AXIS2-6103 Fix remaining 65536 initialWindowSize across all HTTP/2 docs

Update all config examples and tables in WildFly, Tomcat, Spring Boot,
and integration guides to use initialWindowSize=2097152 (2MB) instead
of 65536 (64KB). The 64KB value caused ~156 WINDOW_UPDATE round-trips
per stream for 10MB responses.

Server-side buffer/flush settings (buffer-size, streamingBufferSize,
moshiStreamingBufferSize) remain at 64KB — those are serialization
flush intervals, not flow-control windows.

Author: robertlazarski

src/site/xdoc/docs/http2-integration-guide.xml

@@ -314,7 +314,7 @@ production-ready intelligent defaults. <strong>Minimal configuration required!</
     &lt;parameter name="PROTOCOL"&gt;HTTP/2.0&lt;/parameter&gt;
     &lt;!-- Optional: Override intelligent defaults if required --&gt;
     &lt;parameter name="maxConcurrentStreams"&gt;100&lt;/parameter&gt;        &lt;!-- Default: 100 --&gt;
-    &lt;parameter name="initialWindowSize"&gt;65536&lt;/parameter&gt;         &lt;!-- Default: 65536 (64KB) --&gt;
+    &lt;parameter name="initialWindowSize"&gt;2097152&lt;/parameter&gt;       &lt;!-- Default: 2097152 (2MB: avoids flow-control round trips) --&gt;
     &lt;parameter name="maxConnectionsTotal"&gt;50&lt;/parameter&gt;          &lt;!-- Default: 50 --&gt;
     &lt;parameter name="connectionTimeout"&gt;30000&lt;/parameter&gt;        &lt;!-- Default: 30000 (30s) --&gt;
     &lt;parameter name="responseTimeout"&gt;300000&lt;/parameter&gt;         &lt;!-- Default: 300000 (5m) --&gt;
@@ -355,7 +355,7 @@ msgContext.setProperty("FLOW_CONTROL_WINDOW_SIZE", 2097152); // 2MB
 maxConcurrentStreams = 100        (Memory-constrained: vs library default 1000)
 maxConnectionsTotal = 50          (Memory-constrained: vs library default 100)
 maxConnectionsPerRoute = 10       (Route-specific limit: vs library default 20)
-initialWindowSize = 65536         (64KB optimized for large JSON payloads)
+initialWindowSize = 2097152       (2MB: avoids flow-control round trips)
 streamingBufferSize = 65536       (64KB chunks for 50MB+ processing)
 connectionKeepAliveTime = 300000  (5 minutes balanced timeout)
 responseTimeout = 300000          (5 minutes for large payload processing)

src/site/xdoc/docs/http2-transport-additions.xml

@@ -457,7 +457,7 @@ options.setProperty("HTTP2_MEMORY_OPTIMIZATION", Boolean.TRUE);
 <transportSender name="h2" class="org.apache.axis2.transport.h2.impl.httpclient5.H2TransportSender">
    <parameter name="PROTOCOL">HTTP/2.0</parameter>
    <parameter name="maxConcurrentStreams">100</parameter>
-   <parameter name="initialWindowSize">65536</parameter>
+   <parameter name="initialWindowSize">2097152</parameter>
    <parameter name="http2FallbackEnabled">true</parameter>
 </transportSender>
 </pre>

src/site/xdoc/docs/json-springboot-tomcat11-userguide.xml

@@ -418,7 +418,7 @@ sender configuration to your axis2.xml file:</p>
                  class="org.apache.axis2.transport.h2.impl.httpclient5.H2TransportSender"&gt;
     &lt;parameter name="PROTOCOL"&gt;HTTP/2.0&lt;/parameter&gt;
     &lt;parameter name="maxConcurrentStreams"&gt;100&lt;/parameter&gt;
-    &lt;parameter name="initialWindowSize"&gt;65536&lt;/parameter&gt;
+    &lt;parameter name="initialWindowSize"&gt;2097152&lt;/parameter&gt;
     &lt;parameter name="serverPushEnabled"&gt;false&lt;/parameter&gt;
     &lt;parameter name="connectionTimeout"&gt;30000&lt;/parameter&gt;
     &lt;parameter name="responseTimeout"&gt;300000&lt;/parameter&gt;

