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Curated SQL Posts

Sorting Power Pivot Data On Load

Published 2016-02-09 by Kevin Feasel

Matt Allington suggests pre-sorting results to reduce load in Power Pivot:

Imagine you have 50,000 products in your data table and you have 50,000,000 rows of data.  Power Pivot will take the first 1 million rows it comes to (1 segment worth), work out how to sort and compress the columns, and then compress the data into a single segment before moving to the next 1 million rows it comes to (in the order they are loaded).  When it does this, it is highly likely that every product number will appear in every single segment – all 50 segments.  If we assume an equal number of product records for each product (unlikely but OK for this discussion), then there would be 1,000 records for each product spread throughout the entire data table,and each and every segment is likely to contain all 50,000 product IDs.  This is not good for compression.

This is an interesting result and not something I would have thought intuitive.

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Understanding Logins Versus Users

Published 2016-02-09 by Kevin Feasel

Kenneth Fisher has a user which should have rights but is unable to access the database in question:

The other day I ran across an interesting problem. A user was logging in but didn’t have access to a database they were certain they used to access to. We checked and there they were. Not only was there a database principal (a user) but it was a member of db_owner. But still no go. The user could not connect. I went to the database and impersonated them and then checked sys.fn_my_permissions. They were definitely a member of db_owner. I tested and yes, I could read the tables they needed, and yes they could execute the stored procedures they needed to execute. So what was wrong?

Keep those principals in alignment.

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Dynamic Data Masking In Detail

Published 2016-02-09 by Kevin Feasel

Louis Davidson has a two-part series on dynamic data masking in SQL Server 2016.

Part 1:

An interesting feature that is being added to SQL Server 2016 is Dynamic Data Masking. What it does is, allow you to show a user a column, but instead of showing them the actual data, it masks it from their view. Like if you have a table that has email addresses, you might want to mask the data so most users can’t see the actual data when they are querying the data. It falls under the head of security features in Books Online (https://msdn.microsoft.com/en-us/library/mt130841.aspx), but as we will see, it doesn’t behave like classic security features, as you will be adding some code to the DDL of the table, and (as of this writing in CTP3.2, the ability to fine tune who can and cannot see unmasked data isn’t really there.)

Part 2:

The moral here is that need to be careful about how you use this feature. It is not as strict as column level security (or as Row Level Security will turn out to be, which is the next series of blogs to follow), so if a user has ad-hoc access to your db, they could figure out the data with some simple queries.

Louis’s second part is particularly interesting, as he delves into the various ways in which you can back into answers (some of which, like casting values to other types, have been fixed).

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Installing SSRS 2016

Published 2016-02-08 by Kevin Feasel

James Anderson has a quick runthrough of installing SSRS 2016:

This first post of 3 takes a quick peek at SSRS 2016 using the Community Technical Preview (CTP) 3.2. I will be making a quick post installation tweak and then guiding you through the steps to build your first report. If you are experienced with SSRS you can probably just scan this post to see the differences in 2016. See the past post Installing SQL Server 2016 for details on the install I did prior to working on this post.

Installation and configuration don’t look radically different from the last couple versions, but it’s good to get a refresher on the topic.

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Automating SQL Server Installations

Published 2016-02-08 by Kevin Feasel

Joey D’Antoni argues in favor of automating SQL Server installations:

Anyway, on to my original topic—I know most shops aren’t Comcast where we were deploying multiple servers a week. However, automating your installation process has a lot of other benefits—you don’t have to worry about misconfigurations, unless you put in into your script. It also forces you into adopting a standard drive letter approach to all of your servers. So when something breaks, you know exactly where to go. And more importantly you save 15 minutes of clicking next.

For any shop which deploys SQL Server more than a couple times every few years, automating your installation process is a smart move.  Even if you rarely deploy, the consistency benefits make it worthwhile.

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Beware ROWLOCK Hints

Published 2016-02-08 by Kevin Feasel

Kendra Little points out that ROWLOCK hints might make blocking worse:

Note that the logical reads are the exact same and neither query is doing physical reads (the execution plans are the same– the optimizer doesn’t care what locks you are using). The queries were run with SET STATISTICS IO,TIME OFF and Execution Plans turned off, just to reduce influencing factors on duration and CPU.

The database engine is simply having to do more work here. Locking the pages in the clustered index is less work than locking each of the 1,825,433 rows.

Even though our locks are more granular, making queries run longer by taking out individual locks will typically lead to more blocking down the road.

Kendra follows up with several optimization possibilities, so read the whole thing.

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The Value Of Sparse Columns

Published 2016-02-08 by Kevin Feasel

Erin Stellato discusses sparse columns:

In conclusion, we see a significant reduction in disk space and IO when sparse columns are used, and they perform slightly better than non-sparse columns in our simple data modification tests (note that retrieval performance should also be considered; perhaps the subject of another post).

Sparse columns have a lot of potential value, but in my experience, they fall short in one huge way:  you cannot compress tables with sparse columns.  Given that both sparse columns and data compression are things which benefit from scale, it’s important to make the right choice upfront.

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Lineage Improvements

Published 2016-02-08 by Kevin Feasel

Andy Leonard shows LineageId improvements over the years:

SSIS 2016 CTP3.3 offers a solution. First, there are now two new columns in the SSIS Data Flow Component Error Output – ErrorCode – Description and ErrorColumn – Description:

The new columns provide extremely useful (plain language) error metadata that will, in my opinion, greatly reduce the amount of time required to identify data-related load failures in the Data Flow Task.

But that’s not all. If you configure a log to capture the DiagnosticEx event, you will receive a message that provides the Data Flow column ID. To have a look, add a new log to an SSIS package that contains a configured Data Flow Task. On the Details tab, select the DiagnosticEx event:

Backtracing LineageId was a painful experience for me, so I’m happy that they’re making this better.

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Copying SSIS Packages

Published 2016-02-08 by Kevin Feasel

Andy Galbraith shows how to copy SSIS packages using DTUTIL:

A frequent need when performing a server migration is to copy the SSIS packages from one server to a new server.  There are a couple of different ways to do this, including a wizard in SSMS. (See https://www.mssqltips.com/sqlservertip/2061/how-to-manage-ssis-packages-stored-in-multiple-sql-server-database-instances/).  The catch to this is that these are manual and they only move one package at a time.

I recently had to migrate a server with over twenty packages, and I knew I didn’t want to click-click-click over and over again.  🙂

The best answer would be to have your packages safe and secure in source control, but sometimes that’s not an option.

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