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MySQL Performance Schema :: 5 Performance Schema Event Instrument Naming Conventions
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5. Performance Schema Event 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/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:

  • wait

    A wait instrument.

    • 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/sync

      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/sync/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/sync/mutex

        A mutual exclusion object used to allow access to a resource (such as a section of executable code) while preventing other threads from accessing the resource.

      • wait/sync/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.

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, mysys, or sql) or a plugin name.

  • The name of a variable in the code, in the form XXX (a global variable) or CCC:MMM (a member MMM in class CCC). Examples: COND_thread_cache, THR_LOCK_myisam, BINLOG::LOCK_index.