src/site/xdoc/docs/json-springboot-userguide.xml

@@ -319,7 +319,7 @@ sender configuration to your axis2.xml file:</p>
                  class="org.apache.axis2.transport.h2.impl.httpclient5.H2TransportSender"&gt;
     &lt;parameter name="PROTOCOL"&gt;HTTP/2.0&lt;/parameter&gt;
     &lt;parameter name="maxConcurrentStreams"&gt;100&lt;/parameter&gt;
-    &lt;parameter name="initialWindowSize"&gt;65536&lt;/parameter&gt;
+    &lt;parameter name="initialWindowSize"&gt;2097152&lt;/parameter&gt;
     &lt;parameter name="serverPushEnabled"&gt;false&lt;/parameter&gt;
     &lt;parameter name="connectionTimeout"&gt;30000&lt;/parameter&gt;
     &lt;parameter name="responseTimeout"&gt;300000&lt;/parameter&gt;

src/site/xdoc/docs/tomcat-http2-integration-guide.xml

@@ -92,7 +92,7 @@
                <!-- ALIGNED: Buffer sizes match Enhanced Moshi H2 -->
                upgradeAsyncTimeout="300000"      <!-- HTTP/2 upgrade timeout -->
                http2MaxConcurrentStreams="200"   <!-- High concurrency -->
-               http2InitialWindowSize="65536"    <!-- 64KB - matches Enhanced Moshi H2 -->
+               http2InitialWindowSize="2097152"  <!-- 2MB: avoids flow-control round trips -->
                http2MaxFrameSize="32768"         <!-- 32KB - aligned with buffer management -->
                http2MaxHeaderTableSize="8192"    <!-- 8KB header table -->
                http2MaxHeaderListSize="32768"    <!-- 32KB header list -->
@@ -144,7 +144,7 @@
 <table border="1">
 <tr><th>Parameter</th><th>Tomcat 11 Value</th><th>Optimization Purpose</th><th>WildFly Equivalent</th></tr>
 <tr><td><strong>http2MaxConcurrentStreams</strong></td><td>200</td><td>High multiplexing for large JSON APIs</td><td>http2-max-concurrent-streams="200"</td></tr>
-<tr><td><strong>http2InitialWindowSize</strong></td><td>65536 (64KB)</td><td>Aligned with Enhanced Moshi H2 buffers</td><td>http2-initial-window-size="65536"</td></tr>
+<tr><td><strong>http2InitialWindowSize</strong></td><td>2097152 (2MB)</td><td>Avoids flow-control round trips on large responses</td><td>http2-initial-window-size="2097152"</td></tr>
 <tr><td><strong>http2MaxFrameSize</strong></td><td>32768 (32KB)</td><td>Optimal for JSON streaming</td><td>http2-max-frame-size="32768"</td></tr>
 <tr><td><strong>maxPostSize</strong></td><td>104857600 (100MB)</td><td>Large JSON payload support</td><td>max-post-size="104857600"</td></tr>
 <tr><td><strong>connectionTimeout</strong></td><td>300000 (5min)</td><td>Large payload processing time</td><td>no-request-timeout="300000"</td></tr>
@@ -191,7 +191,7 @@
 
         &lt;!-- Coordination with Tomcat 11 HTTP/2 --&gt;
         &lt;parameter name="maxConcurrentStreams"&gt;200&lt;/parameter&gt;              &lt;!-- Matches Tomcat --&gt;
-        &lt;parameter name="initialWindowSize"&gt;65536&lt;/parameter&gt;               &lt;!-- 64KB - matches Tomcat --&gt;
+        &lt;parameter name="initialWindowSize"&gt;2097152&lt;/parameter&gt;             &lt;!-- 2MB: avoids flow-control round trips --&gt;
         &lt;parameter name="maxFrameSize"&gt;32768&lt;/parameter&gt;                    &lt;!-- 32KB - matches Tomcat --&gt;
         &lt;parameter name="maxConnectionsTotal"&gt;50&lt;/parameter&gt;
         &lt;parameter name="maxConnectionsPerRoute"&gt;10&lt;/parameter&gt;

