Resources limits for elastic pools using the DTU purchasing model

APPLIES TO: Azure SQL Database

This article provides the detailed resource limits for databases in Azure SQL Database that are within an elastic pool using the DTU purchasing model.

Each read-only replica has its own resources such as DTUs, workers, and sessions. Each read-only replica is subject to the resource limits detailed later in this article.

Elastic pool: Storage sizes and compute sizes

For Azure SQL Database elastic pools, the following tables show the resources available at each service tier and compute size. You can set the service tier, compute size, and storage amount using:

Important

For scaling guidance and considerations, see Scale an elastic pool

The resource limits of individual databases in elastic pools are generally the same as for single databases outside of pools based on DTUs and the service tier. For example, the max concurrent workers for an S2 database is 120 workers. So, the max concurrent workers for a database in a Standard pool is also 120 workers if the max DTU per database in the pool is 50 DTUs (which is equivalent to S2).

For the same number of DTUs, resources provided to an elastic pool may exceed the resources provided to a single database outside of an elastic pool. This means it is possible for the eDTU utilization of an elastic pool to be less than the summation of DTU utilization across databases within the pool, depending on workload patterns. For example, in an extreme case with only one database in an elastic pool where database DTU utilization is 100%, it is possible for pool eDTU utilization to be 50% for certain workload patterns. This can happen even if max DTU per database remains at the maximum supported value for the given pool size.

Note

The storage per pool resource limit in each of the following tables do not include tempdb and log storage.

Basic elastic pool limits

eDTUs per pool 50 100 200 300 400 800 1200 1600
Included storage per pool (GB) 5 10 20 29 39 78 117 156
Max storage per pool (GB) 5 10 20 29 39 78 117 156
Max In-Memory OLTP storage per pool (GB) N/A N/A N/A N/A N/A N/A N/A N/A
Max number DBs per pool 1 100 200 500 500 500 500 500 500
Max concurrent workers (requests) per pool 2 100 200 400 600 800 1600 2400 3200
Max concurrent sessions per pool 2 30000 30000 30000 30000 30000 30000 30000 30000
Min DTU per database choices 0, 5 0, 5 0, 5 0, 5 0, 5 0, 5 0, 5 0, 5
Max DTU per database choices 5 5 5 5 5 5 5 5
Max storage per database (GB) 2 2 2 2 2 2 2 2

1 See Resource management in dense elastic pools for additional considerations.

2 For the max concurrent workers (requests) for any individual database, see Single database resource limits. For example, if the elastic pool is using Gen5 and the max vCore per database is set at 2, then the max concurrent workers value is 200. If max vCore per database is set to 0.5, then the max concurrent workers value is 50 since on Gen5 there are a max of 100 concurrent workers per vCore. For other max vCore settings per database that are less 1 vCore or less, the number of max concurrent workers is similarly rescaled.

Standard elastic pool limits

eDTUs per pool 50 100 200 300 400 800
Included storage per pool (GB) 1 50 100 200 300 400 800
Max storage per pool (GB) 500 750 1024 1280 1536 2048
Max In-Memory OLTP storage per pool (GB) N/A N/A N/A N/A N/A N/A
Max number DBs per pool 2 100 200 500 500 500 500
Max concurrent workers (requests) per pool 3 100 200 400 600 800 1600
Max concurrent sessions per pool 3 30000 30000 30000 30000 30000 30000
Min DTU per database choices 0, 10, 20, 50 0, 10, 20, 50, 100 0, 10, 20, 50, 100, 200 0, 10, 20, 50, 100, 200, 300 0, 10, 20, 50, 100, 200, 300, 400 0, 10, 20, 50, 100, 200, 300, 400, 800
Max DTU per database choices 10, 20, 50 10, 20, 50, 100 10, 20, 50, 100, 200 10, 20, 50, 100, 200, 300 10, 20, 50, 100, 200, 300, 400 10, 20, 50, 100, 200, 300, 400, 800
Max storage per database (GB) 1024 1024 1024 1024 1024 1024

1 See SQL Database pricing options for details on additional cost incurred due to any extra storage provisioned.

2 See Resource management in dense elastic pools for additional considerations.

3 For the max concurrent workers (requests) for any individual database, see Single database resource limits. For example, if the elastic pool is using Gen5 and the max vCore per database is set at 2, then the max concurrent workers value is 200. If max vCore per database is set to 0.5, then the max concurrent workers value is 50 since on Gen5 there are a max of 100 concurrent workers per vCore. For other max vCore settings per database that are less 1 vCore or less, the number of max concurrent workers is similarly rescaled.

