MySQL Deadlock

The Mysql2::Error: Deadlock found when trying to get lock; try restarting transaction error occurs when two or more transactions are waiting for each other to release a lock on a resource. To resolve this issue, you can try the following:

  1. Identify the cause of the deadlock: Check the MySQL error log for more information on the deadlock, and determine which transactions are causing the issue. This will help you understand what changes you need to make in your code to prevent deadlocks.

  2. Optimize your queries: Long-running queries or complex transactions can increase the likelihood of deadlocks. Optimize your queries by using appropriate indexing, reducing the number of joins, and fetching only the required data.

  3. Avoid lock escalation: To prevent lock escalation, acquire locks in a consistent order across all transactions. This will help reduce the chances of a deadlock.

  4. Use smaller transactions: Break large transactions into smaller ones. Smaller transactions are less likely to cause deadlocks, as they hold locks for a shorter amount of time.

  5. Retry the transaction: If a deadlock occurs, you can catch the error and retry the transaction. Implement a retry mechanism with exponential backoff to avoid overwhelming the database with retry attempts.

For example, in Ruby on Rails, you can use the following code to retry a transaction:

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RETRY_ATTEMPTS = 3
RETRY_DELAY = 2

def perform_transaction
  retry_count = 0

  begin
    ActiveRecord::Base.transaction do
      # Your transaction logic here
    end
  rescue ActiveRecord::Deadlocked => e
    if retry_count < RETRY_ATTEMPTS
      retry_count += 1
      sleep(RETRY_DELAY * retry_count)
      retry
    else
      raise e
    end
  end
end

In this example, the transaction will be retried up to RETRY_ATTEMPTS times, with an increasing delay between each attempt (determined by RETRY_DELAY).