What are the differences between Database synchronization and replication?

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Database synchronization is closely related to database replication.
In fact, sometimes people use the terms interchangeably. However,
there are big differences, understanding which will help us understand
the different approaches used for solving replication and
synchronization problems.

Replication is mostly used in situations where identical replicas of
the complete data set are maintained on two or more database instances
for high availability and performance reasons. Database instances can
often work independently as backups for each other. The relationships
between the instances are equal, symmetric. Normally the number of DB
instances is small.

On the other hand, in a database synchronization system, typically you
have a big central database on the server side and a large number of
small databases each residing on a device. The central database
contains data for all the devices while each device’s local database
only contains the device’s private data and some shared data.

In the non-database world, Synchronization is also often used to
describe the data exchange between a more temporal sub-set of data and
a more persistent full-set of data. For instance, parts of a file
could be buffered in-memory by an operating system and are
“synchronized” with the file on hard disk. Another example is the
synchronization of the data in a CPU cache memory with the data in the
main memory.

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