MariaDB connection fails randomly but stady - junit

Question

I'm running my junit tests in Ubuntu 20 TLS in Eclipse.
Setup:
mariadb in docker container with testcontainers.org
Spring 5 Application in embedded jetty (for junit tests only)
I was wondering why my embedded jetty runs into failures with connectivity to the database:
Caused by: java.net.SocketTimeoutException: Read timed out
I analysed this for days (and nights :( ) ... nothing found.
So I wrote a test harness to find out, whether the testcontainers setup could be a problem, and - unfortunately - it seems to be:
If i try to connect, call a statement, disconnect and repeat this, mariadb in container seems to refuse the connection after a while.
package de.enno.testcontainers_mariadb;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;
import org.junit.Rule;
import org.junit.Test;
import org.testcontainers.containers.MariaDBContainer;
public class MariaDBTest {
#Rule
public MariaDBContainer mariaDB = new MariaDBContainer("mariadb:10.3.6").withUsername("test").withPassword("test");
#Test
public void test() throws SQLException {
Connection connection = DriverManager.getConnection(mariaDB.getJdbcUrl(), "test", "test");
Statement stmt = connection.createStatement();
stmt.executeUpdate("CREATE TABLE a (id int not null primary key, value varchar(20))");
stmt.close();
connection.close();
for (int i = 0; i < 10000000; i++) {
if (i % 1000 == 0) {
System.err.println("Connect " + i + "...");
}
connection = DriverManager.getConnection(mariaDB.getJdbcUrl(), "test", "test");
stmt = connection.createStatement();
stmt.execute("SELECT * FROM a");
stmt.close();
connection.close();
}
}
}
<?xml version="1.0"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<groupId>de.enno</groupId>
<artifactId>testcontainers-mariadb</artifactId>
<version>0.0.1-SNAPSHOT</version>
<modelVersion>4.0.0</modelVersion>
<name>testcontainers-mariadb app</name>
<build>
<plugins>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>2.0.2</version>
<configuration>
<source>1.11</source>
<target>1.11</target>
<encoding>UTF-8</encoding>
</configuration>
</plugin>
</plugins>
</build>
<dependencies>
<dependency>
<groupId>org.mariadb.jdbc</groupId>
<artifactId>mariadb-java-client</artifactId>
<version>2.7.1</version>
</dependency>
<dependency>
<groupId>org.testcontainers</groupId>
<artifactId>mariadb</artifactId>
<version>1.15.0</version>
<scope>test</scope>
</dependency>
</dependencies>
</project>
...
Connect 0...
Connect 1000...
Connect 2000...
Connect 3000...
Connect 4000...
Connect 5000...
java.sql.SQLNonTransientConnectionException: Could not connect to address=(host=localhost)(port=33135)(type=master) : Read timed out
at org.mariadb.jdbc.internal.util.exceptions.ExceptionFactory.createException(ExceptionFactory.java:73)
at org.mariadb.jdbc.internal.util.exceptions.ExceptionFactory.create(ExceptionFactory.java:192)
at org.mariadb.jdbc.internal.protocol.AbstractConnectProtocol.connectWithoutProxy(AbstractConnectProtocol.java:1392)
at org.mariadb.jdbc.internal.util.Utils.retrieveProxy(Utils.java:635)
at org.mariadb.jdbc.MariaDbConnection.newConnection(MariaDbConnection.java:150)
at org.mariadb.jdbc.Driver.connect(Driver.java:89)
at java.sql/java.sql.DriverManager.getConnection(DriverManager.java:677)
at java.sql/java.sql.DriverManager.getConnection(DriverManager.java:228)
at de.enno.testcontainers_mariadb.MariaDBTest.test(MariaDBTest.java:30)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:566)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.testcontainers.containers.FailureDetectingExternalResource$1.evaluate(FailureDetectingExternalResource.java:30)
at org.junit.rules.RunRules.evaluate(RunRules.java:20)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:89)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:41)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:542)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:770)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:464)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:210)
Caused by: java.sql.SQLNonTransientConnectionException: Read timed out
at org.mariadb.jdbc.internal.protocol.AbstractQueryProtocol.handleIoException(AbstractQueryProtocol.java:2075)
at org.mariadb.jdbc.internal.protocol.AbstractQueryProtocol.readPacket(AbstractQueryProtocol.java:1529)
at org.mariadb.jdbc.internal.protocol.AbstractQueryProtocol.getResult(AbstractQueryProtocol.java:1508)
at org.mariadb.jdbc.internal.protocol.AbstractConnectProtocol.readPipelineAdditionalData(AbstractConnectProtocol.java:1031)
at org.mariadb.jdbc.internal.protocol.AbstractConnectProtocol.postConnectionQueries(AbstractConnectProtocol.java:880)
at org.mariadb.jdbc.internal.protocol.AbstractConnectProtocol.createConnection(AbstractConnectProtocol.java:595)
at org.mariadb.jdbc.internal.protocol.AbstractConnectProtocol.connectWithoutProxy(AbstractConnectProtocol.java:1387)
... 31 more
Caused by: java.net.SocketTimeoutException: Read timed out
at java.base/java.net.SocketInputStream.socketRead0(Native Method)
at java.base/java.net.SocketInputStream.socketRead(SocketInputStream.java:115)
at java.base/java.net.SocketInputStream.read(SocketInputStream.java:168)
at java.base/java.net.SocketInputStream.read(SocketInputStream.java:140)
at java.base/java.io.FilterInputStream.read(FilterInputStream.java:133)
at org.mariadb.jdbc.internal.io.input.ReadAheadBufferedStream.fillBuffer(ReadAheadBufferedStream.java:131)
at org.mariadb.jdbc.internal.io.input.ReadAheadBufferedStream.read(ReadAheadBufferedStream.java:104)
at org.mariadb.jdbc.internal.io.input.StandardPacketInputStream.getPacketArray(StandardPacketInputStream.java:247)
at org.mariadb.jdbc.internal.io.input.StandardPacketInputStream.getPacket(StandardPacketInputStream.java:218)
at org.mariadb.jdbc.internal.protocol.AbstractQueryProtocol.readPacket(AbstractQueryProtocol.java:1527)
... 36 more
It seems to be not a timeout problem - in some cases the test runs for some seconds, and some times it runs for hours, BUT: it happens always
Any ideas, how to solve this?
Thanx in advice !
[update]: when trying to connect to the mariadb after the error occured, the connection is established again.