Category: Warehousing

I just put some result on the output, because as you can imagine there are some certain limits on the amount of the output that will be cached and that will be not. Besides the basic logical stuff, such as having deterministic functions only (functions which output will not be varying depending on the execution), not using System Objects or UDFs (and it seems that scalar UDF inlining is not a part of Azure SQL DW yet), no row-level security or column-level security enabled, the main thing and which seems to be pretty good decision as far as I am concerned – the row size larger than 64KB won’t be cached period.

Read on to see what Niko has learned, including cache performing and limitations. Between this and the data pools in SQL Server Big Data Clusters, Microsoft’s spent some time thinking about data caching in cloud-based versions of SQL Server.

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Query Concurrency + Azure Synapse Analytics

Published 2019-12-30 by Kevin Feasel

James Serra takes us through query concurrency with Azure Synapse Analytics:

A common question I here from customers is because of the performance of Azure Synapse Analytics (formally called Azure SQL Data Warehouse or SQL DW), can they run Power BI dashboards against it using DirectQuery (and not have to use Azure Analysis Services (AAS), Import the data into Power BI, or use Power BI aggregation tables), avoiding having another copy of the data (saving money), and having data “real time” (as of the last refresh of the data warehouse)?
There are two things to think of in considering an answer this question. The first is if you will get the performance you need (discussed in my last blog), the second is if a certain amount of concurrent queries or connections will cause a problem (the subject of this blog).

Read the whole thing.

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Changing Synapse Analytics Resource Classes with Azure Automation

Published 2019-12-19 by Kevin Feasel

John McCormack wins today’s edition of Cloud Bingo:

I was a approached by a data warehouse developer who wanted to be able to take advantage of the feature in Azure Synapse Analytics (Formerly Azure SQL Data Warehouse) called ‘Resource classes’. Resource classes allow users in certain roles to have access to extra compute resources for their queries. This can increase their max memory per query (although there is an overall trade-off on concurrency). Unfortunately, due to this being managed via roles, the person looking to change resource classes needs to be in the db_owner role so they can manage database role membership. As I didn’t want to add the developer to the db_owner role, a different solution was required.

John gives us a nice answer to this problem. Click through for the script.

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New Features in Azure Synapse Analytics

Published 2019-11-14 by Kevin Feasel

James Serra gives us a bullet list of new features in Azure Synapse Analytics:

Almost lost in all the announcements from Ignite was a bunch of amazing new features that were added to the Provisioned Resources/SQL Pool section (read SQLDW functionalities) side of Azure Synapse Analytics (formally called Azure SQL Data Warehouse).

One of the more interesting options is ordered clustered columnstore indexes. That seems like something which would be nice to have on-prem. The segment elimination works on-prem today, but ordering is accidental at best. By that, I mean the way that SQL Server loads data into a CCI—roughly, in the order in which you insert it—is not guaranteed to work that way and could change in the future.

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Databricks + Azure Synapse Analytics

Published 2019-11-11 by Kevin Feasel

David Meyer and Clinton Ford explain how you can integrate Azure Databricks with Azure Synapse Analytics:

In the last two years since it first became available, thousands of companies have adopted Azure Databricks, making it one of the fastest growing data and AI services on Microsoft Azure. Customers now process over 2 exabytes per month with millions of server-hours spinning up every day. All of this is driven by organizations like Electrolux, Shell, and renewables.AI that are using Azure Databricks to process data at massive scale for data science and analytics.
Within this amazing adoption is a specific solution architecture to highlight called the Modern Data Warehouse (MDW). Earlier this year we wrote about the performance and scale benefits of this solution, and part of the pattern’s success has been our close integration to Azure SQL Data Warehouse with a high-performance connector that was jointly engineered to make it fast and easy to move data between the two services.

Something interesting about Synapse is that its implementation of Spark is not the same as the Databricks implementation (perhaps for licensing reasons). But that doesn’t stop us from using Databricks to process and curate data for Synapse Analytics.

