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douardda
olasd
vlorentz

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rDSTO05a4fca1258f: storage: Identify and provide the collision hashes in exception

Summary

Storage clients may need to have details about what's colliding during adding
contents. To determine how to overcome the issue for example [1]

Furthermore, this unifies the inconsistent behavior in the 3 storage backends [2]

Now all storage backends provides the HashCollision exception with the following parameter signatures:
(algo: str, hash_id: bytes, content_hashes: Dict[str, bytes])

I'm not too happy about the implementation though.
I did not find a better way than to parse a specific exception message from
psycopg2 (e.diag.message_detail)... ouch.

[1] https://forge.softwareheritage.org/D2777#66365

[2] Sample output for the collided content prior to this diff (pdb breakpoint during integration test)

in-memory:
(('blake2s256', b"\xd5\xfe\x199We'\xe4,\xfdv\xa9EZ$2\xfe\x7fVf\x95dW}\xd9<B\x80\xe7mf\x1d"), ('sha1', b'4\x972t\xcc\xefj\xb4\xdf\xaa\xf8e\x99y/\xa9\xc3\xfeF\x89'), ('sha1_git', b'\xd8\x1c\xc0q\x0e\xb6\xcf\x9e\xfd[\x92\n\x84S\xe1\xe0qW\xb6\xcd'), ('sha256', b'h6P\xf96\xcb;\n/\x93\xce\t\xd8\x1b\xe1\x07H\xb1\xb2\x03\xc1\x9e\x81v\xb4\xee\xfc\x19d\xa0\xcf:'))

cassandra:
[Row(sha1_git=b'\xd8\x1c\xc0q\x0e\xb6\xcf\x9e\xfd[\x92\n\x84S\xe1\xe0qW\xb6\xcd', sha1=b'4\x972t\xcc\xefj\xb4\xdf\xaa\xf8e\x99y/\xa9\xc3\xfeF\x89', sha256=b'g6P\xf96\xcb;\n/\x93\xce\t\xd8\x1b\xe1\x07H\xb1\xb2\x03\xc1\x9e\x81v\xb4\xee\xfc\x19d\xa0\xcf:', blake2s256=b"\xd5\xfe\x199We'\xe4,\xfdv\xa9EZ$2\xfe\x7fVf\x95dW}\xd9<B\x80\xe7mf\x1d"), Row(sha1_git=b'\xd8\x1c\xc0q\x0e\xb6\xcf\x9e\xfd[\x92\n\x84S\xe1\xe0qW\xb6\xcd', sha1=b'4\x972t\xcc\xefj\xb4\xdf\xaa\xf8e\x99y/\xa9\xc3\xfeF\x89', sha256=b'h6P\xf96\xcb;\n/\x93\xce\t\xd8\x1b\xe1\x07H\xb1\xb2\x03\xc1\x9e\x81v\xb4\xee\xfc\x19d\xa0\xcf:', blake2s256=b"\xd5\xfe\x199We'\xe4,\xfdv\xa9EZ$2\xfe\x7fVf\x95dW}\xd9<B\x80\xe7mf\x1d")]

pgstorage:
Nothing

Test Plan

tox

Diff Detail

Repository

rDSTO Storage manager

Lint

Automatic diff as part of commit; lint not applicable.

Unit

Automatic diff as part of commit; unit tests not applicable.

Event Timeline

ardumont created this revision.Mar 6 2020, 2:09 PM

ardumont added inline comments.Mar 6 2020, 2:13 PM

swh/storage/utils.py
86	This may go away altogether if we use the `BaseContent.hashes` method which returns the equivalent Dict[str, bytes] of content hashes.

ardumont edited the summary of this revision. (Show Details)Mar 6 2020, 2:21 PM

ardumont edited the summary of this revision. (Show Details)

ardumont edited the summary of this revision. (Show Details)Mar 6 2020, 2:55 PM

Why List[Tuple[str, bytes]] instead of Dict[str, bytes]?

This is very hacky but I don't see any alternative (not even using D2248), so let's do that.

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Harbormaster failed remote builds in B10954: Diff 9887!Mar 6 2020, 3:54 PM

Why List[Tuple[str, bytes]] instead of Dict[str, bytes]?

Because i don't really know what's acceptable as type there.
And also, i only thought of checking the model *after* implementing this ;)

I'm all for doing the dict implementation instead.
And at the same time unifying the other storage backends.
Thanks.

