Update FasterKV.md

docs/cs/FasterKV.md

@@ -232,7 +232,9 @@ FASTER also support true "log compaction", where the log is scanned and live rec
   compactUntil = session.Compact(compactUntil, shiftBeginAddress: true);
 ```
 
-This call perform synchronous compaction on the provided session until the specific `compactUntil` address, scanning and copying the live records to the tail. It returns the actual log address that the call compacted until (next nearest record boundary). You can only compact until the log's `SafeReadOnlyAddress` as the rest of the log is still mutable in-place. Typically, you may compact around 20% (up to 100%) of the log, e.g., you set `compactUntil` address to `store.Log.BeginAddress + 0.2 * (store.Log.SafeReadOnlyAddress - store.Log.BeginAddress)`. The parameter `shiftBeginAddress`, when true, causes the compation to also shift the begin address when the compaction is complete. However, since live records are written to the tail, directly shifting the begin address may result in data loss if the store fails immediately. If you do not want to lose data, you need to trigger compaction with `shiftBeginAddress` set to false, then complete a checkpoint (either fold-over or snaphot is fine), and then shift the begin address. Finally, you can take another checkpoint to save the new begin address. This is shown below:
+This call perform synchronous compaction on the provided session until the specific `compactUntil` address, scanning and copying the live records to the tail. It returns the actual log address that the call compacted until (next nearest record boundary). You can only compact until the log's `SafeReadOnlyAddress` as the rest of the log is still mutable in-place. If you wish, you can move the read-only address to the tail by calling `store.Log.ShiftReadOnlyToTail(store.Log.TailAddress, true)` or by simply taking a fold-over checkpoint (`await store.TakeHybridLogCheckpointAsync(CheckpointType.FoldOver)`).
+
+Typically, you may compact around 20% (up to 100%) of the log, e.g., you could set `compactUntil` address to `store.Log.BeginAddress + 0.2 * (store.Log.SafeReadOnlyAddress - store.Log.BeginAddress)`. The parameter `shiftBeginAddress`, when true, causes log compation to also automatically shift the log's begin address when the compaction is complete. However, since live records are written to the tail, directly shifting the begin address may result in data loss if the store fails immediately after the call. If you do not want to lose data, you need to trigger compaction with `shiftBeginAddress` set to false, then complete a checkpoint (either fold-over or snaphot is fine), and then shift the begin address. Finally, you can take another checkpoint to save the new begin address. This is shown below:
 
 ```cs
   long compactUntil = store.Log.BeginAddress + 0.2 * (store.Log.SafeReadOnlyAddress - store.Log.BeginAddress);