In retrospect, I’d say I owe 50% of my BI career to Analysis Services and its flavors: Multidimensional, Tabular, and later Power BI. This is why I closely follow how this technology evolves. Fast forwarding to Fabric, there are no dramatic changes. Unlike the other two Fabric Engines (Lakehouse and Warehouse), Power BI datasets haven’t embraced the delta lake file format to store its data yet. The most significant change is the introduction of a new Direct Lake data access mode alongside the existing Import and DirectQuery.

The Good

Direct Lake will surely enable interesting scenarios, such as real-time BI on top of streaming data. It requires Parquet delta lake files and therefore it’s available only when connecting to the Lakehouse managed area (Tables folder) and Warehouse tables. Given that Parquet is a columnar format, which is what Tabular VertiPaq is, basically Microsoft has changed the engine to read Parquet files as it does with its proprietary IDF file format.

The primary usage scenario is fast analysis on top of large data volumes without importing data and without delegating the query to another server. Therefore, think of Direct Lake is a hybrid between Import and DirectQuery modes. By “large data volumes”, I mean data that otherwise won’t fit into memory and/or it will require substantial time to refresh but low latency access would be preferable.

Microsoft has accomplished this feat by using the following existing and new Analysis Services features:

• Vertiscan – The ability for Analysis Services to query columnar storage. Instead of using the IDF file format to store the Vertipaq data, DirectLake instead uses the Parquet file format in Lakehouse or Warehouse. The AS engine loads the data from the Parquet files (with some extra effort) and maps the column values into (mostly) the same data structures that would have been used if the data was coming from IDF files. After that, Vertiscan is querying the data as if it was Import data, so query performance should be at par with Import mode.
• On-demand data loading – The ability to page in and out data that was introduced in 2021 for imported data. If the data needs to be paged in, there will be some delay but after that it will be fast until and unless it gets paged out later on. Chris Webb covers on-demand loading in his post On-Demand Loading Of Direct Lake Power BI Datasets In Fabric.
• V-order – an extension to the Parquet file format to get a better compression like VertiPaq

The Bad

Naturally, I’d like to see Direct Lake available outside Fabric.

Currently, here is what needs to happen to connect to external Delta Parquet files, such as files located in ADLS:

• Create a lakehouse.
• Create a shortcut in OneLake to the external source table.
• Create the dataset on top of the lakehouse

As you can see, you can’t escape the Fabric gravitational pull to get Direct Lake. Further, the Parquet files produced by the Fabric workloads (Lakehouse/DW/etc.) will typically be faster and more compressed because of the V-order compression.

The Ugly

Among the Direct Lake limitations, the most significant for me is that not only you need Fabric to get Direct Lake, but also you must create the dataset online using the “New Power BI dataset” feature in Lakehouse/Warehouse, which has its own limitations.

Therefore, for now you can’t use Power BI Desktop to create your semantic model that uses Direct Lake connectivity. This will require Write support to be added to the Analysis Services Power BI XMLA endpoint. However, once you create the Direct Lake dataset, you can use Power BI Desktop to connect to it using the OneLake Data Hub connector.

“Patience my tinsel angel, patience my perfumed child
One day they’ll really love you, you’ll charm them with that smile
But for now it’s just another Chelsea [TL: BI] Monday”
Marrillion

Continuing our Power BI Fabric journey, let’s look at another of its engines that I personally care about – Fabric Warehouse (aka as Synapse Data Warehouse). Most of my real-life projects require integrating data from multiple data sources into a centralized repository (commonly referred to as a data warehouse) that centralizes trusted data and serves it as a source to Power BI and Analysis Services semantic models. Due to the venerable history of relational databases and other benefits, I’ve been relying on relational databases powered by SQL Server to host the data warehouse. This usually entails a compromise between scalability and budget. Therefore, Azure-based projects with low data volumes (up to a few million rows) typically host the warehouse in a cost-effective Azure SQL Database, while large scale projects aim for Synapse SQL Dedicated Pools. And now there is a new option on the horizon – Fabric Warehouse. But where does it fit in?

The Good

Why would you care about Fabric Warehouse given that Microsoft has three (and counting) Azure SQL SKUs: Azure SQL Database, Azure SQL Managed Instance, and Synapse SQL Dedicated Pools (based on Azure SQL Database)? Ok, it saves data in an open file format in OneLake (delta tables), but I personally don’t quite care much about how data is saved. We could say that SQL Server is also (although proprietary) a file-based engine that served us well for 30+ years. I care much more about other things, such as performance, budget, and T-SQL parity. However, as I mentioned in the previous Fabric-related blogs, the common delta format across Fabric enables data virtualization, should you decide to put all your eggs in one basket and embrace Fabric for all your data needs. Let’s say you have some files in the lakehouse managed zone. You can shortcut lakehouse delta tables to the Data Warehouse engine and avoid data movement. By contrast, previously you had to spin more ETL to move data from the Synapse serverless endpoint to the Synapse dedicated pools.

