Service limits in Azure Cognitive Search
Maximum limits on storage, workloads, and quantities of indexes and other objects depend on whether you provision Azure Cognitive Search at Free, Basic, Standard, or Storage Optimized pricing tiers.
Free is a multi-tenant shared service that comes with your Azure subscription.
Basic provides dedicated computing resources for production workloads at a smaller scale, but shares some networking infrastructure with other tenants.
Standard runs on dedicated machines with more storage and processing capacity at every level. Standard comes in four levels: S1, S2, S3, and S3 HD. S3 High Density (S3 HD) is engineered for multi-tenancy and large quantities of small indexes (three thousand indexes per service). S3 HD doesn't provide the indexer feature and data ingestion must leverage APIs that push data from source to index.
Storage Optimized runs on dedicated machines with more total storage, storage bandwidth, and memory than Standard. This tier targets large, slow-changing indexes. Storage Optimized comes in two levels: L1 and L2.
You can create multiple services, limited only by the number of services allowed at each tier. For example, you could create up to 16 services at the Basic tier and another 16 services at the S1 tier within the same subscription. For more information about tiers, see Choose an SKU or tier for Azure Cognitive Search.
Maximum service limits can be raised upon request. If you need more services within the same subscription, file a support request.
|Maximum scale in search units (SU)2||N/A||3 SU||36 SU||36 SU||36 SU||36 SU||36 SU||36 SU|
1 Free is based on infrastructure that's shared with other customers. Because the hardware isn't dedicated, scale-up isn't supported on the free tier.
2 Search units are billing units, allocated as either a replica or a partition. You need both resources for storage, indexing, and query operations. To learn more about SU computations, see Scale resource levels for query and index workloads.
A search service is constrained by disk space or by a hard limit on the maximum number of indexes or indexers, whichever comes first. The following table documents storage limits. For maximum object limits, see Limits by resource.
|Service level agreement (SLA)2||No||Yes||Yes||Yes||Yes||Yes||Yes||Yes|
|Storage per partition||50 MB||2 GB||25 GB||100 GB||200 GB||200 GB||1 TB||2 TB|
|Partitions per service||N/A||1||12||12||12||3||12||12|
|Partition size||N/A||2 GB||25 GB||100 GB||200 GB||200 GB||1 TB||2 TB|
1 Basic has one fixed partition. Additional search units can be used to add replicas for larger query volumes.
2 Service level agreements are in effect for billable services on dedicated resources. Free services and preview features have no SLA. For billable services, SLAs take effect when you provision sufficient redundancy for your service. Two or more replicas are required for query (read) SLAs. Three or more replicas are required for query and indexing (read-write) SLAs. The number of partitions isn't an SLA consideration.
|Resource||Free||Basic 1||S1||S2||S3||S3 HD||L1||L2|
|Maximum indexes||3||5 or 15||50||200||200||1000 per partition or 3000 per service||10||10|
|Maximum simple fields per index 2||1000||100||1000||1000||1000||1000||1000||1000|
|Maximum complex collections per index||40||40||40||40||40||40||40||40|
|Maximum elements across all complex collections per document 3||3000||3000||3000||3000||3000||3000||3000||3000|
|Maximum depth of complex fields||10||10||10||10||10||10||10||10|
|Maximum suggesters per index||1||1||1||1||1||1||1||1|
|Maximum scoring profiles per index||100||100||100||100||100||100||100||100|
|Maximum functions per profile||8||8||8||8||8||8||8||8|
1 Basic services created before December 2017 have lower limits (5 instead of 15) on indexes. Basic tier is the only SKU with a lower limit of 100 fields per index.
2 The upper limit on fields includes both first-level fields and nested subfields in a complex collection. For example, if an index contains 15 fields and has two complex collections with five subfields each, the field count of your index is 25. Indexes with a very large fields collection can be slow. Limit fields and attributes to just those you need, and run indexing and query test to ensure performance is acceptable.
3 An upper limit exists for elements because having a large number of them significantly increases the storage required for your index. An element of a complex collection is defined as a member of that collection. For example, assume a Hotel document with a Rooms complex collection, each room in the Rooms collection is considered an element. During indexing, the indexing engine can safely process a maximum of 3000 elements across the document as a whole. This limit was introduced in
api-version=2019-05-06 and applies to complex collections only, and not to string collections or to complex fields.
