Avoiding Distributed Transactions with the Reservation Pattern

Because a long-running business process could last seconds to days, you cannot lock resources within a service using a distributed transaction. So what's the alternative? The real world has a solution, it's a reservation. A reservation allows you to have a time-bound limited guarantee which allows you to coordinate with other services.
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0:00 Intro
1:25 Reservation Real World Example
4:09 Synchronous Example
7:11 Asynchronous Example
#softwarearchitecture #softwaredesign #serviceorientedarchitecture

[@sscapture]

Yes, good for seating, but for user registration we need to stop asking a lot of information like address, etc and just create their account. Additional information is only to be gathered when it's needed and as less info as possible

[@ismile47]

I really like your videos, explaining the context and showing concept with low level codes and also explaining clear disadvatages or trade offs at then end. I want to understand with in a microservice between different entitys or functionality how to communicate write business logics in modern ways.

[@YouToYoub]

What an amazing teacher you are? I would like to see this turned into some sort of an online course in the future.

[@CodeOpinion]

Keep on eye on my channel. I'll announce it here when there is.

[@alucinorbeats]

@@CodeOpinion Any update on this?

[@drewjaqua2905]

As always, this was another great video and I'm glad you take the time to make these.

[@CodeOpinion]

Glad you like them!

[@tarekel-shahawy891]

I don't know how, BUT THANK YOU KZbin ALGORITHM for bringing this channel to my feed.

[@CodeOpinion]

😆

[@mvbelinskiy]

Isn't command pattern just a fancy way of calling methods, that allows very custom decoration options, like for instance reserving some resource? And of course inverts control also!

[@sp-niemand]

Sending commands will work between services too. On this channel there was also a video about planning the initial monolith to simplify breaking it down later.

[@awright18]

This seems like how reserved seating works in some venues. This totally makes sense.

[@CodeOpinion]

Exactly. The concept can be used in different situations where you need a time-bound limited guarantee lock on a "thing" (eg, seat), while someone completes a process.

[@mikeyim9985]

Hi, great video as always. What if the order has a quantity involved? If I’m reserving two tickets in a single order, should two individual reservations be made for those two tickets or just one reservation with the quantity field of two? I ask this because we check for how many reservations are not expired or canceled to prevent over-ordering in the use case you presented in this video, but when we allow ppl to reserve multiple products at once, this checking for the count of active reservation becomes more complex and now we have to check the quantity field of each active reservation and add them up.

[@CodeOpinion]

You could make multiple reservations within a single atomic operation on the reservation side (as well as confirmation). In the real world example, if I ordered a quantity of 2, but only one was available, I would partially be refunded and notified of the change to a reservation of 1.

[@user-qt6tn4xl2e]

what do u think about putting this kind of logic into account adding some status (creating, created)

[@CodeOpinion]

Yes, for example, the order itself would have a status that you transition through to know its going from Placed, Reserved, Completed

[@user-qt6tn4xl2e]

how to control the complexity here? if we have such reservation for each case, we will end up with thousands of events..

[@CodeOpinion]

Yes, in an message/event driven architecture is what drives interaction. Depending on your scale you can have a small or very large number of events.

[@Imploser]

How about concurrent requests? If multiple requests are reserved at the same time, a duplicate entry could be added to the account table. To avoid this, we should at least lock the reservation. We cannot rely on CPU clock time for account reservation and addition.

[@CodeOpinion]

Yes, absolutely required a lock, likely distributed as well. Leverage the DB you're using to provide that (for example_.

[@devagr]

The name of the store you ordered is visible at 3:01, not sure if you care

[@CodeOpinion]

Not really, was trying to remember it but I still can't tell where!

[@devagr]

@@CodeOpinion at the end of "we recommend that you pick up your item...."

[@manmohanmundhraa3087]

how to handle case where 2 user try to reserve same user/order/resource ? Do we need transaction to handle this situation ?

[@CodeOpinion]

You'd need to handle concurrency. You could do that via a trx within the boundary doing the reserve itself.

Isn't this just another use case of Saga pattern? Even last class in example is called UserRegistrationSaga.. On top of that multiple sources describe Saga pattern as a way to manage distributed transactions. Maybe video title should say "Avoiding XA transactions"?

[@CodeOpinion]

Yes, it's illustrating a long running business process with a saga, but adding timeouts to illustrate.

[@neilbarnwell]

Isn't this basically pessimistic locking with a timeout?

[@CodeOpinion]

I'd guess most would think of pessimistic locking related to a database transaction.

[@neilbarnwell]

@@CodeOpinion An interesting point. I would thing about db transaction things in terms of isolation level, but I see what you mean.