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Category: Administration

Postgres Foreign Data Wrappers and fdw_tuple_cost

Published 2024-03-01 by Kevin Feasel

Umair Shahid provides background info on a recent change:

“Why is DEFAULT_FDW_TUPLE_COST so insanely low?”

That was the subject of the email thread initiated by David Rowley to discuss this topic. I found the subject line amusing, accurate, and fully descriptive of the problem at hand. The discussion resulted in a commit that changed the default value from 0.01 to 0.2. Because I had previously written about postgres_fdw and also mentioned fdw_tuple_cost, I figured it would be good to go deeper into what this parameter is about and why it makes sense to default it to 0.2.

Read on to learn more about Foreign Data Wrappers (the Postgres equivalent to PolyBase in SQL Server), tuple costing, and more.

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Installing or Upgrading SQL Server on a Workstation

Published 2024-02-26 by Kevin Feasel

Aaron Bertrand shares some advice:

Lately, I’ve seen many people struggling to upgrade their workstation to the latest version of SQL Server. The main source of the problem is usually the web installer/wrapper, which can fail for a variety of reasons that aren’t always made clear by the error messages. Today, I’m going to walk through one way you can approach a workstation upgrade and avoid these web installer issues altogether. I’ll focus on SQL Server 2022, but most of the information applies to any modern major version. Most of the information applies if you’re installing a brand-new instance, too.

Click through for several good tips and practices.

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Using Databricks System Tables

Published 2024-02-23 by Kevin Feasel

Dustin Vannoy has a primer on system tables in Databricks:

Monitoring is important, so I’ve covered the topic a few times in the past. I’ve talked about collecting your Spark application logs and Spark metrics. These are a good way to track what is happening and what is going wrong as your code runs. In the video related to this post I focus on a different side of monitoring. The evolving capabilities offered by Databricks System Tables. I have some sample queries and links to help you get started and begin to get value from system tables. This will need to be updated (I’ll try) as new tables go into public preview status. So let’s discuss the questions I had when I first started researching this feature:
1) What do the Databricks system tables offer me for monitoring?
2) How much does this overlap with the application logs and metrics?

Click through for a video and a walkthrough.

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Postgres Backup and Recovery with Barman

Published 2024-02-23 by Kevin Feasel

Muhammad Ali shows off another way to back up and restore data in Postgres databases:

Barman is a production grade tool for managing the backup and recovery process of PostgreSQL databases. It not only handles the physical backups but also provides automatic management of retention policies, compression, near zero Recovery point objective(RPO) and enables recovery at any desired point(PITR) in time within the recovery window.

Barman’s Stream Archiving feature stands out as a key component in achieving zero Recovery Point Objective (RPO). This is achieved by using pg_recievewal utility which continuously backs up Write-Ahead Logging (WAL) files in real-time to a designated Barman server. This capability is particularly important for applications where even minimal data loss is unacceptable.

Read on for a couple questions about it and a demonstration of how Barman works.

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The Risk of Query Failure on Readable Secondaries in SQL Server

Published 2024-02-22 by Kevin Feasel

Kendra Little explains a problem:

If you use readable secondaries in Availability Groups or Read-Scale out instances in Azure SQL Managed Instance, you may have queries fail repeatedly if there is a glitch and statistics are not successfully “refreshed” on the secondary replica. Those queries may keep failing until you manually intervene.

This has been the case for a few years, and it’s unclear if Microsoft will fix this. There is a well established support deflection article which documents the issue and provides ‘workarounds’.

Read on for Kendra’s thoughts. I haven’t run into this before, myself, but I also don’t tend to make very heavy use of readable secondaries.

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Feature Toggles for Databases

Published 2024-02-20 by Kevin Feasel

Phil Factor discusses feature toggles for the database:

In software development the concept of feature toggles are used to selectively turn on and off features. They are, for example, used to restrict some newly introduced features to a select group to see how these features work. While this concept has been long used for user-facing application code, it is also a practice that is useful for database code.

In databases, feature toggles are used for several loosely related purposes. One common use is to separate, or decouple, rollout of database features from deployment of new versions of the application code. This allows developers to release software faster and with less risk.

The idea of using roles to determine whether a given user should see a particular feature makes sense, though I was a bit confused at first because I was thinking about feature flags: behavioral changes you slowly turn on for groups of people. This is a bit different.

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Enabling SQL Agent after Upgrading from Express Edition

Published 2024-02-19 by Kevin Feasel

Warwick Rudd ponies up the cash:

With the above limitations, this product can provide all of the functionality for your application to operate as required. Because there is no SQL Agent service in this edition this makes it more difficult for you to implement scheduled database maintenance. We are not going to discuss ways to implement database maintenance on an Express edition of SQL Server in this post.

But at some point in time you may find yourself in the position that you need to perform an upgrade of editions. This may or may not include and upgrade of versions. An upgrade to the version can be achieved and can bring benefits of its own. Normally, I would not be writing about and recommending performing in-place upgrades. However, sometimes due to restrictions of vendor applications it is a requirement to perform an in-place upgrade. 

Read on to see what you’d need to do, knowing that Express Edition does not come with a SQL Server Agent and does not perform the appropriate setup for one.

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Checking SQL Server Connectivity with Powershell in Parallel

Published 2024-02-16 by Kevin Feasel

Rod Edwards builds a script:

The chances are that you have other systems monitoring your SQL servers already, so this task isn’t required at all. However, sometimes a quick ‘knock on the door of SQL’ to confirm a response isn’t a bad thing as a sanity check.

So, building on that, we’re going to use the same technique to essentially perform a sweep of our estate (with a few bells and whistles added) to give us a colour coded quick view of service status like below, with a little bit of additional info.

Click through for the script and explanation.

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Troubleshooting a Problem with sp_send_dbmail

Published 2024-02-16 by Kevin Feasel

Shane O’Neill applies the Sgt. Schultz defense:

I don’t like posting about issues unless I fundamentally understand the root cause. That’s not the case here. A lot of the explanation here will be hand-waving while spouting “here be dragons, and giants, and three-headed dogs”, but I know enough to give you the gist of the issue.

Click through for a fun story about Kerberos and behavioral changes after absolutely nothing happened.

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Horizontal Scale in Postgres with PL/Proxy

Published 2024-02-14 by Kevin Feasel

Umair Shahid gives us the rundown on one mechanism to scale out Postgres:

As databases scale and user demands intensify, the challenge of maintaining performance increases. While PostgreSQL was originally designed (40 years ago!) to scale up, but increasing demands on the database have created the need to enable it to scale horizontally. PL/Proxy is a database partitioning system designed to simplify the process of distributing database loads across multiple servers. It acts as a transparent layer between the application and the database, enabling queries to be directed to the appropriate shard or partition based on predefined rules.

This article will dive into PL/Proxy, taking a look at its benefits, use cases, and best practices to enhance PostgreSQL’s performance through effective scaling.

Click through to learn more about this product.

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