.

wcfs/internal/zdata/δftail.go

@@ -28,7 +28,7 @@ package zdata
 //
 // ΔFtail organization
 //
-// ΔFtail leverages
+// ΔFtail leverages:
 //
 //	- ΔBtail to track changes to ZBigFile.blktab BTree, and
 //	- ΔZtail to track changes to ZBlk objects and to ZBigFile object itself.
@@ -42,7 +42,7 @@ package zdata
 // and handles complexity of recomputing vδB when set of tracked blocks
 // changes.
 //
-// Changes to ZBigFile object indicate epochs. Epochs could be
+// Changes to ZBigFile object indicate epochs. Epochs could be:
 //
 //	- file creation or deletion,
 //	- change of ZBigFile.blksize,
@@ -604,6 +604,11 @@ func (δFtail *ΔFtail) SliceByFileRev(zfile *ZBigFile, lo, hi zodb.Tid) /*reado
 	// δFile	────────o───────o──────x─────x────────────────────────
 
 
+	δftail, err := δFtail.rebuildIfNeeded(zfile.POid())
+	if err != nil {
+		panic(err) // XXX
+	}
+
 	var vδf []*ΔFile
 	// vδfTail returns or creates vδf entry for revision tail
 	// tail must be <= all vδf revisions
@@ -623,11 +628,6 @@ func (δFtail *ΔFtail) SliceByFileRev(zfile *ZBigFile, lo, hi zodb.Tid) /*reado
 		return δfTail
 	}
 
-	δftail, err := δFtail.rebuildIfNeeded(zfile.POid())
-	if err != nil {
-		panic(err) // XXX
-	}
-
 	vδZ := δFtail.δBtail.ΔZtail().SliceByRev(lo, hi)
 	iz := len(vδZ) - 1