MySQL 5.7 Reference Manual Including MySQL NDB Cluster 7.5 and NDB Cluster 7.6
These views summarize file I/O, grouped by user. By default, rows are sorted by descending total file I/O latency.
The user_summary_by_file_io and
x$user_summary_by_file_io views
have these columns:
user
The client user name. Rows for which the
USER column in the underlying
Performance Schema table is NULL are
assumed to be for background threads and are reported with
a host name of background.
ios
The total number of file I/O events for the user.
io_latency
The total wait time of timed file I/O events for the user.