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Atlas Search Best Practices

Use the following recommended best practices to determine whether to refactor your applications that use MongoDB $text and $regex or migrate your applications to Atlas Search $search. The following table shows how MongoDB $regex, $text, and Atlas Search $search address your application's requirements.


You must precede a $regex query on an oplog in an M0 free cluster or M2/M5 shared cluster with a caret (^). Otherwise, the following error occurs:

MongoServerError: Oplog ns RegEx queries must begin with ^
If your application requires...
Datastore to respect write concerns
For transactions with heavy reads after writes, we recommend $regex. For $search, reads after writes should be rare.
Cluster optimized for write performance
Atlas Search indexes don't degrade cluster write performance.
Searching through large data sets
Atlas Search uses an inverted index, which enables fast document retrieval at very large scales.
Language awareness
Atlas Search supports many language analyzers that can tokenize (create searchable terms) languages, remove stopwords, and interpret diacritics for improved search relevance. To learn more, see How to Run Multilingual Atlas Search Queries.
Case-insensitive text search
$search offers more capabilities than $regex.
Highlighting result text
Atlas Search highlighting allows you to contextualize the documents in the results, which is essential for natural language queries.
Geospatial-aware search queries
MongoDB $regex and Atlas Search $search treat geospatial parameters differently. In MongoDB, lines between coordinates are spherical, which is well-suited for coordinates for long distance such as air flight. Atlas Search uses Lucene, which draws a straight line between coordinates and is well-suited for short distance. To learn more, see How to Run an Atlas Search Compound Geo JSON Query.
On-premises or local deployment
Atlas Search is unavailable for on-premise or local deployment. Atlas Search is only available for data on the Atlas cluster.
Autocompletion of search queries

For autocomplete of characters (nGrams), Atlas Search includes edgeGrams for left-to-right autocomplete, nGrams for autocomplete of languages that don't have whitespace, and rightEdgeGram for autocomplete of languages that you write and read right-to-left.

For autocomplete of words (wordGrams), Atlas Search includes shingle token filter, which supports word-based autocomplete by concatenating adjacent words to create a single token.

To learn more, see How to Use Autocomplete with Atlas Search.

Fuzzy matching on text input
Atlas Search text and autocomplete operators support fuzzy matching to filter on input text and address misspelled words (typos).
Filtering based on multiple strings
Atlas Search compound supports filtering based on more than 10 strings.
Relevance score sorted search
Atlas Search uses the BM25 algorithm for determining the search relevance score of documents. It supports advanced configuration through boost expressions like multiply and gaussian decay, as well as analyzers, search operators, and synonyms. To learn more, see How to Run Atlas Search Compound Queries with Weighted Fields.
Partial indexes
Atlas Search doesn't support partial indexing.
Patial match
Atlas Search wildcard and autocomplete operators support partial match queries. To learn more, see How to Run Partial Match Atlas Search Queries.
Single compound index on arrays
Atlas Search term indexes are intersected in a single Atlas Search index and eliminate the need for compound indexes for filtering on arrays.
Synonyms search
Atlas Search supports synonyms defined in a separate collection, which you can reference in your search index for use. To learn more, see How to Use Synonyms with Atlas Search.
Faceting for counts
Atlas Search provides fast counts of documents based on text criteria, and also supports faceted search for numbers and dates. To learn more, see How to Use Facets with Atlas Search.
Custom analyzers
Atlas Search supports custom analyzers to suit your specific indexing requirements. For example, you can index and search email addresses and HTTP or HTTPS URLs using custom analyzers. To learn more, see How to Define a Custom Analyzer and Run an Atlas Search Diacritic-Insensitive Query.
Searching phrases or multiple words
Atlas Search phrase operator supports searching for a sequence of terms.
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