Add key-only ScanKeys interface #226
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Summary of Changes
Hello @bootjp, 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 introduces a new capability to efficiently scan and retrieve only keys from the data stores. By providing a ScanKeys interface, consumers can now perform key-only lookups, which can be more performant for scenarios where the associated values are not needed, reducing data transfer and processing overhead.
Highlights
- New ScanKeys Interface: Introduced a new ScanKeys method to the ScanStore and ScanTxn interfaces, allowing for efficient retrieval of only keys within a specified range, without fetching associated values.
- BoltDB Implementation: Implemented the ScanKeys method for the boltStore, leveraging BoltDB's cursor functionality to iterate and collect keys.
- In-Memory Store Implementation: Implemented the ScanKeys method for the rbMemoryStore (Red-Black Tree based in-memory store), iterating through its elements to collect keys.
- Comprehensive Testing: Added dedicated unit tests (TestBoltStore_ScanKeys and TestRbMemoryStore_ScanKeys) to verify the correct functionality and behavior of the new ScanKeys method across both BoltDB and in-memory store implementations.
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Code Review
This pull request introduces a ScanKeys method to the ScanStore and ScanTxn interfaces, providing an optimized way to scan only keys. The implementations for boltStore and rbMemoryStore are included, along with tests. My review found critical correctness issues in both implementations where internal or temporary byte slices for keys are returned without being copied. This could lead to data corruption or crashes. Additionally, the rbMemoryStore implementation has a significant performance issue in its scanning logic. I've provided detailed comments on these points.
| func (s *rbMemoryStore) ScanKeys(ctx context.Context, start []byte, end []byte, limit int) ([][]byte, error) { | ||
| s.mtx.RLock() | ||
| defer s.mtx.RUnlock() | ||
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| var result [][]byte | ||
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| s.tree.Each(func(key interface{}, _ interface{}) { | ||
| k, ok := key.([]byte) | ||
| if !ok { | ||
| return | ||
| } | ||
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| if start != nil && bytes.Compare(k, start) < 0 { | ||
| return | ||
| } | ||
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| if end != nil && bytes.Compare(k, end) > 0 { | ||
| return | ||
| } | ||
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| if len(result) >= limit { | ||
| return | ||
| } | ||
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| result = append(result, k) | ||
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| }) | ||
| return result, nil | ||
| } |
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This implementation has two major issues:
- Correctness (Critical): It returns direct references to the key slices stored in the tree (
result = append(result, k)). This breaks encapsulation, as a caller could modify the returned slice and corrupt the internal state of thetreemap, leading to unpredictable behavior. - Performance (High): It uses
s.tree.Eachwhich iterates over all elements in the store, regardless of the scan range or limit. This is very inefficient for range scans on large datasets. Theif len(result) >= limitcheck does not stop the iteration early; it only prevents appending more items.
You should refactor this to use a treemap.Iterator to scan the range efficiently, and ensure you return copies of the keys to maintain encapsulation.
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Summary
Testing
go test ./...go test ./store -count=1https://chatgpt.com/codex/tasks/task_e_68b1f4c9eac48324a0ba6eb42c4c270b