25.6 Performance Schema Instrument Naming Conventions
An instrument name consists of a sequence of components 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 components of an instrument name from left to right provide a progression from more general to more specific. The number of components a name has depends on the type of instrument.
The interpretation of a given component in a name depends on the components 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:
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 component of an instrument prefix indicates the type of instrument. This component 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 component (a server module such as
sql) or a plugin name.
The name of a variable in the code, in the form
XXX(a global variable) or
idle: An instrumented idle event. This instrument has no further components.
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 components.
wait: An instrumented wait event.
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 188.8.131.52, “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
code_area is a value such as
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
code_area is a value such as
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
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
mysql_com.hheader file and
sql/sql_parse.cc. For example, the
statement/com/Init DBinstruments correspond to the
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/freturninstruments are used cursor fetch and function return instructions.
An instrumented I/O operation.
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.
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
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
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_currentfor 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.
An instrumented lock operation.
An instrumented table lock operation.
An instrumented metadata lock operation.
An instrumented synchronization object. For synchronization objects, the
TIMER_WAITtime includes the amount of time blocked while attempting to acquire a lock on the object, if any.
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.
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.
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.
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.
sxlocksoptimize concurrency and improve scalability for read-write workloads.