Concurrency

Dynamoid supports basic, ActiveRecord-like optimistic locking on save operations. Simply add a lock_version column to your table like so:

class MyTable
  # ...

  field :lock_version, :integer

  # ...
end

In this example, all saves to MyTable will raise an Dynamoid::Errors::StaleObjectError if a concurrent process loaded, edited, and saved the same row. Your code should trap this exception, reload the row (so that it will pick up the newest values), and try the save again.

Calls to update and update! also increment the lock_version, however, they do not check the existing value. This guarantees that a update operation will raise an exception in a concurrent save operation, however, a save operation will never cause an update to fail. Thus, update is useful & safe only for doing atomic operations (e.g. increment a value, add/remove from a set, etc), but should not be used in a read-modify-write pattern.