This is very hacky but I don't see any alternative (not even using D2248), so let's do that.

yup
but now at least we have information on the content colliding ;)

Unify behavior to all backend storage to Provide the colliding content hashes

ardumont retitled this revision from storage: Identify and provide the collision hash(es) in HashCollision exception to storage(s): Identify and provide the collision hash(es) in HashCollision exception.Mar 6 2020, 11:54 PM

ardumont edited the summary of this revision. (Show Details)

ardumont added a project: Storage manager.

Build is green
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Harbormaster completed remote builds in B10992: Diff 9922.Mar 6 2020, 11:57 PM

lgtm, but I'd like someone else to review it as well

swh/storage/storage.py
167	`c.get_hash(hash_name)`

This revision is now accepted and ready to land.Mar 7 2020, 9:23 AM

ardumont edited the summary of this revision. (Show Details)Mar 7 2020, 2:06 PM

Adapt according to review

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Harbormaster failed remote builds in B10993: Diff 9923!Mar 8 2020, 9:18 AM

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Harbormaster completed remote builds in B10993: Diff 9923.Mar 8 2020, 9:25 AM

Build is green

Cancel the previous build stuck since yesterday for some reason.
Trigger back the build and it's all good now.

ardumont added inline comments.Mar 9 2020, 11:15 AM

swh/storage/utils.py
86	comment deprecated (for the first diff implementation on a method no longer existing now).

As mentioned inline in the pg storage diff, in general we should return /all/ colliding contents that we can find, rather than a single one. So in the end, the exception argument should be a List[Dict[str, bytes]].

swh/storage/cassandra/storage.py
92–102	Am I right that this logic means that we add colliding contents to the storage, /then/ report a collision? We should probably flip the main table add and the index check.
swh/storage/storage.py
168	Why pick a single one instead of all colliding contents?
swh/storage/utils.py
61–62	I suggest using `re.search` on `r'\((?P<type>[^)]+)\)=\(\\x(?P<id>[a-f0-9]+)\)`, then you can drop the `replace` lower down.

This revision now requires changes to proceed.Mar 9 2020, 11:35 AM

vlorentz added inline comments.Mar 9 2020, 11:38 AM

swh/storage/cassandra/storage.py
92–102	Correct. That's intentional to not give the illusion the "test and insert" is atomic. IMO it shouldn't raise the exception at all, it's only to mimic the pgstorage's behavior.

olasd added inline comments.Mar 9 2020, 11:55 AM

swh/storage/cassandra/storage.py
92–102	Even when the test + insert behavior doesn't exhibit a race condition, this choice: voluntarily lets data through that creates an ambiguity between storage and objstorage (by allowing the insertion of contents with colliding `sha1`s). voluntarily lets data through that creates an ambiguity in edges of the archive graph (by allowing the insertion of contents with colliding `sha1_git`s). That feels... quite bad. Given that we're not even close to the point of migrating to another hash for either of these things, we're very far away from not raising the exception at all, and we should consider avoiding inserting colliding data /at the very least/ to the main table, if we can help it.

ardumont added inline comments.Mar 9 2020, 1:24 PM

swh/storage/storage.py
168	Right, I'll fix that.
swh/storage/utils.py
61–62	I remember trying to match the '\\x' and fail to make it work. I could not find the right amount of escaping. I'll try again ;)

ardumont added inline comments.Mar 9 2020, 1:31 PM

swh/storage/utils.py
61–62	Ok, those tests were done prior to me remembering about the `r''` stanza. Now it works \m/

pgstorage: Return the list of colliding content hashes
improve regexp extraction

Align storages to return the list of colliding hashes

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Harbormaster failed remote builds in B10997: Diff 9926!Mar 9 2020, 2:21 PM

ardumont added inline comments.Mar 9 2020, 2:23 PM

swh/storage/cassandra/storage.py
92–102	Ack, i'm keeping this out of the scope of the diff though.

