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/synch/cond/mysys/COND_alarm wait/synch/cond/sql/BINLOG::update_cond wait/synch/mutex/mysys/BITMAP_mutex wait/synch/mutex/sql/Event_scheduler::LOCK_scheduler_state wait/synch/mutex/sql/LOCK_delete wait/synch/rwlock/myisam/MYISAM_SHARE::key_root_lock wait/synch/rwlock/sql/Query_cache_query::lock
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:
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. For the prefix part of
instrument names, the top level indicates the type of instrument.
Currently this is always wait, so the naming
tree has this structure:
waitA wait instrument.
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/syncAn 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/sync/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/sync/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/sync/rwlockA 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.
The suffix part of instrument names comes from the code for the instruments themselves. For example, following the first three levels just described, the next levels are:
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.