feat(pyramid): move topk_factor to IndexSearchParameter base class

[inabao]

• Extract topk_factor from HGraphSearchParameters and IVFSearchParameters
• Add topk_factor to IndexSearchParameter for inheritance by all search parameters
• Implement topk_factor support in Pyramid search to control reorder ratio
• When topk_factor > 1.0, reorder_limit = limit * topk_factor

[gemini-code-assist]

Summary of Changes

Hello @inabao, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request refactors the topk_factor parameter by moving it to a common base class, IndexSearchParameter, making it accessible to all search algorithms. This change streamlines parameter management and enhances the flexibility of search configurations. Additionally, the Pyramid search implementation has been updated to leverage this centralized topk_factor for more precise control over the reordering process, ensuring that the reorder ratio is applied consistently.

Highlights

• Refactoring topk_factor: The topk_factor parameter has been extracted from HGraphSearchParameters and IVFSearchParameters to promote code reuse and a more unified parameter handling.
• Centralized topk_factor in IndexSearchParameter: The topk_factor member and its JSON parsing logic have been moved to the base class IndexSearchParameter, allowing all derived search parameter classes to inherit and utilize it.
• Pyramid Search Reorder Control: The Pyramid search algorithm now explicitly uses the topk_factor to determine the reorder_limit, controlling the number of candidates passed to the reordering step based on the search limit.

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Changelog

• src/algorithm/hgraph_parameter.cpp
  • Removed topk_factor parsing logic from FromJson method.
• src/algorithm/hgraph_parameter.h
  • Removed topk_factor member variable.
• src/algorithm/index_search_parameter.h
  • Added topk_factor member variable with a default value.
  • Implemented parsing of SEARCH_PARAM_FACTOR into topk_factor within the constructor.
• src/algorithm/ivf_parameter.cpp
  • Removed topk_factor parsing logic from FromJson method.
• src/algorithm/ivf_parameter.h
  • Removed topk_factor member variable.
• src/algorithm/pyramid.cpp
  • Modified KnnSearch and RangeSearch to pass parsed_param.topk_factor to search_impl.
  • Updated search_impl signature to accept topk_factor.
  • Implemented logic within search_impl to calculate reorder_limit using topk_factor before calling the reorder function.
• src/algorithm/pyramid.h
  • Updated the declaration of search_impl to include a topk_factor parameter with a default value.

Activity

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[gemini-code-assist]

Code Review

This pull request refactors the topk_factor search parameter by moving it from HGraphSearchParameters and IVFSearchParameters to the base class IndexSearchParameter. This is a good improvement for code reuse. The topk_factor is also newly implemented in Pyramid search to control the reordering ratio. My review has identified a potential precision issue in the calculation of reorder_limit in pyramid.cpp and an unintended change in the default value of topk_factor for IVFSearchParameters which could alter search behavior.

[gemini-code-assist]

By removing topk_factor from IVFSearchParameters, it will now inherit this member from IndexSearchParameter, where its default value is 0.0F. Previously, the default value here was 2.0F. This change in the default value could alter the behavior for users of IVF who were relying on the default reordering factor, potentially affecting search quality.

If IVF search parameters should retain the default topk_factor of 2.0F, you could set it in the IVFSearchParameters constructor. Since the constructor is not in the diff, here is an example of how you could modify it:

// in src/algorithm/ivf_parameter.h
private:
    IVFSearchParameters() {
        topk_factor = 2.0F;
    }

[gemini-code-assist]

When calculating reorder_limit, you're casting limit (which is an int64_t) to a float. A float has limited precision and may not accurately represent large int64_t values (it can only represent all integers exactly up to 2^24). In RangeSearch, limit can be very large, potentially leading to precision loss during the cast and an incorrect reorder_limit.

To avoid this, it's safer to perform the calculation using double, which has much higher precision.

Suggested change

	reorder_limit = static_cast<int64_t>(static_cast<float>(limit) * topk_factor);
	reorder_limit = static_cast<int64_t>(static_cast<double>(limit) * topk_factor);

[codecov]

Codecov Report

❌ Patch coverage is 71.42857% with 2 lines in your changes missing coverage. Please review.

❌ Your patch status has failed because the patch coverage (71.42%) is below the target coverage (80.00%). You can increase the patch coverage or adjust the target coverage.

@@            Coverage Diff             @@
##             main    #1605      +/-   ##
==========================================
+ Coverage   90.76%   90.95%   +0.19%     
==========================================
  Files         329      329              
  Lines       19477    19480       +3     
==========================================
+ Hits        17679    17719      +40     
+ Misses       1798     1761      -37     

Flag	Coverage Δ
cpp	90.95% <71.42%> (+0.19%)	⬆️

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Components	Coverage Δ
common	85.81% <ø> (ø)
datacell	92.20% <ø> (+0.51%)	⬆️
index	90.68% <71.42%> (+0.30%)	⬆️
simd	100.00% <ø> (ø)

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[wxyucs]

lgtm