A big improvement is that you can also cross-query data warehouses and lakehouses, which wasn’t previously possible in Azure Synapse.

You can do this by writing familiar T-SQL queries with three-part-naming, such as querying a lakehouse table in your warehouse:
SELECT TOP (100) * FROM [wwilakehouse].dbo.dimension_customer

In fact, the elimination (or rather fusion) of Synapse Dedicated Pools and Serverless is a big plus for me. The infinite scale and instantaneous scalability that resulted from decoupling compute and store sounds interesting. I don’t know how Fabric Warehouse will evolve over time but I really hope that at some point, it will eliminate the afore-mentioned Azure SQL SKU decision for hosting relational data warehouses. I hope it will support the best of both worlds – the ability to dynamically scale (as serverless Azure SQL Database) up to the large scale of Synapse Dedicated Pools.

The Bad

Now that Azure SQL SKUs are piling up, Microsoft owes us serious benchmarks for Fabric Warehouse analytical and transactional loads.

Speaking of loads and considering that Fabric Warehouse saves data in columnar structures (Parquet files), this is not a tool to use for heavy OLTP loads. Columnar formats fit data analytics like a glove when data is analyzed by columns, but they will probably perform poorly for heavy transactional loads. Again, benchmarks could help determine where that cutoff point is.

Unlike Power BI Premium (P) capacities, Fabric capacities acquired by purchasing an Azure F plan can be scaled up or down (like Power BI Embedded A* plans). However, like A* plans, this requires manual intervention. I was hoping for dynamically scaling up and down workloads within a capacity to meet more demand and reduce cost. For example, I should be able to configure the capacity to auto-pause Fabric Warehouse when it is not in use and the data is imported in a Power BI dataset.

As I mentioned in my Fabric Lakehouse: The Good, The Bad, and the Ugly post, given that both saves data in the same format, I find the Lakehouse and Warehouse engines redundant and confusing. Currently, ADLS shortcomings are implicated for this separation and my hope is that at one point they will merge. If you are a SQL developer, you should be able to use SQL, and if you prefer notebooks for whatever reason, you can use Python or whatever language you prefer on the same data. This will be really nice and naturally resolve the lakehouse-vs-warehouse decision point.

The Ugly

Due to the fact that it’s completely rewritten, a work in progress, and therefore subject to many limitations, as it stands Fabric Warehouse is unusable for me.

After the botched Synapse saga, Microsoft had the audacity to call this offering the next generation of Synapse warehouse (in fact, the Fabric architecture labels is as Synapse Data Warehousing, I guess to save face) despite the fact that they pretty much start from scratch at least in terms of features. I call it “Oops, we did it again, overpromised and underdelivered, got lost in the game, Ooh, baby, baby…” I’ll give Fabric Warehouse a year or so before I revisit. If my hope for Fabric Warehouse as a more straightforward choice for warehousing materializes, I also wish Microsoft decouples it from Fabric and makes it available as a standalone Azure SKU offering. Which is pretty much my wish for all tools in the Fabric bundle. Bundles are great until you decide to opt out and salvage pieces…

Finally, after all the push and marketing hoopla, Synapse SQL Dedicated Pools seems to be on an unofficial deprecated path. I guess Microsoft has seen the writing on the wall from competing with other large-scale DW vendors. The current guidance is to consider them for high-scale performance while the “evolved” and “rewritten” Fabric Synapse Warehouse should be at the forefront for future DW implementations. And there is no migration path from Dedicated SQL Pools.

To know a tool is to know its limitations – Teo’s proverb

In a previous post, I shared my overall impression of Fabric. In this post, I’ll continue exploring Fabric, this time sharing my thoughts on OneLake. If you need a quick intro to Fabric OneLake, the Josh Caplan’s “Build 2023: Eliminate data silos with OneLake, the OneDrive for Data” presentation provides a great overview of OneLake, its capabilities, and the vision behind it from a Microsoft perspective. If you prefer a shorter narrative, you can find it in the “Microsoft OneLake in Fabric, the OneDrive for data” post. As always, we are all learning and constructive criticism would be appreciated if I missed or misinterpreted something.

What’s Fabric OneLake?

