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Table 14.32 Performance Schema Functions

• FORMAT_BYTES(count)

  Given a numeric byte count, converts it to human-readable format and returns a string consisting of a value and a units indicator. The string contains the number of bytes rounded to 2 decimal places and a minimum of 3 significant digits. Numbers less than 1024 bytes are represented as whole numbers and are not rounded. ReturnsNULL ifcount isNULL.

  The units indicator depends on the size of the byte-count argument as shown in the following table.

  Argument Value	Result Units	Result Units Indicator
  Up to 1023	bytes	bytes
  Up to 10242 − 1	kibibytes	KiB
  Up to 10243 − 1	mebibytes	MiB
  Up to 10244 − 1	gibibytes	GiB
  Up to 10245 − 1	tebibytes	TiB
  Up to 10246 − 1	pebibytes	PiB
  10246 and up	exbibytes	EiB

  mysql> SELECT FORMAT_BYTES(512), FORMAT_BYTES(18446644073709551615);+-------------------+------------------------------------+| FORMAT_BYTES(512) | FORMAT_BYTES(18446644073709551615) |+-------------------+------------------------------------+|  512 bytes        | 16.00 EiB                          |+-------------------+------------------------------------+

  FORMAT_BYTES() may be used instead of thesys schemaformat_bytes() function, keeping in mind this difference:

  • FORMAT_BYTES() uses theEiB units indicator.sys.format_bytes() does not.

• FORMAT_PICO_TIME(time_val)

  Given a numeric Performance Schema latency or wait time in picoseconds, converts it to human-readable format and returns a string consisting of a value and a units indicator. The string contains the decimal time rounded to 2 decimal places and a minimum of 3 significant digits. Times under 1 nanosecond are represented as whole numbers and are not rounded.

  Iftime_val isNULL, this function returnsNULL.

  The units indicator depends on the size of the time-value argument as shown in the following table.

  Argument Value	Result Units	Result Units Indicator
  Up to 103 − 1	picoseconds	ps
  Up to 106 − 1	nanoseconds	ns
  Up to 109 − 1	microseconds	us
  Up to 1012 − 1	milliseconds	ms
  Up to 60×1012 − 1	seconds	s
  Up to 3.6×1015 − 1	minutes	min
  Up to 8.64×1016 − 1	hours	h
  8.64×1016 and up	days	d

  mysql> SELECT FORMAT_PICO_TIME(3501), FORMAT_PICO_TIME(188732396662000);+------------------------+-----------------------------------+| FORMAT_PICO_TIME(3501) | FORMAT_PICO_TIME(188732396662000) |+------------------------+-----------------------------------+| 3.50 ns                | 3.15 min                          |+------------------------+-----------------------------------+

  FORMAT_PICO_TIME() may be used instead of thesys schemaformat_time() function, keeping in mind these differences:

  • To indicate minutes,sys.format_time() uses them units indicator, whereasFORMAT_PICO_TIME() usesmin.

  • sys.format_time() uses thew (weeks) units indicator.FORMAT_PICO_TIME() does not.

• PS_CURRENT_THREAD_ID()

  Returns aBIGINT UNSIGNED value representing the Performance Schema thread ID assigned to the current connection.

  The thread ID return value is a value of the type given in theTHREAD_ID column of Performance Schema tables.

  Performance Schema configuration affectsPS_CURRENT_THREAD_ID() the same way as forPS_THREAD_ID(). For details, see the description of that function.

  mysql> SELECT PS_CURRENT_THREAD_ID();+------------------------+| PS_CURRENT_THREAD_ID() |+------------------------+|                     52 |+------------------------+mysql> SELECT PS_THREAD_ID(CONNECTION_ID());+-------------------------------+| PS_THREAD_ID(CONNECTION_ID()) |+-------------------------------+|                            52 |+-------------------------------+

  PS_CURRENT_THREAD_ID() may be used as a shortcut for invoking thesys schemaps_thread_id() function with an argument ofNULL orCONNECTION_ID().

• PS_THREAD_ID(connection_id)

  Given a connection ID, returns aBIGINT UNSIGNED value representing the Performance Schema thread ID assigned to the connection ID, orNULL if no thread ID exists for the connection ID. The latter can occur for threads that are not instrumented, or ifconnection_id isNULL.

  The connection ID argument is a value of the type given in thePROCESSLIST_ID column of the Performance Schemathreads table or theId column ofSHOW PROCESSLIST output.

  The thread ID return value is a value of the type given in theTHREAD_ID column of Performance Schema tables.

  Performance Schema configuration affectsPS_THREAD_ID() operation as follows. (These remarks also apply toPS_CURRENT_THREAD_ID().)

  • Disabling thethread_instrumentation consumer disables statistics from being collected and aggregated at the thread level, but has no effect onPS_THREAD_ID().

  • Ifperformance_schema_max_thread_instances is not 0, the Performance Schema allocates memory for thread statistics and assigns an internal ID to each thread for which instance memory is available. If there are threads for which instance memory is not available,PS_THREAD_ID() returnsNULL; in this case,Performance_schema_thread_instances_lost is nonzero.

  • Ifperformance_schema_max_thread_instances is 0, the Performance Schema allocates no thread memory andPS_THREAD_ID() returnsNULL.

  • If the Performance Schema itself is disabled,PS_THREAD_ID() produces an error.

  mysql> SELECT PS_THREAD_ID(6);+-----------------+| PS_THREAD_ID(6) |+-----------------+|              45 |+-----------------+

  PS_THREAD_ID() may be used instead of thesys schemaps_thread_id() function, keeping in mind this difference:

  • With an argument ofNULL,sys.ps_thread_id() returns the thread ID for the current connection, whereasPS_THREAD_ID() returnsNULL. To obtain the current connection thread ID, usePS_CURRENT_THREAD_ID() instead.