fix: protobuf: serde: exception bypass for canonical repeated nested

[hileef]

Disclaimer

• I have very little CPP experience, please feel free to make any and all constructive feedback to improve this proposal
• I picked the "bugfix" category because I interpret the extraneous entries in system.errors when processing a "canonical"/"valid" proto/schema to be incorrect behaviour. Please correct it if necessary.

On Semantics

The current potobuf serde implementation will always internally generate PROTOBUF_FIELD_NOT_REPEATED
when de/serializing such a canonical example :

syntax = "proto3";

message A {
  repeated B v = 20;
  message B {
    uint32 x = 21;
    uint32 y = 22;
  }
}

CREATE TABLE example (
    `v.x` Array(UInt32),
    `v.y` Array(UInt32)
)

↘️ This PR essentially proposes to change the control flow a bit, such that :

WHEN the proto field we are mapping into is repeated ,
AND when the matching columns are nested and of type Array,
THEN we attempt to serialize via ProtobufSerializerFlattenedNestedAsArrayOfNestedMessages first,
RATHER THAN first going through the try/catch, throwing PROTOBUF_FIELD_NOT_REPEATED and catching it.

In the case where I am missing some use case and/or possible situtation where this control flow would be faulty,
please do comment / let me know, ideally with example proto/sql such that it can be turned into a new test and the implementation adapted 🙏

On Performance

I discovered this behaviour when investigating the performance of a cluster a colleage was running benchmarks on, where he would be consuming complex protobuf messages with the Kafka engine. Since clickhouse currently does not appear to re-use the generated de/serializer impl ( according to #59482 ), I realized that this try/catch flow behaviour was tanking performance, with a huge amount of CPU time spent in libunwind. Incidentally, we were generating millions of PROTOBUF_FIELD_NOT_REPEATED in the system.errors table.

CC

• @vincentbernat per PROTOBUF_FIELD_NOT_REPEATED when ingesting from Kafka #41971
• @filimonov per Kafka Engine improvements RFC #65297
• @jkuklis for helping me with my junior cpp level

---

Changelog category (leave one):

• Bug Fix (user-visible misbehavior in an official stable release)

Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):

Bypass try/catch flow when de/serializing nested repeated protobuf to nested columns ( fixes #41971 )

Documentation entry for user-facing changes

• Documentation is written (mandatory for new features)

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---

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---

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---

• Do not test
• Woolen Wolfdog
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[hileef]

This specific change is not required per se, but it arguably brings all relevant code paths into the diff.
If it may help the review, we can get rid of that 🙏

[robot-ch-test-poll3]

This is an automated comment for commit 167196b with description of existing statuses. It's updated for the latest CI running

❌ Click here to open a full report in a separate page

Check name	Description	Status
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Bugfix validation	Checks that either a new test (functional or integration) or there some changed tests that fail with the binary built on master branch	❌ failure
Stateless tests	Runs stateless functional tests for ClickHouse binaries built in various configurations -- release, debug, with sanitizers, etc	❌ failure

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[Avogar]

Hi! Thank you for the PR, I will take a look at the code. Can you please fix style check first?
It complains that file 03234_proto_simple_nested_repeated_noexception.reference is executable (reference files should be just text files) and style issue in file ProtobufSerializer.cpp:3366 (no space after for)

[hileef]

Hello @Avogar , I'll get on that as soon as possible ( a bit later today ) 👍 Thank you for the help 🙂

[hileef]

After fixing the style issues, I took the liberty of slightly adapting the added tests in order to properly work with the testing system ( format_schemas dir not automatically present , no formats in fasttest , use correct test DB ). If these changes are incorrect, please let me know.

At this point, the tests added in this PR do appear to work, however I'm not sure why the remaining CI checks fail.
I am looking forward to help on the topic 🙂 🙏

[hileef]

I attempted the test 02490_benchmark_max_consecutive_errors ( from this CI run ) on my local build of this branch,
and the test appeared to pass .... maybe this could be related to differences between the CI and my local setup ? 🤔

In any case, the other test failures appear related to timeouts, so I'd be very interested in possibly relaunching the CI jobs that failed to check if they fail again 🙏

[Avogar]

02490_benchmark_max_consecutive_errors test failure is not related to the chagnes, this test is flaky: https://play.clickhouse.com/play?user=play#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
I will create a separate issue for it, don't worry about this test

[hileef]

Alright ! Thanks for letting me know and for the exploration URL, I didn't know this was publicly available 🙂

Looking forward to hearing from you again once you've had an opportunity to review the code and/or
if you have some additional remarks on the other CI checks 🙏

[Avogar]

Looks good, thank you!