The completion data type in Elasticsearch is specifically designed to provide fast auto-complete and search-as-you-type functionality. It's optimized for speed and efficiency in prefix matching, making it ideal for implementing typeahead features in search interfaces. While alternatives like the match_phrase_prefix query exist, the completion suggester offers superior performance for large-scale autocomplete scenarios.
Completion fields are best used when you need to provide instant search suggestions based on prefixes. They're particularly useful for scenarios where users expect immediate feedback as they type, such as product searches, location lookups, or user name searches.
Example
PUT my_index
{
"mappings": {
"properties": {
"suggest_field": {
"type": "completion"
}
}
}
}
PUT my_index/_doc/1
{
"suggest_field": {
"input": ["New York", "NYC", "The Big Apple"],
"weight": 34
}
}
POST my_index/_search
{
"suggest": {
"city_suggestion": {
"prefix": "new y",
"completion": {
"field": "suggest_field"
}
}
}
}
Common issues or misuses
- Overloading with too many inputs per document, which can lead to increased index size and slower performance.
- Not considering memory usage, as completion fields are loaded into memory for fast access.
- Forgetting to update the completion field when the underlying data changes, leading to outdated suggestions.
- Using completion fields for full-text search scenarios where they're not optimized.
Frequently Asked Questions
Q: Can I use completion fields for partial matching in the middle or end of words?
A: No, completion fields are designed for prefix matching only. For infix or suffix matching, consider using n-grams or other text analysis techniques.
Q: How does the weight parameter affect suggestions?
A: The weight parameter allows you to boost certain suggestions. Higher weight values will cause those suggestions to appear higher in the results list.
Q: Is there a limit to the number of inputs I can add to a completion field?
A: While there's no hard limit, adding too many inputs can significantly increase index size and memory usage. It's best to limit inputs to the most relevant terms.
Q: Can I use completion fields with non-Latin characters?
A: Yes, completion fields support Unicode. However, ensure your analyzer is configured correctly for the language and character set you're using.
Q: How can I implement fuzzy matching with completion fields?
A: The completion suggester supports fuzzy queries by adding a fuzzy parameter to your suggestion request, allowing for minor typos or spelling variations.
