Cognitive Search Frequently Asked Questions

Find answers to commonly asked questions about Azure Cognitive Search.


What is Azure Cognitive Search?

Azure Cognitive Search is a service on Azure that provides a dedicated search engine and persistent storage of your searchable content for full text search scenarios. It also includes optional, integrated AI used during indexing to extract more text and structure from raw content.

How do I work with Cognitive Search?

The primary workflow is create, load, and query an index. Although you can use the portal for most tasks, Cognitive Search is intended to be used programmatically, handling requests from client code. Programmatic support is provided through REST APIs and client libraries in .NET, Python, Java, and JavaScript SDKs for Azure.

Are "Azure Search" and "Azure Cognitive Search" the same service?

Azure Search was renamed to Azure Cognitive Search in October 2019 to reflect the expanded (yet optional) use of cognitive skills and AI processing in service operations.

What languages are supported?

The default analyzer used for tokenization is standard Lucene and its language agnostic. Otherwise, language support is expressed through language analyzers that apply linguistic rules to inbound (indexing) and outbound (queries) content. Some features, such as semantic search and speller, are limited to a subset of languages.

How do I integrate search into my solution?

Client code should call the client libraries or REST APIs to connect to a search index, formulate queries, and handle responses. You can also write code that builds and refreshes an index, or runs indexers programmatically or by script.

Is there functional parity across the various APIs?

Not always. The REST API is always the first to implement new features in preview API versions, and the generally available versions support all programmatic operations. The client libraries in Azure SDKs will pick up new features over time, but are released on their own schedule.

Although the REST APIs are first out with newest features, the Azure SDKs provide more coding support, and are recommended over REST unless a required feature is unavailable.

Can I pause the service and stop billing?

You can't pause a search service. In Azure Cognitive Search, computing resources are allocated when the service is created. It's not possible to release and reclaim those resources on-demand.

Can I upgrade, downgrade, rename or move the service?

Service tier, name, and region are fixed for the lifetime of the service.

If I migrate my search service to another subscription or resource group, should I expect any downtime?

As long as you follow the checklist before moving resources and make sure each step is completed, there shouldn't be any downtime.


What does "indexing" mean in Cognitive Search?

It refers to the ingestion, parsing, and storing of textual content and tokens that populate a search index. Indexing creates inverted indexes and other physical data structures that support information retrieval.

Can I move, backup, and restore indexes?

There's no native support for index management. Search indexes are considered downstream data structures, accepting content from other data sources that collect operational data. As such, there's no built-in support for backing up and restoring indexes because the expectation is that you would rebuild an index from source data if you deleted it, or wanted to move it.

However, if you want to move an index between search services, you can try the index-backup-restore sample code in this Azure Cognitive Search .NET sample repo.

Can I restore my index or service once it's deleted?

No, if you delete an Azure Cognitive Search index or service, it can't be recovered. When you delete a search service, all indexes in the service are deleted permanently.

Can I index from SQL Database replicas?

If you're using the search indexer for Azure SQL Database, there are no restrictions on the use of primary or secondary replicas as a data source when building an index from scratch. However, refreshing an index with incremental updates (based on changed records) requires the primary replica. This requirement comes from SQL Database, which guarantees change tracking on primary replicas only. If you try using secondary replicas for an index refresh workload, there's no guarantee you get all of the data.


What is vector search?

Vector search is a technique that finds the most similar documents by comparing their vector representations. Since the goal of a vector representation is to capture the essential characteristics of an item in a numerical format, it can capture abstract concepts and identify matches even if there are no explicit matches based on keywords or tags. When a user performs a search, the query is summarized into a vector representation and the vector search engine identifies the most similar documents. To improve efficiency on large databases, vector search often provides the approximate nearest neighbors for a query vector. See Vector search overview for the specifics of Azure Cognitive Search's vector search product offering.

Does Azure Cognitive Search support vector search?

Azure Cognitive Search supports vector indexing and retrieval, but doesn't generate vector embeddings from input content.

Support for vector search is in public preview and available through the 2023-07-01-Preview REST APIs. Support consists of a vector field, which your documents can provide embeddings for. When you issue a search request with a query vector, the service identifies similar vectors and returns the corresponding documents.

How does vector search work in Azure Cognitive Search?

With standalone vector search, you first use a deep neural network (DNN), such as a large language model (LLM), to transform content into a vector representation within an embedding space. You can then provide these vectors in a document payload to the search index for indexing. To serve search requests, you use the same DNN from indexing to transform the search query into a vector representation, and vector search finds the most similar vectors and return the corresponding documents.

In Cognitive Search, you can index vector data as fields in documents alongside textual and other types of content. The data type for a vector field is Collection(Edm.Single).

