teleren/devto huggingface dataset:
Understanding the "SELECT FOR UPDATE" SQL Statement
Tags: postgres, database
Published: 2024-06-06 06:03:31


## What is "SELECT FOR UPDATE"?

`SELECT FOR UPDATE` is a clause in SQL that is appended to a SELECT statement. It locks the selected rows, preventing other transactions from modifying them until the **current transaction** is committed or rolled back. This ensures that the data being read and potentially updated remains consistent throughout the transaction.

### Syntax of "SELECT FOR UPDATE"

The basic syntax for using "SELECT FOR UPDATE" is:

```sql
BEGIN;
SELECT stock 
FROM items 
WHERE item_id = ? 
FOR UPDATE;
-- Check stock and update if available
UPDATE items 
SET stock = stock - 1 
WHERE item_id = ?;
COMMIT;

```

Here, the `FOR UPDATE` clause at the end indicates that the selected rows should be locked for the duration of the transaction.

## How Does "SELECT FOR UPDATE" Work?

When a transaction issues a "SELECT FOR UPDATE" statement, the following steps occur:

1. **Row Selection:** The database engine identifies the rows that match the specified condition.
2. **Row Locking:** The selected rows are locked, preventing other transactions from acquiring locks that would conflict with the current transaction. This typically means other transactions cannot update or delete these rows until the lock is released.
3. **Data Access:** The transaction can read and potentially update the locked rows.
4. **Transaction Completion:** Once the transaction is committed or rolled back, the locks are released, making the rows available for other transactions.

Postgres: Row-level locks do not affect data querying; they block only writers and lockers to the same row. ([ref](https://www.postgresql.org/docs/current/explicit-locking.html#LOCKING-ROWS))

## Benefits of Using "SELECT FOR UPDATE"

1. **Data Consistency:** By locking the rows during a transaction, "SELECT FOR UPDATE" ensures that the data being read is not changed by other transactions, maintaining consistency.
2. **Avoiding Deadlocks:** Proper use of "SELECT FOR UPDATE" can help avoid deadlocks by managing locks in a controlled manner.
3. **Concurrency Control:** It provides a way to handle concurrent data access and modification efficiently, particularly in applications with high transaction volumes.

## Use Cases of "SELECT FOR UPDATE"

1. **Banking Systems:** Ensuring that account balances are accurate by locking rows representing accounts during transactions.
2. **Inventory Management:** Preventing the same item from being sold to multiple customers simultaneously by locking the inventory records.
3. **Reservation Systems:** Managing bookings by locking the rows representing available slots or seats during the reservation process.

### Conclusion

"SELECT FOR UPDATE" is a vital tool for managing data integrity and consistency in relational databases. By understanding its functionality and applying it thoughtfully, developers can handle concurrent transactions effectively, ensuring reliable and accurate data manipulation. However, it is equally important to be aware of its implications on performance and system architecture to make the best use of this feature.
Managing Concurrent Purchases of Limited Items in a Database
Tags: distributedlock, systemdesign
Published: 2024-06-06 06:00:26

_Imagine that we're developing an e-commerce website. In this case, we have a limited number of items while many users are trying to buy them at the same time. In this article, let's try to resolve this problem with some solutions_

### Database-Level Locking
_You can read this article beforehand to understand Pros an Cons of Optimistic lock & Pessimistic lock: [link](https://dev.to/jacktt/optimistic-lock-pessimistic-lock-4h36)_

#### Optimistic Locking

Optimistic locking operates on the premise that most database transactions do not conflict. It uses a versioning system to detect conflicts and resolve them without locking the entire database row.

**How It Works:**
1. Each item in the database has a version number.
2. When a user attempts to purchase an item, the current version number is checked.
3. If the version number hasn't changed during the transaction, the purchase is processed and the version number is updated.
4. If the version number has changed, indicating another transaction has modified the item, the current transaction must retry or fail. 

In this case, we can use `stock` field itself as the version of item.

**Implementation Example:**
```sql
UPDATE items 
SET stock = stock - 1
WHERE item_id = ? AND stock = ?;
```
This SQL statement ensures that the item is updated only if the stock value has not been changed.

