Tasks:

Add new statistics to track the status of the background compaction server. The list of suggested statistics can be found below:

• The background compaction server encountered an error
  • This stat currently exists and is called background_compact_fail. However, it is not used when the background compaction returns WT_ERROR after being interrupted, it should be added there too - Done in WT-11637
• The table did not meet the requirements to be eligible for compaction
  • To do after WT-11343
• The background compaction server successfully compacted a table
  • After the compact API call, we should check for the ret value and update that stat when it is 0 before any other processing.
• The number of elements present in the queue processed by the background compaction server
  • There is no such queue in the current implementation, this is no longer needed. A stat tracking the number of elements being tracked has been added through WT-11343 background_compact_files_tracked
• The number of blocks moved for compaction

• The amount of space saved by shrinking tables
  • We could make a stat out of compact_bytes_rewritten which appears in the __wt_block struct
• The number of pages visited by compaction
  • This is already covered by the following stat:

  • BtreeStat('btree_compact_pages_reviewed', 'btree compact pages reviewed', 'no_clear,no_scale'), 

• The number of checkpoints generated by compaction
  • This stat should be updated whenever __compact_checkpoint is called.
• The I/O load generated by compaction
  • The current implementation does not allow us to do this.
• When getting EBUSY in __compact_worker before setting another_pass to true and setting ret back to 0.
  • This does not mean a failure but just a possible transient EBUSY on a specific dhandle.
  • There is already a verbose message when this occurs, a stat may not be required.
• When compaction is interrupted by the application - Done in WT-11344

Definition of done:

• A set of new statistics have been defined and implemented for background compaction.