repository: add max_size byte limit to PackWriter, OR-ed with max_count

src/borg/repository.py

@@ -106,7 +106,7 @@ def build_rest_backend(location):
 class PackWriter:
     """Buffers chunks into a pack file and writes to the store when full.
 
-    Collects (chunk_id, cdata) pairs in a list and flushes once max_count is
+    Collects (chunk_id, cdata) pairs in a list and flushes once a limit is
     reached.  PackWriter maintains the ChunkIndex directly: each add() marks the
     chunk as pending (pack_id=UNKNOWN_BYTES32); flush() then assigns the real
     pack_id, offset and size to every pending entry once the pack is on disk.
@@ -116,18 +116,23 @@ class PackWriter:
     uses that repository's single, authoritative index (see the chunks property), so
     there is never a second copy to keep in sync.  Unit tests pass an explicit index.
 
-    max_count bounds how many chunks a pack accumulates before flush() writes it.
-    Raising it produces larger packs without changing this class's interface.
+    max_count bounds how many chunks a pack holds; max_size bounds its byte size.
+    flush() fires when either limit is reached.  Each limit is disabled by setting it
+    to None; at least one must be set.
     """
 
-    def __init__(self, store, *, max_count=1, chunks=None, repository=None):
+    def __init__(self, store, *, max_count=3, max_size=None, chunks=None, repository=None):
         if repository is None and chunks is None:
             raise ValueError("PackWriter requires either a repository or an explicit chunks index")
+        if max_count is None and max_size is None:
+            raise ValueError("PackWriter requires at least one of max_count or max_size")
         self.store = store
-        self.max_count = max_count
+        self.max_count = max_count  # None = no count limit
+        self.max_size = max_size  # None = no size limit
         self.repository = repository  # when set, the one and only index lives there
         self._chunks = chunks  # explicit index for repository-less use (tests)
         self._pieces = []  # list of (chunk_id, cdata)
+        self._size = 0  # byte size of buffered pieces
 
     @property
     def chunks(self):
@@ -142,17 +147,14 @@ def chunks(self):
 
     def add(self, chunk_id, cdata):
         """Buffer a chunk.  Returns flush results if the pack is now full, else None."""
-        # Mark the chunk as pending (pack_id=UNKNOWN_BYTES32).  flush() assigns the real
-        # pack_id and offset for every piece, so the placeholder offset 0 here is never read:
-        # get() refuses a pending entry (PackLocationUnknown) before any offset would matter.
-        # Precondition: callers add only chunks not already stored (the cache dedups via
-        # seen_chunk() first), so add(chunk_id, 0) never resets a real size on an existing entry.
-        # This is also what keeps ChunkIndex.add's "v.size == 0 or v.size == size" assertion happy:
-        # a fresh id has no entry, so the size=0 we pass here is never compared against a real size.
-        self.chunks.add(chunk_id, 0)  # size filled in by cache layer
+        # Mark the chunk as pending; flush() fills in the pack_id, offset and size.
+        self.chunks.add(chunk_id, 0)
         self.chunks.update_pack_info([(chunk_id, UNKNOWN_BYTES32, 0, len(cdata))])
         self._pieces.append((chunk_id, cdata))
-        if len(self._pieces) >= self.max_count:
+        self._size += len(cdata)
+        if (self.max_count is not None and len(self._pieces) >= self.max_count) or (
+            self.max_size is not None and self._size >= self.max_size
+        ):
             return self.flush()
         return None
 
@@ -201,6 +203,7 @@ def flush(self):
             raise
         finally:
             self._pieces = []  # reset even on failure to prevent re-bundling a failed chunk
+            self._size = 0
         self.chunks.update_pack_info(results)  # replace UNKNOWN_BYTES32 with real pack_id
         return results
 
@@ -507,7 +510,7 @@ def open(self, *, exclusive, lock_wait=None, lock=True):
         if lock:
             self.lock = Lock(self.store, exclusive, timeout=lock_wait).acquire()
         self._chunks = None
-        self._pack_writer = PackWriter(self.store, max_count=2, repository=self)
+        self._pack_writer = PackWriter(self.store, repository=self)
         self.opened = True
 
     @property

src/borg/testsuite/repository_test.py

@@ -248,6 +248,7 @@ def test_list(repo_fixtures, request):
     with get_repository_from_fixture(repo_fixtures, request) as repository:
         for x in range(100):
             repository.put(H(x), fchunk(b"SOMEDATA", chunk_id=H(x)))  # unique bytes -> unique pack id
+        repository.flush()  # flush the last partial pack so all 100 objects are listable
         repo_list = repository.list()
         assert len(repo_list) == 100
         first_half = repository.list(limit=50)
@@ -345,6 +346,35 @@ def test_pack_writer_n2_flush():
     assert results[1] == (id2, expected_pack_id, len(data1), len(data2))
 
 
+def test_pack_writer_flushes_on_max_size():
+    # max_count is high, so the flush is driven by max_size alone.
+    store = MockStore()
+    pw = PackWriter(store, max_count=100, max_size=10, chunks=ChunkIndex())
+    assert pw.add(b"a" * 32, b"12345") is None
+    results = pw.add(b"b" * 32, b"67890")
+    assert results is not None
+    assert len(results) == 2
+
+
+def test_pack_writer_max_size_none_is_count_only():
+    store = MockStore()
+    pw = PackWriter(store, max_count=2, max_size=None, chunks=ChunkIndex())
+    assert pw.add(b"a" * 32, b"x" * 10_000) is None
+    assert pw.add(b"b" * 32, b"y" * 10_000) is not None
+
+
+def test_pack_writer_max_count_none_is_size_only():
+    store = MockStore()
+    pw = PackWriter(store, max_count=None, max_size=10, chunks=ChunkIndex())
+    assert pw.add(b"a" * 32, b"12345") is None
+    assert pw.add(b"b" * 32, b"67890") is not None
+
+
+def test_pack_writer_requires_a_limit():
+    with pytest.raises(ValueError):
+        PackWriter(MockStore(), max_count=None, max_size=None, chunks=ChunkIndex())
+
+
 def test_pack_writer_rolls_back_index_on_failed_store():
     # If store.store() fails, flush() must drop the entries add() pre-marked, otherwise the index
     # keeps a phantom (indexed but never stored) chunk that seen_chunk() reports as present and a