Enterprise Search Engineering

Search infrastructure design, relevance tuning, query understanding, index management, quality measurement, and performance optimization. Each mode loads its own reference files on demand.

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Mode Detection

Classify into one mode before proceeding.

Mode	Signal Phrases	Reference
RELEVANCE	tune relevance, BM25, boost, function score, field weight, LTR, learned ranking, ranking model	references/relevance-tuning.md
QUERY	query understanding, intent classification, entity extraction, query expansion, synonyms, spell correction, query rewriting	references/query-understanding.md
INDEX	schema design, mapping, analyzer chain, reindex, alias, ILM, index template, field type	references/index-management.md
QUALITY	nDCG, MRR, precision, recall, search quality, judgment, A/B test, evaluation, search funnel	references/search-quality.md
PERFORMANCE	slow query, shard, cache, circuit breaker, scroll, search_after, query optimization, latency	references/performance-optimization.md
ARCHITECTURE	search architecture, hybrid search, vector search, pipeline design, platform selection, migration	(cross-reference: load relevant references based on sub-topic)

If the request spans modes, pick the primary and note the secondary. ARCHITECTURE mode loads references from whichever sub-topics apply.

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Workflow by Mode

RELEVANCE Mode

Load: references/relevance-tuning.md, references/llm-search-failure-modes.md

1. Diagnose — Identify the relevance problem before tuning.

Problem Class	Symptoms	Starting Point
Poor precision	Good results buried under noise	Field boosting, minimum_should_match
Poor recall	Known-good results missing	Analyzer tuning, query expansion, synonym filters
Wrong ordering	Right results, wrong rank	BM25 parameter tuning, function scoring
Domain mismatch	Generic scoring fails domain	Learned ranking (LTR), custom similarity
Freshness	Stale results ranked too high	Decay functions, recency boosts

2. Baseline — Capture current relevance metrics before making changes. Minimum: nDCG@10, P@5, MRR on a representative judgment set. No tuning without a baseline.

3. Tune — Apply changes from the reference. One variable at a time. Measure after each change.

Tuning Layer	Tools	When to Use
Analyzer chain	Tokenizers, filters, char_filters	Recall problems, morphological mismatch
Field boosting	Multi-match boosts, cross_fields	Some fields matter more than others
BM25 parameters	k1, b per field	Content-type-specific term saturation
Function scoring	Decay, field_value_factor, script_score	Non-textual relevance signals (popularity, freshness, authority)
Rescoring	rescore query with window_size	Expensive scoring on top-N candidates
Learned ranking (LTR)	Feature engineering, model training, SLTR plugin	BM25 + hand-tuned boosts plateau

4. Validate — Compare against baseline. Accept only statistically significant improvements. Check for regression on other query classes.

Gate: Baseline metrics captured. Each tuning change measured independently. No "tuned several things and it got better" — isolate the effect.

QUERY Mode

Load: references/query-understanding.md, references/llm-search-failure-modes.md

1. Classify query intent — Determine what the user wants before constructing the query.

Intent	Example	Query Strategy
Navigational	"OpenSearch documentation"	Exact match, title boost, URL matching
Informational	"how to configure sharding"	Full-text across body fields, snippet extraction
Transactional	"buy enterprise license"	Product/SKU fields, availability filters
Faceted	"red shoes size 10"	Structured filters + text scoring
Exploratory	"machine learning applications"	Broad match, diversified results, related terms

2. Extract entities — People, products, dates, categories, attributes from the query string.

3. Transform — Apply query expansion, spelling correction, synonym injection, and relaxation strategies from the reference.

4. Construct — Build the platform-specific query DSL. Include:

   • bool query structure (must/should/filter/must_not)
   • Field selection and boosting
   • Filters vs scoring clauses (filters for hard constraints, scoring for ranking signals)
   • Aggregations for facets

5. Test — Validate against known queries. Check that transformations improve recall without destroying precision.

Gate: Query pipeline handles the 5 intent types. Entity extraction covers the domain vocabulary. Expansion and relaxation strategies are measurable.

