Hard Consistency - ACID does not apply to microservices
It may have been applicable via 2 Phase Commit in case of Distributed Transaction but the database was still the same
Now its time for Eventual Consistency
ACID on Local Transactions
Multiple steps in Transaction Boundary - Because its just 1
one fails, all Fails
Distributed Transactions
More than 1 Database
Using Multiple Local Transaction
One is committed, Another Fails
Compensatory Transaction(Workaround Steps) - Not Always a Good Practice
https://www.youtube.com/watch?v=jGJT1FRYGcY
Stale Data - Multiple Write -> Dual Write
Begin Txn
Lock
Mutate
Release Lock (Commit) or Rollback ---- Goto State
https://www.youtube.com/watch?v=pSz0Fpvu2Gk
Older Distributed Transaction or Monolithic Architecture
ACID Principles to Multiple External System
2 Phase Commit - Distributed Transactions - Not a Good Fit for Microservices
Distributed Transaction - how ??
Saga
2 Phase Commit --- -Prepare and Commit --> 2 Phases
Prepare1 -> Prepared1 -> Commit1
Prepare2 -> Prepared2 -> Commit2
Commit1 + Commit2 = Commit ----Txn Cordinator ---> Application
2 Phase Commit - Discouraged in Microservices -- HTTP Slowness, LOCKED Resource , Slow
Co-ordinator Fails ? What Then ?
3 Phase allows any Participant to be a Co-ordinator
2Phase / 3-Phase - biggest drawback is - they have a wrapper aroun TXN -
So its long living and synchronous
2 Phase is Okay for - Simple Monolithic Application
But Microservices is already slow,uses HTTP and now u put 2phase commit , Its worse
Asynchronous -- SAGA
Txn1 -> Message
Txn2 -> Message (If Failure, Then Rollback Message)
https://youtu.be/H6F4BorD49g - Hussein Nasser
What is a Distributed Transaction in Microservices?
What 3 Methods
1)Atomic Clocks - Rollback The steps
2)Event Based - Kafka/Rabbit MQ -> Publish/Subscribe -> Reverse
3)MiniMonolith - MacroService [Combine homogenous txns in 1 Service]
Distributed Transactions - Txns between Multiple Processes - Each with their own commit/rollback
Multiple Local Transactions - Dual Write - Inconsistencies
MiniMonolith - MacroService
Monorepo
Microservices
