At the shutdown, write the latest lsn only to the first pages of the ibdata files of the system tablespace, NOT to the .ibd files; writing to tens of thousands .ibd files can take minutes


innobase/fil/fil0fil.c:
  At the shutdown, write the latest lsn only to the first pages of the ibdata files of the system tablespace, NOT to the .ibd files; writing to tens of thousands .ibd files can take minutes