Error: Unable to Establish Connection with the Database

Issue

Syncs fail. The following error appears:

Unable to establish connection with the database. Concurrent connections have exceeded the max allocated limit.

Environment

Connector: PostgreSQL

Considerations

A PostgreSQL database server has the following connection characteristics:

• There is a limit for the total number of concurrent connections defined by the max_connections server parameter. The default value PostgreSQL uses is 100
• Connection limits can be set per user in pg_roles.rolconnlimit

A Fivetran PostgreSQL connector has the following characteristics:

• Each Fivetran PostgreSQL connector uses a minimum of 5 concurrent connections to the underlying database up to a maximum of 20 concurrent connections
• Connectors using the same PostgreSQL database share the concurrent connection limit defined by the max_connections server parameter

Therefore, a PostgreSQL connector may face a situation where the total number of concurrent connections (up to 20 per connector) exceeds the limit of the database server (defined by the max_connections parameter).

Fivetran recommendations

We recommend the following:

• Increase the max_connections limit to accommodate 10 database connections per connector
• For the database user who created the connector, set pg_roles.rolconnlimit to -1 to disable the per-user connection limit and rely on the max_connections server-level limit
• If you have multiple connectors using the same source database, consider using a single connector which syncs everything in the schema instead
• If you set up 12 or more connectors for a single database server, we recommend that you set a lower sync frequency