Posts on software, systems, and whatever else I’m building.https://www.vojtechsima.com/enhttps://www.vojtechsima.com/blog/how-much-does-direct-lake-cost-in-microsoft-fabric/https://www.vojtechsima.com/blog/how-much-does-direct-lake-cost-in-microsoft-fabric/Direct Lake vs Import CU cost, measured over nine replications on F64 and F2. Where the refresh saving goes, and the Lakehouse overhead you don't see.Tue, 25 Aug 2026 00:00:00 GMThttps://www.vojtechsima.com/blog/microsoft-fabric-direct-lake-framing-caching-performance/https://www.vojtechsima.com/blog/microsoft-fabric-direct-lake-framing-caching-performance/How Direct Lake really works in Microsoft Fabric: framing, transcoding, column residency and eviction, with the measured CU cost of each.Wed, 22 Jul 2026 00:00:00 GMThttps://www.vojtechsima.com/blog/fabric-dataflow-gen2-partitioned-compute-setup-and-benchmark/https://www.vojtechsima.com/blog/fabric-dataflow-gen2-partitioned-compute-setup-and-benchmark/Discover how to set up Partitioned Compute in Dataflow Gen2 for parallel processing. Read my setup guide and see the real-world benchmark results in Fabric.Sun, 15 Mar 2026 00:00:00 GMThttps://www.vojtechsima.com/blog/automated-delta-table-maintenance-in-fabric-lakehouse-without-pyspark/https://www.vojtechsima.com/blog/automated-delta-table-maintenance-in-fabric-lakehouse-without-pyspark/Deep dive into Delta table internals, transaction logs, and storage layout. Master maintenance, VACUUM, and Z-Order using Python (delta-rs) in Microsoft Fabric.Fri, 13 Feb 2026 00:00:00 GMThttps://www.vojtechsima.com/blog/power-bi-write-back-to-azure-sql-fabric-udf/https://www.vojtechsima.com/blog/power-bi-write-back-to-azure-sql-fabric-udf/Bypass native Fabric limitations and achieve instant Power BI write-back to Azure SQL. Learn to use User Data Functions to skip the Spark cold start.Mon, 12 Jan 2026 00:00:00 GMThttps://www.vojtechsima.com/blog/fix-slow-refreshes-faster-way-to-load-sharepoint-files-in-power-bi/https://www.vojtechsima.com/blog/fix-slow-refreshes-faster-way-to-load-sharepoint-files-in-power-bi/Optimize Power BI SharePoint data retrieval. Learn technical differences between connectors and implement a custom REST API strategy for faster dataset refreshes.Tue, 30 Dec 2025 00:00:00 GMThttps://www.vojtechsima.com/blog/how-to-fix-slow-sharepoint-list-refresh-in-power-bi/https://www.vojtechsima.com/blog/how-to-fix-slow-sharepoint-list-refresh-in-power-bi/Boost Power BI SharePoint refresh speed. Fix RenderListDataAsStream errors and use a custom M script to cut load times from minutes to seconds.Tue, 23 Dec 2025 00:00:00 GMThttps://www.vojtechsima.com/blog/programmatically-refresh-sync-sql-analytics-endpoint-metadata-in-microsoft-fabric/https://www.vojtechsima.com/blog/programmatically-refresh-sync-sql-analytics-endpoint-metadata-in-microsoft-fabric/Learn how SQL Analytics Endpoint in Microsoft Fabric works and how to fix metadata lag by calling the Refresh SQL Endpoint Metadata API before Power BI refresh.Mon, 17 Nov 2025 00:00:00 GMThttps://www.vojtechsima.com/blog/why-power-bi-says-a-value-is-a-duplicate-when-it-s-not/https://www.vojtechsima.com/blog/why-power-bi-says-a-value-is-a-duplicate-when-it-s-not/Power Query is case sensitive, the model is not, and that mismatch quietly breaks relationship keys. Why it happens, and three ways to fix it.Sat, 01 Nov 2025 00:00:00 GMThttps://www.vojtechsima.com/blog/dataflows-gen1-and-gen2-where-is-my-data-stored/https://www.vojtechsima.com/blog/dataflows-gen1-and-gen2-where-is-my-data-stored/Dataflows explained: Gen1 vs Gen2 storage, CSV vs Delta, SQL cache, and staging Lakehouse and Warehouse. Learn what lives where and how to connect fast.Sun, 26 Oct 2025 00:00:00 GMThttps://www.vojtechsima.com/blog/dax-user-defined-functions-preview/https://www.vojtechsima.com/blog/dax-user-defined-functions-preview/How DAX user defined functions work: declaring UDFx with DEFINE and FUNCTION, val versus expr parameters, and where they hold up in a real model.Sun, 21 Sep 2025 00:00:00 GMThttps://www.vojtechsima.com/blog/why-is-power-query-list-contains-slow-faster-lookup-alternatives/https://www.vojtechsima.com/blog/why-is-power-query-list-contains-slow-faster-lookup-alternatives/Power Query lookup benchmarks. Learn why List.Contains is slow at scale, when buffering