Deprecate Tidb_index_serial_scan_concurrency Variable In TiDB

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Hey guys! Today, we're diving into a proposal to deprecate a specific variable within TiDB. This is super important because it helps keep our systems clean, efficient, and less confusing for everyone. We're going to break down why this variable is on the chopping block, what it means for you, and how we plan to make this transition as smooth as possible. So, let's get started!

Feature Request Overview

The Problem: An Obsolete Variable

So, what's the deal? The session variable tidb_index_serial_scan_concurrency is the variable in question. Our main issue is that this variable isn't actively used anywhere in the TiDB codebase anymore. Think of it like that old tool in your garage that you haven't touched in years – it's just taking up space! Keeping around unused variables can actually cause more harm than good. It can lead to confusion, especially for new users or even seasoned pros trying to figure out how things work under the hood.

Imagine you're trying to optimize a query and you stumble upon this variable. You might spend valuable time trying to understand what it does and how it affects your performance, only to realize it's a dead end. For maintainers, these obsolete elements clutter the codebase, making it harder to navigate, maintain, and evolve the system. So, it's in everyone's best interest to clean things up.

The Feature: Deprecation and Removal

Our proposed solution is straightforward: we want to deprecate and remove the tidb_index_serial_scan_concurrency variable from TiDB. This means a couple of key steps. First, we'll mark the variable as deprecated, signaling that it's on its way out. This gives users a heads-up that they shouldn't rely on it anymore. Then, we'll actually remove it from the codebase. It's like spring cleaning for our database system! We will also ensure that our documentation is updated to reflect this change. No one should be scratching their heads trying to figure out why a variable mentioned in the docs doesn't exist. Finally, we'll make sure to include a clear notification in the release notes, so everyone knows about the removal.

Alternatives Considered: Why Not Just Remove It?

Now, you might be thinking, why not just yank it out without saying anything? Well, that's the "remove without notice" option, and honestly, it's not the friendliest approach. Imagine you're using this variable in a script or configuration (even though it's not doing anything), and suddenly, your system starts throwing errors. That's not a great experience! We value transparency and want to give our users a smooth transition. That's why we're opting for the deprecation route – it's the considerate thing to do.

Diving Deeper: Teachability, Documentation, Adoption, and Migration

Okay, let's get into the nitty-gritty of how we're going to make this happen. Deprecating and removing a variable isn't just about deleting a line of code; it's about ensuring our community can adapt to the change without a hitch. Here's our game plan:

Clear Communication is Key

First and foremost, we're focusing on clear communication. This means making sure the deprecation is prominently mentioned in our documentation and release notes. Think of the documentation as your go-to guide for all things TiDB. We'll update it to explicitly state that tidb_index_serial_scan_concurrency is deprecated and will be removed in a future release. This gives you a clear heads-up if you happen to stumble upon it. The release notes are another crucial channel. They're like the headlines for each new TiDB version, highlighting the important changes. We'll include a note about the deprecation there as well, ensuring it doesn't slip under your radar.

Guidance for Users

We also want to provide guidance for users who might still be referencing this variable in their scripts or configurations. Now, since the variable doesn't actually do anything, removing it shouldn't break your system. However, we understand that seeing an error message or a warning can be unsettling. So, we'll offer some simple advice: if you find tidb_index_serial_scan_concurrency in your scripts, just remove it. It's like decluttering your code – a good habit to have!

Code Cleanup

Behind the scenes, we'll be doing our own code cleanup. This means making sure that all related code paths that might be referencing the variable are cleaned up. It's like making sure all the wires are disconnected before you remove an old appliance. This internal cleanup ensures that the removal is seamless and doesn't leave any lingering issues.

Adoption and Migration Strategy

Our adoption and migration strategy is centered around minimizing disruption. Since the variable is already obsolete, there's no real functionality to migrate. It's more about removing a vestigial organ than performing a complex transplant. By giving ample notice through documentation and release notes, we're giving everyone time to adjust their mental models and scripts, if necessary. The key here is that this change is a simplification – it makes TiDB cleaner and easier to understand.

The Bigger Picture: Why This Matters

Now, you might be thinking, "Okay, it's just one variable. Why all the fuss?" Well, this deprecation is a microcosm of a larger philosophy: we're committed to keeping TiDB lean, efficient, and user-friendly. Here's why this kind of cleanup is so important:

Reducing Cognitive Load

In the world of software, cognitive load refers to the amount of mental effort required to use a system. The more features, options, and variables a system has, the higher the cognitive load. And a high cognitive load can lead to mistakes, confusion, and frustration. By removing unused elements, we're reducing the cognitive load on our users. It's like simplifying a user interface – the fewer options you have, the easier it is to find what you need.

Improving Maintainability

For us as maintainers, a cleaner codebase is a happier codebase. When there are fewer obsolete elements, it's easier to understand how the system works, to find and fix bugs, and to add new features. It's like having a well-organized workshop – you can find your tools quickly and get the job done efficiently.

Preventing Future Confusion

Imagine a new user coming to TiDB and encountering this variable. They might spend hours trying to figure out what it does, reading documentation, and maybe even asking for help. All that effort would be wasted, since the variable doesn't actually do anything. By removing it, we're preventing this kind of confusion and making TiDB more approachable for newcomers.

Embracing Change and Evolution

Software systems aren't static; they evolve over time. Features are added, bugs are fixed, and sometimes, things become obsolete. Being willing to deprecate and remove unused elements is a sign of a healthy, evolving system. It means we're not afraid to let go of the past and embrace the future. It's like pruning a tree – you need to cut away the dead branches to allow new growth.

In Conclusion: A Cleaner, Meaner TiDB

So, there you have it! Our proposal to deprecate and remove the tidb_index_serial_scan_concurrency variable is all about making TiDB a better system for everyone. It's about reducing confusion, improving maintainability, and embracing the natural evolution of software. We believe this change, while small in itself, reflects our commitment to quality, clarity, and user-friendliness.

We'll be sure to keep you updated on the progress of this deprecation. As always, your feedback is invaluable, so if you have any thoughts or concerns, please don't hesitate to share them. Let's continue to make TiDB the best database it can be!