Performance Schema Miscellaneous Tables Within the Performance Schema, the  THREAD_ID  column in the  error_log  table is most similar to the PROCESSLIST_ID  column of the  threads  table: •For foreground threads,  THREAD_ID  and  PROCESSLIST_ID  represent a connection identifier. This is the same value displayed in the  ID  column of the  INFORMATION_SCHEMA PROCESSLIST  table, displayed in the  Id  column of  SHOW PROCESSLIST  output, and returned by the  CONNECTION_ID() function within the thread. •For background threads,  THREAD_ID  is 0 and  PROCESSLIST_ID  is  NULL . Many Performance Schema tables other than  error_log  has a column named  THREAD_ID , but in those tables, the  THREAD_ID  column is a value assigned internally by the Performance Schema. The event priority. Permitted values are  System ,  Error ,  Warning ,  Note . The  PRIO  column is based on the  label  field of error events, which itself is based on the underlying numeric  prio  field value. • PRIO • ERROR_CODE • SUBSYSTEM • DATA •Index on ( THREAD_ID ) •Index on ( PRIO ) •Primary key on ( LOGGED ) •Index on ( ERROR_CODE ) •Index on ( SUBSYSTEM ) TRUNCATE TABLE  is not permitted for the  error_log  table. The  error_log  table has these indexes: Because the error log can be reconfigured to change the log sink component that supplies rows to the error_log  table, and because different sinks produce different output formats, it is possible for rows written to the  error_log  table at different times to have different  DATA  formats. The text representation of the error event. The format of this value depends on the format produced by the log sink component that generates the  error_log  row. For example, if the log sink is log_sink_internal  or  log_sink_json ,  DATA  values represent error events in traditional or JSON format, respectively. (See Section 5.4.2.9, “Error Log Output Format” .) The subsystem in which the event occurred.  SUBSYSTEM  corresponds to the  subsystem  field of error events. The numeric event error code.  ERROR_CODE  corresponds to the  error_code  field of error events. The Performance Schema  error_log  table is populated by error log sink components that write to the table in addition to writing formatted error events to the error log. Performance Schema support by log sinks has two parts: 5079 Implementation and Configuration of the error_log Table