[5.x] Performance Optimisation for Queries - Optimise IteratorBuilder limit queries to avoid loading all items

[jonathan-bird]

Description

This PR optimises the IteratorBuilder to avoid loading all items when a limit() is applied without orderBy() or inRandomOrder(). This significantly improves search query performance, particularly for sites with large datasets.

Fixes #13215

Problem

Previously, IteratorBuilder::getFilteredItems() loaded ALL items before applying limits. For a ->limit(10) query on 10,000 results, it would hydrate all 10,000 items before taking the first 10.

Solution

Added a new abstract method getBaseItemsLazy(): Generator that yields items lazily, enabling early termination when the limit is reached.

Three optimisation paths in getFilteredItems():

• No limit, orderBy, or randomise: Falls back to loading all items (unchanged behaviour)
• Limit without wheres: Loads only offset + limit items
• Limit with wheres: Batches items and stops early when enough matches are collected

Benchmark Results

I wrote a simple benchmark script separately to test the difference in performance between current code and new code for various scenarios (eg wheres, where + limit, limit etc.). I skipped orderBy as this remains the same, but I did test just in case and it's the same.

Scenario	Limit	Old Time	Old Hydrated	New Time	New Hydrated	Improvement
No wheres	10	0.70ms	10,000	0.04ms	10	99.9% fewer
No wheres	50	0.68ms	10,000	0.05ms	50	99.5% fewer
No wheres	100	0.68ms	10,000	0.06ms	100	99% fewer
50% match rate	10	9.13ms	10,000	0.10ms	50	99.5% fewer
50% match rate	50	9.14ms	10,000	0.15ms	100	99% fewer
50% match rate	100	9.12ms	10,000	0.26ms	200	98% fewer
10% match rate	10	9.01ms	10,000	0.18ms	100	99% fewer
10% match rate	50	8.99ms	10,000	0.57ms	500	95% fewer
10% match rate	100	8.98ms	10,000	1.08ms	1,000	90% fewer

Safety checks

• Queries with orderBy() or inRandomOrder() load all items (sorting/shuffling requires all)
• Queries without limit() load all items (no early termination possible)
• Results are identical to previous behaviour, just faster

Files Changed

• src/Query/IteratorBuilder.php - Core optimisation logic
• src/Query/ItemQueryBuilder.php - Implements getBaseItemsLazy()
• src/Search/QueryBuilder.php - Implements getBaseItemsLazy() with batch hydration

Tests

• tests/Query/IteratorBuilderTest.php - 13 tests covering optimisation paths
• tests/Search/QueryBuilderPerformanceTest.php - 14 tests for search-specific behaviour
• tests/Fakes/Query/TestIteratorBuilder.php - Test helper
• tests/Fakes/Query/HydrationTrackingQueryBuilder.php - Test helper

Note: These tests all pass, it's just the UTF-8 which Duncan is fixing in another PR that are failing.

Potential Future Optimisation

This PR optimises hydration by stopping early once the limit is reached. However, the search drivers still fetch all raw results from the index before we apply the limit.

A possible future optimisation could pass the limit down to getSearchResults($query, $limit = null) so drivers can fetch fewer results at the source:

• Algolia: Could use the hitsPerPage API parameter to request fewer hits
• Comb: Could limit raw results before mapping scores/snippets

This would be most beneficial for large indexes where the initial lookup is expensive.

In my testing, this PR still reduces my search from 3.5s down to 600ms using Comb, and with this future optimisation would reduce down to about 400ms.