mirror of https://github.com/borgbackup/borg.git
Track shadowing of log entries
Fixes (benign) index vs. log inconsistencies when segments are skipped during compaction.
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21c3fb3b93
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@ -306,6 +306,10 @@ class Repository:
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except RuntimeError:
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self.check_transaction()
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self.index = self.open_index(transaction_id, False)
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# This is an index of shadowed log entries during this transaction. Consider the following sequence:
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# segment_n PUT A, segment_x DELETE A
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# After the "DELETE A" in segment_x the shadow index will contain "A -> (n,)".
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self.shadow_index = defaultdict(list)
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if transaction_id is None:
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self.segments = {} # XXX bad name: usage_count_of_segment_x = self.segments[x]
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self.compact = FreeSpace() # XXX bad name: freeable_space_of_segment_x = self.compact[x]
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@ -420,9 +424,8 @@ class Repository:
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# complete the current transfer (when some target segment is full)
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nonlocal unused
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# commit the new, compact, used segments
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self.io.write_commit(intermediate=intermediate)
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logger.debug('complete_xfer: wrote %scommit at segment %d', 'intermediate ' if intermediate else '',
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self.io.get_latest_segment())
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segment = self.io.write_commit(intermediate=intermediate)
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logger.debug('complete_xfer: wrote %scommit at segment %d', 'intermediate ' if intermediate else '', segment)
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# get rid of the old, sparse, unused segments. free space.
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for segment in unused:
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logger.debug('complete_xfer: deleting unused segment %d', segment)
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@ -445,7 +448,10 @@ class Repository:
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logger.debug('compacting segment %d with usage count %d and %d freeable bytes',
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segment, segments[segment], freeable_space)
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for tag, key, offset, data in self.io.iter_objects(segment, include_data=True):
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if tag == TAG_PUT and self.index.get(key, (-1, -1)) == (segment, offset):
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if tag == TAG_COMMIT:
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continue
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in_index = self.index.get(key) == (segment, offset)
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if tag == TAG_PUT and in_index:
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try:
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new_segment, offset = self.io.write_put(key, data, raise_full=True)
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except LoggedIO.SegmentFull:
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@ -455,8 +461,22 @@ class Repository:
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segments.setdefault(new_segment, 0)
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segments[new_segment] += 1
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segments[segment] -= 1
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elif tag == TAG_PUT and not in_index:
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# If this is a PUT shadowed by a later tag, then it will be gone when this segment is deleted after
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# this loop. Therefore it is removed from the shadow index.
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try:
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self.shadow_index[key].remove(segment)
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except (KeyError, ValueError):
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pass
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elif tag == TAG_DELETE:
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if index_transaction_id is None or segment > index_transaction_id:
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# If the shadow index doesn't contain this key, then we can't say if there's a shadowed older tag,
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# therefore we do not drop the delete, but write it to a current segment.
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shadowed_put_exists = key not in self.shadow_index or any(
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# If the key is in the shadow index and there is any segment with an older PUT of this
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# key, we have a shadowed put.
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shadowed < segment for shadowed in self.shadow_index[key])
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if shadowed_put_exists or index_transaction_id is None or segment > index_transaction_id:
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# (introduced in 6425d16aa84be1eaaf88)
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# This is needed to avoid object un-deletion if we crash between the commit and the deletion
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# of old segments in complete_xfer().
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@ -714,6 +734,7 @@ class Repository:
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segment, offset = self.index.pop(id)
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except KeyError:
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raise self.ObjectNotFound(id, self.path) from None
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self.shadow_index[id].append(segment)
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self.segments[segment] -= 1
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size = self.io.read(segment, offset, id, read_data=False)
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self.compact[segment] += size
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@ -1026,6 +1047,7 @@ class LoggedIO:
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crc = self.crc_fmt.pack(crc32(header) & 0xffffffff)
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fd.write(b''.join((crc, header)))
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self.close_segment()
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return self.segment - 1 # close_segment() increments it
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MAX_DATA_SIZE = MAX_OBJECT_SIZE - LoggedIO.put_header_fmt.size
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@ -293,7 +293,42 @@ class RepositoryCommitTestCase(RepositoryTestCaseBase):
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assert not self.repository.io.segment_exists(last_segment)
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for segment, _ in self.repository.io.segment_iterator():
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for tag, key, offset, size in self.repository.io.iter_objects(segment):
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assert tag != TAG_DELETE
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if tag == TAG_DELETE:
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assert segment in self.repository.compact
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def test_shadowed_entries_are_preserved(self):
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get_latest_segment = self.repository.io.get_latest_segment
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self.repository.put(H(1), b'1')
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# This is the segment with our original PUT of interest
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put_segment = get_latest_segment()
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self.repository.commit()
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# We now delete H(1), and force this segment to not be compacted, which can happen
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# if it's not sparse enough (symbolized by H(2) here).
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self.repository.delete(H(1))
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self.repository.put(H(2), b'1')
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delete_segment = get_latest_segment()
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# We pretend these are mostly dense (not sparse) and won't be compacted
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del self.repository.compact[put_segment]
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del self.repository.compact[delete_segment]
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self.repository.commit()
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# Now we perform an unrelated operation on the segment containing the DELETE,
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# causing it to be compacted.
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self.repository.delete(H(2))
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self.repository.commit()
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assert self.repository.io.segment_exists(put_segment)
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assert not self.repository.io.segment_exists(delete_segment)
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# Basic case, since the index survived this must be ok
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assert H(1) not in self.repository
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# Nuke index, force replay
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os.unlink(os.path.join(self.repository.path, 'index.%d' % get_latest_segment()))
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# Must not reappear
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assert H(1) not in self.repository
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class RepositoryAppendOnlyTestCase(RepositoryTestCaseBase):
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