255. Logging garbage collectors

Analyzing the GC logs is another approach that can be useful for finding memory issues. Since GC logs don’t add a significant overhead, they can be enabled in production for debugging purposes. Really, GC logs have an insignificant overhead, so you should definitely use them!

Let’s consider some simple Java code that adds and removes from List<String>. Adding and removing the code requires a full GC via System.gc():

private static final List<String> strings = new ArrayList<>();
...
logger.info("Application started ...");
String string = "prefixedString_";
// Add in heap 5 millions String instances
for (int i = 0; i < 5_000_000; i++) {
  String newString = string + i;
  strings.add(newString);
}
logger.info(() -> "List size: " + strings.size());
// Force GC execution
System.gc();
// Remove 10_000 out of 5 millions
for (int i = 0; i < 10_000; i++) {
  String newString = string...