MySQL 5.7 Reference Manual Including MySQL NDB Cluster 7.5 and NDB Cluster 7.6
An instrument name consists of a sequence of elements separated by
'/' characters. Example names:
wait/io/file/myisam/log wait/io/file/mysys/charset wait/lock/table/sql/handler wait/synch/cond/mysys/COND_alarm wait/synch/cond/sql/BINLOG::update_cond wait/synch/mutex/mysys/BITMAP_mutex wait/synch/mutex/sql/LOCK_delete wait/synch/rwlock/sql/Query_cache_query::lock stage/sql/closing tables stage/sql/Sorting result statement/com/Execute statement/com/Query statement/sql/create_table statement/sql/lock_tables
The instrument name space has a tree-like structure. The elements of an instrument name from left to right provide a progression from more general to more specific. The number of elements a name has depends on the type of instrument.
The interpretation of a given element in a name depends on the
elements to the left of it. For example, myisam
appears in both of the following names, but
myisam in the first name is related to file
I/O, whereas in the second it is related to a synchronization
instrument:
wait/io/file/myisam/log wait/synch/cond/myisam/MI_SORT_INFO::cond
Instrument names consist of a prefix with a structure defined by
the Performance Schema implementation and a suffix defined by the
developer implementing the instrument code. The top-level element
of an instrument prefix indicates the type of instrument. This
element also determines which event timer in the
setup_timers table applies to the instrument.
For the prefix part of instrument names, the top level indicates
the type of instrument.
The suffix part of instrument names comes from the code for the instruments themselves. Suffixes may include levels such as these:
A name for the major element (a server module such as
myisam, innodb,
mysys, or sql) or a
plugin name.
The name of a variable in the code, in the form
XXX (a global variable) or
CCC::MMMMMM in class
CCC). Examples:
COND_thread_cache,
THR_LOCK_myisam,
BINLOG::LOCK_index.
idle: An instrumented idle event. This
instrument has no further elements.
memory: An instrumented memory event.
stage: An instrumented stage event.
statement: An instrumented statement
event.
transaction: An instrumented transaction
event. This instrument has no further elements.
wait: An instrumented wait event.
The idle instrument is used for idle events,
which The Performance Schema generates as discussed in the
description of the socket_instances.STATE
column in
Section 25.12.3.5, “The socket_instances Table”.
Most memory instrumentation is disabled by default, and can be
enabled or disabled at startup, or dynamically at runtime by
updating the ENABLED column of the relevant
instruments in the
setup_instruments table. Memory
instruments have names of the form
memory/
where code_area/instrument_namecode_area is a value such as
sql or myisam, and
instrument_name is the instrument
detail.
Instruments named with the prefix
memory/performance_schema/ expose how much
memory is allocated for internal buffers in the Performance
Schema. The memory/performance_schema/
instruments are built in, always enabled, and cannot be disabled
at startup or runtime. Built-in memory instruments are displayed
only in the
memory_summary_global_by_event_name
table. For more information, see
Section 25.17, “The Performance Schema Memory-Allocation Model”.
Stage instruments have names of the form
stage/,
where code_area/stage_namecode_area is a value such as
sql or myisam, and
stage_name indicates the stage of
statement processing, such as Sorting result
or Sending data. Stages correspond to the
thread states displayed by SHOW
PROCESSLIST or that are visible in the Information
Schema PROCESSLIST table.
statement/abstract/*: An abstract
instrument for statement operations. Abstract instruments
are used during the early stages of statement classification
before the exact statement type is known, then changed to a
more specific statement instrument when the type is known.
For a description of this process, see
Section 25.12.6, “Performance Schema Statement Event Tables”.
statement/com: An instrumented command
operation. These have names corresponding to
COM_
operations (see the xxxmysql_com.h header
file and sql/sql_parse.cc. For example,
the statement/com/Connect and
statement/com/Init DB instruments
correspond to the COM_CONNECT and
COM_INIT_DB commands.
statement/scheduler/event: A single
instrument to track all events executed by the Event
Scheduler. This instrument comes into play when a scheduled
event begins executing.
statement/sp: An instrumented internal
instruction executed by a stored program. For example, the
statement/sp/cfetch and
statement/sp/freturn instruments are used
cursor fetch and function return instructions.
statement/sql: An instrumented SQL
statement operation. For example, the
statement/sql/create_db and
statement/sql/select instruments are used
for CREATE DATABASE and
SELECT statements.
wait/io
An instrumented I/O operation.
wait/io/file
An instrumented file I/O operation. For files, the wait
is the time waiting for the file operation to complete
(for example, a call to fwrite()).
Due to caching, the physical file I/O on the disk might
not happen within this call.
wait/io/socket
An instrumented socket operation. Socket instruments
have names of the form
wait/io/socket/sql/.
The server has a listening socket for each network
protocol that it supports. The instruments associated
with listening sockets for TCP/IP or Unix socket file
connections have a
socket_typesocket_type value of
server_tcpip_socket or
server_unix_socket, respectively.
When a listening socket detects a connection, the server
transfers the connection to a new socket managed by a
separate thread. The instrument for the new connection
thread has a socket_type
value of client_connection.
wait/io/table
An instrumented table I/O operation. These include row-level accesses to persistent base tables or temporary tables. Operations that affect rows are fetch, insert, update, and delete. For a view, waits are associated with base tables referenced by the view.
Unlike most waits, a table I/O wait can include other
waits. For example, table I/O might include file I/O or
memory operations. Thus,
events_waits_current for a
table I/O wait usually has two rows. For more
information, see
Section 25.8, “Performance Schema Atom and Molecule Events”.
Some row operations might cause multiple table I/O waits. For example, an insert might activate a trigger that causes an update.
wait/lock
An instrumented lock operation.
wait/lock/table
An instrumented table lock operation.
wait/lock/metadata/sql/mdl
An instrumented metadata lock operation.
wait/synch
An instrumented synchronization object. For synchronization
objects, the TIMER_WAIT time includes the
amount of time blocked while attempting to acquire a lock on
the object, if any.
wait/synch/cond
A condition is used by one thread to signal to other threads that something they were waiting for has happened. If a single thread was waiting for a condition, it can wake up and proceed with its execution. If several threads were waiting, they can all wake up and compete for the resource for which they were waiting.
wait/synch/mutex
A mutual exclusion object used to permit access to a resource (such as a section of executable code) while preventing other threads from accessing the resource.
wait/synch/rwlock
A read/write lock object used to lock a specific variable for access while preventing its use by other threads. A shared read lock can be acquired simultaneously by multiple threads. An exclusive write lock can be acquired by only one thread at a time.
wait/synch/sxlock
A shared-exclusive (SX) lock is a type of
rwlock lock object
that provides write access to a common resource while
permitting inconsistent reads by other threads.
sxlocks optimize concurrency and
improve scalability for read-write workloads.