In the realm of search engine optimization and effective data retrieval, Elasticsearch stands out as a powerful tool. One of its valuable features is the ability to manage synonyms, allowing search queries to match a broader range of terms. However, configuring synonyms, especially simple contraction synonyms, can sometimes lead to unexpected results. This article delves into a common issue where simple contraction synonyms in Elasticsearch behave like equivalent synonyms, causing unintended matches. We’ll explore a practical example and discuss how to ensure your synonyms work as intended for optimal search precision.
Imagine you’re managing an e-commerce platform with a product named “Peak Performance,” a multivitamin supplement. To enhance searchability, you aim to set up a synonym rule: when users search for “vitamin” or “supplement,” the query should match “peak performance.” This is a classic use case for a simple contraction synonym, where a more general term (vitamin, supplement) contracts or maps to a more specific product name (peak performance). Ideally, searching for “vitamin” should lead users to “Peak Performance” products, but searching for “Peak Performance” should not broaden the search to include everything labeled “vitamin” or “supplement.”
However, Elasticsearch can sometimes interpret these rules differently than expected. Let’s consider the following synonym mapping defined in an Elasticsearch analyzer:
"vitamin, supplement => peak performance"The intention here is clear: “vitamin” and “supplement” should contract to “peak performance.” Yet, in practice, users might find that searching for “peak performance” also retrieves results containing “vitamin” or “supplement,” effectively turning the simple contraction into an equivalent synonym. This behavior is contrary to the desired outcome and can dilute search result relevance.
To understand why this might occur, let’s examine a sample Elasticsearch analyzer configuration designed to implement this simple contraction:
{
"filter": {
"english_keywords": {
"keywords": ["example"],
"type": "keyword_marker"
},
"english_stemmer": {
"type": "stemmer",
"language": "english"
},
"synonyms_en": {
"type": "synonym",
"expand": "false",
"synonyms": [
"vitamin, supplement => peak performance",
"soap => wash",
"protein => access",
"kids => koala"
]
},
"english_possessive_stemmer": {
"type": "stemmer",
"language": "possessive_english"
},
"english_stop": {
"type": "stop",
"stopwords": "_english_"
}
},
"analyzer": {
"custom_en": {
"filter": [
"english_possessive_stemmer",
"lowercase",
"synonyms_en",
"english_stop",
"english_keywords",
"english_stemmer"
],
"tokenizer": "standard"
}
}
}In this configuration, expand: false is explicitly set within the synonyms_en filter. According to Elasticsearch documentation, setting expand to false for explicit mappings (those using =>) should ensure simple contraction behavior. Explicit mappings, as per the documentation, should only match tokens on the left-hand side (LHS) of “=>” and replace them with the alternatives on the right-hand side (RHS). They are designed to ignore the expand parameter, ideally enforcing one-way synonym application.
To further illustrate the issue, consider a sample search query:
{
"from": 0,
"size": 10,
"_source": ["name.regular"],
"query": {
"bool": {
"must": {
"multi_match": {
"query": "peak performance",
"fuzziness": "auto",
"operator": "and",
"type": "most_fields",
"fields": ["name.regular.en"]
}
}
}
},
"post_filter": {
"term": {
"channel_id": 1
}
}
}This query specifically searches for “peak performance” in the name.regular.en field. The expectation is to retrieve only products with “peak performance” in their name. However, the actual query response might include items containing “vitamin” or “supplement,” demonstrating the unwanted equivalent synonym behavior:
{
"took": 7,
"timed_out": false,
"_shards": {
"total": 5,
"successful": 5,
"skipped": 0,
"failed": 0
},
"hits": {
"total": 28,
"max_score": 9.393171,
"hits": [
{
"_index": "en_us_primary",
"_type": "_doc",
"_id": "product_2799_1",
"_score": 9.393171,
"_source": {
"name": {
"regular": "Vitality Vitamin D3"
}
}
},
{
"_index": "en_us_primary",
"_type": "_doc",
"_id": "product_3068_1",
"_score": 8.375387,