Build is green
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Harbormaster completed remote builds in B10998: Diff 9927.Mar 9 2020, 2:27 PM

ardumont added inline comments.Mar 9 2020, 4:10 PM

swh/storage/cassandra/converters.py

jsyk i did a test but that types error

$ pytest -x -s -k test_row_to_content_hashes
...
TypeError: tuple() takes no keyword arguments

The test in question:

+# Copyright (C) 2020  The Software Heritage developers
+# See the AUTHORS file at the top-level directory of this distribution
+# License: GNU General Public License version 3, or any later version
+# See top-level LICENSE file for more information
+
+from swh.storage.cassandra.common import Row
+from swh.storage.cassandra import converters
+
+from swh.model.hashutil import DEFAULT_ALGORITHMS
+
+
+def test_row_to_content_hashes():
+    for row in [Row(
+            sha1=b'4\x972t\xcc\xefj\xb4\xdf\xaa\xf8e\x99y/\xa9\xc3\xfeF\x89',
+            sha1_git=b'\xd8\x1c\xc0q\x0e\xb6\xcf\x9e\xfd[\x92\n\x84S\xe1\xe0qW\xb6\xcd',  # noqa
+            sha256=b'g6P\xf96\xcb;\n/\x93\xce\t\xd8\x1b\xe1\x07H\xb1\xb2\x03\xc1\x9e\x81v\xb4\xee\xfc\x19d\xa0\xcf:',  # noqa
+            blake2s256=b"\xd5\xfe\x199We'\xe4,\xfdv\xa9EZ$2\xfe\x7fVf\x95dW}\xd9<B\x80\xe7mf\x1d",  # noqa
+    ),
+                Row(
+                    sha1=b'4\x972t\xcc\xefj\xb4\xdf\xaa\xf8e\x99y/\xa9\xc3\xfeF\x89',  # noqa
+                    sha1_git=b'\xd8\x1c\xc0q\x0e\xb6\xcf\x9e\xfd[\x92\n\x84S\xe1\xe0qW\xb6\xcd',  # noqa
+                    sha256=b'h6P\xf96\xcb;\n/\x93\xce\t\xd8\x1b\xe1\x07H\xb1\xb2\x03\xc1\x9e\x81v\xb4\xee\xfc\x19d\xa0\xcf:',  # noqa
+                    blake2s256=b"\xd5\xfe\x199We'\xe4,\xfdv\xa9EZ$2\xfe\x7fVf\x95dW}\xd9<B\x80\xe7mf\x1d",  # noqa
+                ),
+    ]:
+        actual_hashes = converters.row_to_content_hashes(row)
+
+        assert len(actual_hashes) == len(DEFAULT_ALGORITHMS)
+        for algo in DEFAULT_ALGORITHMS:
+            assert actual_hashes[algo] == getattr(row, algo)

It complains about tuple (Row is a type alias for tuple) that cannot have named fields.
Somehow, in the current execution context, the cassandra Row in question is more than a tuple, it seems:

context:

$ pytest -x -s -k test_content_add_collision
(Pdb++) pks[0]
Row(sha1=b'4\x972t\xcc\xefj\xb4\xdf\xaa\xf8e\x99y/\xa9\xc3\xfeF\x89', sha1_git=b'\xd8\x1c\xc0q\x0e\xb6\xcf\x9e\xfd[\x92\n\x84S\xe1\xe0qW\xb6\xcd', sha256=b'g6P\xf96\xcb;\n/\x93\xce\t\xd8\x1b\xe1\x07H\xb1\xb2\x03\xc1\x9e\x81v\xb4\xee\xfc\x19d\xa0\xcf:', blake2s256=b"\xd5\xfe\x199We'\xe4,\xfdv\xa9EZ$2\xfe\x7fVf\x95dW}\xd9<B\x80\xe7mf\x1d")
(Pdb++) r = pks[0]
(Pdb++) from swh.storage.cassandra.common import Row
(Pdb++) isinstance(r, Row)
True
(Pdb++) r.__class__
<class 'cassandra.io.libevreactor.Row'>

so i don't know how to actually test this...

olasd added inline comments.Mar 9 2020, 4:16 PM

swh/storage/cassandra/converters.py
75	The `Row` objects returned by cassandra-driver are namedtuples generated on the fly; I guess `swh.storage.cassandra.common`'s `Row = tuple` is just a typechecking helper. For your tests, I guess you'll want to create a new namedtuple class with the proper attributes.
swh/storage/cassandra/storage.py
92–102	Of course, I just noticed it while reviewing this code.

vlorentz added inline comments.Mar 9 2020, 4:17 PM

swh/storage/cassandra/converters.py
75	Correct. I recomment `row._asdict()`, I already use it everywhere.

Add coverage on extra conversion step

ardumont added inline comments.Mar 9 2020, 4:39 PM

swh/storage/cassandra/converters.py
75	That works but that does not typecheck... swh/storage/cassandra/converters.py:73: error: "Tuple[Any, ...]" has no attribute "_asdict" so i'll keep that version.