Using isolator with multiple database connections about isolator HOT 4 CLOSED

What you can do is to patch the subscriber and make it ignore queries from non-primary connection.

Do you think we still want to catch violations inside non-primary db transaction?

We should track connections separately using their ids.

It sounds like this statement means we track isolator_transactions per connection? This makes sense to me. Although I think the remaining challenge is to identify and ignore sql of connection establishment. May be we can use it as the trigger for initializing a new isolator_transactions.
Do you think using the db_config's host, adapter, and database would be a good connection identifier?

As for repro example

# This one is using the main db connection
class User < ActiveRecord::Base; end

# this is a different db that connects lazily
class Foo < ActiveRecord::Base
  self.establish_connection db_config
end

# simply reference the class would increment the count

# Thread.current[:isolator_transactions] == 0
User.transaction do
  # Thread.current[:isolator_transactions] == 1
  Foo
  # Thread.current[:isolator_transactions] == 2
end
# Thread.current[:isolator_transactions] == 1

I haven't tried but base on your comment may be the following is enough to throw off the count

User.transaction do
  # Would `Thread.current[:isolator_transactions]` still increment even if the adapter and database are the same as the main connection?
  ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:")
end

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Hey @mquan!

Finally, I found some time to invest into this feature. I took your PR and added some changes: #32

It would be great if you try this branch in your project (we're currently testing it internally, too).

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@palkan awesome, I tested it out in our repo, and it fixes the problem. I also added a few offenses in both main and secondary dbs and it correctly identifies them. Great job 👍

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Do you have a recommended way for dealing with multiple connections?

Unfortunately, no. Isolator was designed for single connection per thread usage, and it's not that simple to make it work with multiple connections.

What you can do is to patch the subscriber and make it ignore queries from non-primary connection. Smth like this:

def self.subscribe!(event)
  ::ActiveSupport::Notifications.subscribe(event) do |_name, _start, _finish, _id, query|
    # not sure about this one
    next unless query[:connection] == ActiveRecord::Base.connection

    Isolator.incr_transactions! if START_PATTERN.match?(query[:sql])
    Isolator.decr_transactions! if FINISH_PATTERN.match?(query[:sql])
  end
end

We should track connections separately using their ids. That would require some work.

Could you please provide a reproduction example or, much better, open a PR to Isolator with a test scenario for multiple connections? That would help us to fix this quicker.

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