https://github.com/Terracotta-OSS/offheap-store/: A library that offers data structures allocated off the java heap. 
public interface org.terracotta.offheapstore.MapInternals
  minor version: 0
  major version: 59
  flags: flags: (0x0601) ACC_PUBLIC, ACC_INTERFACE, ACC_ABSTRACT
  this_class: org.terracotta.offheapstore.MapInternals
  super_class: java.lang.Object
{
  public abstract long getSize();
    descriptor: ()J
    flags: (0x0401) ACC_PUBLIC, ACC_ABSTRACT

  public abstract long getTableCapacity();
    descriptor: ()J
    flags: (0x0401) ACC_PUBLIC, ACC_ABSTRACT

  public abstract long getUsedSlotCount();
    descriptor: ()J
    flags: (0x0401) ACC_PUBLIC, ACC_ABSTRACT

  public abstract long getRemovedSlotCount();
    descriptor: ()J
    flags: (0x0401) ACC_PUBLIC, ACC_ABSTRACT

  public abstract int getReprobeLength();
    descriptor: ()I
    flags: (0x0401) ACC_PUBLIC, ACC_ABSTRACT

  public abstract long getAllocatedMemory();
    descriptor: ()J
    flags: (0x0401) ACC_PUBLIC, ACC_ABSTRACT

  public abstract long getOccupiedMemory();
    descriptor: ()J
    flags: (0x0401) ACC_PUBLIC, ACC_ABSTRACT

  public abstract long getVitalMemory();
    descriptor: ()J
    flags: (0x0401) ACC_PUBLIC, ACC_ABSTRACT

  public abstract long getDataAllocatedMemory();
    descriptor: ()J
    flags: (0x0401) ACC_PUBLIC, ACC_ABSTRACT

  public abstract long getDataOccupiedMemory();
    descriptor: ()J
    flags: (0x0401) ACC_PUBLIC, ACC_ABSTRACT

  public abstract long getDataVitalMemory();
    descriptor: ()J
    flags: (0x0401) ACC_PUBLIC, ACC_ABSTRACT

  public abstract long getDataSize();
    descriptor: ()J
    flags: (0x0401) ACC_PUBLIC, ACC_ABSTRACT
}
SourceFile: "MapInternals.java"