Preventing DBCC DBREINDEX?

Kevin Feasel

2016-11-23

DBCC

Dave Mason is looking for a way to prevent a user from running DBCC REINDEX:

After a little digging, I discovered the related database user is a member of the db_ddladmin fixed database role. Members of that role are permitted to run DBCC REINDEX. Since I have existing (more sensible) code in place for index maintenance, I don’t want the DBCC REINDEX operations to continue. Here’s the problem: I can’t find a direct way to DENY a database user from running DBCC commands. T-SQL syntax doesn’t support something like DENY DBCC TO <user> or DENY DBCC REINDEX TO <user>. MSDN documentation tells me the equivalent ALTER INDEX command requires at minimum ALTER permission on the table or view. I guessed that revoking or denying ALTER TABLE privileges might prevent a user from executing DBCC DBREINDEX, but that does not appear to be the case.

That’s painful.

Saving DBCC Results

Kevin Feasel

2016-11-17

DBCC

Wayne Sheffield shows how to save CHECKDB results to table:

Okay, let’s try this out. At the above BOL links, there are two DBCC commands that are documented to use the TABLERESULTS option: OPENTRAN and SHOWCONTIG. Testing all of the other DBCC commands shows that this option can also be used on the CHECKALLOC, CHECKDB, CHECKFILEGROUP and CHECKTABLE commands. I’m going to continue this post with using DBCC CHECKDB. If you check BOL, it does not mention the TABLERESULTS option.

As Wayne notes, you can do this for other DBCC commands as well.

DBCC OPTIMIZER_WHATIF

Derik Hammer shows how to use DBCC OPTIMIZER_WHATIF to get an idea of how your query would run with different hardware:

DBCC OPTIMIZER_WHATIF can be used to pull down your resources or augment them. Often the differences in the execution plans have to do with parallelism and memory grants. This is an example of an execution plan running on an under powered development machine.

This is a good tool to help figure out what an execution plan probably would look like in production when your test environment is much smaller.

CHECKDB Snapshots

Kevin Feasel

2016-11-11

DBCC

Arun Sirpal shows that the CHECKDB snapshot is no longer hidden:

I am in the middle of some research regarding CHECKDB and learnt something new. From SQL Server 2014 onwards the database snapshot that is used to get to a transactionally-consistent point-in-time is no longer hidden.

Arun includes a sample to prove it.

DBCC SHOW_STATISTICS Update

Erik Darling notes that his Connect item to replace DBCC SHOW_STATISTICS has been marked as resolved:

So what does it look like?

I have no idea. I don’t know if it’s a DMV or a function, I don’t know what it’s called, and I don’t know what information it exposes. I also don’t know how it will get joined to other DMVs. There were no details offered up when the status changed. And I’m fine with that! I’m pretty psyched that it got enough traction to get a fix to begin with. If anyone from MS feels like shooting me an email with details, I won’t complain.

But since we don’t know, we’re free to speculate. Like all those History Channel shows about aliens and fake animals and where the Templars secretly buried Jesus’ gold teeth in Arizona. It’ll be fun!

It’ll be interesting to see the results.

Parsing DBCC MEMORYSTATUS

Kevin Feasel

2016-09-02

DBCC, T-SQL

Slava Murygin has a script to turn DBCC MEMORYSTATUS output into one result set:

When I wanted to research memory problem on a server and started to dig deeper into “DBCC MEMORYSTATUS” command.Very useful links to understand that command were from Microsoft:
https://support.microsoft.com/en-us/kb/271624
https://support.microsoft.com/en-us/kb/907877

During the research I’ve faced two problems:
1. I had to wait several seconds to get the full result set.
2. I had to scroll down and shuffle 115 different data sets to find the counter I want.

To eliminate both these problem all these different counters have to be in the same table/data set.
That will make research easier and data can be stored or compared with the base line.

Read on for the T-SQL script.

CHECKDB And Indexes On Persisted Computed Columns

Kevin Feasel

2016-09-01

DBCC

Arun Sirpal diagnoses a slower-than-usual DBCC CHECKDB run:

All the signs of CHECKDB Latch contention.

DBCC – OBJECT – METADATA this latch can be a major bottleneck for DBCC consistency checks when indexes on computed columns exist.  As a side note DBCC_Multiobject scanner  is used to get the next set of pages to process during a consistency check.

Read on for the details and Arun’s solution.

Running CheckDB On Log Shipping Subscribers

Brent Ozar shows how to support running DBCC CHECKDB on a log shipping subscriber:

 

At first glance, if you set up log shipping the way most folks do, it looks like you can’t run CHECKDB on a subscriber:

On SQL Server Enterprise Edition, you can try working around it by creating a database snapshot – but that won’t work either:

Here’s the trick: your database needs to be in standby mode instead of norecovery. When you run restores with the standby option, you’re able to query the database in between restores.

This doesn’t obviate the need for running CHECKDB on a primary, but it can offload some of that work some of the time.

DBCC CHECKDB’s NOINDEX Option

Kendra Little explains the NOINDEX option of DBCC CHECKDB and how it relates to PHYSICAL_ONLY:

PHYSICAL_ONLY looks at page structures and makes sure something isn’t obviously wrong. If you have the database’s page verification option set to CHECKSUM (the default since SQL Server 2005, and a very good thing), it runs a checksum on the page and compares it to a checksum recorded in the header when the page was last modified.

When you use the PHYSICAL_ONLY option, you’re telling SQL Server to skip logical checks. It won’t do things like make sure the data in a clustered and nonclustered index on a table is consistent with one another.

I like the analogy, as well as the how-to guide on messing up your database.  But try not to do that to a production database…

DBCC Help

Kevin Feasel

2016-06-10

DBCC

Kenneth Fisher describes DBCC Help:

Many years ago during an interview I was asked to “Name the top 7 DBCC commands that you use.” I think I was able to name 3. Ever since then I’ve paid particular attention to DBCC commands in preparation of the day when I hear that question again. Well not to long ago I was watching Erin Stellato’s (b/t) PluralSight course “SQL Server: Understanding and Using DBCC Commands”. Note: It’s a great course and I highly recommend it. In it she goes over quite a few DBCC commands, some documented, some not. In noted two in particular.

The first one I noted gives you a list of the size and free space in the logs of all databases on the instance. Highly useful. I’ve used it repeatedly recently. Unfortunately my memory is not always the best and I can never quite remember the exact name. Which brings us to the other command.

I completely agree that Erin’s Pluralsight course is worth watching.

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