helps, and how joins or Record.FieldOrDefault beat list contains.Thu, 21 Aug 2025 00:00:00 GMThttps://www.vojtechsima.com/blog/how-to-connect-graphql-apis-as-a-data-source-in-power-bi/https://www.vojtechsima.com/blog/how-to-connect-graphql-apis-as-a-data-source-in-power-bi/Learn how to connect GraphQL APIs to Power BI effortlessly. Discover key GraphQL concepts and integrate GraphQL with Power BI for seamless data analysis.Sun, 03 Aug 2025 00:00:00 GMThttps://www.vojtechsima.com/blog/how-power-query-m-evaluates-your-queries-and-why-the-performance-gets-weird/https://www.vojtechsima.com/blog/how-power-query-m-evaluates-your-queries-and-why-the-performance-gets-weird/Lazy versus eager evaluation in Power Query M, what buffering actually changes, and why the same query can return different numbers on each run.Sat, 12 Jul 2025 00:00:00 GMThttps://www.vojtechsima.com/blog/stop-repeating-calculate-iterate-over-categories-in-dax/https://www.vojtechsima.com/blog/stop-repeating-calculate-iterate-over-categories-in-dax/Stop repeating CALCULATE in your DAX. Discover how to iterate and simplify category-level logic with SUMX, AVERAGEX, and virtual tables like VALUES and SUMMARIZE.Mon, 30 Jun 2025 00:00:00 GMThttps://www.vojtechsima.com/blog/native-write-back-in-power-bi-fabric-preview/https://www.vojtechsima.com/blog/native-write-back-in-power-bi-fabric-preview/Write back to SQL straight from a Power BI report using Fabric User Data Functions and Translytical Task Flows. No Power Apps, no Power Automate.Fri, 13 Jun 2025 00:00:00 GMThttps://www.vojtechsima.com/blog/while-loop-in-m-language/https://www.vojtechsima.com/blog/while-loop-in-m-language/Discover how to mimic a while loop in M Language using List.Generate(). Learn to implement while loop logic effectively in Power Query M.Tue, 13 May 2025 00:00:00 GMThttps://www.vojtechsima.com/blog/refresh-semantic-models-every-minute-now-in-fabric-preview/https://www.vojtechsima.com/blog/refresh-semantic-models-every-minute-now-in-fabric-preview/The Refresh Semantic Model activity in a Data Pipeline gets you past Power BI's 30-minute limit, with dependencies and no code. Preview, with caveats.Mon, 05 May 2025 00:00:00 GMThttps://www.vojtechsima.com/blog/make-your-power-query-dynamic-with-parameters/https://www.vojtechsima.com/blog/make-your-power-query-dynamic-with-parameters/Discover how to make your Power Query dynamic with parameters. Learn practical ways to use parameters in Power BI, enhancing flexibility and control.Sun, 23 Mar 2025 00:00:00 GMThttps://www.vojtechsima.com/blog/top-everyday-dax-functions/https://www.vojtechsima.com/blog/top-everyday-dax-functions/The DAX functions worth learning first and what each one is actually for. Not a reference list: the handful you end up using in every model.Tue, 18 Feb 2025 00:00:00 GMThttps://www.vojtechsima.com/blog/ultimate-intro-to-power-query-m-language/https://www.vojtechsima.com/blog/ultimate-intro-to-power-query-m-language/What M actually is, how Power Query writes it for you, and how to start editing it yourself. A beginner introduction built on working examples.Fri, 07 Feb 2025 00:00:00 GMThttps://www.vojtechsima.com/blog/combine-files-quickly-in-power-query/https://www.vojtechsima.com/blog/combine-files-quickly-in-power-query/Power Query's built-in file combiner generates a folder of helper queries. Two simpler ways to combine files, in roughly one line of M.Sun, 22 Dec 2024 00:00:00 GMThttps://www.vojtechsima.com/blog/api-authentication-in-power-query/https://www.vojtechsima.com/blog/api-authentication-in-power-query/The five authentication methods Power Query supports: Anonymous, API Key, Bearer Token, Basic and OAuth 2.0, with working M for each.Mon, 25 Nov 2024 00:00:00 GMThttps://www.vojtechsima.com/blog/pagination-in-power-query/https://www.vojtechsima.com/blog/pagination-in-power-query/How to page through an API from Power Query: offset, cursor and link-header styles, with M that keeps asking until the last page comes back.Tue, 12 Nov 2024 00:00:00 GMThttps://www.vojtechsima.com/blog/introduction-to-api-in-power-query/https://www.vojtechsima.com/blog/introduction-to-api-in-power-query/Calling a REST API from Power Query with Web.Contents and Json.Document: the request, the response, and turning JSON into a usable table.Sat, 09 Nov 2024 00:00:00 GMT