DataIntensive initial commit

Author: iambrj

dataIntensive.md

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+# Replication
+- Many copies of data to scale horizontally and serve more reads
+- Ways of replication
+    1. Leader-follower: writes happen first on leader, then propogated to
+       followers.
+    2. Multi-leader
+    3. Leaderless
+- Types of replication:
+    1. Synchronous: leader sends write and blocks writes till follower ack
+    2. Asynchronous: leader sends write and continues with further writes
+    3. Semi-synchronous: one follower is sync, rest async. if leader fails, the
+       sync follower becomes leader.
+- Setting up new followers: snapshot leader, launch follower, request changes
+  since snapshot
+- Node outage: catch up using on disk log
+- Leader failover:
+    1.