Directions of exchange

Synchronization can be unidirectional or bidirectional. In most cases, you will use bidirectional synchronization.

Unidirectional synchronization is suitable in situations like these:
Figure 1. Unidirectional and bidirectional updating

Unidirectional updates carry some risk. For example, an accidental change of mastership cannot be fixed, and restoring from a replica that does not exchange updates directly with the broken replica involves extra work. Also, you must ensure that no work is done accidentally in a read-only replica.


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