Data Source Error : DataSource.Error: PostgreSQL: 53300: Exceeded session limit of 1

Hi Miguel_Rojo,

Thank you for reaching out to the Microsoft Community Forum.

The 53300: Exceeded session limit of 1 error suggests this is more likely coming from the PostgreSQL/AEP side rather than from the Dataflow transformations themselves. Since the refresh still fails even with a single native SQL query and no transformations, your testing already rules out query complexity as the cause.

Power Query/Dataflows may still perform additional backend operations besides the main query, so a strict session limit of 1 can lead to this behavior. Since this was working previously, I would recommend checking with the team managing the PostgreSQL/AEP environment to see whether the session/connection limit was recently changed.

Hope this helps if you have any queries we are  happy to assist you further.
Regards,
Community Support Team.

Hi Miguel_Rojo, 

Power Query will make multiple connection attempts to the data source. There's usually one to list objects or schemas, one to get column names, and then one to get actual data. Sometimes there can be more depending on your query. 

It does sound like some settings changed on your source side, hopefully you can get those reverted so your dataflow will continue to work.