Page History

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1. re-encryption completed for cache group (and after that at least one checkpoint was completed)
2. last WAL segment in which the key was used is removed (on node startup should check if the WAL history has been cleared manually)

Fault tolerance

If CACHE_GROUP_KEY_CHANGE_PREPARE has not been successfully completed on all nodes, the process is interrupted and must be restarted.
When the process restarts, a new key identifier is generated (an unused key will be removed on finish-phase, when we set the new key for writing).

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