CODEWITHSUNDEEP
ruby-on-railsactiverecordisolation-leveltransaction-isolation
codevj
codevj

Reputation: 103

Setting Isolation level in ruby v 2.1.3

I have been struggling with putting a record level lock on my table, to avoid any dirty reads and race condition while updating the record. I am using ruby 2.1.3 and rails version 3.2.13. I tried using the command:

Account.connection.execute("SET TRANSACTION ISOLATION LEVEL SERIALIZABLE")

and tested by putting sleep, but 2 processes trying to update the same record read the old value and the final data is wrong. For example: if my old value is 100, both processes read 100 and then update, 100+x and 100+y and thus,the data is getting corrupted.

I am using mySQL database. Any help is appreciated.

Upvotes: 2

Views: 102

Answers (2)

codevj
codevj

Reputation: 103

The following solution worked for me (slight modification of dimakura's answer):

  1. When I used find() for active record query:

    acc = Account.lock.find(id)
acc.balance += 100
acc.save!

  2. When I used where() for active record query:

    acc = Account.where(:acc_code => acc_code).first
acc.with_lock do
 acc.balance += 100
 acc.save!
end

Upvotes: 0

dimakura
dimakura

Reputation: 7655

There are two locking mechanisms supported in Rails: optimistic and pessimistic.

Updating account balance, using pessimistic locking, should look like this:

acc = Account.find(id)
acc.with_lock do
  acc.balance += 100
  acc.save!
end

Upvotes: 2

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