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Category: Administration

Postgres Migration via Logical Replication

Published 2025-10-06 by Kevin Feasel

Elizabeth Christensen makes a move:

Moving a Postgres database isn’t a small task. Typically for Postgres users this is one of the biggest projects you’ll undertake. If you’re migrating for a new Postgres major version or moving to an entirely new platform or host, you have a couple options:

Read on for those three options, when logical replication can possibly work, and the process for upgrade. It’s definitely a bit more fiddly than other options, but it’s hard to beat with respect to downtime.

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Creating Database Snapshots with sp_snapshot

Published 2025-10-03 by Kevin Feasel

David Fowler announces a tool update:

Presenting you with an updated version of our sp_snapshot procedure, allowing you to easily create database snapshots.

This new version fixes a bug that we’ve found in version 2 where snapshots will fail for databases with multiple data files.

We’ve also added the @STMTOnly parameter, allowing you to generate the scripts for creating the required snapshots without actually doing so.

Click through for more information, as well as where you can go to download the script.

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RCSI Scenarios

Published 2025-10-03 by Kevin Feasel

Haripriya Naidu digs into a few scenarios:

When RCSI is enabled, I’d like to discuss three scenarios:

  1. UPDATE is in progress, and SELECT starts to run.
    Where does SELECT read from?
  2. SELECT runs, and there are no concurrent operations or uncommitted transactions. Where does SELECT read from?
  3. SELECT is running, and now an UPDATE starts to run concurrently. What happens to SELECT that is in progress? What about the UPDATE that started? Does it wait for SELECT to finish?

Click through to see what happens during each of these scenarios.

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Tracking Memory Consumption in Fabric SQL Database

Published 2025-10-02 by Kevin Feasel

Lance Wright tracks memory utilization:

SQL Database in Fabric continues its commitment to providing you with robust tools for database management, performance monitoring, and optimization. Earlier this year, we released a performance dashboard to help you monitor and improve the performance of your SQL Database in Fabric. We’ve improved upon those performance monitoring capabilities with the ability to track memory consumption. This new capability delivers real-time, actionable data regarding the memory utilization of all database queries to help you make more informed decisions and manage SQL Database resources more efficiently.

Read on to see what you can do with this.

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Linking Fabric Warehouse SQL Query Results to the Capacity Metrics App

Published 2025-09-30 by Kevin Feasel

Chris Webb follows up on a previous post:

Following on from my post two weeks ago about how to get the details of Power BI operations seen in the Capacity Metrics App using the OperationId column on the Timepoint Detail page, I thought it was important to point out that you can do the same thing with TSQL queries against a Fabric Warehouse/SQL Endpoint and with Spark jobs. These two areas of Fabric are outside my area of expertise so please excuse any mistakes or simplifications, but I know a lot of you are Fabric capacity admins so I hope you’ll find this useful.

Read on to learn more.

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Inspecting the Postgres Write-Ahead Log

Published 2025-09-29 by Kevin Feasel

Henrietta Dombrovskaya digs into the write-ahead log:

First, when the users fixed one of the primary suspects jobs, the situation with WAL growth didn’t change. Second, the rate of the growth couldn’t be explained by these suboptimal jobs: the data volumes they were removing and reloading were still magnitudes smaller than the WAL size we were dealing with. Finally, I decided to do what I should have done from the start – to take a look at what exactly was in these super-fast growing WALs.

Read on to learn what Henrietta found. Also check out the comments for some additional context.

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Losing Data with PostgreSQL and Jepsen

Published 2025-09-29 by Kevin Feasel

Jeremy Schneider performs some tests:

This is a follow‑up to the last article: Run Jepsen against CloudNativePG to see sync replication prevent data loss. In that post, we set up a Jepsen lab to make data loss visible when synchronous replication was disabled — and to show that enabling synchronous replication prevents it under crash‑induced failovers.

Since then, I’ve been trying to make data loss happen more reliably in the “async” configuration so students can observe it on their own hardware and in the cloud. Along the way, I learned that losing data on purpose is trickier than I expected.

Click through to learn more. Jepsen has been the gold standard in testing distributed database systems for data loss.

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Memory Grant Feedback Woes

Published 2025-09-26 by Kevin Feasel

Rebecca Lewis explains an issue with memory grant feedback in SQL Server:

Before SQL Server runs a query, it estimates how much memory it needs for sorting and joining. But what if it gets it wrong?

  • Too little memory → Spills to tempdb (slow)
  • Too much memory → Starves other queries

SQL Server 2017+ tries to fix bad estimates based on previous calls with ‘Memory Grant Feedback’.  Kinda like:  ‘Last time I gave you 2GB but you only used 50MB. Next time I’m giving you less.’

This is great in theory, though Rebecca shows a case in which the end result might not be great.

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An Outside-In Triage for SQL Server Performance

Published 2025-09-25 by Kevin Feasel

Kevin Hill triages an issue:

It’s 9:05 AM and your helpdesk lights up: “The SQL Server is down. Nothing works.”

By 9:07, everyone is staring at you.

The trap: you open SSMS and start digging for blocking queries. But what if the database isn’t the problem at all?

I think my biggest gripe about the list is the challenge of being allowed to get several of these metrics. But it is good, in the face of a “Everything is slow fix it now!” style of request, to look at extrinsic factors before digging into SQL Server, as that’s just following the old joke about the drunken man searching for his keys under the streetlamp, despite not having lost them there, because it’s easier to see that area.

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SQL Firewall in Oracle

Published 2025-09-19 by Kevin Feasel

Brendan Tierney tries out the SQL Firewall feature in Oracle:

SQL Firewall allows you to implement a firewall within the database to control what commands are allowed to be run on the data. With SQL Firewall you can:

  • Monitor the SQL (and PL/SQL) activity to learn what the normal or typical SQL commands are being run on the data
  • Captures all commands and logs them
  • Manage a list of allowed commands, etc, using Policies
  • Block and log all commands that are not allowed. Some commands might be allowed to run

Read on to see how it works. It’s an interesting approach that can supplement traditional firewall and web application firewall systems.

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