diff --git a/extensions/reactive-datasource/runtime/src/main/java/io/quarkus/reactive/datasource/runtime/DataSourceReactiveRuntimeConfig.java b/extensions/reactive-datasource/runtime/src/main/java/io/quarkus/reactive/datasource/runtime/DataSourceReactiveRuntimeConfig.java
index 5a8b64802039a..f1004d7d105b4 100644
--- a/extensions/reactive-datasource/runtime/src/main/java/io/quarkus/reactive/datasource/runtime/DataSourceReactiveRuntimeConfig.java
+++ b/extensions/reactive-datasource/runtime/src/main/java/io/quarkus/reactive/datasource/runtime/DataSourceReactiveRuntimeConfig.java
@@ -31,7 +31,7 @@ public class DataSourceReactiveRuntimeConfig {
     /**
      * The datasource pool maximum size.
      */
-    @ConfigItem
+    @ConfigItem(defaultValueDocumentation = "20")
     public OptionalInt maxSize = OptionalInt.empty();
 
     /**
diff --git a/extensions/reactive-db2-client/runtime/src/main/java/io/quarkus/reactive/db2/client/runtime/DB2PoolRecorder.java b/extensions/reactive-db2-client/runtime/src/main/java/io/quarkus/reactive/db2/client/runtime/DB2PoolRecorder.java
index ff9a794e19ef9..7dc4b2276402a 100644
--- a/extensions/reactive-db2-client/runtime/src/main/java/io/quarkus/reactive/db2/client/runtime/DB2PoolRecorder.java
+++ b/extensions/reactive-db2-client/runtime/src/main/java/io/quarkus/reactive/db2/client/runtime/DB2PoolRecorder.java
@@ -96,6 +96,8 @@ private PoolOptions toPoolOptions(Integer eventLoopCount,
 
         if (dataSourceReactiveRuntimeConfig.maxSize.isPresent()) {
             poolOptions.setMaxSize(dataSourceReactiveRuntimeConfig.maxSize.getAsInt());
+        } else {
+            poolOptions.setMaxSize(20);
         }
 
         if (dataSourceReactiveRuntimeConfig.idleTimeout.isPresent()) {
diff --git a/extensions/reactive-mssql-client/runtime/src/main/java/io/quarkus/reactive/mssql/client/runtime/MSSQLPoolRecorder.java b/extensions/reactive-mssql-client/runtime/src/main/java/io/quarkus/reactive/mssql/client/runtime/MSSQLPoolRecorder.java
index 7c14613815975..788320fc3fea3 100644
--- a/extensions/reactive-mssql-client/runtime/src/main/java/io/quarkus/reactive/mssql/client/runtime/MSSQLPoolRecorder.java
+++ b/extensions/reactive-mssql-client/runtime/src/main/java/io/quarkus/reactive/mssql/client/runtime/MSSQLPoolRecorder.java
@@ -96,6 +96,8 @@ private PoolOptions toPoolOptions(Integer eventLoopCount,
 
         if (dataSourceReactiveRuntimeConfig.maxSize.isPresent()) {
             poolOptions.setMaxSize(dataSourceReactiveRuntimeConfig.maxSize.getAsInt());
+        } else {
+            poolOptions.setMaxSize(20);
         }
 
         if (dataSourceReactiveRuntimeConfig.idleTimeout.isPresent()) {
diff --git a/extensions/reactive-mysql-client/runtime/src/main/java/io/quarkus/reactive/mysql/client/runtime/MySQLPoolRecorder.java b/extensions/reactive-mysql-client/runtime/src/main/java/io/quarkus/reactive/mysql/client/runtime/MySQLPoolRecorder.java
index 95eb1aad8645f..28e9f8a3440e5 100644
--- a/extensions/reactive-mysql-client/runtime/src/main/java/io/quarkus/reactive/mysql/client/runtime/MySQLPoolRecorder.java
+++ b/extensions/reactive-mysql-client/runtime/src/main/java/io/quarkus/reactive/mysql/client/runtime/MySQLPoolRecorder.java
@@ -97,6 +97,8 @@ private PoolOptions toPoolOptions(Integer eventLoopCount,
 
         if (dataSourceReactiveRuntimeConfig.maxSize.isPresent()) {
             poolOptions.setMaxSize(dataSourceReactiveRuntimeConfig.maxSize.getAsInt());
+        } else {
+            poolOptions.setMaxSize(20);
         }
 
         if (dataSourceReactiveRuntimeConfig.idleTimeout.isPresent()) {
diff --git a/extensions/reactive-oracle-client/runtime/src/main/java/io/quarkus/reactive/oracle/client/runtime/OraclePoolRecorder.java b/extensions/reactive-oracle-client/runtime/src/main/java/io/quarkus/reactive/oracle/client/runtime/OraclePoolRecorder.java
index a24a80f7997bb..e28834c0dbc09 100644
--- a/extensions/reactive-oracle-client/runtime/src/main/java/io/quarkus/reactive/oracle/client/runtime/OraclePoolRecorder.java
+++ b/extensions/reactive-oracle-client/runtime/src/main/java/io/quarkus/reactive/oracle/client/runtime/OraclePoolRecorder.java
@@ -90,6 +90,8 @@ private PoolOptions toPoolOptions(Integer eventLoopCount,
 
         if (dataSourceReactiveRuntimeConfig.maxSize.isPresent()) {
             poolOptions.setMaxSize(dataSourceReactiveRuntimeConfig.maxSize.getAsInt());
+        } else {
+            poolOptions.setMaxSize(20);
         }
 
         if (dataSourceReactiveRuntimeConfig.idleTimeout.isPresent()) {
diff --git a/extensions/reactive-pg-client/runtime/src/main/java/io/quarkus/reactive/pg/client/runtime/PgPoolRecorder.java b/extensions/reactive-pg-client/runtime/src/main/java/io/quarkus/reactive/pg/client/runtime/PgPoolRecorder.java
index 9c5708b440de5..9760ee690d645 100644
--- a/extensions/reactive-pg-client/runtime/src/main/java/io/quarkus/reactive/pg/client/runtime/PgPoolRecorder.java
+++ b/extensions/reactive-pg-client/runtime/src/main/java/io/quarkus/reactive/pg/client/runtime/PgPoolRecorder.java
@@ -96,6 +96,8 @@ private PoolOptions toPoolOptions(Integer eventLoopCount,
 
         if (dataSourceReactiveRuntimeConfig.maxSize.isPresent()) {
             poolOptions.setMaxSize(dataSourceReactiveRuntimeConfig.maxSize.getAsInt());
+        } else {
+            poolOptions.setMaxSize(20);
         }
 
         if (dataSourceReactiveRuntimeConfig.idleTimeout.isPresent()) {