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Azure Synapse Analytics, Nee Azure SQL DW

Published 2019-11-11 by Kevin Feasel

John Macintire explains Azure Synapse Analytics:

A cloud native, distributed SQL processing engine is at the foundation of Azure Synapse and is what enables the service to support the most demanding enterprise data warehousing workloads. This week at Ignite we introduced a number of exciting features to make data warehousing with Azure Synapse easier and allow organizations to use SQL for a broader set of analytics use cases.

There’s a fair amount of marketing-speak in here, but the gist is Azure SQL Data Warehouse + Spark + on-demand serverless queries (so you can, among other things, write T-SQL against your HDFS data). I think it has a better chance of long-lasting success than Azure SQL Data Warehouse.

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Ordered Clustered Columnstore Indexes in Azure SQL DW

Published 2019-10-07 by Kevin Feasel

Niko Neugebauer takes us through a new feature in preview for Azure SQL Data Warehouse:

After creating (or dropping and recreating a Clustered Columnstore Index we can specify the reserved word ORDER and then one or !!!MULTIPLE!!! columns. This looks like an extremely promising feature!
On Azure SQL Data Warehouse one can of course define table as a Columnstore and with that specification it is also possible to define an ORDER option with one or multiple columns.
For the syntax and basic functionality testing purposes on Azure SQL Data Warehouse, let us then create a table with a Clustered Columnstore Index, load some data and see if by recreating an Ordered Clustered Columnstore Index we can achieve some improvements.

Niko has a few hard-earned lessons from this post.

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Data Warehouse Concepts

Published 2019-09-27 by Kevin Feasel

Katrine Spirina takes us through several basic data warehousing concepts:

There are three basic types of modeling. Conceptual Data Model describes all entities a business needs information about. It provides facts about real-world things, customers, and other business-related objects and relations.
The goal of creating this data model is to synthesize and store all the data needed to gain an understanding of the whole business. The model is designed for the business audience.
Logical Data Model suits more in-depth data. It describes the structure of data elements, their attributes, and ways these elements interrelate. For instance, the model can be used to identify relationships between customers and products of interest for them. This model is characterized by a high level of clarity and accuracy.
Physical Data Model describes specific data and relationships needed for a particular case as well as the way data model is used in database implementation. It provides a wealth of meta-data and facilitates visualizing the structure of a database. Meta-data can involve accesses, limitations, indexes, and other features.

Click through for the whole story.

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Modeling Semi-Additive Measures

Published 2019-09-16 by Kevin Feasel

Paul Poco shows a couple techniques for modeling semi-additive measures in Analysis Services and Power BI:

As mentioned earlier, the most commonly encountered approach is Option 2, the snapshot fact table. The main drawback of this approach is that the fact table’s size will grow extremely fast. For example, if you want to calculate the headcount in a company with 10,000 employees on average, and you want 5 years of historical data, you will add 10,000 rows per day to your fact table – that gives you (10,000 * 365 * 5 =) 18,250,000 rows after 5 years.
If you used the first approach, Option 1, the fact table would be (10,000 * 5 =) 50,000 rows after 5 years, assuming your employees change position or quit the company once a year, on average.
The snapshot fact table (Option 2) is (18,250,000 / 50,000 =) 365 times bigger. On the bright side, as the data is very repetitive, you might get a very good compression ratio on these tables.

Check it out. Semi-additive measures are not as common as additive measures, but you’re liable to have a couple of them in your data model.

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Don’t Truncate Facts and Dimensions when Loading Data

Published 2019-07-26 by Kevin Feasel

Meagan Longoria explains why a truncate-and-reload strategy for data warehouses isn’t a good look:

Every once in a while, I come across a data warehouse where the data load uses a full truncate and reload pattern to populate a fact or dimension. While it may not be the end of the world for a small table, it does concern me and I usually recommend to redesign the load. My thoughts below on why this is an anti-pattern are true for using the actual TRUNCATE TABLE statement as well as executing a DELETE statement with no WHERE clause.

Read on for some great advice, including an exception to the rule.

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