Let us remove the thread-local variable mariadb_stats and introduce
trx_t::pages_accessed, trx_t::active_handler_stats for more
efficiently maintaining some statistics inside InnoDB.
buf_pool.stat.n_page_gets: Reimplemented as Atomic_counter<ulint>.
This will no longer track some accesses in the background where
!current_thd() || !thd_to_trx(current_thd).
trx_t::free(), trx_t::commit_cleanup(): Apply pages_accessed
to buf_pool.stat.n_page_gets.
buf_read_ahead_report(): Report a completed read-ahead batch.
ha_innobase::estimate_rows_upper_bound(): Do not bother updating
trx_t::op_info around some quick arithmetics.
ha_innobase::records_in_range(): Do invoke mariadb_set_stats.
This will change some ANALYZE FORMAT=JSON SELECT results of the test
main.rowid_filter_innodb.
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