The events_waits_current
Table
The events_waits_current
table contains current wait events, one row per thread showing the current status of the thread's most recent monitored wait event.
The events-waits-current
table can be truncated with TRUNCATE TABLE
.
Of the tables that contain wait event rows, events_waits_current
is the most fundamental. Other tables that contain wait event rows are logically derived from the current events. For example, the events_waits_history
and events_waits_history_long
tables are collections of the most recent wait events, up to a fixed number of rows.
The events_waits_current
table has these columns:
THREAD_ID
The thread associated with the event. The
THREAD_ID
andEVENT_ID
values taken together form a primary key that uniquely identifies the row. No two rows will have the same pair of values.EVENT_ID
The thread current event number when the event starts.
END_EVENT_ID
This column is set to
NULL
when the event starts, and updated to the thread current event number when the event ends. This column was added in MariaDB 5.6.4.EVENT_NAME
The name of the instrument that produced the event. This is a
setup_instruments.NAME
value. Instrument names have multiple parts and form a hierarchy, as discussed in , "Performance Schema Instrument Naming Conventions".SOURCE
The name of the source file containing the instrumented code that produced the event and the line number in the file at which the instrumentation occurs. This enables you to check the source to determine exactly what code is involved. For example, if a mutex or lock is being blocked, you can check the context in which this occurs.
TIMER_START
,TIMER_END
,TIMER_WAIT
Timing information for the event. The unit for these values is picoseconds (trillionths of a second). The
TIMER_START
andTIMER_END
values indicate when event timing started and ended.TIMER_WAIT
is the event elapsed time (duration).If an event has not finished,
TIMER_END
andTIMER_WAIT
areNULL
.If an event is produced from an instrument that has
TIMED = NO
, timing information is not collected, andTIMER_START
,TIMER_END
, andTIMER_WAIT
are allNULL
.For discussion of picoseconds as the unit for event times and factors that affect time values, see , "Performance Schema Event Timing".
SPINS
For a mutex, the number of spin rounds. If the value is
NULL
, the code does not use spin rounds or spinning is not instrumented.OBJECT_SCHEMA
,OBJECT_NAME
,OBJECT_TYPE
,OBJECT_INSTANCE_BEGIN
These columns identify the object "being acted on." What that means depends on the object type.
For a synchronization object (
cond
,mutex
,rwlock
):OBJECT_SCHEMA
,OBJECT_NAME
, andOBJECT_TYPE
areNULL
.OBJECT_INSTANCE_BEGIN
is the address of the synchronization object in memory.
For a file I/O object:
OBJECT_SCHEMA
isNULL
.OBJECT_NAME
is the file name.OBJECT_TYPE
isFILE
.OBJECT_INSTANCE_BEGIN
is an address in memory.
For a socket object:
OBJECT_NAME
is theIP:PORT
value for the socket.OBJECT_INSTANCE_BEGIN
is an address in memory.
For a table I/O object:
OBJECT_SCHEMA
is the name of the schema that contains the table.OBJECT_NAME
is the table name.OBJECT_TYPE
isTABLE
for a persistent base table orTEMPORARY TABLE
for a temporary table.OBJECT_INSTANCE_BEGIN
is an address in memory.
An
OBJECT_INSTANCE_BEGIN
value itself has no meaning, except that different values indicate different objects.OBJECT_INSTANCE_BEGIN
can be used for debugging. For example, it can be used withGROUP BY OBJECT_INSTANCE_BEGIN
to see whether the load on 1,000 mutexes (that protect, say, 1,000 pages or blocks of data) is spread evenly or just hitting a few bottlenecks. This can help you correlate with other sources of information if you see the same object address in a log file or another debugging or performance tool.INDEX_NAME
The name of the index used.
PRIMARY
indicates the table primary index.NULL
means that no index was used.NESTING_EVENT_ID
The
EVENT_ID
value of the event within which this event is nested. Before MariaDB 5.6.3, this column is alwaysNULL
.NESTING_EVENT_TYPE
The nesting event type. The value is
statement
,stage
, orwait
. This column was added in MariaDB 5.6.3.OPERATION
The type of operation performed, such as
lock
,read
, orwrite
.NUMBER_OF_BYTES
The number of bytes read or written by the operation. For table I/O waits,
NUMBER_OF_BYTES
isNULL
.FLAGS
Reserved for future use.