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commit 099d347d5103058638bee6c0dd16b8f3e95c1360
Author: Eric Lee <dagang...@huawei.com>
AuthorDate: Thu Feb 8 15:45:34 2018 +0800
SCB-330 add design document
Signed-off-by: Eric Lee <dagang...@huawei.com>
---
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+# Saga Pack Design
+## Overview
+Pack contains two components: *alpha* and *omega*. Alpha is the pack leader
and backed by database to make sure transaction events stored permanently while
omega is the pack worker and embeded inside services to intercept
incoming/outgoing requests and report events to alpha.
+
+
+
+## Omega Internal
+Omega plays as an embeded agent inside services. When a request arrives, omega
intercepts its header and retrieve the global transaction id as its global
transaction id and retrieve the local transaction id as its parent transaction
id. In pre-process phase, a transaction started event will be recorded in
alpha. In post-process phase, a transaction ended event will be recorded in
alpha to mark the end of the sub-transaction.
+
+
+
+## Inter-Service Communication
+The process of Inter-Service Communication is similiar to
[Zipkin](https://github.com/openzipkin/zipkin)'s. In the producer side, omega
intercepts the transaction ids from request to retrieve the transaction
context. In the consumer side, omega inject the transaction ids into request to
pass the transaction context. Sub-transactions can chain as a single global
transaction by co-operating producers and consumers.
+
+
+
+## Workflow
+### Successful Scenario
+In a successful scenario, all started events will have a corresponding ended
event.
+
+
+
+### Exception Scenario
+In an exception scenario, omega inside the abnormal service will report an
aborted event to alpha. Apha will then send compensate commands to the
completed events within the global transaction to make suer all
sub-transactions are either completed or rollbacked.
+
+
+
+### Timeout Scenario
+In timeout scenario, timeouted events will be detected by alpha's periodly
scanner and abort the corresponding global transaction.
+
+
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