Mysql2::Error: Deadlock found when trying to get lock; try restarting transaction: INSERT INTO

My guess is that you are using InnoDB and probably doing concurrent insertions.

To trace and understand the cause, check out these articles:

• MySQL deadlocks with concurrent inserts
• How can I configure MySQL Innodb to handle 1000s of inserts per hour?

One way to fix the issue is to retry like it is shown in the code below:

def add_products
    retries = 0

    begin
        Product.add(self, "product_name", 10)
    rescue  ActiveRecord::StatementInvalid => ex
        if ex.message =~ /Deadlock found when trying to get lock/ #ex not e!!
            retries += 1   
            raise ex if retries > 3  ## max 3 retries 
            sleep 10
            retry
        else
            raise ex
        end
    end
end

Or, there are some gems like transaction_retry to handle MySQL deadlocks.

This has saved me a lot of headaches: transaction_retry ruby gem.

From the README of the gem:

Retries database transaction on deadlock and transaction serialization errors. Supports MySQL, PostgreSQL, and SQLite.