INDEX Mode

Load: references/index-management.md, references/llm-search-failure-modes.md

1. Requirements — Gather before designing.

Question	Why It Matters
Document count and growth rate	Shard count, ILM policy
Average document size	Shard sizing, bulk indexing batch size
Query patterns	Which fields need text analysis vs keyword vs numeric
Update frequency	Near-real-time vs batch, refresh interval
Retention policy	ILM phases, rollover triggers
Access patterns	Hot/warm/cold architecture, read vs write ratio

2. Design schema — Map fields with appropriate types. Use the reference for type selection guidance.

3. Configure analyzers — Build analyzer chains for each text field. Standard analyzer is a starting point, not a solution.

4. Template and alias — Set up index templates for consistent creation. Use aliases for zero-downtime operations.

5. Reindex strategy — Plan for schema evolution. Reindexing is inevitable; design for it.

Gate: Schema covers all query-time field requirements. Analyzer chains tested against representative content. Alias strategy supports zero-downtime reindexing.

QUALITY Mode

Load: references/search-quality.md, references/llm-search-failure-modes.md

1. Define metrics — Select metrics appropriate to the use case.

Metric	Measures	Best For
nDCG@k	Graded relevance at rank k	Rankings with multiple relevance levels
MRR	Position of first relevant result	Navigational queries, single-answer
P@k	Fraction relevant in top k	Precision-critical applications
Recall@k	Fraction of relevant docs found in top k	Recall-critical applications (legal, compliance)
MAP	Average precision across recall levels	Balanced precision/recall

2. Collect judgments — Build the ground truth dataset.

Method	Scale	Quality	Cost
Expert annotation	Small (100s)	Highest	High
Click logs	Large (10K+)	Moderate (position bias)	Low
Crowdsourcing	Medium (1K+)	Variable	Medium
LLM-assisted	Medium-Large	Good for initial pass, needs validation	Low

3. Evaluate — Run offline evaluation. Compare configurations. Report metrics with confidence intervals.

4. Online testing — A/B test or interleave changes against production. Measure engagement metrics alongside relevance metrics.

5. Monitor — Continuous quality dashboards. Alerting on metric degradation. Search funnel analysis (query -> click -> conversion).

Gate: Judgment set exists with documented guidelines. Offline metrics computed with confidence intervals. Online test plan specifies primary metric, minimum detectable effect, and sample size.

PERFORMANCE Mode

Load: references/performance-optimization.md, references/llm-search-failure-modes.md

1. Profile — Identify the bottleneck before optimizing.

Symptom	Likely Cause	Diagnostic
High p99 latency	Slow queries, GC pauses, shard imbalance	Slow query log, node stats, hot threads
Throughput ceiling	Undersized thread pools, too many shards	Thread pool stats, shard count per node
Memory pressure	Field data, too many aggregations, deep pagination	Node stats, circuit breaker trips
Indexing lag	Merge throttling, refresh overhead, slow pipelines	Index stats, merge stats
Cluster instability	Split brain, disk watermarks, master storms	Cluster health, allocation explain

2. Diagnose — Use platform diagnostics to confirm the cause. Measure before changing.

3. Optimize — Apply targeted fixes from the reference. One change at a time, measure the effect.

4. Validate — Load test the change. Check that optimization does not degrade other metrics (latency vs throughput tradeoff, cache hit rate vs memory).

Gate: Bottleneck identified with evidence. Fix targeted at root cause. Load test confirms improvement without regression.

ARCHITECTURE Mode

Cross-cutting mode. Load references based on the specific question.

1. Platform evaluation — When selecting or migrating between platforms.

Platform	Strengths	Consider When
Elasticsearch/OpenSearch	Mature ecosystem, Lucene-based, strong text search	General-purpose search, log analytics
Vespa	Built-in ML serving, tensor computation, real-time updates	ML-heavy ranking, large-scale recommendations
Typesense	Simple API, typo tolerance, easy setup	Developer-facing search, smaller datasets
Solr	Configurable, NRT, strong faceting	Legacy integration, specific Solr features
Meilisearch	Instant search, typo-tolerant, developer-friendly	Frontend search, prototyping
Custom (Lucene/Tantivy)	Full control, embedded	Specialized needs, tight integration

2. Hybrid search design — When combining keyword and vector retrieval.

Strategy	How	Tradeoff
Score fusion (RRF)	Reciprocal rank fusion of BM25 + vector results	Simple, no training needed. Weights are heuristic.
Linear combination	Weighted sum of normalized BM25 + vector scores	Tunable. Requires score normalization.
Re-ranking	BM25 retrieval -> vector re-rank top N	Efficient. Vector search only on candidates.
Two-stage	Coarse retrieval (either) -> fine-grained re-rank (LTR)	Best quality. Most complex.

