Category: Indexing

Kenneth Fisher has a few notes on disabling indexes:

Indexes are probably the number one tool we have to improve performance. That said, there are times when we want to put that index on hold. While indexes dramatically improve read performance they do cause a slight dip in write performance. This isn’t significant most of the time but when doing a large load it can frequently be faster to get rid of the existing indexes and then put them back when you are done.

I don’t think that I’ve ever regularly disabled indexes, even during bulk loading. It’s good to know that the option exists, however.

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Erik Darling shows us how arranging columns in an index can make a huge difference in query performance:

A while back I promised I’d write about what allows SQL Server to perform two seeks rather than a seek with a residual predicate.

More recently, a post touched a bit on predicate selectivity in index design, and how missing index requests don’t factor that in when requesting indexes.

This post should tie the two together a bit. Maybe. Hopefully. We’ll see where it goes, eh?

Also apropos: missing index hints return results in alphabetical order, not in selectivity order or what would be best for queries. In other words, just because the green text in SSMS says it’s the index you want doesn’t mean it’s the index you need.

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Greg Low explains some of the tricky bits behind using filtered indexes:

If you think about it, if all we’re ever going to use is one part of the index, i.e. just the unfinalized rows, having an entry in there for every single row is quite wasteful, as although the vast majority of the index will never be used, it still has to be maintained.
So in SQL Server 2008, we got the ability to create a filtered index. Now these were actually added to support sparse columns. But on their own, they’re incredibly useful anyway.

I use these on occasion but less than I want to, and a big part of the reason why is in this post, particularly around parameters.

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Kevin Chant looks at a few problems that can pop up when using filtered indexes:

In a past post here I did an overview of different index types. I said in that post that I think filtered indexes could be more popular. In this post I will cover fixing some of the problems caused when you first introduce rowstore filtered indexes to a SQL Server database.

Some of you have probably been there already. You’ve put in your first filtered index on a database only to find an issue has happened. I’ve witnessed these issues at a few places. This will hopefully reduce the pain.

I’ve definitely experienced the third issue (which also pops up when using parameterized queries, so the optimizer doesn’t know that it can use the filtered index), but never the first two.

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