C++ Coding

Language

C++20. Prefer standard library over custom implementations when appropriate.

Naming conventions

Proton fences

/// proton: starts
if (isStreamingQuery()) { handleStreamingPath(); }
/// proton: ends

• Use ONLY in ClickHouse-inherited code (upstream-synced files)
• NEVER fence in src/Storages/Stream/ or namespace DB::Streaming
• NEVER nest fences

IProcessor pattern (streaming transforms)

All streaming transforms in src/Processors/Transforms/Streaming/ follow:

class MyTransform : public IProcessor {
    Status prepare() override;  // O(1), non-blocking, check readiness
    void work() override;       // Do actual processing
};

Stateful processors MUST also implement:

• hasState() → return true
• checkpoint(CheckpointContextPtr) → serialize state
• recover(CheckpointContextPtr) → restore from checkpoint

Formatting

Only formats changed code blocks (not entire files). Uses .clang-format config at repo root. The configured brace style is Allman-like: opening braces normally go on a new line.

git clang-format              # format unstaged changes in-place
git clang-format --staged     # format staged changes in-place
git clang-format --diff       # dry-run: show what would change
git clang-format <commit>     # format changes since <commit>

Comments

Use ///. Explain why, not what:

/// Use 10 seconds to allow late events
watermark_delay = 10;