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Category: Administration

PostgreSQL for the Oracle DBA: Tuples and MVCC

Published 2025-07-18 by Kevin Feasel

Kellyn Gorman continues a series on PostgreSQL for Oracle DBAs:

After our first two weeks of ensuring Grant and I didn’t burn down SQLServerCentral figuring out how Steve Jones has kept the pace he has for so long, (quite an impressive feat, I think we’d both agree!) I’m back to working with my comparisons and building more knowledge in PostgreSQL.  What caught my attention this week was the simple concept of a row (or tuple) which might seem universal in relational systems, after all, data is data no matter the platform, right? But under the hood, the way databases store, manage, and control visibility of that data can differ drastically. This is especially true when comparing PostgreSQL with how Oracle manages rows.

Read on to learn more about how these systems work.

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Zone Redundancy in Azure SQL Managed Instance

Published 2025-07-17 by Kevin Feasel

Arun Sirpal explains what zone redundancy is in Azure:

Do you know what happens when you enable zonal redundancy for your SQL managed instance?

Lets define it first (in the context of Business-Critical tier) – zonal redundancy is achieved by placing compute and storage replicas in different availability zones (3) and then using underlying Always On availability group to replicate data changes from the primary instance to standby replicas in other availability zones. 

Availability zones are in the same Azure region, so it works well for high availability but isn’t as good for disaster recovery: if an entire region goes down, zone redundancy won’t help you very much. Also, be aware that you’re paying for what’s running in those three zones because TANSTAAFL.

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Comparing Storage Options in PostgreSQL

Published 2025-07-16 by Kevin Feasel

Hans-Jürgen Schönig compares data sizes:

In this case study, we’ll delve into each of PostgreSQL’s main storage options, their characteristics, and the factors that influence their choice, enabling you to make informed decisions about your database’s storage strategy. You will also learn how you can archive data in a hybrid environment for long term storage. 

Click through for a comparison of two common file formats, plus two PostgreSQL-specific mechanisms for data storage. The comparison here is mostly one of final file size, though common query performance would be interesting to include as well, especially because the columnar data file types (Parquet and Citus-based columnstore) have a very different performance profile versus row-store data.

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Access Limits in Microsoft Fabric Workspaces

Published 2025-07-16 by Kevin Feasel

Brian Kernan announces a change:

In August 2025, Microsoft Fabric will introduce workspace access limits to improve service quality, reliability, and to encourage workspace access control hygiene. This limit will be permanent once it is rolled out – each Fabric & Power BI workspace will be limited to a maximum of 1,000 users or groups in workspaces roles (Admin, Member, Contributor, Viewer). A workspace with a group over 1,000 individuals will not be impacted by this change, the number of users within a group is not impacted. Additionally, workspaces that are overlimit at the time of access limit enforcement will remain overlimit, but no additional users or groups can be added until the workspace is under-limit.

I read this and I say “Hmm…” I’m not in a position where I could say that 1000+ users in a workspace is a bad idea that they’re protecting us from, or if it’s an implicit acknowledgement of failure to scale.

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Copying Azure SQL Databases between Subscriptions

Published 2025-07-15 by Kevin Feasel

Kenneth Fisher is back in the fight:

I recently had to copy an Azure SQL database (SQL db) from one subscription to an Azure SQL Server instance in another subscription. All of the help I found suggested going to the database and hitting the COPY option. Unfortunately, when I did, I ran into a problem.

Read on for the issue, as well as one way to fix it. The route Kenneth landed on was the same one I ended up going with when I had a similar problem and very limited access to SQL DB on both subscriptions.

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Efficiency of Sparse Hash Tables in PostgreSQL

Published 2025-07-15 by Kevin Feasel

Ashutosh Bapat runs some tests:

The hash_create() API in PostgreSQL takes initial size as an argument. It allocates memory for those many hash entries upfront. If more entries are added, it will expand that memory later. The point of argument was what should be the initial size of the hash table, introduced by that patch, containing the derived clauses. During the discussion, David hypothesised that the size of the hash table affects the efficiency of the hash table operations depending upon whether the hash table fits cache line. While I thought it’s reasonable to assume so, the practical impact wouldn’t be noticeable. I thought that beyond saving a few bytes choosing the right hash table size wasn’t going to have any noticeable effects. If an derived clause lookup or insert became a bit slower, nobody would even notice it. It was practically easy to address David’s concern by using the number of derived clauses at the time of creating the hash table to decide initial size of the hash table. The patch was committed.

Read on to see how things didn’t quite turn out this way, and what the results of testing look like.

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Extending Ola’s Backup Scripts for Scale

Published 2025-07-14 by Kevin Feasel

Aaron Bertrand looks at some extensions to a venerable solution:

Where I work, we have hundreds of mission-critical databases. We use Ola Hallengren’s SQL Server backup solution, but, out of necessity, have wrapped it with several enhancements to help us accomplish goals around retention, SQL Server backup frequency, and recovery point objectives. I touched on some of this last year when I talked about automating some of our restore testing, in It’s a recovery strategy, not a backup strategy. Today, we do a lot more than that, and we have to be more flexible about it.

Click through to see what Aaron’s environment looks like and some of the things they’ve done to make recovery work better.

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Goodbye Default Contributor Role in Fabric Workspace Identities

Published 2025-07-10 by Kevin Feasel

Varun Jain makes a security announcement:

A Fabric workspace identity is an automatically managed service principal that can be associated with a Fabric workspace. Fabric workspaces with a workspace identity can securely read or write to firewall-enabled Azure Data Lake Storage Gen2 accounts through trusted workspace access for OneLake shortcuts. Fabric items can use the identity when connecting to resources that support Microsoft Entra authentication. Fabric uses workspace identities to obtain Microsoft Entra tokens without the customer having to manage any credentials. 

Previously, a workspace identity was automatically assigned the workspace contributor role and had access to workspace items.  

Read on to see what’s changing, why, and what you can do instead.

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Random Page Cost and PostgreSQL Query Plans

Published 2025-07-09 by Kevin Feasel

Tomas Vondra takes us through a setting:

Last week I posted about how we often don’t pick the optimal plan. I got asked about difficulties when trying to reproduce my results, so I’ll address that first (I forgot to mention a couple details). I also got questions about how to best spot this issue, and ways to mitigate this. I’ll discuss that too, although I don’t have any great solutions, but I’ll briefly discuss a couple possible planner/executor improvements that might allow handling this better.

Tomas’s points around the random_page_cost setting sound a lot like the cost threshold for parallelism setting in SQL Server in inverse: a setting whose default makes sense in a world of spinning disks at 7200 RPM, but not really in a solid state world.

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