1 # Cumulus: Efficient Filesystem Backup to the Cloud
2 # Copyright (C) 2012 The Cumulus Developers
3 # See the AUTHORS file for a list of contributors.
5 # This program is free software; you can redistribute it and/or modify
6 # it under the terms of the GNU General Public License as published by
7 # the Free Software Foundation; either version 2 of the License, or
8 # (at your option) any later version.
10 # This program is distributed in the hope that it will be useful,
11 # but WITHOUT ANY WARRANTY; without even the implied warranty of
12 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 # GNU General Public License for more details.
15 # You should have received a copy of the GNU General Public License along
16 # with this program; if not, write to the Free Software Foundation, Inc.,
17 # 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
19 """Backup retention policies.
21 Retention policies control how long different backup snapshots should be kept,
22 for example keeping daily snapshots for short periods of time but retaining
23 weekly snapshots going back further in time.
29 TIMESTAMP_FORMAT = "%Y%m%dT%H%M%S"
31 # Different classes of backups--such as "daily" or "monthly"--can have
32 # different retention periods applied. A single backup snapshot might belong
33 # to multiple classes (i.e., perhaps be both a "daily" and a "monthly", though
36 # Backups are classified using partitioning functions, defined below. For a
37 # "monthly" backup classifier, all backups for a given month should map to the
38 # same partition. Then, we apply the class label to the earliest snapshot in
39 # each partition--so the set of "monthly" backups would consist of all backups
40 # which were the first to run after the start of a month.
42 # A partitioning function must take a datetime instance as input and return a
43 # partition representative as output; timestamps that should be part of the
44 # same partition should map to equal partition representatives. For a
45 # "monthly" classifier, an easy way to do this is to truncate the timestamp to
46 # keep only the month and year, and in general truncating timestamps works
47 # well, but the values are not used in any other way than equality testing so
48 # any type is allowed.
50 # _backup_classes is a registry of useful backup types; it maps a descriptive
51 # name to a partition function which implements it.
54 def add_backup_class(name, partioning_function):
55 """Registers a new class of backups for which policies can be applied.
57 The new class will be available as name to RetentionEngine.add_policy.
58 partioning_function should be a function for grouping together backups in
61 Predefined backups classes are: "yearly", "monthly", "weekly", "daily", and
64 _backup_classes[name] = partioning_function
66 add_backup_class("yearly", lambda t: t.date().replace(day=1, month=1))
67 add_backup_class("monthly", lambda t: t.date().replace(day=1))
68 add_backup_class("weekly", lambda t: t.isocalendar()[0:2])
69 add_backup_class("daily", lambda t: t.date())
70 add_backup_class("all", lambda t: t)
73 class RetentionEngine(object):
74 """Class for applying a retention policy to a set of snapshots.
76 Allows a retention policy to be set, then matches a sequence of backup
77 snapshots to the policy to decide which ones should be kept.
83 self._last_snapshots = {}
84 self._now = datetime.datetime.utcnow()
86 def set_utc(self, use_utc=True):
87 """Perform policy matching with timestamps in UTC.
89 By default, the policy converts timestamps to local time, but calling
90 set_utc(True) will select snapshots based on UTC timestamps.
92 self._convert_to_localtime = not use_utc
94 def set_now(self, timestamp):
95 """Sets the "current time" for the purposes of snapshot expiration.
97 timestamp should be a datetime object, expressed in UTC. If set_now()
98 is not called, the current time defaults to the time at which the
99 RetentionEngine object was instantiated.
101 self._now = timestamp
103 def add_policy(self, backup_class, retention_period):
104 self._policies[backup_class] = retention_period
105 self._last_snapshots[backup_class] = (None, None, False)
108 def parse_timestamp(s):
109 if isinstance(s, datetime.datetime):
111 return datetime.datetime.strptime(s, TIMESTAMP_FORMAT)
113 def consider_snapshot(self, snapshot):
114 """Compute whether a given snapshot should be expired.
116 Successive calls to consider_snapshot() must be for snapshots in
117 chronological order. For each call, consider_snapshot() will return a
118 boolean indicating whether the snapshot should be retained (True) or
121 timestamp_utc = self.parse_timestamp(snapshot)
122 snapshot_age = self._now - timestamp_utc
124 # timestamp_policy is the timestamp in the format that will be used for
125 # doing policy matching: either in the local timezone or UTC, depending
126 # on the setting of set_utc().
127 if self._convert_to_localtime:
128 unixtime = calendar.timegm(timestamp_utc.timetuple())
129 timestamp_policy = datetime.datetime.fromtimestamp(unixtime)
131 timestamp_policy = timestamp_utc
135 for (backup_class, retention_period) in self._policies.iteritems():
136 partition = _backup_classes[backup_class](timestamp_policy)
137 last_snapshot = self._last_snapshots[backup_class]
138 if self._last_snapshots[backup_class][0] != partition:
139 self._labels.add(backup_class)
140 retain_label = snapshot_age < retention_period
141 self._last_snapshots[backup_class] = (partition, snapshot,
143 if retain_label: retain = True
146 def last_labels(self):
147 """Return the set of policies that applied to the last snapshot.
149 This will fail if consider_snapshot has not yet been called.
153 def last_snapshots(self):
154 """Returns the most recent snapshot in each backup class."""
155 return dict((k, v[1]) for (k, v)
156 in self._last_snapshots.iteritems() if v[2])