Change Store.put_chunk to choose randomly only the first chunk id.

Subsequent chunks get successive ids.

1 files changed, 9 insertions, 1 deletions

diff --git a/obnamlib/store.py b/obnamlib/store.py
index e23db388..a620826d 100644
--- a/obnamlib/store.py
+++ b/obnamlib/store.py
@@ -616,6 +616,7 @@ class Store(object):
         self.chunksums = ChecksumTree(fs, 'chunksums', len(self.checksum('')))
         self.groupsums = ChecksumTree(fs, 'groupsums', len(self.checksum('')))
         self.chunkgroups = ChunkGroupTree(fs)
+        self.prev_chunkid = None
 
     def checksum(self, data):
         '''Return checksum of data.
@@ -861,11 +862,18 @@ class Store(object):
         
         '''
         
+        max_chunkid = 2**64 - 1
+        def random_chunkid():
+            return random.randint(0, max_chunkid)
+        
+        if self.prev_chunkid is None:
+            self.prev_chunkid = random_chunkid()
         while True:
-            chunkid = random.randint(0, 2**64 - 1)
+            chunkid = (self.prev_chunkid + 1) % max_chunkid
             filename = self._chunk_filename(chunkid)
             if not self.fs.exists(filename):
                 break
+        self.prev_chunkid = chunkid
         dirname = os.path.dirname(filename)
         if not self.fs.exists(dirname):
             self.fs.makedirs(dirname)