Preconditions of apply_pack

[unixod]

Hi,

Could you help to clarify preconditions which apply_pack may rely on? In particular I'm wondering which of cases listed below are possible.

(In the list below by index I refer to first parameter of apply_pack)

1. index < log_store::start_index()
2. index > log_store::next_slot()
3. index + number_of_logs(pack) < log_store::next_slot()

If 3rd case is possible then may we truncate log entries which go after index + number_of_logs(pack) as part of apply_pack execution?

[greensky00]

pack is invoked in leader's side when below conditions are met. Let's say S1 is leader (pack) and S2 is follower (apply_pack).

• params->log_sync_stop_gap_ > 0. AND
• S2's next_slot() < S1's start_index(). AND
• S1's committed index > S2's next_slot() + params->log_sync_stop_gap_.

Then apply_pack's first parameter (index you referred to) will always be S2's next_slot(). Leader always sends the log starting from next_slot() of the follower, so none of three can be possible, unless follower's log store is changed before receiving the pack message from the leader.