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Group by on Redshift Data Source Table causes great many active sessions (connection limit exceeded)



I have a fairly simple report loading 10 tables from a single Redshift Datasource, I never had any troubles so far, until today when I duplicated one of the queries and performed a Group By step in the Edit Queries view.  Now it gives the following error 

DataSource.Error: ODBC: ERROR [53300] [Microsoft][Amazon Redshift] (10) Error occurred while trying to connect: [SQLState 53300] FATAL: connection limit "498" exceeded for non-superusers.


Being a superuser myself, I checked open connections for the power bi user in the stl_connection_log, and low and behold, there's over 400 open connections, starting at the time I added the group by to the stept, a couple of connections starting up per second for this special pbi user I've made (and yes, I'm completely sure no one else and no other reports are querying the datasource with this user), ranging over a couple minutes (so from 12:45:55 to 12:48:14). 

How do all these connections get created?? Are there any known issues creating this behaviour, or is it not a power bi issue at all? I'm in import mode, not in direct query mode, by the way. 



Community Support
Community Support

Hi @Anske 

If you use direct query, it is unsupported to transform data like "group by".

Also, please check if you use any unsupported data types:


If error still occurs, please create a support ticket for further analysis.


Best Regards
Community Support Team _ Maggie Li
If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.

Hi Maggie, 


as I remarked in my initial question, I'm NOT using direct query.




Super User
Super User

I've seen certain operations in Power Query against certain data sources cause problems. You could check the Issues forum and see if it is mentioned and if there is a solution.


Also, you could use a work-a-round by using DAX SUMMARIZE or SUMMARIZECOLUMNS to create a new table in your data model.


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