Azure SQL Database Elasticity – Presentation Notes

This blog covers the content and points to the code used to create the demos in my Azure SQL Database Elasticity presentations. As of today, I have presented this at the Minnesota SQL Server User Group (PASSMN) in September 2020 and as a webinar for 3Cloud in October 2020.

Elastic Queries

Elastic queries allow developers to interact with data from multiple databases supported on the Azure SQL database platform including Synapse. Elastic queries are often referred to as Polybase which is currently implemented in SQL Server 2019 and Azure Synapse. The key difference is that elastic queries only allow you to interact with other Azure SQL Databases but not Hadoop or other database implementations (e.g. Teradata or Oracle). Part of the confusion comes from the fact that the implementation looks very similar. Both toolsets use external tables in SQL Server to interact with the connected data sources. However, Polybase requires additional components to run whereas elastic queries are ready to go without additional setup.

Be aware elastic queries are still in preview. Also, elastic queries are included in the cost of Azure SQL Database in standard and premium tiers.

Elastic Query Strategies

Elastic queries support three key concepts and will influence how you implement the feature.

  1. Vertical partitioning. This concept uses complete tables in separate databases. It could be a shared date table or dimensions in a data warehouse solution. Vertical partitioning is a method to scale out data solutions. This is one method to use Azure SQL database for larger data solutions.
  2. Horizontal partitioning or sharding. Whereas vertical partitioning keeps tables together, horizontal partitioning shards or spreads the data from a single table across multiple Azure SQL Databases. This is the most complex type of partitioning as it requires a shard map. This is typically implemented with .NET or Java applications.
  3. Data virtualization. This concept is a mix of the partitioning solutions to achieve the goal of virtualizing the data. The idea with data virtualization is that we can use a single Azure SQL Database to interact with data from multiple databases. While this concept is limited due to the limit to use Azure SQL Databases, it is a concept to look for more improvements as the product matures even more.

Elastic Query Demo

The demo used in the presentations is configured as shown here:

Three S1 Azure SQL Databases on the same Azure SQL Server. I used ADF (Azure Data Factory) to move Fact.Purchase to WideWorldDW_2 and the three related dimensions (dimDate, dimStockItem, dimSupplier) to WideWorldDW_3. I then used WideWorldDW_3 to implement the external tables to work with the data. The WideWorldImportersDW-Standard was used as the original restore of the sample database. It is the source of the data but is not used in the demos.

One note on the demo. I did not include the ADF jobs. Use the Copy activity to move the tables to the target databases. You can find more information here.

The demo code to set up the environment can be found here.

Elastic Jobs

Elastic jobs is the alternative to SQL Server Agent Jobs in Azure SQL Database. While Agent is included in Azure SQL Managed Instance, the rest of the platform needed an option to create jobs. Elastic jobs solves that issue. Currently this is also in preview and is also included with Azure SQL Database. The only additional cost is that a dedicated job database is required to support elastic jobs.

The best comparison is still with SQL Server Agent. Elastic jobs are structured with jobs which have job steps. The only limitation at the moment is that job steps must be T-SQL. Jobs can be created in the Azure portal, with PowerShell, with REST, or with T-SQL.

Elastic Transactions

One of the key pieces that was originally missing from the Azure SQL Database rollout was cross database transactions that were supported in SQL Server with MSDTC. Elastic transactions add this functionality to Azure SQL Database and is built into the platform. This functionality is application driven and currently supported in the latest .NET libraries. Overall, this will allow you to support transactions across 100 databases or fewer. While there is no limit, Microsoft currently recommends only using this to support distributed transactions over 100 or less databases due to potential performance issues.

There are a few limitations to be aware of:

  • Only supports Azure SQL Databases
  • Only supports .NET transactions
  • Does not support T-SQL Distributed transactions
  • Does not support WCF transactions

Wrap Up

Microsoft continues to improve the functionality in Azure SQL Database. These elastic features are part of that process. While I typically do not have many uses for distributed transactions, we have actively implemented elastic queries and elastic jobs for customers and look to use them more in the future.

Azure SQL Elasticity References

Hopefully you too will be able to use the elastic functionality as you continue to embrace the Azure data platform.

T-SQL Tuesday #87 – Fixing Old Problems with Shiny New Toys: STRING_SPLIT

tsql2sday-300x300Thanks to Matt Gordon (@atsqlspeed) for hosting this T-SQL Tuesday.

Splitting Strings in SQL

A problem that has plagued SQL developers through the years is splitting strings. Many techniques have been used as more capabilities were added to SQL Server including XML datatypes, recursive CTEs and even CLR. I have used XML datatype methods to solve the problem most often. So, without further ado…

T-SQL Function: STRING_SPLIT

I have previously highlighted this function in a webinar with Pragmatic Works as a Hidden Gem in SQL Server 2016. It was not announced with great fanfare, but once discovered, solves a very common problem.

