feat(connectors): Clickhouse Sink Connector

[kriti-sc]

Which issue does this PR close?

Closes #2539

Rationale

Clickhouse is a real-time data analytics engine, and very popular in modern analytics architectures.

What changed?

This PR introduces a Clickhouse Sink Connector that enables writing data from Iggy to Clickhouse.

The Clickhouse writing logic is heavily inspired by the official Clickhouse Kafka Connector.

Local Execution

• Produced messages 30456 + 29060 rows with schema user_id: String, user_type: u8, email: String, source: String, state: String, created_at: DateTime, message: String using sample data producer.
• Consumed messages using the Clickhouse sink and into the particular Clickhouse table.
• Verified schema and number of rows in Clickhouse.
• Added unit tests and e2e tests, both passing.

Images 1&2: Produced 30456 + 29060 rows into Iggy in two batches
Image 3: Verified schema and number of rows in Clickhouse

AI Usage

1. Which tools? (e.g., GitHub Copilot, Claude, ChatGPT) Claude Code
2. Scope of usage? (e.g., autocomplete, generated functions, entire implementation) generated functions
3. How did you verify the generated code works correctly? Manual testing by producing data into Iggy and then running the sink and verifying insertion into Clickhouse, unit tests and e2e tests for different Clickhouse insert configurations.
4. Can you explain every line of the code if asked? Yes

[codecov]

Codecov Report

❌ Patch coverage is 79.47903% with 323 lines in your changes missing coverage. Please review.
✅ Project coverage is 68.54%. Comparing base (ecd7709) to head (fc34e4d).

Files with missing lines	Patch %	Lines
...ore/connectors/sinks/clickhouse_sink/src/binary.rs	79.30%	102 Missing and 46 partials ⚠️
...ore/connectors/sinks/clickhouse_sink/src/schema.rs	76.73%	22 Missing and 65 partials ⚠️
...ore/connectors/sinks/clickhouse_sink/src/client.rs	63.53%	55 Missing and 11 partials ⚠️
core/connectors/sinks/clickhouse_sink/src/body.rs	91.66%	12 Missing and 1 partial ⚠️
core/connectors/sinks/clickhouse_sink/src/lib.rs	96.37%	3 Missing and 2 partials ⚠️
core/connectors/sinks/clickhouse_sink/src/sink.rs	60.00%	4 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #2886      +/-   ##
============================================
+ Coverage     68.36%   68.54%   +0.18%     
  Complexity      739      739              
============================================
  Files          1053     1059       +6     
  Lines         84763    86337    +1574     
  Branches      61297    62879    +1582     
============================================
+ Hits          57948    59183    +1235     
- Misses        24448    24649     +201     
- Partials       2367     2505     +138     

Flag	Coverage Δ
csharp	67.43% <ø> (-0.19%)	⬇️
go	6.27% <ø> (ø)
java	54.83% <ø> (ø)
node	92.18% <ø> (-0.23%)	⬇️
python	81.57% <ø> (ø)
rust	70.30% <79.47%> (+0.24%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
core/connectors/sinks/clickhouse_sink/src/sink.rs	60.00% <60.00%> (ø)
core/connectors/sinks/clickhouse_sink/src/lib.rs	96.37% <96.37%> (ø)
core/connectors/sinks/clickhouse_sink/src/body.rs	91.66% <91.66%> (ø)
...ore/connectors/sinks/clickhouse_sink/src/client.rs	63.53% <63.53%> (ø)
...ore/connectors/sinks/clickhouse_sink/src/schema.rs	76.73% <76.73%> (ø)
...ore/connectors/sinks/clickhouse_sink/src/binary.rs	79.30% <79.30%> (ø)

... and 17 files with indirect coverage changes

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[abonander]

Would you mind explaining the reasoning to choose a bespoke implementation here over using the official Rust client? It uses HTTP and RowBinary serialization by default, so it's not clear what's being gained here.

[kriti-sc]

The official client is not suitable for use with Iggy because it requires the target table schema to be defined at compile time using statically typed Rust structs. In contrast, Iggy connectors expect the schema to be provided dynamically via configuration.

Even if the ClickHouse client were used, a dynamic encoder would still need to be implemented to convert runtime data into the required binary format. In that case, the client would only simplify some HTTP request handling while leaving the core complexity unresolved.

Supporting the binary ingestion format is important because it provides the best ingestion performance in ClickHouse.

Let me know if this addresses your question, or if there are other considerations I may have overlooked.