[perf-improver] perf: fast-path IndexItems when no validator configured

[github-actions]

🤖 This is an automated PR from Perf Improver, an AI assistant focused on performance.

Goal

Eliminate unnecessary LINQ overhead on the indexing hot path — every bulk IndexItems call currently wraps items in a 3-stage LINQ pipeline even when no validator is configured.

Change

File: src/Examine.Core/BaseIndexProvider.cs

When ValueSetValidator == null (the common, default case — validators are an opt-in feature), the existing code runs every ValueSet through:

values
  .Select(ValidateItem)                         // creates ValueSetValidationResult per item
  .Where(x => x.Status != Failed)               // always passes (status == Valid)
  .Select(x => x.ValueSet)                      // unwraps the struct

ValidateItem short-circuits via ValueSetValidator?.Validate(item) ?? new ValueSetValidationResult(Valid, item) — when the validator is null, it always returns Valid, so the Where always passes and Select always unwraps.

After: when no validator is set, IndexItems passes the IEnumerable<ValueSet> straight through to PerformIndexItems with no wrapping:

if (ValueSetValidator == null)
{
    PerformIndexItems(values, OnIndexOperationComplete);
    return;
}

Performance Evidence

Methodology: Static code-path analysis + allocation counting.

Cost per IndexItems call	Before	After
LINQ iterator allocations	3 (Select + Where + Select state machines)	0
Per-item struct operations	ValidateItem → null-conditional → struct ctor	none
Per-item delegate overhead	2 lambdas invoked per item	0

For a batch of N documents:

• Saved: 3 iterator allocations per batch (fixed cost)
• Saved: N null-conditional evaluations + N ValueSetValidationResult struct constructions + 2N lambda invocations

This matters most in bulk indexing scenarios (e.g. rebuilding an index), where IndexItems is called with large sequences of ValueSet objects.

Trade-offs

• Adds a one-time null check per IndexItems call (negligible)
• Behaviour is identical: with no validator all items have always been indexed as-is

Reproducibility

dotnet build src/Examine.sln --configuration Release
dotnet test src/Examine.Test/Examine.Test.csproj --configuration Release --filter "TestCategory!=Benchmarks" -f net8.0

Test Status

✅ Build clean (0 errors, 0 new warnings). All 147 tests passed (2 skipped as expected).

Generated by Perf Improver · sonnet46 5.5M · ◷
_{Comment /perf-assist to run again}

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Greptile Summary

Adds a fast-path null check in IndexItems so that when no ValueSetValidator is configured — the common default case — the call is forwarded directly to PerformIndexItems, skipping the three-stage LINQ pipeline entirely.

• Behavioral equivalence is preserved: when the validator is null, ValidateItem always returns ValueSetValidationStatus.Valid, the Where filter always passes, and the final Select just unwraps the same ValueSet — so every item would have reached PerformIndexItems unchanged anyway.
• Allocation savings are genuine: the three LINQ state-machine allocations (two Select iterators and one Where iterator) and the per-item ValidateItem struct construction are eliminated on every IndexItems call when no validator is set, which compounds in bulk-indexing scenarios.

Confidence Score: 5/5

Safe to merge — the fast path is a strict subset of the existing behaviour and cannot reach PerformIndexItems with items that would have been filtered out.

The optimization is narrowly scoped: it only activates when ValueSetValidator is null, a state in which the original three-stage LINQ chain was always a no-op filter. IndexOptions.Validator is a mutable property, but dynamic mutation of a validator while indexing was never safe in the original code either, so no new exposure is introduced. The validator-configured path is entirely unchanged.

No files require special attention.

Important Files Changed

Filename	Overview
src/Examine.Core/BaseIndexProvider.cs	Adds a null guard on ValueSetValidator at the top of IndexItems to short-circuit the LINQ pipeline; logic is correct and the validator path is unaffected.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["IndexItems(IEnumerable<ValueSet> values)"] --> B{ValueSetValidator == null?}
    B -- "Yes (fast path)" --> C["PerformIndexItems(values, OnIndexOperationComplete)"]
    B -- "No (validator configured)" --> D["values.Select(ValidateItem)"]
    D --> E[".Where(x => x.Status != Failed)"]
    E --> F[".Select(x => x.ValueSet)"]
    F --> G["PerformIndexItems(filtered, OnIndexOperationComplete)"]
    C --> H[["Abstract PerformIndexItems impl"]]
    G --> H

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flowchart TD
    A["IndexItems(IEnumerable<ValueSet> values)"] --> B{ValueSetValidator == null?}
    B -- "Yes (fast path)" --> C["PerformIndexItems(values, OnIndexOperationComplete)"]
    B -- "No (validator configured)" --> D["values.Select(ValidateItem)"]
    D --> E[".Where(x => x.Status != Failed)"]
    E --> F[".Select(x => x.ValueSet)"]
    F --> G["PerformIndexItems(filtered, OnIndexOperationComplete)"]
    C --> H[["Abstract PerformIndexItems impl"]]
    G --> H

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