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Service limits in Azure AI Search

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Maximum limits on storage, workloads, and quantities of indexes and other objects depend on whether you create Azure AI Search at Free, Basic, Standard, or Storage Optimized pricing tiers.

  • Free is a multitenant 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 (3,000 indexes per service). S3 HD doesn't provide the indexer feature and data ingestion must use 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.

Subscription limits

You can create multiple billable search services (Basic and higher), up to the maximum 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 a tier (or SKU) for Azure AI Search.

Maximum service limits can be raised upon request. If you need more services within the same subscription, file a support request.

Resource Free 1 Basic S1 S2 S3 S3 HD L1 L2
Maximum services 1 16 16 8 6 6 6 6
Maximum search units (SU)2 N/A 3 SU 36 SU 36 SU 36 SU 36 SU 36 SU 36 SU

1 You can have one free search service per Azure subscription. The free tier is based on infrastructure shared with other customers. Because the hardware isn't dedicated, scale-up isn't supported, and storage is limited to 50 MB.

2 Search units (SU) are billing units, allocated as either a replica or a partition. You need both. To learn more about SU combinations, see Estimate and manage capacity of a search service.

Service limits

Search service limits for storage, partitions, and replicas vary by service creation date, with higher limits for newer services in supported regions.

A search service is subject to a maximum storage limit (partition size multiplied by the number of partitions) or by a hard limit on the maximum number of indexes or indexers, whichever comes first.

Service level agreements (SLAs) apply to billable services having two or more replicas for query workloads, or three or more replicas for query and indexing workloads. The number of partitions isn't an SLA consideration. For more information, see Reliability in Azure AI Search.

Free services don't have fixed partitions or replicas and they share resources with other subscribers.

Before April 3, 2024

Resource Free Basic S1 S2 S3 S3 HD L1 L2
Service level agreement (SLA) No Yes Yes Yes Yes Yes Yes Yes
Storage (partition size) 50 MB 2 GB 25 GB 100 GB 200 GB 200 GB 1 TB 2 TB
Partitions N/A 1 12 12 12 3 12 12
Replicas N/A 3 12 12 12 12 12 12

After April 3, 2024

For new services created after April 3, 2024:

  • Basic tier can have up to three partitions and three replicas, and a total of nine search units (SU).
  • Basic, S1, S2, S3 have more storage per partition, ranging from 3-7 times more, depending on the tier.
  • Your new search service must be in a supported region to get the extra capacity for Basic and other tiers.

Currently, there's no in-place upgrade. You should create a new search service to benefit from the extra storage.

Resource Free Basic S1 S2 S3 S3 HD L1 L2
Service level agreement (SLA) No Yes Yes Yes Yes Yes Yes Yes
Storage (partition size) 50 MB 15 GB 160 GB 350 GB 700 GB 200 GB 1 TB 2 TB
Partitions N/A 3 12 12 12 3 12 12
Replicas N/A 3 12 12 12 12 12 12

Supported regions with higher storage limits

Services created after April 3, 2024 must be in one of the following regions to get the extra storage. Watch for announcements in What's New in Azure AI Search for expansion to other regions.

Country Regions providing extra capacity per partition
United States East US​, East US 2, ​Central US​, North Central US​, South Central US​, West US​, West US 2​, West US 3​, West Central US​
United Kingdom UK South​, UK West​ ​
United Arab Emirates UAE North​​
Switzerland Switzerland West​
Sweden Sweden Central​​
Poland Poland Central​​
Norway Norway East​​
Korea Korea Central, Korea South​ ​
Japan Japan East, Japan West​
Italy Italy North​​
India Central India, Jio India West​ ​
France France Central​​
Europe North Europe​​
Canada Canada Central​, Canada East​​
Bazil Brazil South​​
Asia Pacific East Asia, Southeast Asia​ ​
Australia Australia East​, Australia Southeast​​

Index limits

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 dimensions per vector field 3072 3072 3072 3072 3072 3072 3072 3072
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
Maximum index size 4 N/A N/A N/A 1.92 TB 2.4 TB 100 GB N/A N/A

1 Basic services created before December 2017 have lower limits (5 instead of 15) on indexes. Basic tier is the only tier 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 3,000 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.