You might find some variation in maximum limits if your service happens to be provisioned on a more powerful cluster. The limits here represent the common denominator. Indexes built to the above specifications will be portable across equivalent service tiers in any region.
There are no longer any document limits per service in Azure Cognitive Search, however, there's a limit of approximately 24 billion documents per index on Basic, S1, S2, S3, L1, and L2 search services. For S3 HD, the limit is 2 billion documents per index. Each element of a complex collection counts as a separate document in terms of these limits.
Document size limits per API call
The maximum document size when calling an Index API is approximately 16 megabytes.
Document size is actually a limit on the size of the Index API request body. Since you can pass a batch of multiple documents to the Index API at once, the size limit realistically depends on how many documents are in the batch. For a batch with a single document, the maximum document size is 16 MB of JSON.
When estimating document size, remember to consider only those fields that can be consumed by a search service. Any binary or image data in source documents should be omitted from your calculations.
Maximum running times exist to provide balance and stability to the service as a whole, but larger data sets might need more indexing time than the maximum allows. If an indexing job can't complete within the maximum time allowed, try running it on a schedule. The scheduler keeps track of indexing status. If a scheduled indexing job is interrupted for any reason, the indexer can pick up where it last left off at the next scheduled run.
|Resource||Free 1||Basic 2||S1||S2||S3||S3 HD 3||L1||L2|
|Maximum indexers||3||5 or 15||50||200||200||N/A||10||10|
|Maximum datasources||3||5 or 15||50||200||200||N/A||10||10|
|Maximum skillsets 4||3||5 or 15||50||200||200||N/A||10||10|
|Maximum indexing load per invocation||10,000 documents||Limited only by maximum documents||Limited only by maximum documents||Limited only by maximum documents||Limited only by maximum documents||N/A||No limit||No limit|
|Minimum schedule||5 minutes||5 minutes||5 minutes||5 minutes||5 minutes||5 minutes||5 minutes||5 minutes|
|Maximum running time 6||1-3 minutes||2 or 24 hours||2 or 24 hours||2 or 24 hours||2 or 24 hours||N/A||2 or 24 hours||2 or 24 hours|
|Maximum running time for indexers with a skillset 5||3-10 minutes||2 hours||2 hours||2 hours||2 hours||N/A||2 hours||2 hours|
|Blob indexer: maximum blob size, MB||16||16||128||256||256||N/A||256||256|
|Blob indexer: maximum characters of content extracted from a blob||32,000||64,000||4 million||8 million||16 million||N/A||4 million||4 million|
1 Free services have indexer maximum execution time of 3 minutes for blob sources and 1 minute for all other data sources. Indexer invocation is once every 180 seconds. For AI indexing that calls into Cognitive Services, free services are limited to 20 free transactions per indexer per day, where a transaction is defined as a document that successfully passes through the enrichment pipeline (tip: you can reset an indexer to reset its count).
2 Basic services created before December 2017 have lower limits (5 instead of 15) on indexers, data sources, and skillsets.
3 S3 HD services don't include indexer support.
4 Maximum of 30 skills per skillset.
5 AI enrichment and image analysis are computationally intensive and consume disproportionate amounts of available processing power. Running time for these workloads has been shortened to give other jobs in the queue more opportunity to run.
6 Indexer execution and indexer-skillset combined execution is subject to a 2-hour maximum duration. Currently, some indexers have a longer 24-hour maximum execution window, but that behavior isn't the norm. The longer window only applies if a service or its indexers can't be internally migrated to the newer runtime behavior. If more than 2 hours are needed to complete an indexer or indexer-skillset process, schedule the indexer to run at 2-hour intervals.
As stated in the Index limits, indexers will also enforce the upper limit of 3000 elements across all complex collections per document starting with the latest GA API version that supports complex types (
2019-05-06) onwards. This means that if you've created your indexer with a prior API version, you will not be subject to this limit. To preserve maximum compatibility, an indexer that was created with a prior API version and then updated with an API version
2019-05-06 or later, will still be excluded from the limits. Customers should be aware of the adverse impact of having very large complex collections (as stated previously) and we highly recommend creating any new indexers with the latest GA API version.
