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Month: June 2018

HASHBYTES Performance In SQL Server

Published 2018-06-01 by Kevin Feasel

Joe Obbish takes a look at how HASHBYTES doesn’t scale well:

The purpose of the MAX aggregate is to limit the size of the result set. This is a cheap aggregate because it can be implemented as a stream aggregate. The operator can simply keep the maximum value that it’s found so far, compare the next value to the max, and update the maximum value when necessary. On my test server, the query takes about 20 seconds. If I run the query without the HASHBYTES call it takes about 3 seconds. That matches intuitively what I would expect. Reading 11 million rows from a small table out of the buffer pool should be less expensive than calculating 11 million hashes.

From my naive point of view, I would expect this query to scale well as the number of concurrent queries increases. It doesn’t seem like there should be contention over any shared resources, so as long as every query gets on its own scheduler I wouldn’t expect a large degradation in overall run time as the number of queries increases.

Joe’s research isn’t complete, but he does have a conjecture as to why HASHBYTES doesn’t scale well.  That said, the most interesting thing in the post to me was to see Microsoft potentially using bcrypt under the covers for HASHBYTES calculation—if that’s really the case, there actually is a chance that sometime in the future, we’d be able to generate cryptographically secure hashes within SQL Server rather than the MD5, SHA1, and SHA2 hashes we have today.

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Securing Power BI Report Server

Published 2018-06-01 by Kevin Feasel

Steve Hughes gives some advice for securing a Power BI Report Server installation:

You have essentially three layers of access to the report file security in Power BI Report Server.

  1. The portal itself can be secured. You can and should limit access to the reports by only allowing specific users or groups access to the report portal.
  2. Folders can be used to provide more granular security over a group of assets in the report portal. In the image above, I created a folder called PBI Secure Reports. A specific AD group has access to this folder. If a user does not have permissions to the folder, the folder does not show up in the portal and they cannot access the folder or the assets, including Power BI reports, stored in this folder.
  3. Individual reports can be secured as well. I never recommend this option as it becomes administratively difficult to manage. However, the capability is there is a single asset needs to be secured in this fashion.

These options work for any asset stored in the Report Portal and are not limited to Power BI reports.

Power BI Report Server is a different animal from standard Power BI, so securing it will be a bit different as well.

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Resizing Azure Managed Instances

Published 2018-06-01 by Kevin Feasel

Jovan Popovic shows how to resize Azure SQL managed instances with Powershell:

Azure SQL Managed Instance is fully-managed SQL Server Database Engine hosted in Azure cloud. With Managed Instance you can easily add/remove cores associated to the instance and change the reserved size of the instance. You can use PowerShell to easily manage size of the instance and automate this process.

As a prerequisite, you need to have Azure SQL PowerShell libraries to configure Managed Instance. You would need to install Azure RM PowerShell and  AzureRm.Sql module that contains the commands for updating properties of Managed Instance.

Read on for a demo.

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