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wcfs/internal/zdata/δftail.go

@@ -727,14 +727,20 @@ func (δFtail *ΔFtail) SliceByFileRev(zfile *ZBigFile, lo, hi zodb.Tid) /*reado
 
 			// take atomic Zinblk snapshot that covers vδZ
 			//
-			// - the reason we take snapshot is because simultaneous Track requests might
-			//   change Zinblk concurrently, and without snapshotting this might result
-			//   in changes to a block being not uniformly present in result (some
-			//   revision indicates change to that block, while another one - where the
-			//   block is too actually changed - does not indicate change to that block).
+			// - the reason we take atomic snapshot is because simultaneous Track
+			//   requests might change Zinblk concurrently, and without snapshotting
+			//   this might result in changes to a block being not uniformly present in
+			//   the returned vδf (some revision indicates change to that block, while
+			//   another one - where the block is too actually changed - does not
+			//   indicate change to that block).
 			//
 			// - the reason we limit snapshot to vδZ is to reduce amount of under-lock
 			//   copying, because original Zinblk is potentially very large.
+			//
+			// NOTE the other approach could be to keep blocks in _RootTrack.Zinblk with
+			// serial (!= zodb serial), and work with that _RootTrack.Zinblk snapshot by
+			// ignoring all blocks with serial > serial of snapshot view. Do not kill
+			// _ZinblkOverlay yet because we keep this  approach in mind for the future.
 			ZinblkSnap := map[zodb.Oid]setI64{}
 			δZAllOid := setOid{}
 			for _, δZ := range vδZ {