Milestone 2 of the "no more auto-splitter" project will require the implementation of an automatic procedure to merge contiguous chunks belonging to the same shard [when possible].

This proof of concept is aimed to prematurely identify potential roadblocks for the project by implementing the most basic merger respecting the following requirements:

• Two or more chunks can be auto-merged only when:
  • They belong to the same shard
  • Their bounds are contiguous
  • The history array of each chunk to merge:
    • Is empty
      OR
    • The first entry has a validAfter value so that (currentTime - minSnapshotHistoryWindowInSeconds > validAfter)

• Auto-merging happens when the balancer is active as part of balancing rounds:
  • Every N seconds (either auto-merging or migrations can happen during a round)
  • If a merge was issued during the last balancing round, then keep on merging. Else, start issuing migrations again.
• Auto-merging is enabled by default and can be disabled via a field in config.settings. Similar to the autosplit field.