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## 28.4.2 sys Schema Tables and Triggers 

## 28.4.2.1 The sys_config Table 

The following sections describe sys  schema tables and triggers. 

This table contains sys  schema configuration options, one row per option. Configuration changes made by updating this table persist across client sessions and server restarts. 

The sys_config  table has these columns: 

• variable 

The configuration option name. 

• value 

The configuration option value. 

• set_time 

The timestamp of the most recent modification to the row. 

• set_by 

The account that made the most recent modification to the row. The value is NULL  if the row has not been changed since the sys  schema was installed. 

As an efficiency measure to minimize the number of direct reads from the sys_config  table, sys  schema functions that use a value from this table check for a user-defined variable with a corresponding name, which is the user-defined variable having the same name plus a @sys.  prefix. (For example, the variable corresponding to the diagnostics.include_raw  option is @sys.diagnostics.include_raw .) 

If the user-defined variable exists in the current session and is non- NULL , the function uses its value in preference to the value in the sys_config  table. Otherwise, the function reads and uses the value from the table. In the latter case, the calling function conventionally also sets the corresponding user-defined variable to the table value so that further references to the configuration option within the same session use the variable and need not read the table again. 

