MySQL 8.0 Release Notes
MySQL 8.0 Source Code Documentation
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
errorsThe 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:
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
component of an instrument prefix indicates the type of
instrument. This component also determines which event timer in
the performance_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
myisam,innodb,mysys, orsql) or a plugin name.The name of a variable in the code, in the form
XXX(a global variable) orCCC::MMMMMMin classCCC). Examples:COND_thread_cache,THR_LOCK_myisam,BINLOG::LOCK_index.
idle: An instrumented idle event. This instrument has no further components.error: An instrumented error 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.
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 26.12.3.5, “The socket_instances Table”.
The error instrument indicates whether to
collect information for server errors and warnings. This
instrument is enabled by default. The TIMED
column for the error row in the
setup_instruments table is
inapplicable because timing information is not collected.
Memory instrumentation is enabled by default. Memory
instrumentation 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 26.17, “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 26.12.6, “Performance Schema Statement Event Tables”.statement/com: An instrumented command operation. These have names corresponding toCOM_operations (see thexxxmysql_com.hheader file andsql/sql_parse.cc. For example, thestatement/com/Connectandstatement/com/Init DBinstruments correspond to theCOM_CONNECTandCOM_INIT_DBcommands.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, thestatement/sp/cfetchandstatement/sp/freturninstruments are used cursor fetch and function return instructions.statement/sql: An instrumented SQL statement operation. For example, thestatement/sql/create_dbandstatement/sql/selectinstruments are used forCREATE DATABASEandSELECTstatements.
Instrumented threads are displayed in the
setup_threads table, which exposes
thread class names and attributes.
Thread instruments begin with thread (for
example, thread/sql/parser_service or
thread/performance_schema/setup).
wait/ioAn instrumented I/O operation.
wait/io/fileAn 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/socketAn 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 asocket_typesocket_typevalue ofserver_tcpip_socketorserver_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 asocket_typevalue ofclient_connection.wait/io/tableAn 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 26.8, “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/lockAn instrumented lock operation.
wait/lock/tableAn instrumented table lock operation.
wait/lock/metadata/sql/mdlAn instrumented metadata lock operation.
wait/synchAn 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.wait/synch/condA 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/mutexA 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/prlockA priority rwlock lock object.
wait/synch/rwlockA plain 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/sxlockA 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.