3. Pipeline design — Ingestion, enrichment, indexing, query, ranking pipelines.

4. Migration planning — Version upgrades, platform changes, zero-downtime strategies.

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LLM Failure Modes in Search Engineering

Load references/llm-search-failure-modes.md for all modes. These are the specific ways LLMs fail at search tasks:

Failure Mode	What Happens	Defense
Hallucinated query DSL	LLM invents plausible-looking query syntax that does not exist	Validate every query against the specific platform version's API docs
Version confusion	Mixing Elasticsearch 7.x and 8.x APIs, or ES and OpenSearch syntax	State the exact platform and version upfront. Reference version-specific docs.
Generic relevance advice	"Improve your relevance by boosting important fields" without specifics	Require concrete field names, boost values, and expected metric impact
Vector search as default	Recommending embeddings when BM25 with good analyzers solves the problem	Start with BM25 tuning. Vector search adds complexity; justify the added value.
Ignoring measurement	Suggesting changes without a quality measurement framework	Require baseline metrics before any tuning recommendation
Deprecated feature suggestions	Recommending removed or deprecated APIs (type mappings, indices.optimize)	Check the deprecation/migration guide for the target version
Over-engineered schemas	Adding 50 fields with sub-fields when 10 fields cover the queries	Schema complexity should match query requirements, not data model completeness
Cargo-cult configuration	Copying cluster settings from blog posts without understanding the workload	Every configuration value should have a justification tied to the specific workload

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Platform-Specific Conventions

When generating configuration or queries, always specify the target platform and version.

Platform	Query Language	Config Format	Key Differences
Elasticsearch 8.x	Query DSL (JSON)	elasticsearch.yml	Security on by default, no type mappings
OpenSearch 2.x	Query DSL (JSON)	opensearch.yml	Fork divergence from ES 7.10, alerting built-in
Solr 9.x	SolrQL / JSON Request API	solrconfig.xml + schema.xml	Config-driven, ZooKeeper coordination
Vespa	YQL	services.xml + schemas	Custom ranking expressions, tensors native
Typesense	REST params	Command-line / JSON	Simpler model, automatic typo tolerance

Cross-platform traps:

• OpenSearch _search API is largely ES 7.10-compatible, but diverges on security, ML, and alerting APIs
• Elasticsearch _field_caps behavior changed between 7.x and 8.x
• Solr edismax and ES multi_match are similar in concept but differ in syntax, defaults, and tie-breaking
• Vespa ranking expressions are not Lucene scoring — different mental model entirely

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Output Conventions

• Markdown with clear headers. Scannable by engineers.
• All query DSL in fenced code blocks with platform and version annotation: ````json // OpenSearch 2.x```
• Tables for parameter comparisons, metric results, configuration options.
• Every recommendation includes: what to change, why, expected effect, how to measure.
• Configuration snippets are copy-pasteable with comments explaining each value.

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Reference Loading Table

Reference	Contents	Load When
references/relevance-tuning.md	BM25 parameters, LTR features, boost strategies, function scoring, field weighting	RELEVANCE mode, or relevance sub-questions in other modes
references/query-understanding.md	Intent classification, entity extraction, query expansion, spell correction, query relaxation	QUERY mode, or query pipeline questions
references/index-management.md	Schema design, analyzer chains, mapping optimization, reindex strategies, ILM	INDEX mode, or schema/mapping questions
references/search-quality.md	nDCG, MRR, P@k, judgment collection, A/B testing, evaluation methodology	QUALITY mode, or measurement questions
references/performance-optimization.md	Query optimization, caching, sharding, pagination, circuit breakers, slow query diagnosis	All modes — always load as guardrail
references/llm-search-failure-modes.md	How LLMs fail at search tasks: hallucinated DSL, version confusion, generic advice, measurement avoidance	All modes — always load as guardrail