#### Pessimistic Locking

With pessimistic locking, we lock the item for the duration of the transaction, preventing other transactions from updating it.

**How It Works:**
1. Begin a transaction.
2. Lock the item row.
3. Check the stock and perform the purchase if stock is available.
4. Commit the transaction.

**Implementation Example:**
```sql
BEGIN;
SELECT stock 
FROM items 
WHERE item_id = ? 
FOR UPDATE;
-- Check stock and update if available
UPDATE items 
SET stock = stock - 1 
WHERE item_id = ?;
COMMIT;
```
This approach locks the row when checking and updating the stock, preventing other transactions from interfering.

### Application-Level Handling

#### Distributed Locking

**How It Works:**
1. Acquire a distributed lock for the item when a user attempts to purchase it.
2. Perform the purchase operation while holding the lock.
3. Release the lock after the operation.

To implement this solution, we can use `SETNX` command, that returns 1 if acquire successfully and 0 if other one acquired. Don't forget to set expire time to prevent deadlock in case the owner of the lock crashes before releasing it.


### Combining Strategies

A robust solution often combines database and application-level strategies:
- Use optimistic or pessimistic locking to maintain immediate consistency in the database.
- Implement distributed locking for higher-level application logic.
Unlock Your Potential with Expert VA Job Resume Help
Published: 2024-06-06 05:55:37

In the competitive landscape of the federal job market, having a standout resume is crucial. If you're eyeing opportunities with the VA or searching for positions on USAJOBS, you need more than just a generic resume. You need tailored **[VA Job Resume Help](https://www.resumeyourway.com/)** and USAJOBS Resume Help that highlights your unique skills and experiences. Our service goes beyond mere document creation; we craft resumes that serve as keys to unlocking your full potential in the federal job market.

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VRK Packers and Movers
Published: 2024-06-06 05:51:57

Address: Shop No. 20, Narayan Niwas, Hanuman Road, Vile Parle East, Mumbai 400057
Mobile No.: 9136064187
Email Id: vrkpackersandmovers11@gmail.com.com
Website: www.vrkpackersmovers.com

VRK Packers And Movers company offering their services across the India including Delhi, Noida, Ghaziabad, Gurgaon, Faridabad, Bangalore, Dehradun, Goa, Mumbai, Chennai, Kolkata, Secunderabad, Pune, Hyderabad, Nagpur, Ludhiana, Chandigarh etc. VRK Packers And Movers Shifting is the promising name in the Moving and Packing industry and have expertise in the transportation of goods, Packing of goods with excellent packing material, office shifting, household shifting, loading etc, offering awesome services to its Clients. VRK Packers And Movers operates on the principles of safety, integrity and reliability. We have our Branch offices all over India to cater the needs of our Customers. Our speciality: we provide vacuum packaging service. Vacuum Packaging is essential for export packaging. Now a day’s Vacuum packaging is used for various products including machinery to food products Now a days vacuum packaging is used for various products including machinery to food products.
My Journey As A Young Programmer.
Tags: datascience, beginners, programming, learning
Published: 2024-06-06 05:43:47

Embarking on the journey of learning programming was like stepping into a vast, unknown world. It was a small achievement, yet it felt monumental. I was diving into a realm where logic and creativity intertwined, and the possibilities seemed endless.

The initial days were filled with confusion and curiosity. Understanding syntax, debugging errors, and grasping core concepts were significant hurdles. I often found myself staring at the screen, puzzled by error messages that seemed to be written in an alien language. However, I soon realized that this struggle was a common experience among beginners.

Talking to others who were also new to programming provided immense comfort and insight. Many shared stories of their initial challenges—spending hours debugging a single line of code or feeling overwhelmed by the sheer volume of information. One individual mentioned how they had almost given up after a particularly frustrating week, but the breakthrough came after persisting through their confusion. Another shared their strategy of breaking down complex problems into smaller, manageable tasks, which helped them gradually build confidence.

