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Azure Cosmos DB for PostgreSQL limits and limitations

  • Artikkeli

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 fails 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 32 TiB of storage is supported on coordinator and worker nodes in multi-node configuration. Up to 2 TiB of storage is supported for single node configurations. See the available storage options and IOPS calculation for various node and cluster sizes.

Customer-managed keys for storage encryption

Data encryption with customer-managed keys (CMK) for Azure Cosmos DB for PostgreSQL clusters has the following limitations.

  • CMK encryption can only be enabled during the creation of a new Azure Cosmos DB for PostgreSQL cluster.
  • CMK encryption isn't supported with private access (Private Link).

Compute

Subscription vCore limits

Azure enforces a vCore quota per subscription per region. There are three independently adjustable quotas: vCores for coordinator nodes, vCores for worker nodes, and vCores for burstable compute. The default quota should be more than enough to experiment with Azure Cosmos DB for PostgreSQL and run small to medium size production. 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
  • Geo-redundant backup
  • The azure_storage extension

Authentication

Microsoft Entra ID authentication

If Microsoft Entra ID is enabled on an Azure Cosmos DB for PostgreSQL cluster, the following is currently not supported:

  • PostgreSQL 11, 12, and 13
  • Microsoft Entra groups

Security

MD5 hashing is disabled in Azure Cosmos DB for PostgreSQL and impacts the following areas:

  • Native Postgres passwords are hashed using SCRAM-SHA-256 method only.
  • pgcrypto extension: MD5 isn't available as a hashing method.
  • uuid-ossp extension: MD5 isn't available as a hashing method.
  • Built-in Postgres functions. For instance, SELECT md5(‘your_string’);
  • Custom functions such as custom functions in PL/pgSQL that use MD5 hashing.

Database creation

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

By default this database is called citus. Azure Cosmos DB for PostgreSQL supports custom database names at cluster provisioning time only.

Backup and restore

Geo-redundant backup and restore

  • Geo-redundant backup can be enabled only during cluster creation.
  • Geo-redundant backup can't be disabled once cluster is created.
  • Geo-redundant backup can't be enabled on single node clusters with burstable compute.
  • Customer managed key (CMK) isn't supported for clusters with geo-redundant backup enabled.
  • Azure Cosmos DB for PostgreSQL cluster with geo-redundant backup enabled can't have a cluster read replica in the region where geo-redundant backup is stored.

Next steps