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Month: August 2019

SQL Server Agent Security

Published 2019-08-15 by Kevin Feasel

Claudio Silva explains how you can provide secure access to manage SQL Agent jobs:

It is common having services accounts that are job owners so they can run within the proper context.

In my humble opinion, this starts to be a little strange when it comes to modifying the agent job. It means that the service account needs permissions on agent roles and someone will need to connect to SQL Server using the service account (run as) so they can manage the agent job. It works, but not practical.

It’s not trivial, but there are roles and you can add a bit of extra code to help.

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Storing Passwords in the Database

Published 2019-08-15 by Kevin Feasel

Randolph West explains the problems with storing passwords in the database and explains the best alternative:

If you are storing passwords in a database, you should stop doing that immediately. We, as software developers and data professionals, should never know what passwords our customers are using. The same goes for most sensitive data: we technical staff probably don’t need to know what’s in there. Some stuff should be hashed, and some stuff should be encrypted.

There’s good advice here.

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Power BI Icon Names

Published 2019-08-15 by Kevin Feasel

Matt Allington is on a quest to find all of the Power BI icons:

The benefit of this approach is you can leverage all the standard icons and then add you own icons as well, effectively extending the default icon set. But where can I find a list of all the names of the standard icons?

I asked this question in the Power BI Blog thread (as did some others). A list of names was provided by Francisco Mullor in the comment section of that blog post (sorry, I can’t seem to link to the exact comment). I have taken the information provided by Francisco and produced the following Power BI report.

Matt also fixes a display issue that you might run into when using these.

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Powershell Dot-Sourcing

Published 2019-08-15 by Kevin Feasel

Shane O’Neill takes us through some of the intricacies of dot-sourcing in Powershell:

The dot used to represent the location is, as I’ve said before, for the current location. Our ConvertTo-Message02 script changed it’s location as part of the script.

When we used the “dot source dot location” method, we weren’t using where our function is as a frame of reference to import the other functions. We were using what directory we are currently in.

Interesting reading.

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Local Randomness and R

Published 2019-08-14 by Kevin Feasel

Evgeni Chasnovski has a problem around generating random data:

Let’s say we have a deterministic (non-random) problem for which one of the solutions involves randomness. One very common example of such problem is a function minimization on certain interval: it can be solved non-randomly (like in most methods of optim()), or randomly (the simplest approach being to generate random set of points on interval and to choose the one with the lowest function value).

What is a “clean” way of writing a function to solve the problem? The issue with direct usage of randomness inside a function is that it affects the state of outer random number generation:

Click through for a solution which uses random numbers but doesn’t change the outside world’s random number generation after it’s done.

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The Databricks File System

Published 2019-08-14 by Kevin Feasel

Brad Llewellyn takes us through the Azure Databricks File System:

Today, we’re going to talk about the Databricks File System (DBFS) in Azure Databricks.  If you haven’t read the previous posts in this series, Introduction, Cluster Creation and Notebooks, they may provide some useful context.  You can find the files from this post in our GitHub Repository.  Let’s move on to the core of this post, DBFS.

As we mentioned in the previous post, there are three major concepts for us to understand about Azure Databricks, Clusters, Code and Data.  For this post, we’re going to talk about the storage layer underneath Azure Databricks, DBFS.  Since Azure Databricks manages Spark clusters, it requires an underlying Hadoop Distributed File System (HDFS).  This is exactly what DBFS is.  Basically, HDFS is the low cost, fault-tolerant, distributed file system that makes the entire Hadoop ecosystem work.  We may dig deeper into HDFS in a later post.  For now, you can read more about HDFS here and here.

Click through for more detail on DBFS.

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Logical Equivalence and Query Tuning

Published 2019-08-14 by Kevin Feasel

Erik Darling didn’t warn us that there would be math:

Often when query tuning, I’ll try a change that I think makes sense, only to have it backfire.

It’s not that the query got slower, it’s that the results that came back were wrong different.

Now, this can totally happen because of a bug in previously used logic, but that’s somewhat rare.

And wrong different results make testers nervous. Especially in production.

This is where knowledge of abstract math and logic (like De Morgan’s Laws, both of which I’ve used to tune queries in the past because I’m a nerd) can pay off

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Pitfalls with Window Functions

Published 2019-08-14 by Kevin Feasel

Itzik Ben-Gan takes us through two issues you might run into when using window functions:

There are two common pitfalls involving window functions, both of which are the result of counterintuitive implicit defaults that are imposed by the SQL standard. One pitfall has to do with calculations of running totals where you get a window frame with the implicit RANGE option. Another pitfall is somewhat related, but has more severe consequences, involving an implicit frame definition for the FIRST_VALUE and LAST_VALUE functions.

There’s a lot going on in these two examples, so read on.

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So Your tempdb is Corrupt

Published 2019-08-14 by Kevin Feasel

Steve Stedman walks us through how to fix corruption in tempdb:

The fact that you know you have corruption in TempDB is good news, that shows that you are running CheckDB against TempDB and many people overlook this.

    The corrupt page in TempDB may cause some issues if it is not cleared up.

    Since the TempDB files are recreated if they don’t exist when SQL Server restarts, here is what I would recommend.

Read on for Steve’s advice.

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