reflink: add processing timestamp to transaction metadata in the reflink DB

Usually in ZODB, we can know when a transaction was committed by
decoding its TID, and by default it's the only way.

However in a reflink DB, transactions are committed with explicit TIDs,
which come from the main DB, for the following purpose: if you truncate
the main DB, just truncate the reflink DB at the same TID.

With this commit, it will be possible to know when reflink has processed
a TID by looking at transaction metadata.

neo/scripts/reflink.py

@@ -385,10 +385,11 @@ class Changeset(object):
 
     def commit(self, tid, info=''):
         storage = self.storage
+        now = time()
         logger.info('commit @ %x (%s)', u64(tid), info or
-            'Δ %s' % timedelta(0, time() - TimeStamp(tid).timeTime()))
+            'Δ %s' % timedelta(0, now - TimeStamp(tid).timeTime()))
         buckets = self.buckets
-        txn = TransactionMetaData()
+        txn = TransactionMetaData(extension={'time': now})
         storage.tpc_begin(txn, tid)
         def shortenVal(i):
             if i:

neo/tests/threaded/testPack.py

@@ -331,6 +331,7 @@ class GCTests(NEOThreadedTest):
         track = threading.Lock()
         with commit_patch, committed, track, NEOCluster() as reflink_cluster:
             stop = False
+            start = time()
             reflink_cluster.start()
             reflink_thread = self.newThread(reflink_run)
             t, conn = cluster.getTransaction()
@@ -393,6 +394,13 @@ class GCTests(NEOThreadedTest):
             self.assertLess(tid1, tid2)
             self.assertEqual(tid2, reflink_cluster.last_tid)
 
+            end = time()
+            for x in reflink_cluster.client.iterator():
+                x = x.extension['time']
+                self.assertLess(start, x)
+                start = x
+            self.assertLess(x, end)
+
         cluster.neoctl.truncate(tid1)
         self.tic()