These shared experiences taught me that perseverance is key. The world of programming is not something that can be mastered overnight. It requires dedication, continuous learning, and a willingness to embrace failure as part of the learning process. The satisfaction of solving a problem or creating a functioning program outweighs the initial struggles. Every error message and every bug fixed is a step forward.

As I progressed, I found that programming is not just about writing code. It's about problem-solving, thinking logically, and being creative. It's about collaborating with others, learning from their experiences, and sharing knowledge. The programming community, with its culture of openness and support, played a crucial role in my journey. Online forums, coding bootcamps, and study groups became invaluable resources, where I could seek help and also assist others.

Reflecting on my journey, I realize that the path of a beginner in programming is a mix of frustration and joy, challenges and triumphs. Each step, whether forward or backward, is a valuable part of the learning process. The initial hurdles make the achievements all the more rewarding. I’ve come to appreciate that being a beginner is not just a phase but a continuous process of learning and growth. The journey has just begun, and with each line of code, I am moving closer to mastering the art of programming.

**THE END**
List of top free API testing tools and their Comparison
Published: 2024-06-06 05:40:15

Are you in search of the right API testing tool or a viable alternative?

Explore this detailed list of the top 15 free API testing tools. The list includes information on features, pros, cons, pricing, recommended use cases, and a comparison to help you choose the best fit for your needs.

https://www.checkops.com/top-free-automated-api-testing-tools-2024/
Suggestions needed to modify my Gaming Store Website
Tags: webdev, javascript, beginners, productivity
Published: 2024-06-06 05:30:33

Here's my GitHub link for my project Gaming Store website-
[Gaming-Store](https://github.com/Akanksha12-i/Gaming-Store-Website)
I would really appreciate your suggestion about any modification needed. Please provide the method to implement the modification along with the suggestion. It will help me learn more.

Akanksha Sinha
Conventional Commits for Writing Effective Git Commit Messages
Tags: git, github, gitlab, armanrahman
Published: 2024-06-06 05:27:30

Conventional Commits is a compact, well-organized way of making commit messages. It provides a set of principles for adding human and computer-readable meaning to commits. Its principal objective is to enable the development of automated tools based on commit messages.

In this regard, it adds some distinctive items in the commit messages where the type of the commit stands out as one. The next table gives an overview of common types of commits that are described in the specification:

_**Structure:**_
 
```
<type>: <subject-description>
```

![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/nrgdzqcq9y6bl50j5ms3.png)

_**Example:**_
> $git commit -m "feat: added new nav bar on template"


## In addition,
A convention that sets the subject for a commit message thusly:

Following this structure, a commit that adds, for example, a new endpoint to an API to allow the creation of coupons, should have a subject that looks like this:

_**Structure:**_
 
```
<type>(optional scope): <subject-description>
```

A commit that adds a new endpoint to an API to allow the creation of coupons, for instance, should have a subject that looks like this:

_**Example:**_
> $git commit -m "feat(api): Add support to create coupons"

Besides, we can append BREAKING CHANGE: in the footer of the commit to indicate that it introduces breaking changes. On the other hand, after the commit type, we can insert ! to highlight the breaking changes.

_**Example:**_

> "chore!: Update PHP version to min 8.2

also you can add '**BREAKING CHANGE**' footer for extra description to the commit. 

> "chore!: downgraded PHP version to 8.1 from 8.2
>
> BREAKING CHANGE: use packages that supports php 8.1"
List of Top Affiliate Networks
Published: 2024-06-06 05:25:54

[](url)OpenAFF
OpenAFF is the first technology affiliate network, using artificial intelligence technologies in processing incoming traffic to achieve better conversion rates. With years of experience and working with large volumes of traffic, OpenAFF offers the best CPA, CPL, and CRG terms from direct advertisers to their partners. Continue []()https://brolinks.com/Ptyhfq
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Tags: programming, python, css, webdev
Published: 2024-06-06 05:24:17

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Latest JavaScript Tool Releases: PM2 5.4, Melange 4.0, Neutralinojs 5.2, and More!
Tags: javascript, release, tools
Published: 2024-06-06 05:10:04

