Scheduled Refresh against data source updates

[dtrovato]

Hi y'all!

I'm looking for a document that explains what happens with the following scenario:

- power bi service, with a scheduled refresh every t1-time, connected to an azure data source 

- that data source is updated with a t2-random time 

if t1 = t2, what happens to the reports in the service?

does it throw an error or show the "old" report? 

in case of an error...how to handle it? 

[Seth_C_Bauer]

@dtrovato Are you suggesting that the data table in the database is being updated, and there could be a conflict when the Dataset in Power BI refreshes and when the table refreshes?

Depending on your access methods and what is happening in the datasource. It could lock and force a wait, which may time out. You could dirty read from the source, if the data source refreshed quickly it could return after the fact as a call would be in process... a number of things could happen.

[dtrovato]

hi @Seth_C_Bauer, yes that's what I'm suggesting and I agree on that a number of things can happen. Just wondered if there was any doc.

Anyway, what do you mean with "dirty read from the source"? Still using Power BI?

[Seth_C_Bauer]

@dtrovato If your queries include "with(nolock)" they will perform dirty reads on the data. This means that the query will run and return data despite any locks being held on the table. The "dirty" means that if there is a process writing against the table as you query it, you may get the "old" data. In many cases this is ok, in others it wouldn't be. Depends largely on what you are reporting on.

[GilbertQ]

Just a note with the dirty reads is that they still place a schema lock on the table. So if there is a dirty read happening and for example an Index rebuild is trying to start, it cannot start until the dirty read completes.

[Anonymous]

HI @dtrovato,

I would think in this case it migt be a better option to setup a more confident schedule. This would prevent these errors if any from occurring.

[dtrovato]

hi @Anonymous , that's exactly what I had in mind, but in case of a random time you never know what the best settings are. Thanks for your suggestion though