Storage engines

InnoDB

Supports transactions, row-level locking, foreign keys and encryption for tables

[ Variables | Buffer Pool | InnoDB Status ]

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2026-09-14 22:47:33 0x411c INNODB MONITOR OUTPUT
=====================================
Per second averages calculated from the last 56 seconds
-----------------
BACKGROUND THREAD
-----------------
srv_master_thread loops: 7936 srv_active, 0 srv_shutdown, 13464 srv_idle
srv_master_thread log flush and writes: 21400
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SEMAPHORES
----------
OS WAIT ARRAY INFO: reservation count 62229
OS WAIT ARRAY INFO: signal count 13573
RW-shared spins 2754, rounds 79668, OS waits 2593
RW-excl spins 440, rounds 3824, OS waits 57
RW-sx spins 4, rounds 37, OS waits 1
Spin rounds per wait: 28.93 RW-shared, 8.69 RW-excl, 9.25 RW-sx
------------------------
LATEST FOREIGN KEY ERROR
------------------------
2026-09-14 21:15:42 0x3454 Transaction:
TRANSACTION 20628, ACTIVE 0 sec inserting
mysql tables in use 1, locked 1
3 lock struct(s), heap size 1128, 1 row lock(s), undo log entries 1
MySQL thread id 22330, OS thread handle 13396, query id 1201826 localhost ::1 root Update
INSERT INTO subjects (name) VALUES ('additional')
Foreign key constraint fails for table `study_doc`.`subjects`:
,
  CONSTRAINT `fk_subject_course` FOREIGN KEY (`course_id`) REFERENCES `courses` (`id`) ON DELETE CASCADE in parent table, in index unique_subject_per_course tuple:
DATA TUPLE: 3 fields;
 0: len 4; hex 80000000; asc     ;;
 1: len 10; hex 6164646974696f6e616c; asc additional;;
 2: len 4; hex 8000000a; asc     ;;

But in parent table `study_doc`.`courses`, in index PRIMARY,
the closest match we can find is record:
PHYSICAL RECORD: n_fields 4; compact format; info bits 0
 0: len 4; hex 80000001; asc     ;;
 1: len 6; hex 000000000000; asc       ;;
 2: len 7; hex 80000000000000; asc        ;;
 3: len 3; hex 4c4b47; asc LKG;;

------------
TRANSACTIONS
------------
Trx id counter 21102
Purge done for trx's n:o < 21102 undo n:o < 0 state: running but idle
History list length 2
LIST OF TRANSACTIONS FOR EACH SESSION:
---TRANSACTION 282964930838888, not started
0 lock struct(s), heap size 1128, 0 row lock(s)
---TRANSACTION 282964930834720, not started
0 lock struct(s), heap size 1128, 0 row lock(s)
---TRANSACTION 282964930830552, not started
0 lock struct(s), heap size 1128, 0 row lock(s)
---TRANSACTION 282964930826384, not started
0 lock struct(s), heap size 1128, 0 row lock(s)
--------
FILE I/O
--------
I/O thread 0 state: native aio handle (insert buffer thread)
I/O thread 1 state: native aio handle (log thread)
I/O thread 2 state: native aio handle (read thread)
I/O thread 3 state: native aio handle (read thread)
I/O thread 4 state: native aio handle (read thread)
I/O thread 5 state: native aio handle (read thread)
I/O thread 6 state: native aio handle (write thread)
I/O thread 7 state: native aio handle (write thread)
I/O thread 8 state: native aio handle (write thread)
I/O thread 9 state: native aio handle (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
15532 OS file reads, 79234 OS file writes, 48132 OS fsyncs
0.23 reads/s, 16384 avg bytes/read, 1.52 writes/s, 0.95 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 4441, node heap has 1 buffer(s)
Hash table size 4441, node heap has 0 buffer(s)
Hash table size 4441, node heap has 0 buffer(s)
Hash table size 4441, node heap has 0 buffer(s)
Hash table size 4441, node heap has 0 buffer(s)
Hash table size 4441, node heap has 1 buffer(s)
Hash table size 4441, node heap has 1 buffer(s)
Hash table size 4441, node heap has 1 buffer(s)
1.86 hash searches/s, 2.98 non-hash searches/s
---
LOG
---
Log sequence number 11473543
Log flushed up to   11473543
Pages flushed up to 11473543
Last checkpoint at  11473534
0 pending log flushes, 0 pending chkp writes
23331 log i/o's done, 0.54 log i/o's/second
----------------------
BUFFER POOL AND MEMORY
----------------------
Total large memory allocated 33554432
Dictionary memory allocated 95152
Buffer pool size   1003
Free buffers       741
Database pages     258
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 15494, created 480, written 47297
0.23 reads/s, 0.00 creates/s, 0.84 writes/s
Buffer pool hit rate 979 / 1000, young-making rate 0 / 1000 not 0 / 1000
Pages read ahead 0.00/s, evicted without access 0.00/s, Random read ahead 0.00/s
LRU len: 258, unzip_LRU len: 0
I/O sum[58]:cur[2], unzip sum[0]:cur[0]
--------------
ROW OPERATIONS
--------------
0 queries inside InnoDB, 0 queries in queue
0 read views open inside InnoDB
Process ID=7920, Main thread ID=6032, state: sleeping
Number of rows inserted 120, updated 10054, deleted 9, read 226746
0.00 inserts/s, 0.20 updates/s, 0.00 deletes/s, 1.61 reads/s
Number of system rows inserted 0, updated 0, deleted 0, read 12426
0.00 inserts/s, 0.00 updates/s, 0.00 deletes/s, 0.00 reads/s
----------------------------
END OF INNODB MONITOR OUTPUT
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