Identity cache inside transaction

Identity cache gem does not fetch from the cache store when fetch method was used inside any transaction, this is to avoid inconsistency in cache data as the changes will be commited at the end of transaction.

But they might be use case where we only load and not do updation. One way to solve this having a transaction which is not joinable to parent transaction. Usually identity_cache has should_use_cache? method which decides to fetch from cache or DB. should_use_cache? checks for any open transaction which is joinable, if so it make the DB call instead of fetching from cache. But if we wrap the fetch call inside transaction which is new and not joinable , then we can make use of advantage of the cache store and can save query at many places.

In the below code, fetch is happening inside the new transaction which is not joinable, should_use_cache? method returns true in this case and fetch from cache store.

Sample code:

ApplicationRecord.transaction do
    ApplicationRecord.transaction(requires_new: true, joinable: false) do
        ApplicationRecord.fetch(1)
     end
end

Start by tracing ApplicationRecord.fetch and the should_use_cache? decision around ActiveRecord transactions. Reproduce the nested requires_new, joinable: false example, then verify that cache reads occur there without changing cache-consistency behavior in other transactions.