4 On most tiers, maximum index size is all available storage on your search service. For S2, S3, and S3 HD, the maximum size of any index is the number provided in the table. Applies to search services created after April 3, 2024.

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 are portable across equivalent service tiers in any region.

Document limits

You can have 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 instance 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.

Vector index size limits

When you index documents with vector fields, Azure AI Search constructs internal vector indexes using the algorithm parameters you provide. The size of these vector indexes is restricted by the memory reserved for vector search for your service's tier (or SKU).

The service enforces a vector index size quota for every partition in your search service. Each extra partition increases the available vector index size quota. This quota is a hard limit to ensure your service remains healthy, which means that further indexing attempts once the limit is exceeded results in failure. You can resume indexing once you free up available quota by either deleting some vector documents or by scaling up in partitions.

The table describes the vector index size quota per partition across the service tiers. For context, it includes:

  • Partition storage limits for each tier, repeated here for context.
  • Amount of each partition (in GB) available for vector indexes (created when you add vector fields to an index).
  • Approximate number of embeddings (floating point values) per partition.

Use the GET Service Statistics to retrieve your vector index size quota or review the Indexes page or Usage tab in the Azure portal.

Vector limits vary by service creation date and tier. To check the age of your search service and learn more about vector indexes, see Vector index size and staying under limits.

Vector limits on services created after April 3, 2024 in supported regions

The highest vector limits are available on search services created after April 3, 2024 in a supported region.

Tier Storage quota (GB) Vector quota per partition (GB) Approx. floats per partition (assuming 15% overhead)
Basic 15 5 1,100 million
S1 160 35 8,200 million
S2 350 100 23,500 million
S3 700 200 47,000 million
L1 1,000 12 2,800 million
L2 2,000 36 8,400 million

Notice that L1 and L2 limits are unchanged in the April 3 rollout.

Vector limits on services created between July 1, 2023 and April 3, 2024

The following limits applied to new services created between July 1 and April 3, 2024, except for the following regions, which have the original limits from before July 1, 2023:

  • Germany West Central
  • West India
  • Qatar Central

All other regions have these limits:

Tier Storage quota (GB) Vector quota per partition (GB) Approx. floats per partition (assuming 15% overhead)
Basic 2 1 235 million
S1 25 3 700 million
S2 100 12 2,800 million
S3 200 36 8,400 million
L1 1,000 12 2,800 million
L2 2,000 36 8,400 million

Vector limits on services created before July 1, 2023

Tier Storage quota (GB) Vector quota per partition (GB) Approx. floats per partition (assuming 15% overhead)
Basic 2 0.5 115 million
S1 25 1 235 million
S2 100 6 1,400 million
S3 200 12 2,800 million
L1 1,000 12 2,800 million
L2 2,000 36 8,400 million

Indexer limits

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 5 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 6 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 Azure AI 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 Regarding the 2 or 24 hour maximum duration for indexers: a 2-hour maximum is the most common and it's what you should plan for. The 24-hour limit is from an older indexer implementation. If you have unscheduled indexers that run continuously for 24 hours, it's because those indexers couldn't be migrated to the newer infrastructure. As a general rule, for indexing jobs that can't finish within two hours, put the indexer on a 2-hour schedule. When the first 2-hour interval is complete, the indexer picks up where it left off when starting the next 2-hour interval.

6 Skillset execution, and image analysis in particular, 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.

Note

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.

Indexers can access other Azure resources over private endpoints managed via the shared private link resource API. This section describes the limits associated with this capability.

Resource Free Basic S1 S2 S3 S3 HD L1 L2
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 ensure 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.

Synonym limits

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.

Resource Free Basic S1 S2 S3 S3-HD L1 L2
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.

Resource Free Basic S1 S2 S3 S3-HD L1 L2
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 an Azure AI 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.

Throttling limits

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 1,000 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 1,000 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 AI 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 1,000 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