Sets timestap for interval comparision just once

No more fetching new now() timestamp for every check. Hard to test for
this, but could have once in a blue moon caused a missed archive due to
the timestamp changing during iteration.

Author: Goddesen

src/borg/archiver/prune_cmd.py

@@ -100,7 +100,7 @@ def quarterly_3monthly_period_func(a):
 )
 
 
-def prune_split(archives, rule, n_or_interval, kept_because=None):
+def prune_split(archives, rule, n_or_interval, base_timestamp, kept_because=None):
     if isinstance(n_or_interval, int):
         n, interval = n_or_interval, None
     else:
@@ -119,7 +119,7 @@ def prune_split(archives, rule, n_or_interval, kept_because=None):
         period = period_func(a)
         if period != last:
             last = period
-            if a.id not in kept_because and (interval is None or a.ts >= datetime.now().astimezone() - interval):
+            if a.id not in kept_because and (interval is None or a.ts >= base_timestamp - interval):
                 keep.append(a)
                 kept_because[a.id] = (rule, len(keep))
                 if len(keep) == n:
@@ -180,11 +180,12 @@ def do_prune(self, args, repository, manifest):
         #   (<rulename>, <how many archives were kept by this rule so far >)
         kept_because = {}
 
+        base_timestamp = datetime.now().astimezone()
         # find archives which need to be kept because of the various time period rules
         for rule in PRUNING_PATTERNS.keys():
             num_or_interval = getattr(args, rule, None)
             if num_or_interval is not None:
-                keep += prune_split(archives, rule, num_or_interval, kept_because)
+                keep += prune_split(archives, rule, num_or_interval, base_timestamp, kept_because)
 
         to_delete = set(archives) - set(keep)
         with Cache(repository, manifest, iec=args.iec) as cache:

src/borg/testsuite/helpers_test.py

@@ -494,7 +494,7 @@ def subset(lst, ids):
         MockArchive(datetime(2017, 10, 1, 10, 0, 5, tzinfo=None), 13),
     ]
     kept_because = {}
-    keep = prune_split(archives, rule, num_to_keep, kept_because)
+    keep = prune_split(archives, rule, num_to_keep, datetime.now().astimezone(), kept_because)
 
     assert set(keep) == subset(archives, expected_ids)
     for item in keep:
@@ -517,7 +517,7 @@ def subset(lst, ids):
 
     # Keep oldest when retention target can't otherwise be met
     kept_because = {}
-    keep = prune_split(archives, "yearly", 3, kept_because)
+    keep = prune_split(archives, "yearly", 3, datetime.now().astimezone(), kept_because)
 
     assert set(keep) == subset(archives, [1, 3, 4])
     assert kept_because[1][0] == "yearly[oldest]"
@@ -526,7 +526,7 @@ def subset(lst, ids):
 
     # Otherwise, prune it
     kept_because = {}
-    keep = prune_split(archives, "yearly", 2, kept_because)
+    keep = prune_split(archives, "yearly", 2, datetime.now().astimezone(), kept_because)
 
     assert set(keep) == subset(archives, [3, 4])
     assert kept_because[3][0] == "yearly"
@@ -537,7 +537,7 @@ def test_prune_split_no_archives():
     archives = []
 
     kept_because = {}
-    keep = prune_split(archives, "yearly", 3, kept_because)
+    keep = prune_split(archives, "yearly", 3, datetime.now().astimezone(), kept_because)
 
     assert keep == []
     assert kept_because == {}