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Category: Indexing

An Overview of SQL Server Indexes

Published 2023-09-07 by Kevin Feasel

Adron Hall gives us a tour of indexes in several relational database management systems:

1. Structure of the Craft: Dive deep, and you’d find tree-like structures, be it the B-tree or its illustrious cousins – the B+ tree and B* tree. These aren’t ordinary trees; they’re a labyrinth that efficiently guides the system to the row it seeks in a jiffy.
2. Guiding Stars – Pointers: Each entry in this labyrinth isn’t just a dead end. It carries a key value and – wait for it – a pointer. Think of it as a magical compass pointing directly to the treasure, or in this case, the row in the table.
3. Supercharged Searches: Now, imagine sifting through a library without a catalog – agonizingly slow, right? That’s how a database without an index feels. But bring in an index, and suddenly even the vastest of tables become a playground of swift searches.

Read on for an overview of what purposes indexes fulfill in these data platforms. I use “purposes they fulfill” rather than “types of indexes” because there are a couple entries on the list which are not, strictly speaking, actual types of indexes.

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Index Maintenance in Azure SQL DB with Elastic Jobs

Published 2023-08-22 by Kevin Feasel

Scott Klein continues a series on index maintenance in Azure SQL Database:

It’s finally here: the third and final blog post about Azure automation. The first blog covered how to automate Azure using Runbooks, the second blog post showed how to do it using Azure Functions, and this blog post will cover how to do it using Azure Elastic jobs.

To be fair, I titled this blog “Automating Azure with Elastic Jobs”, but Elastic Jobs isn’t part of Azure Automation, so please don’t get confused. The goal with this is to demonstrate how to automate some Azure database DBA tasks.

Read on for a brief primer on elastic jobs and how to use them.

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Index Maintenance in Azure SQL DB

Published 2023-07-18 by Kevin Feasel

Kendra Little gives an answer:

Have you ever received advice that was technically correct, but which was delivered in such a way that it was too hard to understand?

I think of this as “accidental bad advice,” because it leads to confusion. There’s a LOT of accidental bad advice out there on index maintenance for SQL Server and cloud versions like Azure SQL, even in the official documentation.

In this post I’m answering a common index maintenance question, and we’re going to keep it simple.

The answer is essentially the same as it would be on-premises: yes, but perform index maintenance when it is appropriate. Read on to learn what that means in this case.

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Recommended Automatic Indexes and BACPACs

Published 2023-07-12 by Kevin Feasel

Jose Manuel Jurado Diaz shares a note:

During a remote session with a customer, a comparison between the source and target databases revealed a discrepancy in the indexes. Specifically, while the source database contained three types of indexes (PK_xxx, IX_xxx, and NCI_xxx), only the manually created PK_xxx and IX_xxx indexes were visible in the target database after restoration. The absence of NCI_xxx indexes prompted an investigation into the BACPAC export process.

This meant that the BACPAC file didn’t have the set of recommended automatic indexes. Click through for the explanation, though I’m not sure there’s a good way to fix it, short of manually scripting out those automated indexes yourself.

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Performance Optimizing Cosmos DB

Published 2023-07-07 by Kevin Feasel

Harshvardhan Singh has a few tips for us:

As with the other databases, indexing is the first go-to option to improve query performance. The same is the case with Cosmos DB as well. Below are a few points which you can leverage to optimize the indexing strategy for Cosmos DB. 

Indexes are kind of similar to indexing in SQL Server in intent, though different enough in implementation that you’ll want to read up on them. Harshvardhan also includes some tips around data modeling and querying data.

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Stopping a Resumable Index

Published 2023-06-28 by Kevin Feasel

Andrea Allred doesn’t want that index to resume:

It had been building for about 10 minutes, when I realized I had the fields in the wrong order. No big deal, I just canceled it, corrected it and tried to start it again. “Tried” was the keyword here. I got an error because I had set RESUMABLE = ON but hadn’t properly cleared it out of the system. I started to furiously dig through articles about how to clear out an index that was resumable but had been canceled.

Read on to see what Andrea found.

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Indexes and Stats on Tables with Always Encrypted

Published 2023-06-21 by Kevin Feasel

Matthew McGiffen gives us the low-down:

In a previous post we looked at executing queries against columns encrypted using Always Encrypted. In this short post we look at the ability to be able to have (or not) indexes on those columns. This information is relevant to the case where you are using Always Encrypted without enclaves, we’ll look at working with enclaves later on.

Click through to see how this all works.

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Missing Index Hints and Index Rebuilds

Published 2023-06-13 by Kevin Feasel

Forrest McDaniel abuses that poor server:

The prod version of this issue manifested as 1-3 minutes of SCH-M blocking for index ops, yet only on a single server; I couldn’t replicate it anywhere else. Of course, bad blocking meant nasty timeouts, and that in turn meant I was reluctant to run live diagnostics. Better to just stop index rebuilds. One does not take down production in order to test weird SQL behavior.

An important clue came from a tiny table with a rebuild, and is visible in the whoisactive screenshot above. Why would such a small rebuild need so much CPU? That worker was definitely doing something – the question was what.

Read on to find out the answer, a repro script (that you should not run in your own production environment!), and what you can do about it.

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Bugs in SQL Server 2022 CU4

Published 2023-05-29 by Kevin Feasel

Brent Ozar facepalms:

<sigh> Okay, so, the last few Cumulative Updates have had known issues around broken remote queries using the generic ODBC connector and errors with contained availability groups, but I couldn’t really care less about those. If you use those features, I give you bombastic side eye anyway.

However, in the last few days, two more known issues have surfaced.

And those two issues are definitely bad. Click through to see what they are and what the workarounds are until fixes come in.

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Troubleshooting Issues with Full-Text Indexing

Published 2023-05-17 by Kevin Feasel

Jose Manuel Jurado Diaz digs into a customer problem:

Today, we got a new service request where our customer asks about the time spent populating the full-text. Following, I would like to share with you some lessons learned during this process, specifically working with Azure SQL Database.

For this example, we are going to use a General Purpose database with 8 vCores. Let’s get started with the creation of the table and fulltext.

Read on for a walkthrough of setting up full-text indexing and figuring out what the indexing engine is doing at any point in time.

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