In a nutshell, OneLake is a Microsoft-provisioned storage where the ingested data and the data from the analytical (compute) engines are stored (see the screenshot below). Currently, PBI datasets (Analysis Services) are not saved in OneLake although one could anticipate that in the long run all Power BI data artifacts could (and should) end up in OneLake for Power BI Fabric-enabled workspaces.

Behind the scenes, OneLake uses Azure Data Lake Storage (ADLS) Gen2, but there is an application wrapper on top of it that handles various tasks, such as management (you don’t have to provision storage accounts or external tables), security (Power BI security is enforced), and governance. OneLake is tightly coupled with the Power BI catalog and security. In fact, you can’t create folders outside the Power BI catalog so proper catalog planning is essential. When you create a Fabric workspace in Power BI, Microsoft provisions an empty blob container in OneLake for that workspace. As you provision additional Fabric Services, Fabric creates more folders and save data in these folders. For example, I can use Azure Storage Explorer to connect to a Fabric Lakehouse Tutorial workspace (https://onelake.blob.fabric.microsoft.com/fabric lakehouse tutorial) and see that I have provisioned a data warehouse called dw and a lakehouse called wwilakehouse. Microsoft has also added two additional system folders for data staging.

The Good

I like to have the data from the compute engines saved in one place and to be able to access that data as delta Parquet files. There is something serene to have this transparency after decades of not being able to pick under hood of some proprietary file format.

I also like very much the ability to use different engines to access that data (Microsoft calls this OneCopy although a more appropriate term in my opinion would be OneShare).

For example, I can query a table in the lakehouse directly from the data warehouse (such as select * from [wwilakehouse].dbo.dimension_customer) without having to create PolyBase external tables or use the serverless endpoint.

I welcome the possibility for better data virtualization both within and outside the organization. For example, in a lakehouse I can create shortcuts to other Fabric lakehouses, ADLS folders, and even external storage systems, such as S3 (Google and Dataverse coming up).

I’d like the governance aspect and the possibility it enables, such as lineage tracking and data security. In fact, OneSecurity is on the roadmap, where once you secure the data at OneLake, the data security bubbles up. It would be interesting to see how this will work and its limitations, as I’d imagine it won’t be as flexible as Power BI RLS.

The Bad

An API wrapper is a double-edged sword because it wraps and abstracts things. You really have to embrace the Power BI catalog and its security model along with their limitations, because there is no way around it.

For example, you can’t use Azure Data Explorer to change the ACL permissions on the folder or create folders where OneLake doesn’t like them (OneLake simply ignores certain APIs). Isn’t this a good thing though to centralize at a higher level, such as the Power BI workspace and prevent users to pain outside the canvas? Well, how about granting some external vendor permissions to write to OneLake, such as to upload files. From what I can see, even Shared Access Signature is not allowed. Storage account key is not an option too as you don’t have access to the storage account. So, to get around such limitations, you’d have to create separate storage accounts, but this defeats the promise of one lake.

Perhaps, this is an example that you don’t care much about. How about the lakehouse medallion architecture pattern which is getting popular nowadays for lakehouse-centric implementations. While you can create subfolders in the Lakehouse “unmanaged” zone (the Files folder), no such luck with the Tables folder to organize your delta lake tables in Bronze, Silver, and Gold zones. I can’t see another solution but to create a Power BI workspace for each zone.

Further, what if you must address data residency requirements of some litigation-prone country? The above-cited presentation correctly states that content can be geo-located but that will require purchasing more Power BI capacities irrespective of the fact that ADLS storage accounts can be created in different geo locations. Somehow, I start longing about bringing your own data lake and I don’t think that provisioning storage accounts is that difficult (in fact, a Power BI workspace already has the feature to link to BYO ADLS storage to save the output of Power Query dataflows). Speaking of accounts, I’m looking forwards to seeing how Fabric would address DevOps, such as Development and Production environments. Currently, a best practice is to separate all services so more than likely Microsoft will enhance Power BI pipelines to handle all Fabric content.

The Ugly

How can I miss another opportunity to harp again on Power BI for the lack of hierarchical workspaces? The domain feature that Microsoft shows in the presentation to logically group workspaces could be avoided to a great extent if Finance could organize content in subfolders and break security inheritance when needed, instead of ending up with workspaces, such as Finance North America, Finance EMEA, etc. Since OneLake is married to the Power BI catalog, more catalog flexibility is essential.

Given that OneLake and ADLS in general would be a preferred location for business users to store reference data, such as Excel files, Microsoft should enhance Office to support ADLS. Currently, Office apps can’t directly open and save files in ADLS (the user must download the file somehow, edit it, and then upload it back to ADLS). Consequently, business users favor other tools, such as SharePoint Online, which leads to decentralizing the data required for analytics.