Voice of the DBA

Category: Editorial

  • Migrations are Worth the Effort

    I work with a lot of customers that are trying to find better ways to build and deploy database code. Some of them use a state or model method with SQL Compare or another Redgate product, and some want to use Flyway and its hybrid migration-based framework. It’s always interesting to me how customers lean one way or the other, for various reasons.

    No matter which choice people make, we know that using migrations is more effort than a state-based approach. However, I think that it’s a better approach, especially because no matter how simple or smooth you think your development process is, at some time there will be a situation that needs a more complex approach. a migrations-based framework allows you to handle the complexity smoothly, without depending on a person to sort out the issues.

    It’s not just me, but many developers feel the same way. There’s an interesting article from a developer that gives some examples of why using migrations work well in different situations. It also acknowledges that the effort is high, but by using migrations you can accomplish complex tasks across time. something I try to get more developers to do. Don’t big-bang-deploy-everything, but break things into chunks.

    It’s not just a simple change. There are a few reasons that migrations are hard, one of which I loved. The author compares migrations to working with live electrical wires. Imagine hanging a ceiling lamp and wiring it up without turning off the power (note: don’t try that).

    One of the best reasons I have for migrations is that lots of work isn’t done at the same time, especially in a team. If each team or each piece of work is broken into separate migrations, choosing which ones to move over from developer is much easier than if all the changes are captured in a state-ful model. You still have to be aware of dependencies between migrations, but having them all separate at the beginning (and hopefully tagged to pieces of work) makes this easier.

    The other reason to choose migrations is that I can stage future changes. Imagine I need to make a change to add something in one migration and remove it later. Suppose we add a new tax column and then after Jan 1, we remove the old tax column. With migrations I can pre-write the removal and create a pull request with the “Tax Removal – DO NOT MERGE UNTIL 2024 JAN 1” title, which should be obvious to anyone. I like keeping things simple, which helps when I never know who might need to handle this work in the future.

    Steve Jones

    Listen to the podcast at Libsyn, Spotify, or iTunes.

  • Try, Try Again, Until It’s Right

    One of the challenges with making changes in a database environment is that undoing those changes can be hard. What’s often preferred is rolling forward with a new change to correct the issue, but that’s often done with limited analysis and thought. Instead, we hope our staff makes a quick patch and a better decision under pressure than they did with more time to examine the problem. That works if it’s a simple mistake that was made in implementation but not if we haven’t designed our solution well at the start.

    I ran across an article on DoorDash that I thought was interesting. During the pandemic, their business exploded and they outgrew the Aurora PostgreSQL database. They migrated to Cockroach, a cloud version of PostgreSQL that’s distributed and can (theoretically) scale much higher.

    The thing I found interesting is that the engineers at DoorDash were trying to break apart their monolith and get better scalability, primarily from certain tables, by extracting their tables to get single writers in a cluster, which should help them handle a larger workload. They wanted to use their main identity table as a test, which I assume is the table that tracks each user in the system. They tried to migrate this and cutover to a new cluster 4 times before a fifth attempt worked.

    I think any large migration is fraught with issues, but I appreciated the design here that allowed them to rollback their change and revert to the previous version of the database. That’s something I don’t see many teams think about or build into their database change process. I think having a clear, known, tested way to undo changes is important, at least for some of your tables.

    There are two pieces of advice they give that I often give to customers as well. First, learn to spread out changes across batches. When I work with Flyway customers, I always let them know they need to think of a migration script as a unit of deployment and break those apart as best you can. Those often also become units of rollback, so keep them small. Not necessarily every change in its own script, but don’t bundle too many things together.

    Second, keep things simple. Too often I find engineers build clever solutions that make sense to them, but no one else. You never know the quality of your next hire, so don’t overcomplicate things without a really good reason.

    Did their process work? They’ve grown to about 1.9PB of data. That’s a lot of food orders. They’ve also had other metrics of success, and seem to be saving time for their tech team, which is often one of the main reasons to build a better process and use it consistently.

