Recovery buffer size 16B smaller (#50100)

G1GC will use humongous allocations when an allocation exceeds half the
chosen region size, which is minimum 1MB. By reducing the recovery
buffer size by 16 bytes we ensure that the recovery buffer is never
allocated as a humongous allocation.

server/src/main/java/org/elasticsearch/indices/recovery/RecoverySettings.java

@@ -81,7 +81,8 @@ public class RecoverySettings {
             INDICES_RECOVERY_INTERNAL_LONG_ACTION_TIMEOUT_SETTING::get, TimeValue.timeValueSeconds(0),
             Property.Dynamic, Property.NodeScope);
 
-    public static final ByteSizeValue DEFAULT_CHUNK_SIZE = new ByteSizeValue(512, ByteSizeUnit.KB);
+    // choose 512KB-16B to ensure that the resulting byte[] is not a humongous allocation in G1.
+    public static final ByteSizeValue DEFAULT_CHUNK_SIZE = new ByteSizeValue(512 * 1024 - 16, ByteSizeUnit.BYTES);
 
     private volatile ByteSizeValue maxBytesPerSec;
     private volatile int maxConcurrentFileChunks;