## 28.2 Using the sys Schema

 You can make the [`sys`](sys-schema.html) schema the default schema so that references to its objects need not be qualified with the schema name:

```
mysql> USE sys;
Database changed
mysql> SELECT * FROM version;
+-------------+---------------+
| sys_version | mysql_version |
+-------------+---------------+
| 2.1.1       | 8.0.26-debug  |
+-------------+---------------+
```

 (The [`version`](sys-version.html) view shows the [`sys`](sys-schema.html) schema and MySQL server versions.)

 To access [`sys`](sys-schema.html) schema objects while a different schema is the default (or simply to be explicit), qualify object references with the schema name:

```
mysql> SELECT * FROM sys.version;
+-------------+---------------+
| sys_version | mysql_version |
+-------------+---------------+
| 2.1.1       | 8.0.26-debug  |
+-------------+---------------+
```

 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`](sys-host-summary-by-file-io.html) 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`](sys-host-summary-by-file-io.html) 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$` prefix is intended to provide output that is more user friendly and easier for humans to read. The view with the `x$` 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. For additional information about the differences between non-`x$` and `x$` views, see [Section 28.4.3, “sys Schema Views”](sys-schema-views.html).

 To examine [`sys`](sys-schema.html) schema object definitions, use the appropriate [`SHOW`](show.html) statement or [`INFORMATION_SCHEMA`](information-schema.html) query. For example, to examine the definitions of the [`session`](sys-session.html) view and [`format_bytes()`](sys-format-bytes.html) function, use these statements:

```
mysql> SHOW CREATE VIEW sys.session;
mysql> SHOW CREATE FUNCTION sys.format_bytes;
```

 However, those statements display the definitions in relatively unformatted form. To view object definitions with more readable formatting, access the individual `.sql` files found under the `scripts/sys_schema` in MySQL source distributions. Prior to MySQL 8.0.18, the sources are maintained in a separate distribution available from the [`sys`](sys-schema.html) schema development website at [https://github.com/mysql/mysql-sys](https://github.com/mysql/mysql-sys).

 Neither [**mysqldump**](mysqldump.html) nor [**mysqlpump**](mysqlpump.html) dump the [`sys`](sys-schema.html) schema by default. To generate a dump file, name the [`sys`](sys-schema.html) schema explicitly on the command line using either of these commands:

```
mysqldump --databases --routines sys > sys_dump.sql
mysqlpump sys > sys_dump.sql
```

 To reinstall the schema from the dump file, use this command:

```
mysql < sys_dump.sql
```