Shared private link resource limits
|Private endpoint indexer support||No||Yes||Yes||Yes||Yes||No||Yes||Yes|
|Private endpoint support for indexers with a skillset1||No||No||No||Yes||Yes||No||Yes||Yes|
|Maximum private endpoints||N/A||10 or 30||100||400||400||N/A||20||20|
|Maximum distinct resource types2||N/A||4||7||15||15||N/A||4||4|
1 AI enrichment and image analysis are computationally intensive and consume disproportionate amounts of available processing power. For this reason, private connections are disabled on lower tiers to avoid an adverse impact on the performance and stability of the search service itself.
2 The number of distinct resource types are computed as the number of unique
groupId values used across all shared private link resources for a given search service, irrespective of the status of the resource.
Maximum number of synonym maps varies by tier. Each rule can have up to 20 expansions, where an expansion is an equivalent term. For example, given "cat", association with "kitty", "feline", and "felis" (the genus for cats) would count as 3 expansions.
|Maximum synonym maps||3||3||5||10||20||20||10||10|
|Maximum number of rules per map||5000||20000||20000||20000||20000||20000||20000||20000|
Index alias limits
Maximum number of index aliases varies by tier. In all tiers, the maximum number of aliases is double the maximum number of indexes allowed.
|Maximum aliases||6||10 or 30||100||400||400||2000 per partition or 6000 per service||20||20|
Data limits (AI enrichment)
An AI enrichment pipeline that makes calls to Azure Cognitive Services for Language resource for entity recognition, entity linking, key phrase extraction, sentiment analysis, language detection, and personal-information detection is subject to data limits. The maximum size of a record should be 50,000 characters as measured by
String.Length. If you need to break up your data before sending it to the sentiment analyzer, use the Text Split skill.
API requests are throttled as the system approaches peak capacity. Throttling behaves differently for different APIs. Query APIs (Search/Suggest/Autocomplete) and indexing APIs throttle dynamically based on the load on the service. Index APIs and service operations API have static request rate limits.
Static rate request limits for operations related to an index:
- List Indexes (GET /indexes): 3 per second per search unit
- Get Index (GET /indexes/myindex): 10 per second per search unit
- Create Index (POST /indexes): 12 per minute per search unit
- Create or Update Index (PUT /indexes/myindex): 6 per second per search unit
- Delete Index (DELETE /indexes/myindex): 12 per minute per search unit
Static rate request limits for operations related to a service:
- Service Statistics (GET /servicestats): 4 per second per search unit
API request limits
- Maximum of 16 MB per request 1
- Maximum 8 KB URL length
- Maximum 1000 documents per batch of index uploads, merges, or deletes
- Maximum 32 fields in $orderby clause
- Maximum 100,000 characters in a search clause
- The maximum number of clauses in
search(expressions separated by AND or OR) is 1024
- Maximum search term size is 32,766 bytes (32 KB minus 2 bytes) of UTF-8 encoded text
- Maximum search term size is 1000 characters for prefix search and regex search
- Wildcard search and Regular expression search are limited to a maximum of 1000 states when processed by Lucene.
1 In Azure Cognitive Search, the body of a request is subject to an upper limit of 16 MB, imposing a practical limit on the contents of individual fields or collections that aren't otherwise constrained by theoretical limits (see Supported data types for more information about field composition and restrictions).
Limits on query size and composition exist because unbounded queries can destabilize your search service. Typically, such queries are created programmatically. If your application generates search queries programmatically, we recommend designing it in such a way that it doesn't generate queries of unbounded size.
API response limits
- Maximum 1000 documents returned per page of search results
- Maximum 100 suggestions returned per Suggest API request
API key limits
API keys are used for service authentication. There are two types. Admin keys are specified in the request header and grant full read-write access to the service. Query keys are read-only, specified on the URL, and typically distributed to client applications.
- Maximum of 2 admin keys per service
- Maximum of 50 query keys per service