From patchwork Mon Mar 31 23:19:46 2014
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Subject: [4,of,7,V2] transaction: add support for non-append files
From: Durham Goode <durham@fb.com>
X-Patchwork-Id: 4170
Message-Id: <498a1087dd60ec7234c4.1396307986@dev2000.prn2.facebook.com>
To: mercurial-devel@selenic.com
Date: Mon, 31 Mar 2014 16:19:46 -0700

# HG changeset patch
# User Durham Goode <durham@fb.com>
# Date 1395699711 25200
#      Mon Mar 24 15:21:51 2014 -0700
# Node ID 498a1087dd60ec7234c4352e566abe977eb63332
# Parent  f85f9ea96d16e180de3e38cfc468e53441f41743
transaction: add support for non-append files

This adds support for normal, non-append-only files in transactions.  For
example, .hg/store/fncache and .hg/store/phaseroots should be written as part of
the transaction, but are not append only files.

This adds a journal.backupfiles along side the normal journal. This tracks which
files have been backed up as part of the transaction.  transaction.addbackup()
creates a backup of the file (using a hardlink), which is later used to recover
in the event of the transaction failing.

Using a seperate journal allows the repository to still be used by older
versions of Mercurial. A future patch will use this functionality and add tests
for it.

diff --git a/mercurial/transaction.py b/mercurial/transaction.py
--- a/mercurial/transaction.py
+++ b/mercurial/transaction.py
@@ -12,8 +12,8 @@
 # GNU General Public License version 2 or any later version.
 
 from i18n import _
-import errno
-import error
+import errno, os
+import error, util
 
 def active(func):
     def _active(self, *args, **kwds):
@@ -24,22 +24,35 @@
     return _active
 
 def _playback(journal, report, opener, entries, unlink=True):
+    backupfiles = []
     for f, o, ignore in entries:
         if o or not unlink:
-            try:
-                fp = opener(f, 'a')
-                fp.truncate(o)
-                fp.close()
-            except IOError:
-                report(_("failed to truncate %s\n") % f)
-                raise
+            if isinstance(o, int):
+                try:
+                    fp = opener(f, 'a')
+                    fp.truncate(o)
+                    fp.close()
+                except IOError:
+                    report(_("failed to truncate %s\n") % f)
+                    raise
+            else:
+                fpath = opener.join(f)
+                opath = opener.join(o)
+                util.copyfile(opath, fpath)
+                backupfiles.append(o)
         else:
             try:
                 opener.unlink(f)
             except (IOError, OSError), inst:
                 if inst.errno != errno.ENOENT:
                     raise
+
     opener.unlink(journal)
+    backuppath = "%s.backupfiles" % journal
+    if opener.exists(backuppath):
+        opener.unlink(backuppath)
+    for f in backupfiles:
+        opener.unlink(f)
 
 class transaction(object):
     def __init__(self, report, opener, journal, after=None, createmode=None,
@@ -56,9 +69,12 @@
         self.journal = journal
         self._queue = []
 
+        self.backupfilesjournal = "%s.backupfiles" % journal
         self.file = opener.open(self.journal, "w")
+        self.backupsfile = opener.open(self.backupfilesjournal, 'w')
         if createmode is not None:
             opener.chmod(self.journal, createmode & 0666)
+            opener.chmod(self.backupfilesjournal, createmode & 0666)
 
     def __del__(self):
         if self.journal:
@@ -71,11 +87,23 @@
     @active
     def endgroup(self):
         q = self._queue.pop()
-        d = ''.join(['%s\0%d\n' % (x[0], x[1]) for x in q])
         self.entries.extend(q)
+
+        offsets = []
+        backups = []
+        for f, o, _ in q:
+            if isinstance(o, int):
+                offsets.append((f, o))
+            else:
+                backups.append((f, o))
+        d = ''.join(['%s\0%d\n' % (f, o) for f, o in offsets])
         self.file.write(d)
         self.file.flush()
 
+        d = ''.join(['%s\0%s\0' % (f, o) for f, o in backups])
+        self.backupsfile.write(d)
+        self.backupsfile.flush()
+
     @active
     def add(self, file, offset, data=None):
         if file in self.map:
@@ -91,6 +119,27 @@
         self.file.flush()
 
     @active
+    def addbackup(self, file):
+        if file in self.map:
+            return
+        backupfile = "journal.%s" % file
+        if self.opener.exists(file):
+            filepath = self.opener.join(file)
+            backuppath = self.opener.join(backupfile)
+            util.copyfiles(filepath, backuppath, hardlink=True)
+        else:
+            self.add(file, 0)
+            return
+
+        if self._queue:
+            self._queue[-1].append((file, backupfile))
+            return
+        self.entries.append((file, backupfile, None))
+        self.map[file] = len(self.entries) - 1
+        self.backupsfile.write("%s\0%s\0" % (file, backupfile))
+        self.backupsfile.flush()
+
+    @active
     def find(self, file):
         if file in self.map:
             return self.entries[self.map[file]]
@@ -136,11 +185,16 @@
         if self.count != 0:
             return
         self.file.close()
-        self.entries = []
         if self.after:
             self.after()
         if self.opener.isfile(self.journal):
             self.opener.unlink(self.journal)
+        if self.opener.isfile(self.backupfilesjournal):
+            self.opener.unlink(self.backupfilesjournal)
+            for f, o, _ in self.entries:
+                if not isinstance(o, int):
+                    self.opener.unlink(o)
+        self.entries = []
         self.journal = None
 
     @active
@@ -162,6 +216,7 @@
             if not self.entries:
                 if self.journal:
                     self.opener.unlink(self.journal)
+                    self.opener.unlink(self.backupfilesjournal)
                 return
 
             self.report(_("transaction abort!\n"))
@@ -189,4 +244,14 @@
         except ValueError:
             report(_("couldn't read journal entry %r!\n") % l)
 
+    backupjournal = "%s.backupfiles" % file
+    if opener.exists(backupjournal):
+        fp = opener.open(backupjournal)
+        data = fp.read()
+        if len(data) > 0:
+            parts = data.split('\0')
+            for i in xrange(0, len(parts), 2):
+                f, o = parts[i:i + 1]
+                entries.append((f, o, None))
+
     _playback(file, report, opener, entries)