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Limits in Azure Database for PostgreSQL - Flexible Server

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APPLIES TO: Azure Database for PostgreSQL - Flexible Server

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, it is recommended to 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

  • At this time, scaling up 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. Only way to do is dump and restore it to a new Flexible Server.

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 can't 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 isn't available. You can 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 whichever is more, the server is automatically switched to read-only mode to avoid errors associated with disk-full situations. In rare cases, if the rate of data growth outpaces the time it takes switch to read-only mode, your Server may still run out of storage.
  • 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.
  • If you're using logical replication, then you must drop the logical replication slot in the primary server if the corresponding subscriber no longer exists. Otherwise the WAL files start to get accumulated in the primary filling up the storage. If the storage threshold exceeds certain threshold and if the logical replication slot isn't in use (due to non-available subscriber), Flexible server automatically drops that unused logical replication slot. That action releases accumulated WAL files and avoids your server becoming unavailable due to storage getting filled situation.

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 aren't 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 can't 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. However, you can enable HA using the preferred AZ as the standby zone. Once established, you can fail over to the standby and subsequently disable HA.

Postgres engine, extensions, and PgBouncer

  • Postgres 10 and older aren't supported as those are already retired by the open-source community. If you must use one of these versions, you'll need to use the Single Server option which supports the older major versions 95, 96 and 10.
  • Flexible Server supports all contrib extensions and more. Please refer to PostgreSQL extensions.
  • Built-in PgBouncer connection pooler is currently not available for Burstable servers.
  • SCRAM authentication isn't supported with connectivity using built-in PgBouncer.

Stop/start operation

  • Once you stop the Flexible Server, it automatically starts after 7- days.

Scheduled maintenance

  • You can change custom maintenance window to any day/time of the week. However, any changes made after receiving the maintenance notification will have no impact on the next maintenance. Changes only take effect with the following monthly scheduled maintenance.

Backing up a server

  • Backups are managed by the system, there's currently no way to run these backups manually. We recommend using pg_dump instead.
  • The first snapshot is a full backup and consecutive snapshots are differential backups. The differential backups only back up the changed data since the last snapshot backup. For example, if the size of your database is 40GB and your provisioned storage is 64GB, the first snapshot backup will be 40GB. Now, if you change 4GB of data, then the next differential snapshot backup size will only be 4GB. The 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 isn't 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 doesn't 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 isn't supported.
  • Cross region restore isn't supported.
  • Restore to a different subscription is not supported but as a workaround, you can restore the server within the same subscription and then migrate the restored server to a different subscription.

Next steps