SHOW ENGINE INNODB STATUS is a specific form of the SHOW ENGINE statement that
displays the InnoDB Monitor output, which is extensive InnoDB information
which can be useful in diagnosing problems.

The following sections are displayed

* Status: Shows the timestamp, monitor name and the number of seconds, or the
elapsed time between the current time and the time the InnoDB Monitor output
was last displayed. The per-second averages are based upon this time.
* BACKGROUND THREAD: srv_master_thread lines show work performed by the main
background thread.
* SEMAPHORES: Threads waiting for a semaphore and stats on how the number of
times threads have needed a spin or a wait on a mutex or rw-lock semaphore. If
this number of threads is large, there may be I/O or contention issues.
Reducing the size of the innodb_thread_concurrency system variable may help if
contention is related to thread scheduling. Spin rounds per wait shows the
number of spinlock rounds per OS wait for a mutex. 
* LATEST FOREIGN KEY ERROR: Only shown if there has been a foreign key
constraint error, it displays the failed statement and information about the
constraint and the related tables.
* LATEST DETECTED DEADLOCK: Only shown if there has been a deadlock, it
displays the transactions involved in the deadlock and the statements being
executed, held and required locked and the transaction rolled back to.
* TRANSACTIONS: The output of this section can help identify lock contention,
as well as reasons for the deadlocks.
* FILE I/O: InnoDB thread information as well as pending I/O operations and
I/O performance statistics.
* INSERT BUFFER AND ADAPTIVE HASH INDEX: InnoDB insert buffer (old name for
the change buffer) and adaptive hash index status information, including the
number of each type of operation performed, and adaptive hash index
performance.
* LOG: InnoDB log information, including current log sequence number, how far
the log has been flushed to disk, the position at which InnoDB last took a
checkpoint, pending writes and write performance statistics.
* BUFFER POOL AND MEMORY: Information on buffer pool pages read and written,
which allows you to see the number of data file I/O operations performed by
your queries. See InnoDB Buffer Pool for more. Similar information is also
available from the INFORMATION_SCHEMA.INNODB_BUFFER_POOL_STATS table.
* ROW OPERATIONS:Information about the main thread, including the number and
performance rate for each type of row operation.

If the innodb_status_output_locks system variable is set to 1, extended lock
information will be displayed.

Example output:

=====================================
2019-09-06 12:44:13 0x7f93cc236700 INNODB MONITOR OUTPUT
=====================================
Per second averages calculated from the last 4 seconds
-----------------
BACKGROUND THREAD
-----------------
srv_master_thread loops: 2 srv_active, 0 srv_shutdown, 83698 srv_idle
srv_master_thread log flush and writes: 83682
----------
SEMAPHORES
----------
OS WAIT ARRAY INFO: reservation count 15
OS WAIT ARRAY INFO: signal count 8
RW-shared spins 0, rounds 20, OS waits 7
RW-excl spins 0, rounds 0, OS waits 0
RW-sx spins 0, rounds 0, OS waits 0
Spin rounds per wait: 20.00 RW-shared, 0.00 RW-excl, 0.00 RW-sx
------------
TRANSACTIONS
------------
Trx id counter 236
Purge done for trx's n:o < 236 undo n:o < 0 state: running
History list length 22
LIST OF TRANSACTIONS FOR EACH SESSION:
---TRANSACTION 421747401994584, not started
0 lock struct(s), heap size 1136, 0 row lock(s)
---TRANSACTION 421747401990328, not started
0 lock struct(s), heap size 1136, 0 row lock(s)
--------
FILE I/O
--------
I/O thread 0 state: waiting for completed aio requests (insert buffer thread)
I/O thread 1 state: waiting for completed aio requests (log thread)
I/O thread 2 state: waiting for completed aio requests (read thread)
I/O thread 3 state: waiting for completed aio requests (read thread)
I/O thread 4 state: waiting for completed aio requests (read thread)
I/O thread 5 state: waiting for completed aio requests (read thread)
I/O thread 6 state: waiting for completed aio requests (write thread)
I/O thread 7 state: waiting for completed aio requests (write thread)
I/O thread 8 state: waiting for completed aio requests (write thread)
I/O thread 9 state: waiting for completed aio requests (write thread)
Pending normal aio reads: [0, 0, 0, 0] , aio writes: [0, 0, 0, 0] ,
 ibuf aio reads:, log i/o's:, sync i/o's:
Pending flushes (fsync) log: 0; buffer pool: 0
286 OS file reads, 171 OS file writes, 22 OS fsyncs
0.00 reads/s, 0 avg bytes/read, 0.00 writes/s, 0.00 fsyncs/s
-------------------------------------
INSERT BUFFER AND ADAPTIVE HASH INDEX
-------------------------------------
Ibuf: size 1, free list len 0, seg size 2, 0 merges
merged operations:
 insert 0, delete mark 0, delete 0
discarded operations:
 insert 0, delete mark 0, delete 0
Hash table size 34679, node heap has 0 buffer(s)
Hash table size 34679, node heap has 0 buffer(s)
Hash table size 34679, node heap has 0 buffer(s)
Hash table size 34679, node heap has 0 buffer(s)
Hash table size 34679, node heap has 0 buffer(s)
Hash table size 34679, node heap has 0 buffer(s)
Hash table size 34679, node heap has 0 buffer(s)
Hash table size 34679, node heap has 0 buffer(s)
0.00 hash searches/s, 0.00 non-hash searches/s
---
LOG
---
Log sequence number 445926
Log flushed up to   445926
Pages flushed up to 445926
Last checkpoint at  445917
0 pending log flushes, 0 pending chkp writes
18 log i/o's done, 0.00 log i/o's/second
----------------------
BUFFER POOL AND MEMORY
----------------------
Total large memory allocated 167772160
Dictionary memory allocated 50768
Buffer pool size   8012
Free buffers       7611
Database pages     401
Old database pages 0
Modified db pages  0
Percent of dirty pages(LRU & free pages): 0.000
Max dirty pages percent: 75.000
Pending reads 0
Pending writes: LRU 0, flush list 0, single page 0
Pages made young 0, not young 0
0.00 youngs/s, 0.00 non-youngs/s
Pages read 264, created 137, written 156
0.00 reads/s, 0.00 creates/s, 0.00 writes/s
No buffer pool page gets since the last printout
Pages read ahead 0.00/s, evicted without access 0.00/s, Random read ahead
0.00/s
LRU len: 401, unzip_LRU len: 0
I/O sum[0]:cur[0], unzip sum[0]:cur[0]
--------------
ROW OPERATIONS
--------------
0 queries inside InnoDB, 0 queries in queue
0 read views open inside InnoDB
Process ID=4267, Main thread ID=140272021272320, state: sleeping
Number of rows inserted 1, updated 0, deleted 0, read 1
0.00 inserts/s, 0.00 updates/s, 0.00 deletes/s, 0.00 reads/s
Number of system rows inserted 0, updated 0, deleted 0, read 0
0.00 inserts/s, 0.00 updates/s, 0.00 deletes/s, 0.00 reads/s
----------------------------
END OF INNODB MONITOR OUTPUT
============================

URL: https://mariadb.com/kb/en/show-engine-innodb-status/