SHOW ENGINE engine_name {STATUS | MUTEX}
SHOW ENGINE displays operational
information about a storage engine. It requires the
PROCESS privilege. The statement
has these variants:
SHOW ENGINE INNODB STATUS
SHOW ENGINE INNODB MUTEX
SHOW ENGINE {NDB | NDBCLUSTER} STATUS
SHOW ENGINE PERFORMANCE_SCHEMA STATUS
SHOW ENGINE INNODB
STATUS displays extensive information from the
standard InnoDB Monitor about the state of
the InnoDB storage engine. For information
about the standard monitor and other InnoDB
Monitors that provide information about
InnoDB processing, see
Section 14.20, “InnoDB Monitors”.
SHOW ENGINE INNODB
MUTEX displays InnoDB
mutex and
rw-lock statistics.
Statement output has the following columns:
Type
Always InnoDB.
Name
The source file where the mutex is implemented, and the line number in the file where the mutex is created. The line number is specific to your version of MySQL.
Status
The mutex status. This field displays several values if
UNIV_DEBUG was defined at MySQL
compilation time (for example, in
include/univ.i in the
InnoDB part of the MySQL source tree). If
UNIV_DEBUG was not defined, the statement
displays only the os_waits value. In the
latter case (without UNIV_DEBUG), the
information on which the output is based is insufficient to
distinguish regular mutexes and mutexes that protect
rw-locks (which permit multiple readers or a single writer).
Consequently, the output may appear to contain multiple rows
for the same mutex.
count indicates how many times the
mutex was requested.
spin_waits indicates how many times
the spinlock had to run.
spin_rounds indicates the number of
spinlock rounds. (spin_rounds divided
by spin_waits provides the average
round count.)
os_waits indicates the number of
operating system waits. This occurs when the spinlock
did not work (the mutex was not locked during the
spinlock and it was necessary to yield to the operating
system and wait).
os_yields indicates the number of
times a thread trying to lock a mutex gave up its
timeslice and yielded to the operating system (on the
presumption that permitting other threads to run will
free the mutex so that it can be locked).
os_wait_times indicates the amount of
time (in ms) spent in operating system waits. In MySQL
5.5 timing is disabled and this value is
always 0.
As of MySQL 5.5, SHOW ENGINE INNODB MUTEX
skips the mutexes and
rw-locks of
buffer pool blocks, as
the amount of output can be overwhelming on systems with a large
buffer pool. (There is one mutex and one rw-lock in each 16K
buffer pool block, and there are 65,536 blocks per gigabyte.)
SHOW ENGINE INNODB MUTEX also does not list
any mutexes or rw-locks that have never been waited on
(os_waits=0). Thus, SHOW ENGINE
INNODB MUTEX only displays information about mutexes
and rw-locks outside of the buffer pool that have caused at
least one OS-level wait.
SHOW ENGINE INNODB MUTEX information can be
used to diagnose system problems. For example, large values of
spin_waits and spin_rounds
may indicate scalability problems.
Use SHOW ENGINE
PERFORMANCE_SCHEMA STATUS to inspect the internal
operation of the Performance Schema code:
mysql> SHOW ENGINE PERFORMANCE_SCHEMA STATUS\G
...
*************************** 3. row ***************************
Type: performance_schema
Name: events_waits_history.row_size
Status: 76
*************************** 4. row ***************************
Type: performance_schema
Name: events_waits_history.row_count
Status: 10000
*************************** 5. row ***************************
Type: performance_schema
Name: events_waits_history.memory
Status: 760000
...
*************************** 57. row ***************************
Type: performance_schema
Name: performance_schema.memory
Status: 26459600
...
This statement is intended to help the DBA understand the effects that different Performance Schema options have on memory requirements.
Name values consist of two parts, which name
an internal buffer and a buffer attribute, respectively.
Interpret buffer names as follows:
An internal buffer that is not exposed as a table is named
within parentheses. Examples:
(pfs_cond_class).row_size,
(pfs_mutex_class).memory.
An internal buffer that is exposed as a table in the
performance_schema database is named
after the table, without parentheses. Examples:
events_waits_history.row_size,
mutex_instances.row_count.
A value that applies to the Performance Schema as a whole
begins with performance_schema. Example:
performance_schema.memory.
Buffer attributes have these meanings:
row_size is the size of the internal
record used by the implementation, such as the size of a row
in a table. row_size values cannot be
changed.
row_count is the number of internal
records, such as the number of rows in a table.
row_count values can be changed using
Performance Schema configuration options.
For a table,
tbl_name.memoryrow_size and
row_count. For the Performance Schema as
a whole, performance_schema.memory is the
sum of all the memory used (the sum of all other
memory values).
In some cases, there is a direct relationship between a
Performance Schema configuration parameter and a SHOW
ENGINE value. For example,
events_waits_history_long.row_count
corresponds to
performance_schema_events_waits_history_long_size.
