This should allow to start the svn ingestion while ignoring previous ingestion result.When trying to load again some subversion repositories into the archive, the loader detects that the history got altered and
It current raises while it should notabort the loading process, see T3694#73221 and [related sentry issue](https://sentry.softwareheritage.org/organizations/swh/issues/8064/?project=14&query=is%3Aunresolved).
The following stacktrack (KeyError) [1] shows some assertions were wrong.For some rare cases, it can come from the subversion history being rewritten server side using `svnadmin` command
So this needs investigation and fix.
[1]
```
swhworker@worker17:~$ swh loader run svn https://profs.scienze.univr.it/posenato/svn/sw/CSTNU start_from_scratch=True
INFO:swh.loader.svn.SvnLoader:Load origin 'https://profs.scienze.univr.it/posenato/svn/sw/CSTNU' with type 'svn'
INFO:swh.loader.svn.SvnLoader:Processing revisions [1-619] for {'swh-origin': 'https://profs.scienze.univr.it/posenato/svn/sw/CSTNU', 'remote_url': 'https://profs.scienze.univr.it/posenato/svn/sw/CSTNU', 'local_url': b'/tmp/swh.loader.svn.qhb2pmup-99331/CSTNU', 'uuid': b'782453a1-1937-45d1-8845-2a6fcc2839b7'}
ERROR:swh.loader.svn.SvnLoader:90
Traceback (most recent call last):
File "/usr/lib/python3/dist-packages/swh/loader/svn/loader.py", line 457, in fetch_data
data = next(self.swh_revision_gen)
File "/usr/lib/python3/dist-packages/swh/loader/svn/loader.py", line 364, in process_svn_revisions
rev, commit, dir_id, revision_parents[rev]
KeyError: 90but most of the times it means that the filesystem associated to a revision and reconstructed using the [svn_ra API](https://subversion.apache.org/docs/api/latest/svn__ra_8h.html)
ERROR:swh.loader.svn.SvnLoader:Loading failure, updating to `failed` status
Traceback (most recent call last):
File "/usr/lib/python3/dist-packages/swh/loader/core/loader.py", line 339, in load
self.store_data()
File "/usr/lib/python3/dist-packages/swh/loader/svn/loader.py", line 489, in store_data
revision=self._last_revision, snapshot=self._snapshot
File "/usr/lib/python3/dist-packages/swh/loader/svn/loader.py", line 525, in generate_and_load_snapshot
"generate_and_load_snapshot called with null revision and snapshot!"
ValueError: generate_and_load_snapshot called with null revision and snapshot!
{'status': 'failed'}
```diverges from the one obtained by a `svn export` operation on the same revision.
Note: start-from-scratch parameter should probably be renamed ignore-history along the way.
That'd unify with the equivalent parameter in the loader-gitLet's try to analyze and fix those issues in that task.