How to handle transactions

[codeliner]

Question extracted from prooph/proophessor#20:

MongoDB does not support transactions, but it has atomic modifiers and ttl documents, so enough tools to build transactions manually. For the event stream a transactional behavior would be useful, right?
I think of something like this:

- Start transaction sets a property into the adapter that transaction is running
- During in-transaction persistence we add a "inTransaction":true property on the document.
- All findById and findAll and similar queries check for the inTransaction property
- After transaction is finished, we can remove the inTransaction property with an atomic modifier to enable the new state
- An entry marked "inTransation" has a ttl (time-to-life) on the server side, in case the process dies, we don't want to have pending transactions in the database, so they get cleaned up after some time.

If we do something like this, which TTL will we use? MySQL InnoDB has a innodb_lock_wait_timeout of 50 secs by default f.e.

[codeliner]

Unfortunately, I have no production experience with mongoDB. Used it for a private project only. My clients always use Oracle. Don't ask me why :-)
Do we have other (simpler) options? Or maybe we should first have a look on how the event stream(s) can be organized with mongoDB. Let us discuss this in #3 first.

[prolic]

I can do that, if you want to ;)

[codeliner]

Transaction support would be great. I'm also fine with the way you want to implement it. It sounds good and works without magic so go for it 👍

[codeliner]

#4 ships with transaction support.