Merge pull request #1724 from redis/DOC-5438-rdi-checkpoint-at-least-once

DOC-5348 RDI: info about at-least-once delivery and checkpointing

Author: andy-stark-redis

content/integrate/redis-data-integration/architecture.md

@@ -42,7 +42,8 @@ in sequence:
     currently uses an open source collector called
     [Debezium](https://debezium.io/) for this step.
 
-1.  The collector records the captured changes using Redis streams
+1.  The collector records the captured changes using
+[Redis streams]({{< relref "/develop/data-types/streams" >}})
     in the RDI database.
 
 1.  A *stream processor* reads data from the streams and applies
@@ -68,6 +69,28 @@ RDI automatically enters a second phase called *change streaming*, where
 changes in the data are captured as they happen. Changes are usually
 added to the target within a few seconds after capture.
 
+## At-least-once delivery guarantee
+
+RDI guarantees *at-least-once delivery* to the target. This means that
+a given change will never be lost, but it might be added to the target
+more than once. Apart from a slight performance overhead, adding a
+change multiple times is harmless because the multiple writes
+are [*idempotent*](https://en.wikipedia.org/wiki/Idempotence) (that is
+to say that all writes after the first one make no change to the
+overall state).
+
+## Checkpointing
+
+RDI uses Redis streams to store the sequence of change events
+captured from the source. The events are then retrieved in order
+from the streams, processed, and written to the target. The stream
+processor uses a *checkpoint* mechanism to keep track of the last
+event in the sequence that it has successfully processed and stored. If the processor fails
+for any reason, it can restart from the last checkpoint and
+re-process any events that might not have been written to the target.
+This ensures that all changes are eventually recorded, even in the
+face of failures.
+
 ## Backpressure mechanism
 
 Sometimes, data records can get added to the streams faster than RDI can
@@ -85,7 +108,7 @@ an error, just an informative message to note that RDI has applied
 the backpressure mechanism.
 {{</note>}}
 
-### Supported sources
+## Supported sources
 
 RDI supports the following database sources using [Debezium Server](https://debezium.io/documentation/reference/stable/operations/debezium-server.html) connectors: