# `CAP` and `HA`
+ Why does `TiDB/TiKV` choose `CP & HA`?
+ Compatible with `MySQL`, reducing the burden of application developers
+ Impossible to achieve 100% availability
  + `HA`: 0.9999...
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Accuracy: One of TiDB's positions is OLTP, and this requirement is absolutely correct. It is difficult to write the right program under the guarantee of weak consistency (such as eventual consistency), and developers must consider various edge situations.

HA: There is no 100% availability, only high availability can be pursued, that is, constantly adding `9`.