.

bigfile/_file_zodb.pyx

@@ -153,7 +153,7 @@ class ZSync:
         zsync.zconn = zconn     # XXX -> weakref
         zsync.wconn = wconn
 
-        # NOTE zcon.onOpenCallback is not enought: zconn.at can change even
+        # NOTE zconn.onOpenCallback is not enough: zconn.at can change even
         # without zconn.close/zconn.open, e.g.:
         # zconn = DB.open(transaction_manager=tm)
         # tm.commit()   # zconn.at updated          (zconn.afterCompletion -> zconn.newTransaction)

wcfs/client/wcfs.cpp

@@ -61,7 +61,9 @@
 // wendelin.core semantic wcfs client mmaps-in zeros for Mapping regions after
 // wcfs/head/f.size. For simplicity it is assumed that bigfiles only grow and
 // never shrink. It is indeed currently so, but will have to be revisited
-// if/when wendelin.core adds bigfile truncation.
+// if/when wendelin.core adds bigfile truncation. Wcfs client restats
+// wcfs/head/f at every transaction boundary (Conn.resync) and remembers f.size
+// in FileH.headfsize for use during one transaction.
 //
 // Every FileH maintains
 //
@@ -574,6 +576,9 @@ error _FileH::close() {
 }
 
 // resync resyncs connection and its file mappings onto different database view.
+//
+// bigfile/_file_zob.pyx arranges to call Conn.resync at transaction boundaries
+// to keep Conn view in sync with updated zconn database view.
 error _Conn::resync(zodb::Tid at) {
     _Conn& wconn = *this;
     error err;