In other cases, the relationship is more complex. For example,
events_waits_history.row_count corresponds to
performance_schema_events_waits_history_size
(the number of rows per thread) multiplied by
performance_schema_max_thread_instances
( the number of threads).
If the server has the NDBCLUSTER
storage engine enabled,
SHOW ENGINE NDB
STATUS displays cluster status information such as the
number of connected data nodes, the cluster connectstring, and
cluster binary log epochs, as well as counts of various Cluster
API objects created by the MySQL Server when connected to the
cluster. Sample output from this statement is shown here:
mysql> SHOW ENGINE NDB STATUS;
+------------+-----------------------+--------------------------------------------------+
| Type | Name | Status |
+------------+-----------------------+--------------------------------------------------+
| ndbcluster | connection | cluster_node_id=7,
connected_host=192.168.0.103, connected_port=1186, number_of_data_nodes=4,
number_of_ready_data_nodes=3, connect_count=0 |
| ndbcluster | NdbTransaction | created=6, free=0, sizeof=212 |
| ndbcluster | NdbOperation | created=8, free=8, sizeof=660 |
| ndbcluster | NdbIndexScanOperation | created=1, free=1, sizeof=744 |
| ndbcluster | NdbIndexOperation | created=0, free=0, sizeof=664 |
| ndbcluster | NdbRecAttr | created=1285, free=1285, sizeof=60 |
| ndbcluster | NdbApiSignal | created=16, free=16, sizeof=136 |
| ndbcluster | NdbLabel | created=0, free=0, sizeof=196 |
| ndbcluster | NdbBranch | created=0, free=0, sizeof=24 |
| ndbcluster | NdbSubroutine | created=0, free=0, sizeof=68 |
| ndbcluster | NdbCall | created=0, free=0, sizeof=16 |
| ndbcluster | NdbBlob | created=1, free=1, sizeof=264 |
| ndbcluster | NdbReceiver | created=4, free=0, sizeof=68 |
| ndbcluster | binlog | latest_epoch=155467, latest_trans_epoch=148126,
latest_received_binlog_epoch=0, latest_handled_binlog_epoch=0,
latest_applied_binlog_epoch=0 |
+------------+-----------------------+--------------------------------------------------+
The rows with connection and
binlog in the Name column
were added to the output of this statement in MySQL 5.1. The
Status column in each of these rows provides
information about the MySQL server's connection to the cluster
and about the cluster binary log's status, respectively. The
Status information is in the form of
comma-delimited set of name/value pairs.
The connection row's
Status column contains the name/value pairs
described in the following table.
| Name | Value |
|---|---|
cluster_node_id | The node ID of the MySQL server in the cluster |
connected_host | The host name or IP address of the cluster management server to which the MySQL server is connected |
connected_port | The port used by the MySQL server to connect to the management server
(connected_host) |
number_of_data_nodes | The number of data nodes configured for the cluster (that is, the number
of [ndbd] sections in the cluster
config.ini file) |
number_of_ready_data_nodes | The number of data nodes in the cluster that are actually running |
connect_count | The number of times this mysqld has connected or reconnected to cluster data nodes |
The binlog row's Status
column contains information relating to MySQL Cluster
Replication. The name/value pairs it contains are described in
the following table.
| Name | Value |
|---|---|
latest_epoch | The most recent epoch most recently run on this MySQL server (that is, the sequence number of the most recent transaction run on the server) |
latest_trans_epoch | The most recent epoch processed by the cluster's data nodes |
latest_received_binlog_epoch | The most recent epoch received by the binary log thread |
latest_handled_binlog_epoch | The most recent epoch processed by the binary log thread (for writing to the binary log) |
latest_applied_binlog_epoch | The most recent epoch actually written to the binlog |
See Section 18.6, “NDB Cluster Replication”, for more information.
The remaining rows from the output of
SHOW ENGINE NDB
STATUS which are most likely to prove useful in
monitoring the cluster are listed here by
Name:
NdbTransaction: The number and size of
NdbTransaction objects that have been
created. An NdbTransaction is created
each time a table schema operation (such as
CREATE TABLE or
ALTER TABLE) is performed on
an NDB table.
NdbOperation: The number and size of
NdbOperation objects that have been
created.
NdbIndexScanOperation: The number and
size of NdbIndexScanOperation objects
that have been created.
NdbIndexOperation: The number and size of
NdbIndexOperation objects that have been
created.
NdbRecAttr: The number and size of
NdbRecAttr objects that have been
created. In general, one of these is created each time a
data manipulation statement is performed by an SQL node.
NdbBlob: The number and size of
NdbBlob objects that have been created.
An NdbBlob is created for each new
operation involving a BLOB
column in an NDB table.
NdbReceiver: The number and size of any
NdbReceiver object that have been
created. The number in the created column
is the same as the number of data nodes in the cluster to
which the MySQL server has connected.
SHOW ENGINE NDB
STATUS returns an empty result if no operations
involving NDB tables have been
performed during the current session by the MySQL client
accessing the SQL node on which this statement is run.