Elasticsearch

Also Known As

TL;DR

Explanation

Elasticsearch stores documents as JSON in an inverted index — each unique term maps to the documents containing it. Queries: match (full-text), term (exact), bool (combine queries), range (numeric/date ranges), and aggregations (faceted counts). Relevance scoring uses BM25 by default. PHP clients: ruflin/elastica, elastic/elasticsearch-php. Alternatives: Meilisearch (simpler setup, instant search), Typesense (typo-tolerant), OpenSearch (AWS fork). For PHP apps with moderate search needs, Meilisearch is often simpler to operate.

Diagram

flowchart TD
    DOC[Document - JSON] --> INDEX[(Index<br/>like a DB table)]
    INDEX --> SHARDS[Shards<br/>split for scale]
    SHARDS --> REPLICAS[Replica shards<br/>for redundancy]
    subgraph Query Flow
        SEARCH[Search request] --> COORD[Coordinating node]
        COORD --> ALL[Query all shards in parallel]
        ALL --> MERGE[Merge and rank results]
        MERGE --> TOP[Return top N hits]
    end
    subgraph Indexing
        PHP_DOC[PHP sends doc] --> INVERTED[Build inverted index<br/>token to doc list]
    end
style INDEX fill:#6e40c9,color:#fff
style COORD fill:#1f6feb,color:#fff
style TOP fill:#238636,color:#fff

Common Misconception

Why It Matters

Common Mistakes

• High-cardinality keyword fields not mapped as 'keyword' type — text fields are analysed and tokenised; exact values need keyword type.
• Storing large binary or irrelevant data in Elasticsearch — only index what needs to be searched, store everything else in the primary database.
• Not defining mappings before indexing — auto-mapping guesses types and often maps numbers as text.
• Querying without a filter context for exact matches — filters are cached and much faster than queries for boolean conditions.

Code Examples

// Auto-mapping leads to wrong type inferences:
$client->index(['index' => 'products', 'body' => [
    'price' => '19.99',    // Auto-mapped as text! Cannot range query
    'in_stock' => 'true',  // Auto-mapped as text! Cannot boolean filter
    'description' => 'Great product',
]]);
// Range query: {"range":{"price":{"gte":10}}} — fails silently on text field

// Explicit mapping before indexing:
$client->indices()->putMapping(['index' => 'products', 'body' => [
    'properties' => [
        'name'        => ['type' => 'text'],          // Analysed for full-text
        'name_exact'  => ['type' => 'keyword'],        // Exact match/aggregation
        'price'       => ['type' => 'float'],          // Numeric range queries
        'in_stock'    => ['type' => 'boolean'],
        'description' => ['type' => 'text'],
        'tags'        => ['type' => 'keyword'],
    ]
]]);

References

• ↗ https://www.elastic.co/guide/en/elasticsearch/client/php-api/current/index.html

Tags

Related Terms