Prevent deadlock during command deletion in MySQL #61
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NanoMDM allows for a single command to be queued for multiple devices. Since micromdm#48 landed, both queued commands and the command data itself is deleted after a device in finished with a command. However, I have observed deadlocks which occur when multiple devices trigger deletion for a shared command at once. This can be avoided by placing a record lock on the command row before attempting a delete, so that only one device's enrollment queue can be cleared at a time. This should have minimal impacts on performance as it will only serialize deletes to a single command. Furthermore, as the lock on the command record must be taken anyway, this does not add any additional locking to the transaction. Testing: I have tested this, and have confirmed that it prevents deadlocks in NanoMDM. Furthermore, I have tested that commands are still delivered and responded to.
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NanoMDM allows for a single command to be queued for multiple devices. Since #48 landed, both queued commands and the command data itself is deleted after a device in finished with a command. However, I have observed deadlocks which occur when multiple devices trigger deletion for a shared command at once.
This can be avoided by placing a record lock on the command row before attempting a delete, so that only one device's enrollment queue can be cleared at a time.
This should have minimal impacts on performance as it will only serialize deletes to a single command. Furthermore, as the lock on the command record must be taken anyway, this does not add any additional locking to the transaction.
Testing
I have tested this, and have confirmed that it prevents deadlocks in NanoMDM. Furthermore, I have tested that commands are still delivered and responded to.