This is a problem with your MySQL Server, it gets stuck and therefore cannot process operations. It’s usually because of a problem due to an incomplete “frozen” transaction. Connect to your MySQL server and execute:
show innodb status \G
Search for something similar to:
------------ TRANSACTIONS ------------ Trx id counter 0 2005868535 Purge done for trx's n:o <0 2005868523 undo n:o <0 0 History list length 4 Total number of lock structs in row lock hash table 12990 LIST OF TRANSACTIONS FOR EACH SESSION: ---TRANSACTION 0 2005868508, not started, process no 6801, OS thread id 1150482768 MySQL thread id 67, query id 5223 localhost root show innodb status ---TRANSACTION 0 2005868518, ACTIVE 833 sec, process no 6801, OS thread id 1150617936 rollback mysql tables in use 2, locked 2 ROLLING BACK 12992 lock struct(s), heap size 1685488, undo log entries 1557131 MySQL thread id 70, query id 5111 localhost pandora end DELETE FROM tagente_datos WHERE id_agente_modulo IN (SELECT id_agente_modulo FROM tagente_modulo WHERE delete_pending = 1)
Another easy way to list current operations is the command:
SHOW FULL PROCESSLIST
In this example, transaction ID 70 , has been active for 833, and seems to be DEAD that’s why it’s blocking the access to some data, and probably it’s the explanation for those “lock wait” errors.
Kill the transaction with:
Sometimes a KILL could take some time, so be patient. Killing (kill -9) a MySQL daemon IS NOT A GOOD IDEA, and you will get a corrupted database with a 99% chance, so you’ll need to wait to finish.