feat: add multi_get() for batch point reads

[polaz]

Summary

• Add multi_get() to AbstractTree trait for batch point reads
• Default implementation calls get() in a loop; Tree and BlobTree provide optimized versions
• BlobTree extracts a resolve_key helper for shared blob resolution logic
• Accepts unsorted keys — callers don't need to pre-sort

Test plan

• New integration test multi_get covering basic retrieval, snapshot isolation, missing keys, unsorted input
• All existing tests pass
• Full cargo test --all-features green

Closes #96

Supersedes #264 (clean rebased branch — sorry about the mess in that one).

Summary by CodeRabbit

• New Features

  • Added a batch retrieval API to fetch multiple keys in one call, preserving input order and duplicates, and providing consistent snapshot isolation across tree structures.

• Tests

  • Added thorough tests covering ordered/missing/duplicate keys, snapshot visibility across versions, tombstone handling, on-disk persistence, large-value (blob) indirection, and empty-input behavior.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro

Run ID: c6bc7b24-8df4-47c8-95db-e53ba21db278

📥 Commits

Reviewing files that changed from the base of the PR and between 3acf517 and bae6679.

📒 Files selected for processing (1)

• src/abstract_tree.rs

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📝 Walkthrough

Walkthrough

Adds a batch-read API multi_get to AbstractTree and implements it for Tree and BlobTree, performing snapshot-consistent retrieval of multiple keys (preserving input order and duplicates). Includes comprehensive tests exercising memtable, disk, tombstones, snapshots, blobs, and duplicate/empty inputs.

Changes

Cohort / File(s)	Summary
Trait Definition src/abstract_tree.rs	Adds fn multi_get<K: AsRef<[u8]>>(&self, keys: impl IntoIterator<Item = K>, seqno: SeqNo) -> crate::Result<Vec<Option<UserValue>>>; to AbstractTree with a default implementation delegating to get per key.
Tree Implementation src/tree/mod.rs	Implements multi_get for Tree: obtains a snapshot/version for seqno, iterates keys, looks up internal entries per-version, maps to UserValue, and returns results in input order.
BlobTree Implementation src/blob_tree/mod.rs	Implements multi_get for BlobTree, refactors get to use a new resolve_key helper that resolves a key against a SuperVersion, and implements multi_get by calling resolve_key for each input key.
Tests tests/multi_get.rs	Adds tests covering: basic batch reads, mixed present/missing keys, empty input, snapshot isolation, tombstones, reads from disk+memtable, blob KV separation, and unsorted/duplicate-key behavior.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'feat: add multi_get() for batch point reads' clearly and concisely summarizes the primary change: adding a multi_get method for batch operations.
Linked Issues check	✅ Passed	The PR successfully implements the batch point-read API requested in issue #96, with multi_get accepting keys and returning Vec<Option> with snapshot isolation support, matching the core requirements.
Out of Scope Changes check	✅ Passed	All changes directly support the multi_get feature: trait definition, implementations for Tree and BlobTree, helper refactoring, and comprehensive test coverage. No unrelated modifications detected.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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📝 Coding Plan

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[Copilot]

Pull request overview

Adds a new batch point-read API (multi_get) to the AbstractTree interface, with optimized implementations for Tree and BlobTree, plus integration tests to validate snapshot semantics and mixed-key behavior.

Changes:

• Added AbstractTree::multi_get() with a default implementation that delegates to get() per key.
• Implemented optimized multi_get() for Tree and BlobTree using a single snapshot (SuperVersion) per call.
• Added an integration test suite covering existing/missing keys, tombstones, disk vs memtable, snapshot isolation, and unsorted/duplicate inputs.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
tests/multi_get.rs	New integration tests validating multi_get correctness across key mixes, snapshots, tombstones, disk/memtable, and kv-separation.
src/tree/mod.rs	Adds a Tree override of multi_get that reads from a single snapshot for all keys.
src/blob_tree/mod.rs	Extracts a shared resolve_key helper and adds a BlobTree override of multi_get using a single snapshot.
src/abstract_tree.rs	Introduces the multi_get API and documents snapshot/locking behavior and a usage example.

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[Copilot]

Pull request overview

Adds a multi_get() batch point-read API to the AbstractTree trait, with optimized implementations for Tree and BlobTree, plus integration coverage to validate ordering/duplicates and MVCC snapshot semantics.

Changes:

• Added AbstractTree::multi_get() with a default implementation and documented output contract (order/length/duplicates).
• Implemented optimized multi_get() for Tree (single snapshot acquisition) and BlobTree (single snapshot + shared resolve_key helper).
• Added tests/multi_get.rs integration tests covering existing/missing keys, empty input, snapshot isolation, tombstones, disk+memtable, blob separation, and unsorted/duplicate keys.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
tests/multi_get.rs	New integration tests validating multi_get() behavior across storage layers and MVCC semantics.
src/tree/mod.rs	Adds an optimized Tree::multi_get() using a single snapshot version.
src/blob_tree/mod.rs	Refactors blob resolution into resolve_key() and adds BlobTree::multi_get() using a single snapshot.
src/abstract_tree.rs	Adds the multi_get() API with default behavior and documented output contract + example.

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[codecov]

Codecov Report

❌ Patch coverage is 86.66667% with 8 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/abstract_tree.rs	61.11%	7 Missing ⚠️
src/blob_tree/mod.rs	96.55%	1 Missing ⚠️

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