[Zodb-checkins] CVS: ZODB3/ZODB/FileStorage - FileStorage.py:1.1.2.14

[Jeremy Hylton]

Update of /cvs-repository/ZODB3/ZODB/FileStorage
In directory cvs.zope.org:/tmp/cvs-serv27082/ZODB/FileStorage

Modified Files:
      Tag: ZODB3-mvcc-2-branch
	FileStorage.py 
Log Message:
Fix loadNonCurrent() for the abort version case,

but add an optimization that avoids seek+read for the txn header for
cases where it is safe to just use the serialno.


=== ZODB3/ZODB/FileStorage/FileStorage.py 1.1.2.13 => 1.1.2.14 ===
--- ZODB3/ZODB/FileStorage/FileStorage.py:1.1.2.13	Thu Nov 20 16:01:10 2003
+++ ZODB3/ZODB/FileStorage/FileStorage.py	Sat Nov 22 00:05:45 2003
@@ -542,7 +542,7 @@
             pos = self._lookup_pos(oid)
             h = self._read_data_header(pos, oid)
             if h.version and h.version != version:
-                # Retrun data and serial from pnv (non-version data).
+                # Return data and serial from pnv (non-version data).
 
                 # If we return the old record's transaction id, then
                 # it will look to the cache like old data is current.
@@ -603,11 +603,29 @@
         end_tid = None
         while True:
             h = self._read_data_header(pos, oid)
-            # XXX abort version?
-            if h.serial < tid and not h.version:
-                break
+            # Is this the first data record written before tid?
+            #
+            # In most cases, we can just use the serial number which
+            # is more efficient.  In the presence of abort version,
+            # the record's serial number will be the tid of the old
+            # non-version txn.  So we can only use the serial test
+            # if there is no backpointer; abortVersion always writes
+            # a backpointer.
+
+            # The logic is a bit complicated, so explicitly track
+            # whether we need to read the txn header.
+            th = None
+            if not h.version:
+                if not h.back:
+                    if h.serial < tid:
+                        break
+                else:
+                    th = self._read_txn_header(h.tloc)
+                    if th.tid < tid:
+                        break
+            if th is None:
+                th = self._read_txn_header(h.tloc)
             pos = h.prev
-            th = self._read_txn_header(h.tloc)
             end_tid = th.tid
             if not pos:
                 return None