    Steve Jones

    Listen to the podcast at Libsyn, Spotify, or iTunes.

  • Who Still Uses SP_ for Naming?

    An interesting post recently from Chad Callihan on the reasons why someone shouldn’t use sp_ to prefix their stored procedures. This is advice that I’ve seen for years, but I haven’t run into this lately with many customers. It seems I do see some usp_, but not sp_. I think that’s good, and if you’re not sure why, read Chad’s post.

    I think my main reason for not doing this is that I sometimes create procs in master. Not because it’s a good idea (it isn’t) or I want to, but because I’ll make mistakes. I’ll accidentally connect to master and deploy a script, because I’m not paying enough attention. Usually, I’ll catch this right away, but if not, soon after I’ve told a client things are working, they’ll let me know they aren’t. Then I connect to the right database.

    In a vacuum, or even as you sit reading this today, it’s easy to criticize someone else for making the mistake of connecting to the wrong database, or even forgetting to delete the object in master after I’ve created it in the right one. However, all of us are human. We’ll make mistakes. We’ll be pressed for time or sick or tired or want to leave or some other situation where we aren’t using all of our faculties. Even if none of those are true, we might depend on muscle memory because we’ve done this 1,000 times (or may 12 times in the last hour) and then don’t notice we’ve connected to the wrong database.

    What might be even worse if when we’re updating objects and potentially update in one place but not another. What if v7 of the proc is in the user database, but v5 is in master. Who knows if we (or the client) will notice things aren’t working as expected right away.

    Mistakes are one of the reasons I try hard to get everyone to follow a DevOps approach. Put your code in version control (so you know where it is when you make mistakes), use automation and CLI calls to deploy code. Whether you use something like Flyway or your own SQLCMD scripts, make sure things are automated. Then ensure you have logs with commands run, and if needed, output from the scripts.

    We’re human, we make mistakes, so figuring out how to automate a process and then ensuring that automation is running results in repeatable, reliable deployments. Something we should all want, especially the control-obsessive DBAs.

    Steve Jones

    Listen to the podcast at Libsyn, Spotify, or iTunes.

  • Breaking Biometrics

    In the movies, when someone needs to bypass some sort of fingerprint biometric system, they use tape to lift a fingerprint, or in the more gory films, cut off a body part. In any case, there have been a lot of attempts to replicate this in the real world. Sometimes these work, though the consensus is modern hardware isn’t as susceptible as older hardware. I don’t know if that’s true, but I did see an interesting look at the main three sensors used in most laptops.

    All the laptops had their authentication bypassed, though not with any fake biometric device, but rather with attacking the actual communications between the sensor and the OS. There’s a great report from two people who were asked by Microsoft to evaluate the security of the top three sensors. It’s a fascinating look at how the hardware and software of the OS are set up to provide secure authentication and how both can be fooled.

    Some of the problems are users not enabling features and some are that manufacturers aren’t understanding or implementing the secure protocols from Microsoft. I both get how this happens and I feel it’s not acceptable. Certainly someone might read a spec and not completely understand it, even across a team of people. However, for vendors, this can’t be something they don’t have researchers, pen testers, or some security professional examine. Hardware vendors spending money designing these devices ought to include the money for a few people to try and break the security before they are sold.

    At least for security features.

    I like the enhancements made with multi-factor authentication, and I appreciate biometrics as a convenient way to access things. At the same time, I want to be able to trust them. The efforts made by the researchers are pretty high, not something that someone in a coffee shop can do in 5 minutes while you go to the bathroom. At least, apart from the Surface. It appears that one can be quick.

    At the same time, if you lose your laptop, within hours someone can break past the biometrics with a man-in-the-middle attack. Even if you’ve encrypted the disk, your data can be accessed since this attack gets the OS to authenticate them.

    Security is tricky, but I don’t plan on disabling my fingerprint scanner. However, if I were carrying around data that was more important than the work I do now or data worth a lot of money, I don’t know I’d ever enable biometrics.

    Steve Jones

    Listen to the podcast at Libsyn, Spotify, or iTunes.