Document garbage collection

Information related to garbage collection for Oak Segment Tar should be documented. In particular, the following topics should be treated.

• Garbage collection - Describe the role of garbage collection.
  • Generational garbage collection - Outline the basic concepts behind the generational garbage collection algorithm.
  • Estimation, compaction and cleanup - Describe the main phases of garbage collection and how they interact with each other.
  • Offline garbage collection - How offline garbage collection works and what to expect from it.
  • Online garbage collection - Describe the role of online garbage collection and the reason why it is needed.
    • Monitoring the log - The information you can look up in the log about garbage collection.
      • When did garbage collection start?
      • When did estimation start?
      • Is estimation disabled?
      • Was estimation cancelled?
      • When did estimation complete?
      • What was the output of estimation?
      • When did compaction start?
      • Is compaction disabled?
      • Was compaction cancelled?
      • When did compaction complete?
      • How did compaction cope with concurrent writes?
      • What was the output of compaction?
      • When did clean-up start?
      • Was cleanup cancelled?
      • When did cleanup complete?
      • What was the output of cleanup?
    • Monitoring via JMX - The information you can lookup via JMX about garbage collection.
      • SegmentRevisionGC
        • Garbage collection options - Which properties are available for the user to get and set, and their impact on garbage collection.
        • Start garbage collection - How to manually start garbage collection.
        • Garbage collection statistics - Statistics about garbage collection and how to interpret them.