Standard elastic pool limits (continued)

eDTUs per pool 1200 1600 2000 2500 3000
Included storage per pool (GB) 1 1200 1600 2000 2500 3000
Max storage per pool (GB) 2560 3072 3584 4096 4096
Max In-Memory OLTP storage per pool (GB) N/A N/A N/A N/A N/A
Max number DBs per pool 2 500 500 500 500 500
Max concurrent workers (requests) per pool 3 2400 3200 4000 5000 6000
Max concurrent sessions per pool 3 30000 30000 30000 30000 30000
Min DTU per database choices 0, 10, 20, 50, 100, 200, 300, 400, 800, 1200 0, 10, 20, 50, 100, 200, 300, 400, 800, 1200, 1600 0, 10, 20, 50, 100, 200, 300, 400, 800, 1200, 1600, 2000 0, 10, 20, 50, 100, 200, 300, 400, 800, 1200, 1600, 2000, 2500 0, 10, 20, 50, 100, 200, 300, 400, 800, 1200, 1600, 2000, 2500, 3000
Max DTU per database choices 10, 20, 50, 100, 200, 300, 400, 800, 1200 10, 20, 50, 100, 200, 300, 400, 800, 1200, 1600 10, 20, 50, 100, 200, 300, 400, 800, 1200, 1600, 2000 10, 20, 50, 100, 200, 300, 400, 800, 1200, 1600, 2000, 2500 10, 20, 50, 100, 200, 300, 400, 800, 1200, 1600, 2000, 2500, 3000
Max storage per database (GB) 1024 1536 1792 2304 2816

1 See SQL Database pricing options for details on additional cost incurred due to any extra storage provisioned.

2 See Resource management in dense elastic pools for additional considerations.

3 For the max concurrent workers (requests) for any individual database, see Single database resource limits. For example, if the elastic pool is using Gen5 and the max vCore per database is set at 2, then the max concurrent workers value is 200. If max vCore per database is set to 0.5, then the max concurrent workers value is 50 since on Gen5 there are a max of 100 concurrent workers per vCore. For other max vCore settings per database that are less 1 vCore or less, the number of max concurrent workers is similarly rescaled.

Premium elastic pool limits

eDTUs per pool 125 250 500 1000 1500
Included storage per pool (GB) 1 250 500 750 1024 1536
Max storage per pool (GB) 1024 1024 1024 1024 1536
Max In-Memory OLTP storage per pool (GB) 1 2 4 10 12
Max number DBs per pool 2 50 100 100 100 100
Max concurrent workers per pool (requests) 3 200 400 800 1600 2400
Max concurrent sessions per pool 3 30000 30000 30000 30000 30000
Min eDTUs per database 0, 25, 50, 75, 125 0, 25, 50, 75, 125, 250 0, 25, 50, 75, 125, 250, 500 0, 25, 50, 75, 125, 250, 500, 1000 0, 25, 50, 75, 125, 250, 500, 1000
Max eDTUs per database 25, 50, 75, 125 25, 50, 75, 125, 250 25, 50, 75, 125, 250, 500 25, 50, 75, 125, 250, 500, 1000 25, 50, 75, 125, 250, 500, 1000
Max storage per database (GB) 1024 1024 1024 1024 1536

1 See SQL Database pricing options for details on additional cost incurred due to any extra storage provisioned.

2 See Resource management in dense elastic pools for additional considerations.

3 For the max concurrent workers (requests) for any individual database, see Single database resource limits. For example, if the elastic pool is using Gen5 and the max vCore per database is set at 2, then the max concurrent workers value is 200. If max vCore per database is set to 0.5, then the max concurrent workers value is 50 since on Gen5 there are a max of 100 concurrent workers per vCore. For other max vCore settings per database that are less 1 vCore or less, the number of max concurrent workers is similarly rescaled.

