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76fc3d4aa1
Fixes https://github.com/neondatabase/neon/issues/6337 Add safekeeper support to switch between `Present` and `Offloaded(flush_lsn)` states. The offloading is disabled by default, but can be controlled using new cmdline arguments: ``` --enable-offload Enable automatic switching to offloaded state --delete-offloaded-wal Delete local WAL files after offloading. When disabled, they will be left on disk --control-file-save-interval <CONTROL_FILE_SAVE_INTERVAL> Pending updates to control file will be automatically saved after this interval [default: 300s] ``` Manager watches state updates and detects when there are no actvity on the timeline and actual partial backup upload in remote storage. When all conditions are met, the state can be switched to offloaded. In `timeline.rs` there is `StateSK` enum to support switching between states. When offloaded, code can access only control file structure and cannot use `SafeKeeper` to accept new WAL. `FullAccessTimeline` is now renamed to `WalResidentTimeline`. This struct contains guard to notify manager about active tasks requiring on-disk WAL access. All guards are issued by the manager, all requests are sent via channel using `ManagerCtl`. When manager receives request to issue a guard, it unevicts timeline if it's currently evicted. Fixed a bug in partial WAL backup, it used `term` instead of `last_log_term` previously. After this commit is merged, next step is to roll this change out, as in issue #6338.