2. Primary-Copy Replication

• Designate one replica as the primary copy (publisher)

• Transactions may update only the primary copy

• Updates to the primary are sent later to secondary replicas (subscribers) in the order they were applied to the primary

T1: Start

… Write(x1) ...

Commit

x1

T2

Tn

...

Primary

Copy

x2

xm

...

Secondaries

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