src/site/xdoc/docs/wildfly-http2-integration-guide.xml

@@ -200,10 +200,16 @@ large-payload workloads. See
     <td>✅ WildFly manages 128 concurrent HTTP/2 streams, Moshi H2 handles async processing for large payloads</td>
 </tr>
 <tr>
-    <td><strong>Buffer Management</strong></td>
-    <td><code>http2-initial-window-size="65535"</code></td>
+    <td><strong>Flow Control Window</strong></td>
+    <td><code>http2-initial-window-size="2097152"</code></td>
+    <td><code>initialWindowSize="2097152"</code> (in axis2.xml)</td>
+    <td>✅ 2MB window prevents round-trip latency on large responses</td>
+</tr>
+<tr>
+    <td><strong>Streaming Flush Buffer</strong></td>
+    <td><code>buffer-size="65536"</code></td>
     <td><code>moshiStreamingBufferSize="65536"</code></td>
-    <td>✅ Aligned buffer sizes prevent memory waste and optimize streaming</td>
+    <td>✅ 64KB server-side flush interval — good TTFB, independent of flow-control window</td>
 </tr>
 <tr>
     <td><strong>Large Payload Handling</strong></td>
@@ -243,7 +249,7 @@ large-payload workloads. See
                 enable-http2="true"
                 http2-enable-push="false"
                 http2-header-table-size="4096"           &lt;!-- Conservative headers --&gt;
-                http2-initial-window-size="65536"        &lt;!-- Matches Enhanced Moshi H2 buffer --&gt;
+                http2-initial-window-size="2097152"      &lt;!-- 2MB: avoids flow-control round trips --&gt;
                 http2-max-concurrent-streams="100"       &lt;!-- Coordinated with transport-h2 --&gt;
                 http2-max-frame-size="32768"             &lt;!-- ALIGNED: Matches buffer pool --&gt;
                 http2-max-header-list-size="16384"       &lt;!-- Sufficient for JSON APIs --&gt;
@@ -305,10 +311,10 @@ Complete HTTP/2 + JSON Optimization Stack:
 </tr>
 <tr>
     <td><strong>Window Sizes</strong></td>
-    <td><code>http2-initial-window-size="65536"</code></td>
-    <td><code>initialWindowSize="65536"</code></td>
+    <td><code>http2-initial-window-size="2097152"</code></td>
+    <td><code>initialWindowSize="2097152"</code></td>
     <td><code>AsyncProcessingThreshold="1MB"</code></td>
-    <td>✅ <strong>COORDINATED</strong>: 64KB windows, 1MB async threshold</td>
+    <td>✅ <strong>TUNED</strong>: 2MB flow-control windows, 1MB async threshold</td>
 </tr>
 <tr>
     <td><strong>Stream Limits</strong></td>
@@ -390,7 +396,7 @@ Complete HTTP/2 + JSON Optimization Stack:
                        enable-http2="true"
                        http2-enable-push="false"
                        http2-header-table-size="4096"
-                       http2-initial-window-size="65536"        &lt;!-- Matches transport-h2 + Moshi --&gt;
+                       http2-initial-window-size="2097152"      &lt;!-- 2MB: avoids flow-control round trips --&gt;
                        http2-max-concurrent-streams="100"       &lt;!-- Matches transport-h2 limit --&gt;
                        http2-max-frame-size="32768"             &lt;!-- ALIGNED: Matches buffer pool --&gt;
                        http2-max-header-list-size="16384"
@@ -406,7 +412,7 @@ Complete HTTP/2 + JSON Optimization Stack:
                         enable-http2="true"
                         http2-enable-push="false"
                         http2-header-table-size="4096"
-                        http2-initial-window-size="65536"        &lt;!-- Matches transport-h2 + Moshi --&gt;
+                        http2-initial-window-size="2097152"      &lt;!-- 2MB: avoids flow-control round trips --&gt;
                         http2-max-concurrent-streams="100"       &lt;!-- Matches transport-h2 limit --&gt;
                         http2-max-frame-size="32768"             &lt;!-- ALIGNED: Matches buffer pool --&gt;
                         http2-max-header-list-size="16384"
@@ -464,7 +470,7 @@ Complete HTTP/2 + JSON Optimization Stack:
 
         &lt;!-- Coordination with WildFly HTTP/2 --&gt;
         &lt;parameter name="maxConcurrentStreams"&gt;100&lt;/parameter&gt;              &lt;!-- Matches WildFly --&gt;
-        &lt;parameter name="initialWindowSize"&gt;65536&lt;/parameter&gt;               &lt;!-- Matches WildFly + Moshi --&gt;
+        &lt;parameter name="initialWindowSize"&gt;2097152&lt;/parameter&gt;             &lt;!-- 2MB: avoids flow-control round trips --&gt;
         &lt;parameter name="maxConnectionsTotal"&gt;50&lt;/parameter&gt;
         &lt;parameter name="maxConnectionsPerRoute"&gt;10&lt;/parameter&gt;
         &lt;parameter name="connectionTimeout"&gt;30000&lt;/parameter&gt;