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26.12.14 Performance Schema Status Variable Tables
The MySQL server maintains many status variables that provide information about its operation (see Section 5.1.10, “Server Status Variables”). Status variable information is available in these Performance Schema tables:
global_status
: Global status variables. An application that wants only global values should use this table.session_status
: Status variables for the current session. An application that wants all status variable values for its own session should use this table. It includes the session variables for its session, as well as the values of global variables that have no session counterpart.status_by_thread
: Session status variables for each active session. An application that wants to know the session variable values for specific sessions should use this table. It includes session variables only, identified by thread ID.
There are also summary tables that provide status variable information aggregated by account, host name, and user name. See Section 26.12.17.12, “Status Variable Summary Tables”.
The session variable tables
(session_status
,
status_by_thread
) contain
information only for active sessions, not terminated sessions.
The Performance Schema collects statistics for global status
variables only for threads for which the
INSTRUMENTED
value is YES
in the threads
table. Statistics
for session status variables are always collected, regardless of
the INSTRUMENTED
value.
The Performance Schema does not collect statistics for
Com_
status
variables in the status variable tables. To obtain global and
per-session statement execution counts, use the
xxx
events_statements_summary_global_by_event_name
and
events_statements_summary_by_thread_by_event_name
tables, respectively. For example:
The global_status
and
session_status
tables have these
columns:
VARIABLE_NAME
The status variable name.
VARIABLE_VALUE
The status variable value. For
global_status
, this column contains the global value. Forsession_status
, this column contains the variable value for the current session.
The global_status
and
session_status
tables have these
indexes:
Primary key on (
VARIABLE_NAME
)
The status_by_thread
table contains
the status of each active thread. It has these columns:
THREAD_ID
The thread identifier of the session in which the status variable is defined.
VARIABLE_NAME
The status variable name.
VARIABLE_VALUE
The session variable value for the session named by the
THREAD_ID
column.
The status_by_thread
table has
these indexes:
Primary key on (
THREAD_ID
,VARIABLE_NAME
)
The status_by_thread
table contains
status variable information only about foreground threads. If
the
performance_schema_max_thread_instances
system variable is not autoscaled (signified by a value of
−1) and the maximum permitted number of instrumented
thread objects is not greater than the number of background
threads, the table will be empty.
The Performance Schema supports TRUNCATE
TABLE
for status variable tables as follows:
global_status
: Resets thread, account, host, and user status. Resets global status variables except those that the server never resets.session_status
: Not supported.status_by_thread
: Aggregates status for all threads to the global status and account status, then resets thread status. If account statistics are not collected, the session status is added to host and user status, if host and user status are collected.Account, host, and user statistics are not collected if the
performance_schema_accounts_size
,performance_schema_hosts_size
, andperformance_schema_users_size
system variables, respectively, are set to 0.
FLUSH STATUS
adds the session
status from all active sessions to the global status variables,
resets the status of all active sessions, and resets account,
host, and user status values aggregated from disconnected
sessions.
Document created the 26/06/2006, last modified the 26/10/2018
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