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Azure Cosmos DB for PostgreSQL limits and limitations

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APPLIES TO: Azure Cosmos DB for PostgreSQL (powered by the Citus database extension to PostgreSQL)

The following section describes capacity and functional limits in the Azure Cosmos DB for PostgreSQL service.

Naming

Cluster name

A cluster must have a name that is 40 characters or shorter.

Networking

Maximum connections

Every PostgreSQL connection (even idle ones) uses at least 10 MB of memory, so it's important to limit simultaneous connections. Here are the limits we chose to keep nodes healthy:

  • Maximum connections per node
    • 300 for 0-3 vCores
    • 500 for 4-15 vCores
    • 1000 for 16+ vCores
  • Maximum connections per node with burstable compute
    • 20 for 1 vCore burstable
    • 40 for 2 vCores burstable

The connection limits above are for user connections (max_connections minus superuser_reserved_connections). We reserve extra connections for administration and recovery.

The limits apply to both worker nodes and the coordinator node. Attempts to connect beyond these limits will fail with an error.

Connection pooling

You can scale connections further using connection pooling. Azure Cosmos DB for PostgreSQL offers a managed pgBouncer connection pooler configured for up to 2,000 simultaneous client connections.

Storage

Storage scaling

Storage on coordinator and worker nodes can be scaled up (increased) but can't be scaled down (decreased).

Storage size

Up to 2 TiB of storage is supported on coordinator and worker nodes. See the available storage options and IOPS calculation above for node and cluster sizes.

Compute

Subscription vCore limits

Azure enforces a vCore quota per subscription per region. There are two independently adjustable quotas: vCores for coordinator nodes, and vCores for worker nodes. The default quota should be more than enough to experiment with Azure Cosmos DB for PostgreSQL. If you do need more vCores for a region in your subscription, see how to adjust compute quotas.

Burstable compute

In Azure Cosmos DB for PostgreSQL clusters with burstable compute enabled, the following features are currently not supported:

  • Accelerated networking
  • Local caching
  • PostgreSQL and Citus version upgrades
  • PostgreSQL 11 support
  • Read replicas
  • High availability
  • The azure_storage extension

PostgreSQL

Database creation

The Azure portal provides credentials to connect to exactly one database per cluster, the citus database. Creating another database is currently not allowed, and the CREATE DATABASE command will fail with an error.

Next steps