DBCC – Curated SQL

Working with DBCC OPTIMIZER_WHATIF

Published 2025-01-15 by Kevin Feasel

Yvonne Vanslageren shows off a very uncommon DBCC command:

DBCC OPTIMIZER_WHATIF is a powerful diagnostic command in SQL Server that allows database administrators and developers to simulate various hardware configurations. By doing so, it shows how the query optimizer would behave under different CPU and memory allocations—without requiring you to physically change server hardware. This makes it an invaluable tool for performance tuning, troubleshooting, and strategic planning in SQL Server environments.

This obviously won’t actually make things faster, but will help you answer questions like “would more CPU cores improve this query or do I need to dump more RAM into the server?”

Automating DBCC CHECKDB on Full Backups

Published 2025-01-15 by Kevin Feasel

Shane O’Neill riffs off of a script:

Like many shops out there, we can’t run corruption checking on our main production database instance. So, then, what do we do? We take the backups and restore them to a test instances, and then run corruption checking on those restored databases.

At least this way we can test the backups we take can be restored, as well.

But, I don’t want to spend every day manually restoring and corruption checking these databases, so let’s automate this bit…

Click through for a script that Shane built off of a Madeira Data Solutions script that Eitan Blumin put together.

Incremental Integrity Checks for SQL Server Databases

Published 2024-10-29 by Kevin Feasel

Eitan Blumin eats the elephant:

Traditional database integrity checks in SQL Server can be time-consuming and resource-intensive, especially for large databases, even when using super cool tools like Ola Hallengren’s maintenance solution.

To address this challenge, I developed a TSQL script for performing incremental integrity checks, which significantly optimizes the process and reduces its impact on the server.

Click through for that script and notes from Eitan.

I’ll also shill for Minion CheckDB whenever I can. I was an early beta tester for the product and it was designed specifically for dealing with large databases.

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Fixing an Error in DBCC CloneDatabase

Published 2024-07-18 by Kevin Feasel

Steve Jones runs into an issue:

This was an interesting error, and I was able to duplicate it, so I decided to write a post on how to find the problem and fix it. The error after running DBCC CLONEDATABASE is:
NO_STATISTICS and NO_QUERYSTORE options turned ON as part of VERIFY_CLONE.
Database cloning for 'atest' has started with target as 'aSmallTest'.
Msg 2601, Level 14, State 1, Line 11
Cannot insert duplicate key row in object 'sys.sysschobjs' with unique index 'clst'. The duplicate key value is (885578193).
The final key value (885578193) for you might be different, but the error is the same.

Read on to learn more about the issue, as well as how Steve was able to fix the problem.

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DBCC CLONEDATABASE and Production Deployments

Published 2024-03-28 by Kevin Feasel

Madhumita Tripathy takes a step back:

DBCC CLONEDATABASE command generates a schema-only copy of a database. Effective March 1, 2025, Microsoft will discontinue support for the use of the DBCC CLONEDATABASE command as a tool to copy database to production environment. The command is intended for diagnostic and troubleshooting purposes only. Any use of the command for purposes other than those specified will not be supported by Microsoft from the aforementioned date. All editions of Microsoft SQL Server 2016 and later versions are affected by this change.

Now I’m a bit curious about the why behind this post.

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Breaking out a CHECKDB Run

Published 2024-02-14 by Kevin Feasel

Mikey Bronowski fixed a problem:

Regular execution of DBCC CHECKDB is a cornerstone practice for DBAs, ensuring that databases are free from corruption. However, this routine maintenance can sometimes feel more like a Herculean task, especially when DBCC CHECKDB runs slower than a snail in molasses, or worse, gets terminated because it runs too slow.

Read on to see what Mikey did to fix the issue. This is a good reminder that sometimes, there is no single silver bullet, but a whole magazine of lead can still get you to the same location.

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Table Results for DBCC PAGE

Published 2023-12-22 by Kevin Feasel

Andy Yun is pleased:

Am playing around with Always Encrypted for the first time. I was just following along the basic tutorial and encrypted some columns in my AutoDealershipDemo database. But then I decided to go crack open the data page using my friend DBCC PAGE.

Read on to see how you can get the results of DBCC PAGE into a table. My recollection is that there are some limits to what it can write into the table, but it’s pretty good on the whole.

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Triggering Dumps for Specific Errors and States

Published 2022-09-29 by Kevin Feasel

Bob Dorr has a plan:

I had an inquiry about dbcc dumptrigger today and realized that state filtering was added to dbcc dumptrigger but not well known.
You can collect a process dump (SQL Dumper) when a specific error occurs using XEvent (error_reported/ex_raise2 events with dump capture action) or dbcc dumptrigger.
The common use of dbcc dumptrigger is: dbcc dumptrigger(‘set’, 208) to produce a dump when error 208 is encountered.

This is pretty useful, especially if you’re troubleshooting a bug in the database engine.

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When DBCC_OBJECT_METADATA becomes a Bottleneck

Published 2021-07-28 by Kevin Feasel

Paul Randal takes us through another latch:

Continuing my series of articles on latches, this time I’m going to discuss the DBCC_OBJECT_METADATA latch and show how it can be a major bottleneck for consistency checks prior to SQL Server 2016 under certain circumstances. The issue affects DBCC CHECKDB, DBCC CHECKTABLE, and DBCC CHECKFILEGROUP, but for clarity I’ll just reference DBCC CHECKDB for the rest of this post.
You might wonder why I’m writing about an issue that affects older versions, but there are still a huge number of SQL Server 2014 and older instances out there, so it’s a valid topic for my series.

Read on to understand what DBCC_OBJECT_METADATA does and how it can become a bottleneck on those older versions of SQL Server.

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CHECKDB: Repairing with Data Loss

Published 2021-06-08 by Kevin Feasel

Chad Callihan explains what that CHECKDB option which should sound really scary means:

Just because REPAIR_ALLOW_DATA_LOSS might get your database up and running quickly doesn’t make it a good option. It could wrongly be considered a shortcut or an easy button to get handle corruption. Some may run REPAIR_ALLOW_DATA_LOSS, see their database back online, and call it a day. Let’s look at why some things are too good to be true.

Read the whole thing.

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Category: DBCC