Which HTTP methods do not preserve idempotent effects and can lead to server state changes upon repeated use?

HTTP methods that are not idempotent and can change the server state upon repeated requests include:

• POST — typically used for creating resources or performing operations that change state. Repeating POST can lead to duplicate creation or other changes.
• PATCH — used for partial updates of a resource; repeated requests can change the state multiple times.
• PUT — although considered idempotent, in some cases, repeated requests can cause changes if the server processes them with side effects.

Methods that do not change the state and are idempotent:

• GET — only retrieves data.
• DELETE — deletes a resource; repeated requests usually do not change the state after the first deletion.

Thus, POST and PATCH are the main methods that do not preserve the effect of repeated requests and can change the server state upon repeated use.