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Indexing

SQL ConstantCare

Things to Consider When SQL Server Asks for an Index

Last Updated March 1, 2020

Indexing, SQL ConstantCare

One of the things I love about SQL Server is that during query plan compilation, it takes a moment to consider whether an index would help the query you’re running. Regular blog readers will know that I make a lot of jokes about the quality of these recommendations – they’re often incredibly bad – but…

Making TRY_CAST and TRY_CONVERT Queries Faster with Indexed Computed Columns

Last Updated March 1, 2020

Computed columns, Execution Plans, T-SQL

I know this is gonna sound crazy, but let’s say you had a table where people stored all kinds of things in one column: dates, integers, file names, sale prices, file names, you name it. And let’s say your application frequently ran a query looking for dates in that column, like this: Transact-SQL SELECT *…

WHERE GETDATE() BETWEEN StartDate AND COALESCE(CancelDate, EndDate) Is Even Harder to Tune.

Last Updated February 12, 2020

Development, Indexing

In my last post, we started with a memberships table, and each membership had start & end dates. I’m going to create the table and populate it with everyone having an active membership – their StartDate is the same as their Stack Overflow account creation date, and their EndDate is around a year or two…

WHERE GETDATE() BETWEEN StartDate AND EndDate Is Hard to Tune.

Last Updated February 19, 2020

Development, Indexing

Say you’ve got a memberships (or policies) table, and each membership has start & end dates: Transact-SQL USE StackOverflow; GO DROP TABLE IF EXISTS dbo.UsersMemberships; CREATE TABLE dbo.UsersMemberships (Id INT IDENTITY(1,1) PRIMARY KEY CLUSTERED, UserId INT NOT NULL, StartDate DATETIME NOT NULL, EndDate DATETIME NOT NULL, CancelledEarlyDate DATETIME NULL); GO 1234567891011 USE StackOverflow;GODROP TABLE IF…

Building SQL ConstantCare: Let’s Tune an Index in Postgres.

Last Updated January 14, 2020

Indexing, PostgreSQL

This week, our SQL ConstantCare® back end services started having some query timeout issues. Hey, we’re database people – we can do this, right? Granted, I work with Microsoft SQL Server most of the time, but we host our data in Amazon Aurora Postgres – is a query just a query and an index just…

How to Make SELECT COUNT(*) Queries Crazy Fast

Last Updated December 22, 2019

Columnstore Indexes, Execution Plans

When you run a SELECT COUNT(*), the speed of the results depends a lot on the structure & settings of the database. Let’s do an exploration of the Votes table in the Stack Overflow database, specifically the 2018-06 ~300GB version where the Votes table has 150,784,380 rows taking up ~5.3GB of space. I’m going to measure…

How to Think Like the Engine: When a Seek Isn’t

Last Updated November 19, 2019

Execution Plans, How to Think Like the SQL Server Engine, Indexing

In our last episode, I introduced the concept of scan predicates: execution plan operations that weren’t able to seek directly to the rows they needed. Let’s take another query: Transact-SQL DropIndexes; GO CREATE INDEX IX_LastAccessDate_Id_DisplayName_Age ON dbo.Users(LastAccessDate, Id, DisplayName, Age); GO SELECT Id FROM dbo.Users WHERE LastAccessDate > '1800/01/01' AND DisplayName = N'Brent Ozar'; GO…

How to Think Like the Engine: Index Column Order Matters a LOT.

Last Updated November 19, 2019

Execution Plans, How to Think Like the SQL Server Engine, Indexing

We’ve been working with the clustered index of the Users table, which is on the Identity column – starts at 1 and goes up to a bajillion: And in a recent episode, we added a wider nonclustered index on LastAccessDate, Id, DisplayName, and Age: Transact-SQL CREATE INDEX IX_LastAccessDate_Id_DisplayName_Age ON dbo.Users(LastAccessDate, Id, DisplayName, Age); GO 123…

The Many Problems with SQL Server’s Index Recommendations

Last Updated November 13, 2019

These days, I jump back & forth a lot between SQL Server and Postgres. (We use AWS Aurora Postgres to store SQL ConstantCare®‘s data.) Whenever I come back to the sweet, sweet graphical execution plans in SQL Server Management Studio, I breathe a sigh of relief. Dang, these things are so much easier for me…

How to Think Like the SQL Server Engine: Included Columns Aren’t Free.

Last Updated November 11, 2019

How to Think Like the SQL Server Engine, Indexing

In our last cliffhanger episode, I said that if we ran this query: Transact-SQL UPDATE dbo.Users SET Age = Age + 1 WHERE Id = 643; 123 UPDATE dbo.Users SET Age = Age + 1 WHERE Id = 643; And we had this index: Transact-SQL CREATE INDEX IX_LastAccessDate_Id_DisplayName_Age ON dbo.Users(LastAccessDate, Id, DisplayName, Age); 12 CREATE INDEX IX_LastAccessDate_Id_DisplayName_Age ON…

How to Think Like the SQL Server Engine: Should Columns Go In the Key or the Includes?

