CODEWITHSUNDEEP
pythonmysqldjangotransactions
Prabhakar Shanmugam
Prabhakar Shanmugam

Reputation: 6144

Does creating atomic transaction in django create a lock automatically

I have a code block within transaction.atomic() within a view. My question is does django create some inbuilt table locking behind the scenes. 

with transaction.atomic():
    #code block that does database operations
    update_user() #this updates user table
    create_customer_products() #this updates user id to customer products table

The reason is I get a "Lock wait timeout exceeded; try restarting transaction" error when I run the code block.

The setup is django mysql on centos

Upvotes: 2

Views: 1709

Answers (1)

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Reputation: 34231

In order to modify or insert a record in an innodb table, the transaction needs to acquire an exclusive lock in MySQL:

UPDATE ... WHERE ... sets an exclusive next-key lock on every record the search encounters. However, only an index record lock is required for statements that lock rows using a unique index to search for a unique row.

...

INSERT sets an exclusive lock on the inserted row. This lock is an index-record lock, not a next-key lock (that is, there is no gap lock) and does not prevent other sessions from inserting into the gap before the inserted row.

If the same record (or gap) is already locked by another transaction, then MySQL waits for the lock to be released or the above mentioned timeout occurs.

Based on the above code there is no way we can tell what has gone wrong (if anything). You can check out innodb status monitor to get more information, but without a deadlock its use will be limited as well.

This behaviour is intrinsic to MySQL, the application's programming language and libraries cannot influence this.

Upvotes: 3

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