✅ **ReleasesKnip 5.17.0** – Finds and removes unused files, dependencies and exports. Now with more.
✅ **PM2 5.4** – Popular Node.js-based process manager for production.
✅ **Melange 4.0** – OCaml compiler for JavaScript developers.
✅ **Neutralinojs 5.2** – Lightweight cross-platform desktop app framework.
✅ **Billboard.js 3.12** – The popular chart library gets funnel charts.
✅ **Peaks.js 3.4** – BBC-created audio waveform UI component.
✅ **Happy DOM 14.12** – JS implementation of a web browser sans UI.
✅ **Retire.js 5.0** – Scans for JS libraries with known vulnerabilities.
✅ **React Native Boilerplate 4.2** – A starter template for RN apps.
✅ **RE:DOM 4.1** – Tiny library for creating user interfaces.
✅ **AlaSQL.js 4.4** – Isomorphic JavaScript SQL database.
✅ **is-what 5.0** – Simple, small JS type check functions.
✅ **FxTS 1.0** – Functional programming library.
Diamond Perfection Home & Property Inspections
Tags: home, inspector
Published: 2024-06-06 05:09:34

When it comes to ensuring the integrity of your home investment in Salt Lake City, UT, trust [Diamond Perfection Home & Property Inspections](https://www.diamondperfectionhpi.com/). Our seasoned inspectors meticulously evaluate every aspect of your property, from the foundation to the roof, providing you with a comprehensive understanding of its condition. With our detailed reports, you'll gain invaluable insights into potential issues and necessary repairs, empowering you to make informed decisions. Whether you're buying, selling, or maintaining a home, Diamond Perfection is committed to delivering thorough, professional, and reliable inspection services. Schedule your inspection with us today for peace of mind and confidence in your investment.

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Design Quality: The Cornerstone of a Lasting Brand Legacy
Tags: startup, productivity, design, product
Published: 2024-06-06 05:00:00

In today's fast-paced world, brands are constantly vying for our attention.  But what truly sets a brand apart and ensures its longevity?  The answer lies in design quality.  High-quality design isn't just about aesthetics; it's a strategic approach that shapes user experience, fosters emotional connections, and ultimately, contributes to a brand's enduring legacy.

**The Power of Design:**

* **Building Brand Identity:**  Design is the visual language of a brand.  High-quality design establishes a distinct visual identity that is memorable, consistent, and reflects the brand's core values. 
* **Elevating User Experience:**  Good design goes beyond aesthetics. It prioritizes usability, functionality, and intuitive navigation. This creates user experiences that are positive, efficient, and leave a lasting impression.
* **Emotional Connection:**  Design has the power to evoke emotions.  Well-crafted design elements like color palettes, imagery, and typography can build trust, inspire confidence, and create an emotional connection between users and the brand.
* **Differentiation in a Crowded Market:**  In a sea of competitors, high-quality design can make a brand stand out. Innovative and user-centric design solutions can position a brand as a leader and attract a loyal following.

**Investing in Design for Long-Term Success:**

A brand's legacy is built over time. Here's how design quality contributes to a lasting impact:

* **Brand Consistency:**  Maintaining high-quality design standards across all touchpoints, from packaging to marketing materials and digital platforms, fosters brand recognition and trust.
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HTTP/2 Server Push Arrives: Faster Delivery for a Smoother User Experience
Published: 2024-06-06 04:52:45

 [Node.js 21](https://www.clariontech.com/blog/exploring-whats-new-in-node.js-21) introduces HTTP/2 Server Push, a feature that allows servers to anticipate client requests and proactively deliver additional resources. This can significantly improve page load times and enhance the overall user experience.

The enhancements to Worker Threads in Node.js 21 solidify their position as a valuable tool for developers working with computationally intensive tasks. By leveraging Worker Threads effectively, developers can create more responsive and performant Node.js applications, ultimately providing a better user experience. As Node.js continues to evolve, Worker Threads are poised to play an even more significant role in the future of server-side JavaScript development.