Last Updated November 11, 2019

How to Think Like the SQL Server Engine, Indexing

In our last episode, in between crab rangoons, I had you create either one of these two indexes: Transact-SQL CREATE INDEX IX_LastAccessDate_Id_Includes ON dbo.Users(LastAccessDate, Id) INCLUDE (DisplayName, Age); GO CREATE INDEX IX_LastAccessDate_Id_DisplayName_Age ON dbo.Users(LastAccessDate, Id, DisplayName, Age); GO 1234567 CREATE INDEX IX_LastAccessDate_Id_Includes ON dbo.Users(LastAccessDate, Id) INCLUDE (DisplayName, Age);GOCREATE INDEX IX_LastAccessDate_Id_DisplayName_Age ON dbo.Users(LastAccessDate, Id, DisplayName, Age);GO And I said…

How to Think Like the SQL Server Engine: Building Wider Indexes to Deal with Bad T-SQL

Last Updated November 9, 2019

How to Think Like the SQL Server Engine, Indexing

In our last episode, we were running into problems with these two queries: Transact-SQL SELECT LastAccessDate, Id, DisplayName, Age FROM dbo.Users WHERE LastAccessDate BETWEEN '2018-08-31' AND '2018-09-01' ORDER BY LastAccessDate; SELECT LastAccessDate, Id, DisplayName, Age FROM dbo.Users WHERE CAST(LastAccessDate AS DATE) = '2018-08-31' ORDER BY LastAccessDate; 123456789 SELECT LastAccessDate, Id, DisplayName, Age FROM dbo.Users WHERE LastAccessDate BETWEEN…

How to Think Like the SQL Server Engine: What’s a Key Lookup?

Last Updated October 22, 2019

How to Think Like the SQL Server Engine, Indexing

In our last couple of queries, we’ve been using a simple query to find the Ids of everyone who accessed the system since mid-2014: Transact-SQL SELECT Id FROM dbo.Users WHERE LastAccessDate > '2014-07-01' ORDER BY LastAccessDate; 1234 SELECT Id FROM dbo.Users WHERE LastAccessDate > '2014-07-01' ORDER BY LastAccessDate; But Ids alone aren’t all that useful – so let’s…

How to Think Like the SQL Server Engine: Adding a Nonclustered Index

Last Updated October 22, 2019

How to Think Like the SQL Server Engine, Indexing

When we left off in the last post, our users kept running this query, and they want it to be really fast: Transact-SQL SELECT Id FROM dbo.Users WHERE LastAccessDate > '2014/07/01' ORDER BY LastAccessDate; 1234 SELECT Id FROM dbo.Users WHERE LastAccessDate > '2014/07/01' ORDER BY LastAccessDate; Let’s pre-bake the data by creating a copy of…

Time to partition my wine collection

DBA Training Plan 17: Should You Partition Your Tables?

Last Updated September 2, 2019

DBA Training Plan, Partitioning

In the last episode, I talked about knowing when it’s time to scale out: identifying when our data is getting to be so large that we have to split it across multiple servers, and I explained why that is so challenging. But what about table partitioning – SQL Server’s ability to break up a single…

Automatically Indexing in Azure SQL DB

Research Paper Week: Automatic Indexing in Azure SQL DB

Last Updated August 11, 2019

Architecture, Azure SQL DB, Indexing

Before I give you the link to the next research paper in this week’s series, I wanna give you a few questions to think about: If you had to build something to automatically add indexes to SQL Server databases, where would you start? What data would you use to make your decisions? How would you…

Query Execution in Column-Oriented Database Systems

Research Paper Week: Query Execution in Column-Oriented Database Systems

Last Updated August 20, 2019

Columnstore Indexes

This week, I’m sharing some of my favorite papers that I’ve read. Sometimes they’re about future technologies that haven’t shipped yet – and may never ship! Sometimes, like this one, they’re not from Microsoft at all, but from someone else in the industry who’s explaining a problem that we face in SQL Server. SQL Server…

Defrag

DBA Training Plan 10: Managing Index Fragmentation

Last Updated May 7, 2020

DBA Training Plan, Index Maintenance

In the last episode, we looked at your index designs with the output of sp_BlitzIndex. You might have gotten a little overwhelmed what with all the different warnings (and all the learning resources!) You might have thought, “Is there an easier way?” “Is there a way I can just run a job, and have something…

DBA Training Plan 9: My 3 Index Guidelines

Last Updated August 15, 2019

DBA Training Plan, Indexing

In our last episode, we used sp_BlitzIndex @Mode = 2 to get to know the contents of our database, sorted our indexes from biggest to smallest, and started asking questions about leftover backup tables that we probably didn’t need to keep around anymore. Now that you’ve taken out the trash, let’s have a closer look…

DBA Training Plan 8: What’s Inside Your Own Databases

Last Updated August 13, 2019

DBA Training Plan, Indexing

In the last episode of the DBA Training Plan, we talked about what’s inside the MDF file: a series of pages that store a database’s tables. Now, it’s time to check out the contents of YOUR database to understand what’s using the most space, what’s getting used the most often, and what you might be…

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