使用ChronicleMap测试堆外缓存：该代码是否会创建堆外内存映射？

Hey there, great question! The short answer is: Yes, this code absolutely creates an off-heap memory-mapped ChronicleMap.

Let me break down why this works the way it does:

• ChronicleMap is built specifically to leverage off-heap memory (via memory-mapped files) as its core storage. By default, any instance created with the create() method will store all key-value pairs outside the JVM heap—only minimal internal reference objects live on the heap, not the actual data you're caching.
• Looking at your code snippet:

  chronicleMap = ChronicleMapBuilder.of(String.class, ByteBuffer.class)
      .entries(aMaxSize)
      .averageKeySize(100)
      .averageValueSize(1000)
      .create();
  

  You've configured all the critical parameters (max entries, average key/value sizes) that ChronicleMap needs to allocate the appropriate amount of off-heap space. Even with ByteBuffer as the value type, the actual byte content of the buffer gets serialized directly to the off-heap region—you're not just storing a heap-based ByteBuffer reference, you're persisting its raw data outside the JVM heap.

A couple quick clarifications to keep in mind:

• If you want the off-heap map to persist to a disk file (instead of a temporary, process-specific off-heap region that vanishes when your app exits), swap out create() for createPersistedTo(new File("/path/to/your/map-file.dat")).
• Double-check that your averageKeySize and averageValueSize align with your real-world data—this helps ChronicleMap allocate off-heap space efficiently, avoiding unnecessary overhead or resizing.

内容的提问来源于stack exchange，提问作者Fredrik LS