Premium elastic pool limits (continued)

eDTUs per pool 2000 2500 3000 3500 4000
Included storage per pool (GB) 1 2048 2560 3072 3548 4096
Max storage per pool (GB) 2048 2560 3072 3548 4096
Max In-Memory OLTP storage per pool (GB) 16 20 24 28 32
Max number DBs per pool 2 100 100 100 100 100
Max concurrent workers (requests) per pool 3 3200 4000 4800 5600 6400
Max concurrent sessions per pool 3 30000 30000 30000 30000 30000
Min DTU per database choices 0, 25, 50, 75, 125, 250, 500, 1000, 1750 0, 25, 50, 75, 125, 250, 500, 1000, 1750 0, 25, 50, 75, 125, 250, 500, 1000, 1750 0, 25, 50, 75, 125, 250, 500, 1000, 1750 0, 25, 50, 75, 125, 250, 500, 1000, 1750, 4000
Max DTU per database choices 25, 50, 75, 125, 250, 500, 1000, 1750 25, 50, 75, 125, 250, 500, 1000, 1750 25, 50, 75, 125, 250, 500, 1000, 1750 25, 50, 75, 125, 250, 500, 1000, 1750 25, 50, 75, 125, 250, 500, 1000, 1750, 4000
Max storage per database (GB) 2048 2560 3072 3584 4096

1 See SQL Database pricing options for details on additional cost incurred due to any extra storage provisioned.

2 See Resource management in dense elastic pools for additional considerations.

3 For the max concurrent workers (requests) for any individual database, see Single database resource limits. For example, if the elastic pool is using Gen5 and the max vCore per database is set at 2, then the max concurrent workers value is 200. If max vCore per database is set to 0.5, then the max concurrent workers value is 50 since on Gen5 there are a max of 100 concurrent workers per vCore. For other max vCore settings per database that are less 1 vCore or less, the number of max concurrent workers is similarly rescaled.

Important

More than 1 TB of storage in the Premium tier is currently available in all regions except: China East, China North, Germany Central, and Germany Northeast. In these regions, the storage max in the Premium tier is limited to 1 TB. For more information, see P11-P15 current limitations.

If all DTUs of an elastic pool are used, then each database in the pool receives an equal amount of resources to process queries. The SQL Database service provides resource sharing fairness between databases by ensuring equal slices of compute time. Elastic pool resource sharing fairness is in addition to any amount of resource otherwise guaranteed to each database when the DTU min per database is set to a non-zero value.

Note

For tempdb limits, see tempdb limits.

For additional information on storage limits in the Premium service tier, see Storage space governance.

Database properties for pooled databases

For each elastic pool, you can optionally specify per database minimum and maximum DTUs to modify resource consumption patterns within the pool. Specified min and max values apply to all databases in the pool. Customizing min and max DTUs for individual databases in the pool is not supported.

You can also set maximum storage per database, for example to prevent a database from consuming all pool storage. This setting can be configured independently for each database.

The following table describes per database properties for pooled databases.

Property Description
Max DTUs per database The maximum number of DTUs that any database in the pool may use, if available based on utilization by other databases in the pool. Max DTUs per database is not a resource guarantee for a database. If the workload in each database does not need all available pool resources to perform adequately, consider setting max DTUs per database to prevent a single database from monopolizing pool resources. Some degree of over-committing is expected since the pool generally assumes hot and cold usage patterns for databases, where all databases are not simultaneously peaking.
Min DTUs per database The minimum number of DTUs reserved for any database in the pool. Consider setting a min DTUs per database when you want to guarantee resource availability for each database regardless of resource consumption by other databases in the pool. The min DTUs per database may be set to 0, and is also the default value. This property is set to anywhere between 0 and the average DTUs utilization per database.
Max storage per database The maximum database size set by the user for a database in a pool. Pooled databases share allocated pool storage, so the size a database can reach is limited to the smaller of remaining pool storage and maximum database size. Maximum database size refers to the maximum size of the data files and does not include the space used by the log file.

Important

Because resources in an elastic pool are finite, setting min DTUs per database to a value greater than 0 implicitly limits resource utilization by each database. If, at a point in time, most databases in a pool are idle, resources reserved to satisfy the min DTUs guarantee are not available to databases active at that point in time.

Additionally, setting min DTUs per database to a value greater than 0 implicitly limits the number of databases that can be added to the pool. For example, if you set the min DTUs to 100 in a 400 DTU pool, it means that you will not be able to add more than 4 databases to the pool, because 100 DTUs are reserved for each database.

While the per database properties are expressed in DTUs, they also govern consumption of other resource types, such as data IO, log IO, buffer pool memory, and worker threads. As you adjust min and max per database DTUs values, reservations and limits for all resource types are adjusted proportionally.

Min and max per database DTU values apply to resource consumption by user workloads, but not to resource consumption by internal processes. For example, for a database with a per database max DTU set to half of the pool eDTU, user workload cannot consume more than one half of the buffer pool memory. However, this database can still take advantage of pages in the buffer pool that were loaded by internal processes. For more information, see Resource consumption by user workloads and internal processes.

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