSubscribe(FluxMapFuseable.java:90)
        at reactor.core.publisher.FluxHandleFuseable$HandleFuseableSubscriber.onSubscribe(FluxHandleFuseable.java:148)
        at reactor.core.publisher.MonoCurrentContext.subscribe(MonoCurrentContext.java:35)
        at reactor.core.publisher.Mono.subscribe(Mono.java:4213)
        at reactor.core.publisher.FluxUsingWhen.subscribe(FluxUsingWhen.java:103)
        at reactor.core.publisher.Flux.subscribe(Flux.java:8325)
        at kotlinx.coroutines.reactive.PublisherAsFlow.collectImpl(ReactiveFlow.kt:83)
        at kotlinx.coroutines.reactive.PublisherAsFlow.collect(ReactiveFlow.kt:68)
        at kotlinx.coroutines.flow.FlowKt__CollectionKt.toCollection(Collection.kt:32)
        at kotlinx.coroutines.flow.FlowKt.toCollection(Unknown Source)
        at kotlinx.coroutines.flow.FlowKt__CollectionKt.toList(Collection.kt:15)
        at kotlinx.coroutines.flow.FlowKt.toList(Unknown Source)
        at kotlinx.coroutines.flow.FlowKt__CollectionKt.toList$default(Collection.kt:15)
        at kotlinx.coroutines.flow.FlowKt.toList$default(Unknown Source)
        at 
......

Reproduce step

For test, I changed MySQL's default timeout value to 15s, and max-idle-time and max-life-time of R2DBC config to 10s. I create a breakpoint on the below line, in ExecuteSpecSupport class. After connections are established, I wait on the breakpoint until 15s passes, in order to wait for the connection to be expired. When I continue after than, I could be able to reproduce the issue.

return new DefaultSqlResult<>(DefaultDatabaseClient.this, //  <<<< Here
					sql, //
					resultFunction, //
					it -> sumRowsUpdated(resultFunction, it), //
					mappingFunction);