System Variables

The Twitter MySQL server maintains system variables that indicate how it is configured. System variables can be set at server startup using options on the command line or in an option file.

Name	Cmd-Line	Option file	System Var	Var Scope	Dynamic
max_statement_time	No	No	Yes	Session	Yes
minidump_dir	Yes	Yes	Yes	Global	No
protocol_mode	Yes	Yes	Yes	Both	Yes
super_only	Yes	Yes	Yes	Global	Yes
superuser_connections	Yes	Yes	Yes	Global	Yes
twitter_audit_logging	Yes	Yes	Yes	Global	Yes
twitter_query_stats	Yes	Yes	Yes	Global	Yes
innodb_deadlock_check	Yes	Yes	Yes	Global	Yes
twitter_query_throttling_limit	Yes	Yes	Yes	Global	Yes
twitter_write_throttling_limit	Yes	Yes	Yes	Global	Yes

--max_statement_time=value

The number of milliseconds to wait for a statement to execute, after which it is interrupted. This timeout applies only to top-level statements.

Variable Name	max_statement_time
Variable Scope	Session
Dynamic Variable	Yes
Type	Numeric
Default	0
Valid Values	[0, (2^64)-1]

--minidump_dir=value

The name of the directory where minidumps are created. The default value is initialized tmpdir.

Variable Name	minidump_dir
Variable Scope	Global
Dynamic Variable	No
Type	String
Default	@@tmpdir

--protocol-mode=value[,value[,value...]]

The current server protocol mode, which can be set dynamically.

Command-Line Format	--protocol-mode=name
Option-File Format	protocol-mode
Option Sets Variable	Yes, protocol_mode
Variable Name	protocol_mode
Variable Scope	Global, Session
Dynamic Variable	Yes
Type	Set
Default	""
Valid Values	MINIMAL_OBJECT_NAMES_IN_RESULT_SET_METADATA Minimal metadata includes only the column name in the Result Set Metadata.

--super-only

Whether the server permits non-superusers to execute statements.

Command-Line Format	--super-only
Option-File Format	super_only
Option Sets Variable	Yes, super_only
Variable Name	super_only
Variable Scope	Global
Dynamic Variable	Yes
Type	Numeric
Default	0
Valid Values	0 Any user can execute statements. 1 Only superusers can execute statements.

--superuser_connections

Configurable number of reserved connections for superusers.

Command-Line Format	--superuser_connections
Option-File Format	superuser_connections
Option Sets Variable	Yes, superuser_connections
Variable Name	superuser_connections
Variable Scope	Global
Dynamic Variable	Yes
Type	Numeric
Default	1
Valid Values	1 The minimal number of reserved connections. 10 The maximum number of reserved connections.

--twitter_audit_logging

Twitter DBA audit logging.

Command-Line Format	--twitter_audit_logging
Option-File Format	twitter_audit_logging
Option Sets Variable	Yes, twitter_audit_logging
Variable Name	twitter_audit_logging
Variable Scope	Global
Dynamic Variable	Yes
Type	Numeric
Default	0
Valid Values	0 Do not log users operations in Twitter DBA audit log. 1 Log non-exempt users operations in error log. 2 Log non-exempt users operations incl. SELECT and SHOW commands in error log.

--twitter_query_stats

Twitter Query Type Statistics.

Command-Line Format	--twitter_query_stats
Option-File Format	twitter_query_stats
Option Sets Variable	Yes, twitter_query_stats
Variable Name	twitter_query_stats
Variable Scope	Global
Dynamic Variable	Yes
Type	Numeric
Default	0
Valid Values	0 Do not track any query type stats. 1 Track execution stats per query type. 2 Track execution stats per query type and client ID.

--innodb_deadlock_check=value

When set to OFF, disables deadlock detection to improve performance in heavily concurrent workloads.

Variable Name	innodb_deadlock_check
Variable Scope	Global
Dynamic Variable	Yes
Type	Boolean
Default	1
Valid Values	0 Don't check for deadlocks 1 Check for deadlocks

--twitter_query_throttling_limit=value

The maximum of query threads to allow simultaneously. Any attempt to create more will return the error ER_QUERY_THROTTLED.

Variable Name	twitter_query_throttling_limit
Variable Scope	Global
Dynamic Variable	Yes
Type	Numeric
Default	0
Valid Values	[0, 10000]

--twitter_write_throttling_limit=value

The maximum of write threads to allow simultaneously. Any attempt to create more will return the error ER_QUERY_THROTTLED.

Variable Name	twitter_write_throttling_limit
Variable Scope	Global
Dynamic Variable	Yes
Type	Numeric
Default	0
Valid Values	[0, 5000]