To use the MySQL Performance Schema, it must be enabled at server startup to enable event collection to occur.
The Performance Schema is enabled by default. To enable or disable
it explicitly, start the server with the
performance_schema variable set
to an appropriate value. For example, use these lines in the
If the server is unable to allocate any internal buffer during
Performance Schema initialization, the Performance Schema disables
itself and sets
OFF, and the server runs without
The Performance Schema also permits instrument and consumer configuration at server startup.
To control an instrument at server startup, use an option of this form:
instrument_name is an instrument
name such as
value is one of these values:
0: Disable the instrument
1: Enable and time the instrument
COUNTED: Enable and count (rather than time) the instrument
option can specify only one instrument name, but multiple
instances of the option can be given to configure multiple
instruments. In addition, patterns are permitted in instrument
names to configure instruments that match the pattern. To
configure all condition synchronization instruments as enabled and
counted, use this option:
To disable all instruments, use this option:
instruments are built in and cannot be disabled at startup.
Longer instrument name strings take precedence over shorter pattern names, regardless of order. For information about specifying patterns to select instruments, see Section 5.9, “Naming Instruments or Consumers for Filtering Operations”.
An unrecognized instrument name is ignored. It is possible that a plugin installed later may create the instrument, at which time the name is recognized and configured.
To control a consumer at server startup, use an option of this form:
consumer_name is a consumer name
value is one of these values:
0: Do not collect events for the consumer
1: Collect events for the consumer
For example, to enable the
consumer, use this option:
The permitted consumer names can be found by examining the
setup_consumers table. Patterns are
not permitted. Consumer names in the
setup_consumers table use
underscores, but for consumers set at startup, dashes and
underscores within the name are equivalent.
The Performance Schema includes several system variables that provide configuration information:
mysql> SHOW VARIABLES LIKE 'perf%'; +--------------------------------------------------------+---------+ | Variable_name | Value | +--------------------------------------------------------+---------+ | performance_schema | ON | | performance_schema_accounts_size | 100 | | performance_schema_digests_size | 200 | | performance_schema_events_stages_history_long_size | 10000 | | performance_schema_events_stages_history_size | 10 | | performance_schema_events_statements_history_long_size | 10000 | | performance_schema_events_statements_history_size | 10 | | performance_schema_events_waits_history_long_size | 10000 | | performance_schema_events_waits_history_size | 10 | | performance_schema_hosts_size | 100 | | performance_schema_max_cond_classes | 80 | | performance_schema_max_cond_instances | 1000 | ...
OFF to indicate
whether the Performance Schema is enabled or disabled. The other
variables indicate table sizes (number of rows) or memory
With the Performance Schema enabled, the number of Performance Schema instances affects the server memory footprint, perhaps to a large extent. The Performance Schema autoscales many parameters to use memory only as required; see The Performance Schema Memory-Allocation Model.
To change the value of Performance Schema system variables, set
them at server startup. For example, put the following lines in a
my.cnf file to change the sizes of the
history tables for wait events:
[mysqld] performance_schema performance_schema_events_waits_history_size=20 performance_schema_events_waits_history_long_size=15000
The Performance Schema automatically sizes the values of several of its parameters at server startup if they are not set explicitly. For example, it sizes the parameters that control the sizes of the events waits tables this way. The Performance Schema allocates memory incrementally, scaling its memory use to actual server load, instead of allocating all the memory it needs during server startup. Consequently, many sizing parameters need not be set at all. To see which parameters are autosized or autoscaled, use mysqld --verbose --help and examine the option descriptions, or see Chapter 12, Performance Schema System Variables.
For each autosized parameter that is not set at server startup, the Performance Schema determines how to set its value based on the value of the following system values, which are considered as “hints” about how you have configured your MySQL server:
max_connections open_files_limit table_definition_cache table_open_cache
To override autosizing or autoscaling for a given parameter, set it to a value other than −1 at startup. In this case, the Performance Schema assigns it the specified value.
SHOW VARIABLES displays
the actual values that autosized parameters were set to.
Autoscaled parameters display with a value of −1.
If the Performance Schema is disabled, its autosized and
autoscaled parameters remain set to −1 and
SHOW VARIABLES displays −1.