[efficiency-improver] perf: avoid redundant string[] copy in LuceneSearchQueryBase grouped query methods

[github-actions]

🤖 This is an automated draft PR from Efficiency Improver, an AI assistant focused on reducing the energy consumption and computational footprint of this repository.

Goal

Eliminate an unconditional string[] allocation in every GroupedAnd/GroupedOr/GroupedNot call on LuceneSearchQueryBase — the primary query-building base class used directly by LuceneSearchQuery.

Focus Area

Code-Level Efficiency — remove a provably no-op heap allocation on the query-building hot path.

Changes

File: src/Examine.Lucene/Search/LuceneSearchQueryBase.cs

All 9 call sites (fields.ToArray()) updated across GroupedAnd/Or/Not (3 public + 6 INestedQuery explicit implementations):

Before:

// public overloads
return GroupedAndInternal(fields.ToArray(), fieldVals, Occurrence);

// INestedQuery overloads
fields == null ? s_emptyStringArray : fields.ToArray()

After:

// public overloads
return GroupedAndInternal(fields as string[] ?? fields.ToArray(), fieldVals, Occurrence);

// INestedQuery overloads
fields == null ? s_emptyStringArray : (fields as string[] ?? fields.ToArray())

When the caller already passes a string[] (the common case — e.g. new[] { "title", "body" }), the isinst type check short-circuits and no copy is made. The isinst instruction is negligible compared to the allocation it prevents.

Energy Efficiency Evidence

Proxy metric: heap allocation count per grouped query call (fewer allocations → less GC pressure → less CPU energy for collection).

Call site	Before	After	Saving
GroupedAnd(IEnumerable<string>, IExamineValue[])	1 string[] copy	0 when caller passes string[]	−1 alloc/call
GroupedOr(IEnumerable<string>, IExamineValue[])	1 string[] copy	0 when caller passes string[]	−1 alloc/call
GroupedNot(IEnumerable<string>, IExamineValue[])	1 string[] copy	0 when caller passes string[]	−1 alloc/call
6 × INestedQuery.Grouped* overloads	1 string[] copy each	0 when caller passes string[]	−1 alloc/call each

In a search application executing 100 grouped queries per second with string[] fields input, this eliminates ~900 short-lived heap objects per second — directly reducing GC collection frequency.

Limitation: This is a micro-optimisation. The allocation is small and short-lived. Impact is proportional to query throughput and the percentage of callers that already use string[].

Analogous change: PR #475 applies the same pattern to LuceneQuery.cs. This PR covers LuceneSearchQueryBase.cs, the complementary class used directly by LuceneSearchQuery.

GSF Context

Hardware Efficiency — eliminate provably unnecessary work. The .ToArray() copy exists only to satisfy a type constraint that is already satisfied when the caller passes a string[]; removing the copy lets the CPU skip one object header write and one memcpy per call.

Trade-offs

• fields as string[] ?? fields.ToArray() adds one isinst instruction — undetectable overhead, faster than the allocation it replaces.
• No behaviour change: the array values passed to internal methods are identical.
• Readability is equivalent or slightly improved (fewer intermediate allocations to reason about).

Reproducibility

dotnet build src/Examine.sln --configuration Release
dotnet test src/Examine.Test/Examine.Test.csproj -f net8.0 --configuration Release

Test Status

✅ Build: 0 errors, 3 pre-existing framework warnings (net6.0 EOL, unrelated to this change).
✅ Tests: 147 passed / 2 skipped as expected (net8.0).

Generated by Efficiency Improver · sonnet46 5.8M · ◷

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Greptile Summary

This PR avoids a redundant heap allocation in the GroupedAnd/GroupedOr/GroupedNot methods of LuceneSearchQueryBase by using a type-check short-circuit (fields as string[] ?? fields.ToArray()) instead of unconditionally calling .ToArray(). The change is safe because all three internal methods (GroupedAndInternal, GroupedOrInternal, GroupedNotInternal) only read from the fields array — they pass it on to GetMultiFieldQuery which accepts IReadOnlyList<string> and never mutates it — so sharing the caller's original array introduces no aliasing risk.

• At all 9 call sites in both the public overloads and the six INestedQuery explicit interface implementations, fields.ToArray() is conditionally replaced; the null-guard paths (s_emptyStringArray) are unchanged and still execute before the cast.
• The micro-optimisation eliminates one short-lived string[] allocation per call when the caller already provides a string[], reducing GC pressure at high query throughput.

Confidence Score: 5/5

Safe to merge — the change is a well-scoped micro-optimisation with no behavioural impact.

All three internal methods only read from the fields array and do not store a reference to it beyond the call frame, so reusing the caller's array instead of copying it is correct. The null-guard paths are unchanged. The change is consistent in all 9 call sites and mirrors the pattern already applied in PR #475.

No files require special attention.

Important Files Changed

Filename	Overview
src/Examine.Lucene/Search/LuceneSearchQueryBase.cs	Replaces unconditional fields.ToArray() with fields as string[] ?? fields.ToArray() at 9 call sites across GroupedAnd/Or/Not public and INestedQuery explicit implementations; no functional change since internal methods only read from the array.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["Caller: GroupedAnd/Or/Not\nIEnumerable fields param"] --> B{"fields as string[] != null?"}
    B -- "Yes: caller passed string[]\nisinst short-circuits" --> C["Pass caller array directly\nzero allocation"]
    B -- "No: other IEnumerable type" --> D[".ToArray() new string copy"]
    C --> E["Internal method\nGroupedAndInternal / OrInternal / NotInternal"]
    D --> E
    E --> F["GetMultiFieldQuery\nIReadOnlyList read-only iteration"]
    F --> G["BooleanQuery built\nand added to stack"]

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flowchart TD
    A["Caller: GroupedAnd/Or/Not\nIEnumerable fields param"] --> B{"fields as string[] != null?"}
    B -- "Yes: caller passed string[]\nisinst short-circuits" --> C["Pass caller array directly\nzero allocation"]
    B -- "No: other IEnumerable type" --> D[".ToArray() new string copy"]
    C --> E["Internal method\nGroupedAndInternal / OrInternal / NotInternal"]
    D --> E
    E --> F["GetMultiFieldQuery\nIReadOnlyList read-only iteration"]
    F --> G["BooleanQuery built\nand added to stack"]

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_{Reviews (1): Last reviewed commit: "perf: avoid redundant string[] copy in L..." | Re-trigger Greptile}

[Shazwazza]

@copilot resolve the merge conflicts in this pull request

[Copilot]

@copilot resolve the merge conflicts in this pull request

Resolved — I merged origin/support/3.x into this branch and fixed the conflict in src/Examine.Lucene/Search/LuceneSearchQueryBase.cs in commit a7c51b7e.