Optimize seek

[eatbreads]

Here are some reminders before you submit the pull request

• Add tests for the change
• Document changes
• Reference the link of issue using fixes eloqdb/eloqstore#issue_id
• Reference the link of RFC if exists
• Pass ctest --test-dir build/tests/

Summary by CodeRabbit

• Performance Improvements
  • Optimized internal buffer management with reduced memory allocations for improved efficiency.

_{✏️ Tip: You can customize this high-level summary in your review settings.}

[coderabbitai]

Walkthrough

The changes optimize the IndexPageIter class by introducing a private member variable prev_key_ to track the previous key and refactoring buffer operations from dynamic append patterns to pre-allocated memcpy operations, reducing allocations and improving performance.

Changes

Cohort / File(s)	Summary
Header declaration include/storage/mem_index_page.h	Added private member prev_key_ (std::string) to IndexPageIter class for tracking previous key state during iteration.
Implementation optimizations src/storage/mem_index_page.cpp	Added <cstring> include; modified constructors to reserve buffer capacity for key_ and prev_key_; refactored key assembly and PeekNextKey to use memcpy into pre-allocated buffers instead of append operations; replaced local prev_key string usage with member prev_key_ for improved state management.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐰 A buffer hops with newfound grace,
No more appends, memcpy takes their place!
With prev_key_ to mark the way,
Keys march faster, day by day! ✨

🚥 Pre-merge checks | ❌ 3

❌ Failed checks (2 warnings, 1 inconclusive)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The PR description only contains an unchecked checklist template without any actual description of the changes, rationale, or implementation details.	Add a description explaining the optimization strategy (memcpy usage, buffer pre-allocation), why these changes improve performance, and which issues/RFCs this addresses.
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.
Title check	❓ Inconclusive	The title 'Optimize seek' is vague and generic, using a broad performance term without specifying what aspect of the seek operation is being optimized.	Provide a more specific title that describes the optimization approach, such as 'Use memcpy and buffer reservation in seek operations' or 'Reduce allocations in IndexPageIter seek paths'.

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch Optimize_seek

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