strong_consistency: improve the text.

Author: knz

strong-consistency.md

@@ -4,23 +4,44 @@ summary: CockroachDB implements consistent replication via majority consensus be
 toc: false
 ---
 
-CockroachDB replicates your data multiple times and guarantees consistency between replicas 
-using the [Raft consensus algorithm](https://raft.github.io/), a popular alternative to 
-[Paxos](http://research.microsoft.com/en-us/um/people/lamport/pubs/paxos-simple.pdf). 
-A consensus algorithm guarantees that any majority of replicas together can always provide 
-the most recently written data on reads. Writes must reach a majority of replicas (2 out of 
-3 by default) before they are considered committed. If a write does not reach a majority of 
-replicas, it will fail, not be permanent, and will never be visible to readers. This means 
-that clients always see serializable consistency when viewing data (i.e., stale reads are 
-not possible).  
+CockroachDB replicates your data multiple times and guarantees consistency between replicas.
 
+Key properties:
+
+-   CockroachDB guarantees serializable SQL transactions
+    [as long as system clocks are synchronized with NTP](https://www.cockroachlabs.com/blog/living-without-atomic-clocks/)
 -   No downtime for server restarts, machine failures, or datacenter outages
 -   Local or wide-area replication with no stale reads on failover
 -   Employs Raft, a popular successor to Paxos
 
+How does this work?
+
+- Stored data is versioned with MVCC, so reads simply limit
+  their scope to the data visible at the time the read transaction started.
+
+- Writes are serviced using the
+  [Raft consensus algorithm](https://raft.github.io/), a popular
+  alternative to
+  [Paxos](http://research.microsoft.com/en-us/um/people/lamport/pubs/paxos-simple.pdf).
+  A consensus algorithm guarantees that any majority of replicas
+  together always agree on whether an update was committed
+  successfully. Updates (writes) must reach a majority of replicas (2
+  out of 3 by default) before they are considered committed.
+
+  To ensure that a write transaction does not interfere with
+  read transactions that start after it, CockroachDB also uses
+  a [timestamp cache](https://www.cockroachlabs.com/blog/serializable-lockless-distributed-isolation-cockroachdb/)
+  which remembers when data was last read by ongoing transactions.
+
+  This ensures that clients always observe serializable consistency
+  with regards to other concurrent transactions.
+
 <img src="images/2strong-consistency.png" alt="Strong consistency in CockroachDB" style="width: 400px" />
 
 ## See Also
 
+- [Serializable, Lockless, Distributed: Isolation in CockroachDB](https://www.cockroachlabs.com/blog/serializable-lockless-distributed-isolation-cockroachdb/)
 - [Consensus, Made Thrive](https://www.cockroachlabs.com/blog/consensus-made-thrive/)
 - [Trust, But Verify: How CockroachDB Checks Replication](https://www.cockroachlabs.com/blog/trust-but-verify-cockroachdb-checks-replication/)
+- [Living Without Atomic Clocks](https://www.cockroachlabs.com/blog/living-without-atomic-clocks/)
+- [The CockroachDB Architecture Document](https://github.com/cockroachdb/cockroach/blob/master/docs/design.md)