Limits in Azure Database for PostgreSQL - Flexible Server

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The following sections describe capacity and functional limits in the database service. If you'd like to learn about resource (compute, memory, storage) tiers, see the compute and storage article.

Maximum connections

The maximum number of connections per pricing tier and vCores are shown below. The Azure system requires three connections to monitor the Azure Database for PostgreSQL - Flexible Server.

SKU Name vCores Memory Size Max Connections Max User Connections
Burstable
B1ms 1 2 GiB 50 47
B2s 2 4 GiB 100 97
General Purpose
D2s_v3 / D2ds_v4 2 8 GiB 859 856
D4s_v3 / D4ds_v4 4 16 GiB 1719 1716
D8s_v3 / D8ds_V4 8 32 GiB 3438 3435
D16s_v3 / D16ds_v4 16 64 GiB 5000 4997
D32s_v3 / D32ds_v4 32 128 GiB 5000 4997
D48s_v3 / D48ds_v4 48 192 GiB 5000 4997
D64s_v3 / D64ds_v4 64 256 GiB 5000 4997
Memory Optimized
E2s_v3 / E2ds_v4 2 16 GiB 1719 1716
E4s_v3 / E4ds_v4 4 32 GiB 3438 3433
E8s_v3 / E8ds_v4 8 64 GiB 5000 4997
E16s_v3 / E16ds_v4 16 128 GiB 5000 4997
E20ds_v4 20 160 GiB 5000 4997
E32s_v3 / E32ds_v4 32 256 GiB 5000 4997
E48s_v3 / E48ds_v4 48 384 GiB 5000 4997
E64s_v3 / E64ds_v4 64 432 GiB 5000 4997

When connections exceed the limit, you may receive the following error:

FATAL: sorry, too many clients already.

Important

For best experience, we recommend that you use a connection pool manager like PgBouncer to efficiently manage connections. Azure Database for PostgreSQL - Flexible Server offers pgBouncer as built-in connection pool management solution.

A PostgreSQL connection, even idle, can occupy about 10 MB of memory. Also, creating new connections takes time. Most applications request many short-lived connections, which compounds this situation. The result is fewer resources available for your actual workload leading to decreased performance. Connection pooling can be used to decrease idle connections and reuse existing connections. To learn more, visit our blog post.

Functional limitations

Scale operations

  • Scaling the server storage requires a server restart.
  • Server storage can only be scaled in 2x increments, see Compute and Storage for details.
  • Decreasing server storage size is currently not supported.

Server version upgrades

  • Automated migration between major database engine versions is currently not supported. If you would like to upgrade to the next major version, take a dump and restore it to a server that was created with the new engine version.

Storage

  • Once configured, storage size cannot be reduced. You have to create a new server with desired storage size, perform manual dump and restore and migrate your database(s) to the new server.
  • Currently, storage auto-grow feature is not available. Please monitor the usage and increase the storage to a higher size.
  • When the storage usage reaches 95% or if the available capacity is less than 5 GiB, the server is automatically switched to read-only mode to avoid errors associated with disk-full situations.
  • We recommend to set alert rules for storage used or storage percent when they exceed certain thresholds so that you can proactively take action such as increasing the storage size. For example, you can set an alert if the storage percent exceeds 80% usage.

Networking

  • Moving in and out of VNET is currently not supported.
  • Combining public access with deployment within a VNET is currently not supported.
  • Firewall rules are not supported on VNET, Network security groups can be used instead.
  • Public access database servers can connect to public internet, for example through postgres_fdw, and this access cannot be restricted. VNET-based servers can have restricted outbound access using Network Security Groups.

High availability (HA)

Availability zones

  • Manually moving servers to a different availability zone is currently not supported.
  • The availability zone of the HA standby server cannot be manually configured.

Postgres engine, extensions, and PgBouncer

  • Postgres 10 and older are not supported. We recommend using the Single Server option if you require older Postgres versions.
  • Extension support is currently limited to the Postgres contrib extensions.
  • Built-in PgBouncer connection pooler is currently not available for Burstable servers.
  • SCRAM authentication is not supported with connectivity using built-in PgBouncer.

Stop/start operation

  • Server can't be stopped for more than seven days.

Scheduled maintenance

  • Changing the maintenance window less than five days before an already planned upgrade, will not affect that upgrade. Changes only take effect with the next scheduled maintenance.

Backing up a server

  • Backups are managed by the system, there is currently no way to run these backups manually. We recommend using pg_dump instead.
  • Backups are always snapshot-based full backups (not differential backups), possibly leading to higher backup storage utilization. Note that transaction logs (write ahead logs - WAL) are separate from the full/differential backups, and are archived continuously.

Restoring a server

  • When using the Point-in-time-Restore feature, the new server is created with the same compute and storage configurations as the server it is based on.
  • VNET based database servers are restored into the same VNET when you restore from a backup.
  • The new server created during a restore does not have the firewall rules that existed on the original server. Firewall rules need to be created separately for the new server.
  • Restoring a deleted server is not supported.
  • Cross region restore is not supported.

Other features

  • Azure AD authentication is not yet supported. We recommend using the Single Server option if you require Azure AD authentication.
  • Read replicas are not yet supported. We recommend using the Single Server option if you require read replicas.
  • Moving resources to another subscription is not supported.

Next steps