"_source": {
"name": {
"regular": "Calmicid Antacid Supplement"
}
}
},
{
"_index": "en_us_primary",
"_type": "_doc",
"_id": "product_861_1",
"_score": 8.023193,
"_source": {
"name": {
"regular": "Peak Performance Men Save $47.95"
}
}
},
{
"_index": "en_us_primary",
"_type": "_doc",
"_id": "product_862_1",
"_score": 7.4778767,
"_source": {
"name": {
"regular": "Peak Performance Longevity 50+ Save $47.95"
}
}
},
{
"_index": "en_us_primary",
"_type": "_doc",
"_id": "product_980_1",
"_score": 7.229685,
"_source": {
"name": {
"regular": "Peak Performance Brain Women Save $90.92"
}
}
},
{
"_index": "en_us_primary",
"_type": "_doc",
"_id": "product_7798_1",
"_score": 7.229685,
"_source": {
"name": {
"regular": "Peak Performance Heart Men Save $93.92"
}
}
},
{
"_index": "en_us_primary",
"_type": "_doc",
"_id": "product_2708_1",
"_score": 6.8760505,
"_source": {
"name": {
"regular": "Sei Bella Fortifying Vitamin Lotion"
}
}
},
{
"_index": "en_us_primary",
"_type": "_doc",
"_id": "product_967_1",
"_score": 6.7668524,
"_source": {
"name": {
"regular": "Peak Performance Metabolic Pack Men Save $78.93"
}
}
},
{
"_index": "en_us_primary",
"_type": "_doc",
"_id": "product_860_1",
"_score": 6.45929,
"_source": {
"name": {
"regular": "Peak Performance Women Save $47.95"
}
}
},
{
"_index": "en_us_primary",
"_type": "_doc",
"_id": "product_592_1",
"_score": 6.414261,
"_source": {
"name": {
"regular": "Peak Performance Total Men Save $131.89"
}
}
}
]
}
}The query response clearly shows results like “Vitality Vitamin D3” and “Calmicid Antacid Supplement” appearing alongside “Peak Performance” products when searching for “peak performance.” This indicates that the simple contraction synonym is not behaving as expected and is instead acting as an equivalent synonym, causing bi-directional matching.
This issue highlights the complexities of synonym management in Elasticsearch. While the configuration appears to be correctly set for a simple contraction, the actual behavior suggests otherwise. Potential reasons for this discrepancy could include:
- Analyzer Order: The order of filters in the custom analyzer might be influencing synonym processing. Ensure that the
synonyms_enfilter is placed appropriately within the filter chain. - Tokenization: The tokenizer used (in this case, “standard”) could be tokenizing terms in a way that affects synonym matching. Review how terms are tokenized and if it aligns with the synonym definitions.
- Elasticsearch Version: While the example specifies v6.2, behavior might subtly vary across Elasticsearch versions. Refer to the documentation specific to your Elasticsearch version for the most accurate understanding of synonym behavior.
- Underlying Synonym Implementation: There might be nuances in Elasticsearch’s synonym implementation that are not immediately apparent from the documentation. Deeper investigation or community consultation might be necessary.
To resolve this, consider the following troubleshooting steps:
- Verify Analyzer: Double-check the custom analyzer definition and ensure it is correctly applied to the relevant index fields.
- Test Analyzer: Use the Elasticsearch Analyze API to test how the analyzer processes terms like “vitamin,” “supplement,” and “peak performance.” This can reveal how synonyms are being applied at the token level.
- Simplify Configuration: Start with a minimal configuration focusing solely on the synonym filter to isolate the issue. Gradually add other filters to observe their impact.
- Consult Documentation: Revisit the Elasticsearch documentation on synonyms and analyzers, paying close attention to explicit mappings and the
expandparameter. - Community Support: Engage with the Elasticsearch community forums or Stack Overflow to seek insights from experienced users who might have encountered similar issues.
By systematically investigating these potential causes and employing the suggested troubleshooting steps, you can gain a clearer understanding of why your simple contraction synonyms might be behaving like equivalent synonyms. Achieving precise synonym control in Elasticsearch is crucial for delivering relevant and accurate search results, and meticulous configuration and testing are key to unlocking its full potential.
