MySQL 5.7 Reference Manual Including MySQL NDB Cluster 7.5 and NDB Cluster 7.6
These views summarize file I/O, grouped by host. By default, rows are sorted by descending total file I/O latency.
The host_summary_by_file_io and
x$host_summary_by_file_io views
have these columns:
host
The host from which the client connected. Rows for which
the HOST 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 host.
io_latency
The total wait time of timed file I/O events for the host.