Syntax

STRING_SPLIT(string, delimiter)

The STRING_SPLIT function will return a single column result set. The column name is “value”. The datatype will be NVARCHAR for strings that are NCHAR or NVARCHAR. VARCHAR is used for strings that are CHAR or VARCHAR types.

Example

DECLARE @csvString AS VARCHAR(100)
SET @csvString = 'Monday, Tuesday, Wednesday, Thursday, Friday'
SELECT value AS WorkDayOfTheWeek 
FROM STRING_SPLIT (@csvString, ',');

The initial example returns the follow results:#tsql2sday

value
Monday
 Tuesday
 Wednesday
 Thursday
 Friday

As you can see in the example, the results returned a leading space which was in the original string. The following example trims leading and trailing spaces.

DECLARE @csvString AS VARCHAR(100)
SET @csvString = 'Monday, Tuesday, Wednesday, Thursday, Friday'
SELECT LTRIM(RTRIM(value)) AS WorkDayOfTheWeek 
FROM STRING_SPLIT (@csvString, ',');

The cleaned example returns the follow results:

value
Monday
Tuesday
Wednesday
Thursday
Friday

Thanks again Matt for this opportunity to share an underrated, but really useful shiny new tool in SQL Server 2016.

SQL Saturday #492 Follow Up – A Window into Your Data

sqlsat492_web

Thanks for attending my session on window functions in TSQL. I hope you learned something you can take back and use in your projects or at your work. You will find an link to the session and code I used below. If you have any questions about the session post them in comments and I will try to get you the answers.

Questions and Comments

  1. Does RATIO_TO_REPORT exist in SQL Server? It is in Oracle.
    • Currently this function is not available in SQL Server
    • Here is the equivalent functionality using existing functions in SQL Server:
      • OrderAmt / SUM(OrderAmt) OVER (PARTITION BY OrderDate)
      • This example can use the source code I have referenced below. It uses the current value as the numerator and the sum by partition as the denominator. While not a simple function, the equivalent is still fairly simple using window functions to help.
  2. Demo issues with Azure SQL Database
    • During the session I ran into an issue with Azure SQL Database. It turns out that the following two functions are not supported there.
      • PERCENTILE_CONT
      • PERCENTILE_DISC

Slides, Code, and Follow Up Posts

The presentation can be found here: A Window into Your Data

The code was put into a Word document that you can get here: TSQL Window Function Code

This session is also backed by an existing blog series I have written.

T-SQL Window Functions – Part 1- The OVER() Clause

T-SQL Window Functions – Part 2- Ranking Functions

T-SQL Window Functions – Part 3: Aggregate Functions

T-SQL Window Functions – Part 4- Analytic Functions

Microsoft Resources:

SQL Saturday #486 Richmond – A Window Into Your Data

 

sqlsat486_web

Thanks for attending my session on window functions in TSQL. I hope you learned something you can take back and use in your projects or at your work. You will find an link to the session and code I used below. If you have any questions about the session post them in comments and I will try to get you the answers.

Questions

  1. Can an OVER clause be used in the WHERE clause?
    • No. The OVER clause can only be used in SELECT and ORDER BY clauses.
  2. Some follow up on ROWS and RANGE with context to CURRENT ROW.
    • We had a lot of discussion around this. In our examples below, RANGE aggregated all the data that fit into the ORDER BY clause. ROWS only referenced the row it was in. So, RANGE looks at everything that meets the criteria established by the PARTITION BY and ORDER BY clauses. ROWS is bound to the physical row.
    • Code examples:
      • OVER (PARTITION BY CustomerName ORDER BY OrderDate RANGE CURRENT ROW)
        • Summed two rows of data for the customer with the date. Both rows had the same date.
      • OVER (PARTITION BY CustomerName ORDER BY OrderDate ROWS CURRENT ROW)
        • Each row only contained the data for the row it was in.

Slides, Code, and Follow Up Posts

The presentation can be found here: A Window into Your Data

The code was put into a Word document that you can get here: TSQL Window Function Code

This session is also backed by an existing blog series I have written.

T-SQL Window Functions – Part 1- The OVER() Clause

T-SQL Window Functions – Part 2- Ranking Functions

T-SQL Window Functions – Part 3: Aggregate Functions

T-SQL Window Functions – Part 4- Analytic Functions

Microsoft Resources:

SQL Saturday #437–Boston BI Edition 2015–You Can Still Analyze Data with T-SQL

image3

Thanks for attending my session on analyzing data with TSQL. I hope you learned something you can take back and use in your projects or at your work. You will find an link to the session and code I used below. If you have any questions about the session post them in comments and I will try to get you the answers.

The presentation can be found here: Analyzing with TSQL

The code was put into a Word document that you can get here: Code to support the analysis with TSQL Sessions

This session is also backed by an existing blog series I have written.

T-SQL Window Functions – Part 1- The OVER() Clause

T-SQL Window Functions – Part 2- Ranking Functions

T-SQL Window Functions – Part 3: Aggregate Functions

T-SQL Window Functions – Part 4- Analytic Functions

Microsoft Resources: