Record type for all statistics that will be collected. There is a single instance (which we refer to as "the instance" below) which is returned by get.

reset_stats () will call the relevant clear function on each field of the instance. This typically resets the fields (e.g. to 0 for an int field).

get () returns the instance of t that stores the satistics. If report_pack_store or report_index is not called before, the content will be filled with default value, decided at create time (most the time, 0).

report_pack_store ~field increments the field value in the pack_store stats. It also increments the total field in Pack_store.t when the field is related to finds.

report_index () fills the stats with value from the Index.Stats module. This essentially copies the "current" values from Index.Stats to the get() instance index field.

incr_appended_hashes () increments the field appended_hashes for pack_store in the instance.

incr_appended_offsets increments the field appended_offsets for pack_store in the instance.

offset_ratio: appended_offsets / (appended_offsets + appended_hashes); offset_significance: appended_offsets + appended_hashes

get_cache_stats() uses the instance pack_store field to compute cache misses.

get_offset_stats() uses the instance pack_store field to compute offset stats.

incr_fm_field field increments the chosen stats field for the File_manager

report_latest_gc gc_stats sets (get ()).latest_gc to the stats of the latest successful GC.