[Store] Skip BatchQuery when offloading_objects is empty (#2138)

[io-wy]

Fixes #2138

When no objects need offloading (steady state without eviction), OffloadObjects() still built an empty bucket and called BatchQuerySegmentSlices with an empty keys vector. BatchQuery() returned an empty result, triggering an INVALID_REPLICA error log that confused operators.

Root cause

In the non-BucketStorageBackend path:

std::vector<std::string> keys;
keys.reserve(offloading_objects.size());  // 0 when empty
buckets_keys.emplace_back(std::move(keys)); // buckets_keys = { {} }

The empty bucket is then iterated, and BatchQuerySegmentSlices([]) returns INVALID_REPLICA because BatchQuery([]) yields an empty result vector.

Fix

Early-return from OffloadObjects when the input map is empty, avoiding the unnecessary query and log noise.

if (offloading_objects.empty()) return {};

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds a fast-path in FileStorage::OffloadObjects to skip bucketization/backend work when there’s nothing to offload.

Changes:

• Return early from OffloadObjects when offloading_objects is empty.

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[gemini-code-assist]

Code Review

This pull request introduces an early return in the FileStorage::OffloadObjects function when the offloading_objects map is empty, preventing unnecessary processing. As there were no review comments provided for this change, I have no feedback to provide.

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
mooncake-store/src/file_storage.cpp	0.00%	1 Missing ⚠️

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[LujhCoconut]

Thanks for this fix. Your approach is correct. However, this issue has already been fixed in PR #2151.