Add example for customizing quarkus jpa connection

keycloak/extensions/src/main/java/com/github/thomasdarimont/keycloak/custom/jpa/CustomQuarkusJpaConnectionProviderFactory.java

@@ -0,0 +1,40 @@
+package com.github.thomasdarimont.keycloak.custom.jpa;
+
+import com.google.auto.service.AutoService;
+import jakarta.persistence.EntityManagerFactory;
+import lombok.extern.jbosslog.JBossLog;
+import org.keycloak.connections.jpa.JpaConnectionProviderFactory;
+import org.keycloak.models.KeycloakSessionFactory;
+import org.keycloak.quarkus.runtime.storage.legacy.database.QuarkusJpaConnectionProviderFactory;
+
+import java.util.HashMap;
+import java.util.Map;
+
+@JBossLog
+@AutoService(JpaConnectionProviderFactory.class)
+public class CustomQuarkusJpaConnectionProviderFactory extends QuarkusJpaConnectionProviderFactory {
+
+    @Override
+    protected EntityManagerFactory getEntityManagerFactory() {
+        // apply tuning suggestions from https://github.com/keycloak/keycloak/issues/26162
+
+        Map<String, String> tuningProperties = new HashMap<>();
+        tuningProperties.put("hibernate.jdbc.batch_size", "50");
+        tuningProperties.put("hibernate.order_inserts", "true");
+        tuningProperties.put("hibernate.order_updates", "true");
+        tuningProperties.put("hibernate.jdbc.fetch_size", "50");
+        tuningProperties.put("hibernate.query.in_clause_parameter_padding", "true");
+        log.infof("apply custom hibernate tuning properties: %s", tuningProperties);
+
+        EntityManagerFactory emf = super.getEntityManagerFactory();
+        emf.getProperties().putAll(tuningProperties);
+
+        return emf;
+    }
+
+    @Override
+    public void postInit(KeycloakSessionFactory factory) {
+        log.info("### Using custom Quarkus JPA Connection factory");
+        super.postInit(factory);
+    }
+}