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Frequent Visitor

Lack of information from Microsoft - SSAS Tabular behind scene

Hello,

 

I have a project in SSAS Tabular in production, of which I use its data in a power bi.

I use an "In-Live" connection.

 

I am trying to find out what happens when I filter a visual using a metric inside the power bi for example, I would like to know if this metric is recalculated and if it consumes RAM again to calculate it or if it simply has it stored and this does not imply any use of RAM. I find it very strange that there is no documentation of how the hardware works behind the scenes between PBI and SSAS Tabular live. 

@PBICommunity @v-huizhn-msft 

 

Extra Info: We have a gateway with 1 p2 and 2 p1

 

 

Many thanks in advance

2 REPLIES 2
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Memorable Member
Memorable Member

Re: Lack of information from Microsoft - SSAS Tabular behind scene

Hi @subirana21 ,

 

When Power BI connected to a source Live or via DirectQuery then each visual sends a request to a source and a result is returned to a visual. In your case your visual sends a DAX request to Tabular which consume some RAM (memory) at a machine where Tabular is running.

 

If Power BI uses live connection then it will not consume almost any memory. You can see it if you open such report and then open Windows Task Manager -> Power BI Desktop and look at memory usage.

 

If you want to see which requests are sent to Tabular then use SQL Server Profiler or DAX Studio. Both can track and provide detailed information about it.

 

Power BI file with Import mode and Tabular are using the same engine called Vertipaq (or sometimes xVelocity). If you are interested in its behavior then just read about it. Here is a free part of good book "The Definitive Guide to DAX: Business intelligence with Microsoft Excel, SQL Server Analysis Services, and Power BI" by Marco Russo and Alberto Ferrari - https://www.microsoftpressstore.com/articles/article.aspx?p=2449192.  

 

Regards,
Ruslan Zolotukhin (zoloturu)
BI Engineer at Akvelon Inc. / Kharkiv Power BI User Group Leader / DAX & Power BI Trainer
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Regular Visitor

Re: Lack of information from Microsoft - SSAS Tabular behind scene

@zoloturu  Many thanks for your answer! But  is not what I meant.

When we use a filter of a visual, a query is generated in DAX that is executed against the tabular server, but what I want to know is if it recalculates the metrics as when we do a ProcessRecalc or simply when we have them already calculated, it doesn't do it again.

 

In fact I've been putting in and taking out the same filter and at a certain point the change in the visual is instantaneous, making me suspicious if he's caching the metric.

 

Many thanks!

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