Truncate log messages at 10,000 characters

config/logging.yml

@@ -38,7 +38,7 @@ appender:
     datePattern: "'.'yyyy-MM-dd"
     layout:
       type: pattern
-      conversionPattern: "[%d{ISO8601}][%-5p][%-25c] %m%n"
+      conversionPattern: "[%d{ISO8601}][%-5p][%-25c] %.10000m%n"
 
   # Use the following log4j-extras RollingFileAppender to enable gzip compression of log files. 
   # For more information see https://logging.apache.org/log4j/extras/apidocs/org/apache/log4j/rolling/RollingFileAppender.html

docs/reference/migration/migrate_2_0.asciidoc

@@ -508,3 +508,8 @@ Settings settings = ImmutableSettings.settingsBuilder()
         .put("cluster.name", "myClusterName").build();
 Client client = TransportClient.builder().settings(settings).build();
 --------------------------------------------------
+
+=== Logging
+
+Log messages are now truncated at 10,000 characters. This can be changed in the
+`logging.yml` configuration file.