Voice of the DBA

Author: way0utwest

Practical Hekaton

I got into a debate recently with someone about the In-Memory OLTP tables (formerly Hekaton) feature that was released with SQL Server 2014. This person asked if anyone was actually using the technology, given all the limitations that were placed on these structures in this first release.

I’ve had quite a few people actually get upset with Microsoft releasing a “feature” that doesn’t just work as a replacement for the regular tables in SQL Server. They feel that Microsoft should have spent more time working to make the transition to these tables seemless, perhaps not releasing in-Memory tables until SQL Server 2016.

I feel differently. I think that Microsoft should get the technology working and stable, and then release it. Even if it has limitations, I’d like to see an implementation available early and give companies the chance to see how it performs in real world workloads. If you can’t workaround the limitations, then you can’t use it, but then does it matter if the feature is available in 2014 or 2016? I’m not sure it does.

We would really like to publish more guidance here, and help people understand the feature better. If anyone is out there actually using Hekaton in production, or has a development project underway that should get to production soon, we’d like to contact you and work out a way to publish information. You’re welcome to write an article, or we can write one for you with a little interview time, either way is fine; we’d just like to get some practical, real world information out for everyone to learn from.

Please contact us if you’re using In-Memory OLTP tables and natively compiled stored procedures.

Steve Jones

The Voice of the DBA Podcast

Listen to the MP3 Audio ( 2.4MB) podcast or subscribe to the feed at iTunes and LibSyn.

June 11, 2015
Unexpected Windows 10

This was strange. I noticed a new icon in the taskbar today. When I hovered over it, I saw this:

I downloaded the Windows 10 beta in a VM, but not here. However apparently some update added this. If I click on it, I see this:

I hadn’t been reading about Windows 10 too much. Mostly I want it for the copy/paste in the command line, but apparently I need to download it to get the upgrade. I hadn’t heard this before, and I was concerned.

If I click the reserve upgrade, I see this:

I don’t need a download now. Apparently I’ll get an automatic one when the OS goes to RTM, which is fine. I assume I can install it elsewhere, but perhaps I’m limited to this device?

It’s hard to tell. This will be an interesting process. I went through the FAQ and it appears I could upgrade later. The upgrade I reserved is for this device, so I’ll need to do this separately on my laptop.

A new process for Windows, and I’m interested to see how it works. I’ve seen a few MS people have issues with Windows 10 in demos, so I’m a little concerned about upgrading now, but I am looking forward to seeing the new OS in July or August.

June 10, 2015
Archive Every Day

I regularly see questions posted online from people struggling to manage a large archive process. Often the inserts into an archive table and the deletes from the source require large amounts of resources that strain systems and block other activity. These types of processes can also require lots of transaction log space, something many people forget about.

The best solution, in my mind, is to archive regularly. Decide how much data you need and then trim your working set back to that level on a regular, preferably daily, level. That way you limit the amount of resources you need at one time.

However that’s not always easy to implement in a system. I’ve encountered many applications that were set up to read from a single table and archiving data means no one can access that data unless it’s inserted back into the main table.

I wish that we would have better patterns and frameworks for building archiving into systems from the start. I almost wonder if we should be using a view built across a a regular table and archive table from the start for accessing data. This isn’t a complete solutions, and there are certainly problems here. Maybe we should have partitioning implemented early on, though the edition limits on that technology are problematic.

Microsoft is bringing us “stretch” tables in SQL Server 2016. Not a bad idea for archiving cold data, but as Brent Ozar points out, are they going to do better partition elimination? Will Microsoft give us a good way to handle backups? There are certainly issues here, and likely room for improvement in later versions.

Ultimately I think the complexity of archival data doesn’t matter for most systems. These days 10GB of data is a pittance, and since many applications (and their databases) are smaller than this, why bother. If you have a larger system, however, I’d encourage you to think about archival before you need it. When you actually have time to implement it well.

Steve Jones

The Voice of the DBA Podcast

Listen to the MP3 Audio ( 2.5MB) podcast or subscribe to the feed at iTunes and LibSyn.

June 9, 2015
T-SQL Tuesday #67 – Extended Events for DBCC

It’s the second Tuesday of the month and time for another T-SQL Tuesday. This time it’s #67 from Jes Borland on Extended Events. You can read the invite, and whether you can participate today or not, write your blog and leave a comment for Jes on her blog.

If you want to see all the topics from the past, I have them on a post here.

If you want to host, contact the founder of T-SQL Tuesday, Adam Machanic. He chooses the hosts and is always looking for people that want to participate. You just need a blog and a good idea.

Who Ran DBCC?

I ran across a question recently from someone that said DBCC messages had appeared in the error log, but no one had run DBCC. That’s not possible as DBCC isn’t run without someone, whether that’s a human or a service, executing the DBCC command.

In the past, I might recommend a trace to track this, but not I’d choose an Extended Events (XE) session. I’ll show how to set up a simple session, though be aware I’m not an XE guru. I’m sure there are better ways to structure this, but it worked well for me.

You can start quickly building a specific XE session by right clicking the Sessions folder under Extended Events in SSMS under Management. I tend to pick the wizard for getting started, though be sure to save the script later.

From here we get the opening screen for XE, which I won’t show. The next screen asks for a name for the session. It doesn’t matter, but once you start using XE, you’ll start to get quite a few session, so it’s handy to pick something that’s simple and easy to understand later.

I can choose to start the session here when I’m done, but don’t worry if you’re not sure. You’ll get a chance again later.

The next step is to decide whether you use a template or build a session from scratch. I’m not sure if any of these templates will work well as I haven’t dug in. In my case, I decided to just choose a generic session.

Now I need to pick the events. There are a lot, but I went down to get the sql_statement_completed as my event. This will let me see the text of a call, which is what I need.

A couple notes here. One, you might want to grow this screen so that you can read what’s in the lower windows. I know there’s a lot of data here, but this screen doesn’t seem well defined.

The second note is that don’t forget to add the event with the arrow button. Until you have an event (or multiple events) in the right window, you can’t click "Next".

The next step is to get the data fields you need. Again, there are a lot, and I limited this to what I needed. I grabbed the client host and app, as well as the database. Then I grabbed the service_principal_name and sql_text as well. This should let me determine who’s running the command.

I’ve got lots of data here, but I only care about the execution of dbcc checkdb. This means I need to filter things, which is my choice with the next screen.

Here I need to click in the top line to get a place to add a filter. Then I select sql_text from the drop down and choose like for the operator and "dbcc checkdb" for the value. This should grab events that execute with a dbcc call.

I have to choose where to store this data. Since this is mostly a check for me, I can just use the ring buffer and keep data in memory. I lowered this to 10 events, but you can certainly pick what works for you. If you care about auditing, drop this in a file. For a small session like this, there’s not much data that’s going to be captured.

I get a summary screen, which lets me review settings. I haven’t shown it here, but once I pass that, I get the "Success" screen. This is where I can start the session, and actually watch live data if I want.

For this, I’ll watch the live data.

I decided to test this first and see if it captures anything else. I ran a few queries, and then this:

Still a blank, live data screen. Then I ran checkdb. I saw the results, and then ran it a few more times.

As you can see, I now can see that I ran checkdb against the EncryptionPrimer database.

This lets me do some quick auditing of what’s happening with my DBCCs. A smart DBA might even use this to ensure that DBCC is being run against some databases, perhaps on a spare machine.

June 9, 2015