Vector queries can be issued standalone or in combination with other query types, including term queries and filters in the same search request.

Can Cognitive Search vectorize my content or queries?

Today Cognitive Search doesn't perform vectorization. It's up to the application layer to pick the best model for the data and generate embeddings for the content that it indexes and for the queries.

Both vector search and semantic search are used to improve the relevance of your search results. However, they're orthogonal features, meaning you can use them independently or together. They both use deep neural networks (DNNs) to improve relevance, but the models and infrastructure are different for each feature.

You can use vector search and semantic search together if the search request contains a text query - hybrid search. The search engine uses Reciprocal Rank Fusion to merge results from both vector and term queries before semantic search reranking is applied.

Does my search service support vector search?

Most existing services support vector search. If you're using the 2023-07-01-Preview and index creation fails, the underlying search service doesn't support vector search, and a new service must be created. This may occur for a small subset of services created prior to January 1, 2019.

Can I add vector search to an existing index?

If your search service supports vector search, both existing and new indexes support vector search using the 2023-07-01-Preview REST API.

Why do I see different vector index size limits between my new search services and existing search services?

We're rolling out improved vector index size limits worldwide for new search services, but we're still building out infrastructure capacity in certain regions. New search services created in supported regions will see increased vector index size limits. Unfortunately, we can't migrate existing services to the new limits.

How do I enable vector search on a search index?

To enable vector search in an index, you should:

  • Add one or more fields of type Collection(Edm.Single), with a "dimensions" property and an "vectorSearchConfiguration" property.

  • Add a "vectorSearch" section to the index schema specifying the configuration used by vector search fields, including the parameters of the Approximate Nearest Neighbor algorithm used, like HNSW.

  • Use the 2023-07-01-Preview API to create or update the index, load documents, and issue queries.


Where does query execution occur?

Queries execute over a single search index that's hosted on your search service. You can't join multiple indexes to search content in two or more indexes, but you can query same-name indexes in multiple search services.

Why are there zero matches on terms I know to be valid?

The most common case isn't knowing that each query type supports different search behaviors and levels of linguistic analyses. Full text search, which is the predominant workload, includes a language analysis phase that breaks down terms to root forms. This aspect of query parsing casts a broader net over possible matches, because the tokenized term matches a greater number of variants.

Wildcard, fuzzy and regex queries, however, aren't analyzed like regular term or phrase queries and can lead to poor recall if the query doesn't match the analyzed form of the word in the search index. For more information on query parsing and analysis, see query architecture.

Why are my wildcard searches slow?

Most wildcard search queries, like prefix, fuzzy and regex, are rewritten internally with matching terms in the search index. This extra processing adds to latency. Further, broad search queries, like a* for example, are likely to be rewritten with many terms, which can be slow. For performant wildcard searches, consider defining a custom analyzer.

Can I search across multiple indexes?

No, a query is always scoped to a single index.

Why is the search score a constant 1.0 for every match?

Search scores are generated for full text search queries, based on the statistical properties of matching terms, and ordered high to low in the result set. Query types that aren't full text search (wildcard, prefix, regex) aren't ranked by a relevance score. This behavior is by design. A constant score allow matches found through query expansion to be included in the results, without affecting the ranking.

For example, suppose an input of "tour*" in a wildcard search produces matches on "tours", "tourettes", and "tourmaline". Given the nature of these results, there's no way to reasonably infer which terms are more valuable than others. For this reason, term frequencies are ignored when scoring results in queries of types wildcard, prefix, and regex. Search results based on a partial input are given a constant score to avoid bias towards potentially unexpected matches.


Where does Cognitive Search store customer data?

It stores your data wherever your service is deployed. Cognitive Search doesn't store customer data outside of the deployment region.

Does Cognitive Search send customer data to other services for processing?

Yes, if you use the built-in skills based on Azure AI services, the indexer sends requests to Azure AI services over the internal network. If you add a custom skill, the indexer sends content to the URI provided in the custom skill over the public network.

Can I control access to search results based on user identity?

Not exactly. Typically, users who are authorized to run your application are also authorized to see all search results. Cognitive Search doesn't have built-in support for row-level or document-level permissions, but you can implement security filters as a workaround.

Can I control access to operations based on user identity?

Yes, you can use role-based authorization for data plane operations over content.

Can I use the Azure portal to view and manage search content if the search service is behind an IP firewall or a private endpoint?

You can use the Azure portal on a network-protected search service if you create a network exception that allows client and portal access. For more information, see connect through an IP firewall or connect through a private endpoint.

Next steps

If your question isn't answered here, you can refer to the following sources for more questions and answers.

Stack Overflow: Azure Cognitive Search
How full text search works in Azure Cognitive Search
What is Azure Cognitive Search?