SHOW ENGINE

Display status information for a storage engine. This statement retrieves operational logs or status details for a specific engine.

Syntax

SHOW ENGINE [engine-name] {STATUS | MUTEX}

Description

SHOW ENGINE displays operational information about a storage engine. The following statements currently are supported:

SHOW ENGINE INNODB STATUS
SHOW ENGINE INNODB MUTEX
SHOW ENGINE PERFORMANCE_SCHEMA STATUS
SHOW ENGINE ROCKSDB STATUS

If the Sphinx Storage Engine is installed, the following is also supported:

SHOW ENGINE SPHINX STATUS

SHOW ENGINE INNODB STATUS

SHOW ENGINE INNODB STATUS displays extensive information from the standard InnoDB Monitor about the state of the InnoDB storage engine. See SHOW ENGINE INNODB STATUS for more.

SHOW ENGINE INNODB MUTEX

SHOW ENGINE INNODB MUTEX displays InnoDB mutex statistics.

The statement displays the following output fields:

• 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 dependent on the MariaDB version.

• Status: This field displays the following values if UNIV_DEBUG was defined at compilation time (for example, in include/univ.h in the InnoDB part of the source tree). Only the os_waits value is displayed if UNIV_DEBUG was not defined. Without UNIV_DEBUG, the information on which the output is based is insufficient to distinguish regular mutexes and mutexes that protect rw-locks (which allow 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 the thread trying to lock a mutex gave up its timeslice and yielded to the operating system (on the presumption that allowing 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, if the timed_mutexes system variable is 1 (ON). If timed_mutexes is 0 (OFF), timing is disabled, so os_wait_times is 0. timed_mutexes is off by default.

Information from this statement can be used to diagnose system problems. For example, large values of spin_waits and spin_rounds may indicate scalability problems.

The information_schema.INNODB_MUTEXES table provides similar information.

SHOW ENGINE PERFORMANCE_SCHEMA STATUS

This statement shows how much memory is used for performance_schema tables and internal buffers.

The output contains the following fields:

• Type: Always performance_schema.

• Name: The name of a table, the name of an internal buffer, or the performance_schema word, followed by a dot and an attribute. Internal buffers names are enclosed by parenthesis. performance_schema means that the attribute refers to the whole database (it is a total).

• Status: The value for the attribute.

The following attributes are shown, in this order, for all tables:

• row_size: The memory used for an individual record. This value will never change.

• row_count: The number of rows in the table or buffer. For some tables, this value depends on a server system variable.

• memory: For tables and performance_schema, this is the result of row_size * row_count.

For internal buffers, the attributes are:

• count

• size

SHOW ENGINE ROCKSDB STATUS

See also MyRocks Performance Troubleshooting

_{This page is licensed: GPLv2, originally from fill_help_tables.sql}