A Fine Slice Of SQL Server
Andy Brownsword reviews the list:
When running queries, reviewing execution plans, or diving into Query Store it’s not uncommon to see missing index recommendations, particularly for more complex queries. But are they any good?
The answer is yes, but also no. Read on to learn how it is useful, but only if you take into account the foibles of the missing indexes dynamic management view.
Leave a CommentStephen Planck explains the value (and limitations) of filtered indexes:
When a table holds millions of rows yet most queries touch only a small, well-defined subset, a traditional non-clustered index feels like using a searchlight to find something sitting under a desk lamp: the index still stores an entry for every row even though the workload rarely needs most of them. SQL Server’s answer is the filtered index—introduced in SQL Server 2008 and still under-used today—allowing you to index just the rows that match a predicate you supply in a
WHEREclause.
I always thought I would get more value out of filtered indexes. Instead, they’re very useful for specific circumstances, but not the all-purpose performance dynamos you’d want them to be, particularly because of the limitations.
Comments closedDaniel Hutmacher gives it a try:
Starting today, the public preview of SQL Server 2025 is available to download!
One really interesting new feature that got my attention was the addition of JSON indexes. I’m a big fan of everything that makes working with JSON easier, since JSON blobs are so much easier to work with than table variables when you’re moving data from point A to point B. This is especially true when you’re working with complex, relational data.
Daniel lays out some of the limitations of JSON index creation and also some of the performance gains you might see from it. This will be most helpful in data engineering scenarios, shredding JSON from various services, but the normalization purist in me says that if you’re shredding JSON enough to need indexes, it’s probably time to normalize that data.
1 CommentKevin Hill shares some thoughts:
Here’s the truth: if you’re doing this daily on indexes smaller than 10,000 pages, you might be chewing up CPU, bloating your logs, and annoying your users for zero gain.
Let’s fix that.
I disagree with Kevin on index reorganization, in that I would never perform index reorgs—there’s no there there. Even so, I firmly agree with the thrust of Kevin’s argument and believe that, in the majority of cases, companies with DBAs (or people who have stumbled through maintenance plans before) are maintaining indexes too much rather than not enough.
Comments closedLukas Vileikis explains how hash indexes work in MySQL:
In MySQL, hash indexes are indexes that are used in queries that use the equality operators like
=or<=>(which is the MySQLNULLsafe equality operator, equivalent to the SQL StandardIS NOT DISTINCTFROM). Hash indexes are not used in other situations, so they can be useful for things like random or generated PRIMARY KEY values where you are looking up single rows and not needing to order rows or searching for a range of values.
Just like in SQL Server hash indexes only work for in-memory tables, and some of the mechanisms look very similar.
Comments closedErik Darling has some doozies today:
Many of our Tables have 15 plus guid s from other tables, but not declared as Foreign Key. Plus Foreigne Keys. When I add a Index on for every Foreign Key plus Indexes for declared foreign keys we end up with tables with 30 plus indexes for fks only. We don’t have write performance issues. would you index every fk for every possible join?
Click through for the answer to this and four other questions.
Comments closedDavid Fitzjarrell wants to see which indexes are in use:
Database performance is one of the biggest areas for DBAs to address, measured primarily in time. Users usually complain when queries “take too long” and immediately run to the DBA team to register their disappointment. One avenue used to address such concerns is the creation and maintenance of indexes, and as any DBA with any experience can attest, simply throwing indexes at a table isn’t necessarily the smartest play; a major concern is if the index is actually being utilized. Oracle, in its wisdom, has provided tools to monitor these objects in the form of system views. Let’s look at what is available and how to get the most benefit out of them.
Click through for some scripts and information on how to tell whether an index is in use or not.
Comments closedKevin Hill goes back to basics:
“What Is an Index?”
I get this question a lot, especially from developers and sysadmins who’ve been handed a SQL Server and told, “Keep it running fast.” No pressure.
Given that the percentage of people in this industry who have actually seen a phone book continually decreases, it’s for the best that Kevin didn’t use that worn-out example.
If you’re new to indexing in SQL Server, this is a good way to jump-start your knowledge. Then, you spend a while learning the exceptions to the rules and the foibles in existing systems.
Comments closedHans-Jürgen Schönig builds some indexes on vector data:
In the previous post we have imported a fairly large data set containing Wikipedia data, which we downloaded using pgai. However, importing all this data is not enough because we also need to keep an eye on efficiency. Therefore, it is important to understand that indexing is the key to success.
Click through for an overview of what options are available for indexing vectors in PostgreSQL, as well as the trade-offs and disk space requirements.
Comments closedRyan Booz continues a series on pgNow:
In that first article, I shared how pgNow can be a lifesaver when you need immediate performance insights, highlighting features like query tuning and current activity monitoring. The tool’s ability to take periodic snapshots of query activity and spotlight active sessions has already been a significant help for early users.
Today, I wanted to look at another area of information that pgNow can help you explore during times of performance degradation or even as part of a regular database maintenance and hygiene: the Indexing tab.
Click through to see what’s in the feature and to get a free copy of the preview for pgNow.
Comments closed