Query paginated metrics efficiently

[mcserep]

Paginated metric querying introduced in #784 uses LIMIT + OFFSET SQL closures to select the appropriate AST Node IDs or File IDs.
However DISTINCT is also applied on the projected IDs, therefore the OFFSET does not provide any performance benefit: the database engine still needs to process (deduplicate) all offseted elements.

This PR introduces a new approach: Keyset Pagination (a.k.a. Seek Method); where instead of using OFFSET, we use a last / previous ID to start querying records "after" that.

[Copilot]

Pull Request Overview

This PR refactors paginated metric querying from traditional LIMIT + OFFSET pagination to keyset pagination (seek method) for improved performance. The change eliminates the inefficiency where OFFSET doesn't provide benefits when DISTINCT is applied, as the database still needs to process all offset elements for deduplication.

• Replaces pageNumber_ parameters with previousId_ parameters in paginated query methods
• Implements new pageAstNodeMetrics and pageFileMetrics functions using keyset pagination
• Removes the generic template-based pageMetrics function in favor of specific implementations

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 5 comments.

File	Description
cppmetricsservice.cpp	Implements keyset pagination logic and replaces template-based pagination with specific methods
cppmetricsservice.h	Updates method signatures and removes template-based pagination declaration
cxxmetrics.thrift	Updates service interface to use previousId instead of pageNumber parameters

[Copilot]

The std::stoull function can throw std::invalid_argument or std::out_of_range exceptions when the string cannot be converted to an unsigned long long. Consider adding proper error handling or validation for the previousId_ parameter.

[Copilot]

The std::stoull function can throw std::invalid_argument or std::out_of_range exceptions when the string cannot be converted to an unsigned long long. Consider adding proper error handling or validation for the previousId_ parameter.

[Copilot]

The std::stoull function can throw std::invalid_argument or std::out_of_range exceptions when the string cannot be converted to an unsigned long long. Consider adding proper error handling or validation for the previousId_ parameter.

Suggested change

	std::vector<model::FileId> paged_files = pageFileMetrics(
	path_, pageSize_, previousId_.empty() ? 0 : std::stoull(previousId_));
	std::uint64_t previousIdValue = 0;
	if (!previousId_.empty()) {
	try {
	previousIdValue = std::stoull(previousId_);
	} catch (const std::invalid_argument& e) {
	core::InvalidInput ex;
	ex.__set_msg("Invalid previousId_: " + previousId_ + ". Must be a numeric value.");
	throw ex;
	} catch (const std::out_of_range& e) {
	core::InvalidInput ex;
	ex.__set_msg("Invalid previousId_: " + previousId_ + ". Value out of range.");
	throw ex;
	}
	}
	std::vector<model::FileId> paged_files = pageFileMetrics(path_, pageSize_, previousIdValue);

[Copilot]

Pre-sizing the vector with paged_nodes.size() may not be accurate since the result set size might differ from the allocated size. Consider using reserve() instead of sizing the constructor, or use emplace_back() in the transform operation.

[Copilot]

Pre-sizing the vector with paged_nodes.size() may not be accurate since the result set size might differ from the allocated size. Consider using reserve() instead of sizing the constructor, or use emplace_back() in the transform operation.

Suggested change

	std::vector<model::FileId> paged_ids(paged_nodes.size());
	std::transform(paged_nodes.begin(), paged_nodes.end(), paged_ids.begin(),
	[](const model::CppModuleMetricsDistinctView& e){
	return e.fileId;
	});
	std::vector<model::FileId> paged_ids;
	paged_ids.reserve(paged_nodes.size());
	for (const auto& e : paged_nodes) {
	paged_ids.emplace_back(e.fileId);
	}

[mcserep]

CI only failed for SQLite due to #803.