TOP 1 Tuning

Kenneth Fisher has a good case study on tuning with the help of Rob Farley:

Here we are looking at the difference between the estimated and actual number of rows for an element of the plan. To look at this information you can either mouse over the element or right click and open the properties tab. In this case you will see that the estimated number of rows (what the optimizer thought would happen) is fairly low (117) particularly compared to what actually happened (1494900). When you see a big difference like that in a query plan there is something wrong.

This is a really nice and detailed walkthrough in which Rob plays Socrates and Kenneth your favorite of the group (Thrasymachus anyone?).

Writable Partition Failure

Paul White shows us a scenario in which attempts to update a writable partition could fail:

The where clause is exactly the same as before. The only difference is that we are now (deliberately) setting the partitioning column equal to itself. This will not change the value stored in that column, but it does affect the outcome. The update now succeeds (albeit with a more complex execution plan):

The optimizer has introduced new Split, Sort, and Collapse operators, and added the machinery necessary to maintain each potentially-affected nonclustered index separately (using a wide, or per-index strategy).

Read on for the reason why this happens, as well as a few solutions.

Autostart XE With Powershell

Rob Sewell shows us how to set a particular extended event to start automatically when SQL Server starts up:

Very quick and simple and hopefully of use to people, this could easily be turned into a function. The full script is below and also available here on the Powershell gallery or by running  Save-Script -Name Set-ExtendedEventsSessionstoAutoStart -Path <path>

This is indeed a quick and easy script, and quite useful when checking across a large number of instances.

Memory Pressure

Thomas Rushton walks us through determining if there’s memory pressure on an instance:

If you’ve been paying attention, you’ll have noticed that I’ve done the rownumbering in reverse order, and added a dummy (RowNum 0) field at the top of the list – this is to make sure that, if the most recent record is a RESOURCE_MEMPHYSICAL_LOW record, that we can get results that include that value.

This all looks OK in theory. But we’re still getting stupidly high values for the SecondsPressure field, and wait – what’s this? Multiple ring buffer records with the same ID?

More importantly, he shows us how bad the situation is:  is this something that happened for a couple of seconds, or is it persistent?  This is a great walkthrough.

SSAS Auditing

Matt Smith links to Analysis Services auditing details and includes an audit table:

There are various types of Auditing in the Microsoft BI stack. There is auditing in SSRS, SharePoint, SSAS and not forgetting SQL has its own auditing.

Today I am looking at the SSAS auditing – you can find out more about it onTechNet.

Olaf Helper has published some TSQL code for querying the audit data -on theScript Center.

Just because it’s in a cube doesn’t mean we shouldn’t be able to audit it.

Analyze In Excel

Avi Singh notes that Power BI will soon allow you to analyze data sets in Excel:

As a Modern Excel enthusiast (Modern Excel = Excel + Power Pivot + Power Query = Magic!), I found myself hesitant in embracing the new world of Power BI. Many of those inhibitions have shed away as Microsoft has continued to innovate and deliver an outstanding experience with Power BI. But I could not get over the feeling that going from Excel to Power BI felt like a one-way street.

You could upload/import an Excel Power Pivot model into Power BI desktop or onto PowerBI.com. But then you could not get it back. You could not get it back in Excel. In thefirst blog post on the site (yes the very first) Rob called us gridheads, and that we are.

Excel is still the top tool for business users.  Anything you can do to make life easier for your Excel users makes life easier for you as well.

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