MySQL 8.0 Reference Manual Including MySQL NDB Cluster 8.0

30.4.3 sys Schema Views

The following sections describe sys schema views.

The sys schema contains many views that summarize Performance Schema tables in various ways. Most of these views come in pairs, such that one member of the pair has the same name as the other member, plus a x$ prefix. For example, the host_summary_by_file_io view summarizes file I/O grouped by host and displays latencies converted from picoseconds to more readable values (with units);

mysql> SELECT * FROM sys.host_summary_by_file_io;
| host       | ios   | io_latency |
| localhost  | 67570 | 5.38 s     |
| background |  3468 | 4.18 s     |

The x$host_summary_by_file_io view summarizes the same data but displays unformatted picosecond latencies:

mysql> SELECT * FROM sys.x$host_summary_by_file_io;
| host       | ios   | io_latency    |
| localhost  | 67574 | 5380678125144 |
| background |  3474 | 4758696829416 |

The view without the x$ prefix is intended to provide output that is more user friendly and easier to read. The view with the x$ prefix that displays the same values in raw form is intended more for use with other tools that perform their own processing on the data.

Views without the x$ prefix differ from the corresponding x$ views in these ways: