line·Sep 26, 2025Original article

PD1 AI Hackathon: Into the (opens in new tab)

The PD1 AI Hackathon 2025 served as a strategic initiative by LY Corporation to embed innovative artificial intelligence directly into the LINE messaging ecosystem. Over 60 developers collaborated during an intensive 48-hour session to transition AI from a theoretical concept into practical features for messaging, content, and internal development workflows. The event successfully produced several high-utility prototypes that demonstrate how AI can enhance user safety, creative expression, and technical productivity. ## Transforming Voice Communication through NextVoIP * The "NextVoIP" project utilized Speech-to-Text (STT) technology to convert 1:1 and group call audio into real-time data for AI analysis. * The system was designed to provide life security features by detecting potential emergency situations or accidents through conversation monitoring. * AI acted as a communication assistant by suggesting relevant content and conversation topics to help maintain a seamless flow during calls. * Features were implemented to allow callers to enjoy shared digital content together, enriched by AI-driven recommendations. ## Creative Expression with MELODY LINE * This project focused on the intersection of technology and art by converting chat conversations into unique musical compositions. * The system analyzed the context and emotional sentiment of messages to automatically generate melodies that matched the atmosphere of the chat. * The implementation showcased the potential for generative AI to provide a multi-sensory experience within a standard messaging interface. ## AI-Driven QA and Test Automation * The grand prize-winning project, "IPD," addressed the bottleneck of repetitive manual testing by automating the entire Quality Assurance lifecycle. * AI was utilized to automatically generate and manage complex test cases, significantly reducing the manual effort required for mobile app validation. * The system included automated test execution and a diagnostic feature that identifies the root cause of failures when a test results in an error. * The project was specifically lauded for its immediate "production-ready" status, offering a direct path to improving development speed and software reliability. The results of this hackathon suggest that the most immediate value for AI in large-scale messaging platforms lies in two areas: enhancing user experience through contextual awareness and streamlining internal engineering via automated QA. Organizations should look toward integrating AI-driven testing tools to reduce technical debt while exploring real-time audio and text analysis to provide proactive security and engagement features for users.

AIGenerative AITest AutomationMobile Development+2

line·Sep 19, 2025Original article

P-Canvas: An Engineering Technique for (opens in new tab)

The concept of "Managing Engineering" treats team leadership as a systematic process designed to reduce the "reproduction costs" of solving recurring human and organizational challenges. By implementing the P-Canvas framework, managers can move away from abstract, directionless 1-on-1 meetings and toward a data-driven approach that visualizes a member's growth and psychological state. This methodology concludes that management can be systemized just like software engineering, allowing leads to proactively identify and resolve team issues through trend analysis and visual indicators. ### The Concept of Managing Engineering * Engineering is defined as the act of lowering reproduction costs; if a solution to a problem can be reused by others to save time and effort, it is considered engineering. * Applying this logic to management involves creating reusable frameworks for handling complex interpersonal relationships, professional growth, and team care. * The goal is to move beyond "neglect disguised as autonomy" by building a system that ensures team members are truly supported rather than just left to work independently. ### Structure and Design of P-Canvas * P-Canvas is a visual management framework consolidated into a single page, updated monthly over a five-month cycle to track changes over time. * The framework utilizes three 2D coordinate systems to map complex nuances: communication proactivity, the relationship between growth and performance, and the emotional state regarding stable versus challenging tasks. * Scale-based indicators measure quantitative factors such as workload distribution, project participation, job satisfaction, motivation levels, and the degree of "radical candor" practiced by the member. * A hexagonal skill chart tracks six dimensions of competency: communication, team-specific values (Platform 10 rules), job expertise, work completion, knowledge generalization, and cultural contribution. ### Data-Driven 1-on-1s and Problem Identification * The framework shifts 1-on-1 conversations from vague questions like "How are you?" to specific inquiries based on data patterns, such as a sudden dip in satisfaction paired with a rise in candor. * It functions as an early warning system, allowing leads to detect signs of burnout or interpersonal conflict before they escalate into long-term performance issues. * By visualizing data, the lead and the member can engage in "joint problem-solving," identifying whether a decline in motivation is due to unclear roles, cultural clashes, or inefficient processes. * The system emphasizes the "trajectory of change" rather than absolute scores, focusing on how a member recovers and grows following specific management interventions or project shifts. ### Benefits of Visualized Management * Proactive Intervention: Leads can catch subtle signals of dissatisfaction early through shifting data points rather than waiting for a member to voice a complaint. * Objective Communication: The presence of a visual chart provides a neutral ground for discussing sensitive topics, making it easier for members to express their feelings through data. * Verification of Support: The framework allows leads to track the effectiveness of their own management actions by observing if a member’s indicators improve in subsequent months. Implementing a tool like P-Canvas is highly recommended for leads who find traditional 1-on-1 meetings too abstract or difficult to facilitate. By treating management as an engineering discipline, leaders can create a more predictable and supportive environment where individual growth is measured not just by output, but by a holistic view of a member’s professional and emotional well-being.

ProductivityManaging EngineeringTeam Management1on1 Meetings+2

line·Sep 12, 2025Original article

Code Quality Improvement Techniques Part (opens in new tab)

When implementing resource management patterns similar to Kotlin's `use` or Java's try-with-resources, developers often face the challenge of handling exceptions that occur during both primary execution and resource cleanup. Simply wrapping these multiple failures in a custom exception container can inadvertently break the calling code's error-handling logic by masking the original exception type. To maintain code quality, developers should prioritize the primary execution exception and utilize the `addSuppressed` mechanism to preserve secondary errors without disrupting the expected flow. ### The Risks of Custom Exception Wrapping Creating a new exception class to consolidate multiple errors during resource management can lead to significant issues for the caller. * Wrapping an expected exception, such as an `IOException`, inside a custom `DisposableException` prevents specific `catch` blocks from identifying and handling the original error. * This pattern often results in unhandled exceptions or the loss of specific error context, especially when the wrapper is hidden inside utility functions. * While this approach aims to be "neat" by capturing all possible failures, it forces the caller to understand the internal wrapping logic of the utility rather than the business logic errors. ### Prioritizing Primary Logic over Cleanup When errors occur in both the main execution block and the cleanup (e.g., `dispose()` or `close()`), it is critical to determine which exception takes precedence. * The exception from the main execution block is typically the "primary" failure that reflects a business logic or IO error, whereas a cleanup failure is often secondary. * Throwing a cleanup exception while discarding the primary error makes debugging difficult, as the root cause of the initial failure is lost. * In a typical `try-finally` block, if the `finally` block throws an exception, it naturally suppresses any exception thrown in the `try` block unless handled manually. ### Implementing Better Suppression Logic A more robust implementation mimics the behavior of Kotlin’s `Closeable.use` by ensuring the most relevant error is thrown while keeping others accessible for debugging. * Instead of creating a wrapper class, use `Throwable.addSuppressed()` to attach the cleanup exception to the primary exception. * If only the primary block fails, throw that exception directly to satisfy the caller's `catch` requirements. * If both the primary block and the cleanup fail, throw the primary exception and add the cleanup exception as a suppressed error. * If only the cleanup fails, it is then appropriate to throw the cleanup exception as the standalone failure. ### Considerations for Checked and Unchecked Exceptions The impact of exception handling varies by language, particularly in Java where checked exceptions are enforced by the compiler. * Converting a checked exception into an unchecked `RuntimeException` inside a wrapper can cause the compiler to miss necessary error-handling requirements. * If exceptions have parent-child relationships, such as `IOException` and `Exception`, wrapping can cause a specific handler to be bypassed in favor of a more generic one. * It is generally recommended to only wrap checked exceptions in `RuntimeException` when the error is truly unrecoverable and the caller is not expected to handle it. When designing custom resource management utilities, always evaluate which exception is most critical for the caller to see. Prioritize the primary execution error and use suppression for auxiliary cleanup failures to ensure that your error-handling remains transparent and predictable for the rest of the application.

KotlinJavaCode QualityResource Management+2

line·Sep 3, 2025Original article

Code Quality Improvement Techniques Part 19: Child Lock (opens in new tab)

The "child lock" technique focuses on improving code robustness by restricting the scope of what child classes can override in an inheritance hierarchy. By moving away from broad, overridable functions that rely on manual `super` calls, developers can prevent common implementation errors and ensure that core logic remains intact across all subclasses. This approach shifts the responsibility of maintaining the execution flow to the parent class, making the codebase more predictable and easier to maintain. ## Problems with Open Functions and Manual Super Calls Providing an `open` function in a parent class that requires child classes to call `super` creates several risks: * **Missing `super` calls:** If a developer forgets to call `super.bind()`, the essential logic in the parent class (such as updating headers or footers) is skipped, often leading to silent bugs that are difficult to track. * **Implicit requirements:** Relying on inline comments to tell developers they must override a function is brittle. If the method isn't `abstract`, the compiler cannot enforce that the child class implements necessary logic. * **Mismatched responsibilities:** When a single function handles both shared logic and specific implementations, the responsibility of the code becomes blurred, making it easier for child classes to introduce side effects or incorrect behavior. ## Implementing the "Child Lock" with Template Methods To resolve these issues, the post recommends a pattern often referred to as the Template Method pattern: * **Seal the execution flow:** Remove the `open` modifier from the primary entry point (e.g., the `bind` method). This prevents child classes from changing the overall sequence of operations. * **Separate concerns:** Move the customizable portion of the logic into a new `protected abstract` function. * **Enforced implementation:** Because the new function is `abstract`, the compiler forces every child class to provide an implementation, ensuring that specific logic is never accidentally omitted. * **Guaranteed execution:** The parent class calls the abstract method from within its non-overridable method, ensuring that shared logic (like UI updates) always runs regardless of how the child is implemented. ## Refining Overridability and Language Considerations Designing for inheritance requires careful control over how child classes interact with parent logic: * **Avoid "super" dependency:** Generally, if a child class must explicitly call a parent function to work correctly, the inheritance structure is too loose. Exceptions are usually limited to lifecycle methods like `onCreate` in Android or constructors/destructors. * **C++ Private Virtuals:** In C++, developers can use `private virtual` functions. These allow a parent class to define a rigid flow in a public method while still allowing subclasses to provide specific implementations for the private virtual components, even though the child cannot call those functions directly. To ensure long-term code quality, the range of overridability should be limited as much as possible. By narrowing the interface between parent and child classes, you create a more rigid "contract" that prevents accidental bugs and clarifies the intent of the code.

KotlinCode QualitySoftware DesignCpp+3

line·Aug 29, 2025Original article

Extracting Trending Keywords from OpenChat (opens in new tab)

To enhance user engagement on the LINE OpenChat main screen, LY Corporation developed a system to extract and surface "trending keywords" from real-time message data. By shifting focus from chat room recommendations to content-driven keyword clusters, the team addresses the lack of context in individual messages while providing a more dynamic discovery experience. This approach utilizes a combination of statistical Z-tests to identify frequency spikes and MinHash clustering to eliminate near-duplicate content, ensuring that the trending topics are both relevant and diverse. **The Shift from Chat Rooms to Content-Driven Recommendations** * Traditional recommendations focus on entire chat rooms, which often require significant user effort to investigate and evaluate. * Inspired by micro-blogging services, the team aimed to surface messages as individual content pieces to increase the "main screen visit" KPI. * Because individual chat messages are often fragmented or full of typos, the system groups them by keywords to create meaningful thematic content. **Statistical Detection of Trending Keywords** * Simple frequency counts are ineffective because they capture common social fillers like greetings or expressions of gratitude rather than actual trends. * Trends are defined as keywords showing a sharp increase in frequency compared to a baseline from seven days prior. * The system uses a Z-test for two-sample proportions to assign a score to each word, filtering for terms with at least a 30% frequency growth. * A seven-day comparison window is specifically used to suppress weekly cyclical noise (e.g., mentions of "weekend") and to capture topics whose popularity peaks over several consecutive days. **MinHash-based Message Deduplication** * Redundant messages, such as copy-pasted text, are removed prior to frequency aggregation to prevent skewed results and repetitive user experiences. * The system employs MinHash, a dimensionality reduction technique, to identify near-duplicate messages based on Jaccard similarity. * The process involves "shingling" messages into sets of tokens (primarily nouns) and generating $k$-length signatures; messages with identical signatures are clustered together. * To evaluate the efficiency of these clusters without high computational costs, the team developed a "SetDiv" (Set Diversity) metric that operates in linear time complexity. By combining Z-test statistical modeling with MinHash deduplication, this methodology successfully transforms fragmented chat data into a structured discovery layer. For developers working with high-volume social data, using a rolling weekly baseline and signature-based clustering offers a scalable way to surface high-velocity trends while filtering out both routine social noise and repetitive content.

AIMachine LearningNatural Language ProcessingStatistical Analysis+5

line·Aug 27, 2025Original article

Code Quality Improvement Techniques Part 18 (opens in new tab)

Effective refactoring often fails when developers focus on the physical structure of code rather than its conceptual meaning. When nested loops for paged data are extracted into separate functions based solely on their technical boundaries, the resulting code can remain difficult to read and maintain. The article argues that true code quality is achieved by aligning function boundaries with logical units, such as abstracting data retrieval into sequences to flatten complex structures. ## Limitations of Naive Extraction - Traditional paged data processing often results in nested loops, where an outer `while` loop manages page indices and an inner `for` loop iterates through items in a chunk. - Simply extracting the inner loop into a private method like `saveMetadataInPage(page)` frequently fails to improve readability because it splits the conceptual task of "fetching all items" into two disconnected locations. - This "mechanical extraction" preserves the underlying implementation complexity, forcing the reader to track the state of pagination and loop conditions across multiple function calls. ## Refactoring Based on Conceptual Boundaries - A more effective approach identifies the high-level semantic units: "retrieving all items" and "processing each item." - In Kotlin, the pagination logic can be encapsulated within a `Sequence<Item>` using the `sequence` builder and `yieldAll` keywords. - By transforming the data source into a sequence, the consumer function can replace a nested loop with a single, clean `for` loop. - This abstraction allows the main business logic to focus on "what" is being done (saving metadata) while hiding the "how" (managing page indices and `hasNext` flags). ## Forest over Trees - When refactoring, developers should prioritize the "forest" (the relationship between operations) over the "trees" (individual functions). - This methodology is not limited to loops; it applies equally to nested conditional branches and complex data structures. - The goal should always be to ensure that the code reflects the meaning of the task, which often requires restructuring the data flow rather than just splitting existing blocks of code.

KotlinCode QualityRefactoringKotlin Sequences+1

line·Aug 14, 2025Original article

Case Study: Improving Video (opens in new tab)

Engineers at LINE identified a recurring monthly degradation in video call quality, specifically in Japan, where packet loss increased and frames per second (FPS) dropped toward the end of each month. Investigation revealed that this pattern was caused by mobile ISP bitrate throttling once users exhausted their monthly data caps, which the existing congestion control mechanisms were failing to handle efficiently. To resolve this, the team improved their proprietary CCFS (Congestion Control based on Forward path Status) algorithm to more accurately detect these specific network constraints and maintain stable playback. ### Analysis of Monthly Quality Degradation * Data analysis showed a "monthly cycle" where video decoding FPS was highest at the start of the month and progressively declined toward the end. * This quality drop was specifically tied to an increase in video packet loss, which prevents normal decoding and results in stuttering or frozen frames. * Statistical segmentation revealed the issue occurred almost exclusively on 4G mobile networks rather than Wi-Fi, and was more pronounced in high-bitrate video calls than in voice calls. * The root cause was identified as mobile data plan policies; as users hit their monthly data limits, ISPs impose speed restrictions that create network congestion if the application continues to send high-bitrate data. ### Limitations of Standard Congestion Control * While the IETF RMCAT working group has standardized algorithms like NADA (RFC8698) and SCReAM (RFC8298), real-time two-way communication requires more sensitive response times than one-way streaming. * In two-way calls, even a one-second delay makes natural conversation difficult, meaning the system cannot rely on large buffers to smooth out network instability. * Existing mechanisms were not reacting fast enough to the rigid throughput limits imposed by carrier throttling, leading to packet accumulation in network queues and subsequent loss. ### The CCFS Proprietary Algorithm * LINE utilizes a custom-developed, sender-based algorithm called CCFS (Congestion Control based on Forward path Status). * Unlike older algorithms that rely on Round Trip Time (RTT), CCFS focuses on the "forward path"—the actual path packets take to the receiver—by analyzing feedback on packet arrival times and loss. * CCFS categorizes network status into four distinct states: Default, Probing, Throttled, and Competing. * The system monitors "delay variation"; when it detects a continuous increase in delay exceeding a specific threshold, it transitions to the "Throttled" state to proactively reduce bitrate before the queue overflows. ### Strategies for Quality Improvement * The team focused on refining how CCFS handles the transition into the Throttled state to better align with the artificial bandwidth ceilings created by ISPs. * By improving the sensitivity of forward path status monitoring, the application can more rapidly adjust its transmission rate to stay within the user's current data plan limits. * This technical adaptation ensures that even when a user's mobile speed is restricted, the video remains smooth, albeit at a lower resolution, rather than breaking up due to packet loss. To provide a high-quality communication experience, developers must account for external factors like regional ISP policies. Refining proprietary congestion control algorithms to detect specific patterns, such as monthly data-cap throttling, allows for a more resilient service that maintains stability across diverse mobile environments.

Real Time CommunicationVideo StreamingCongestion ControlNetwork Adaptation+4

line·Aug 12, 2025Original article

The Current State of LY Corporation (opens in new tab)

Tech-Verse 2025 showcased LY Corporation’s strategic shift toward an AI-integrated ecosystem following the merger of LINE and Yahoo Japan. The event focused on the practical hurdles of deploying generative AI, concluding that the transition from experimental models to production-ready services requires sophisticated evaluation frameworks and deep contextual integration into developer workflows. ## AI-Driven Engineering with Ark Developer LY Corporation’s internal "Ark Developer" solution demonstrates how AI can be embedded directly into the software development life cycle. * The system utilizes a Retrieval-Augmented Generation (RAG) based code assistant to handle tasks such as code completion, security reviews, and automated test generation. * Rather than treating codebases as simple text documents, the tool performs graph analysis on directory structures to maintain structural context during code synthesis. * Real-world application includes a seamless integration with GitHub for automated Pull Request (PR) creation, with internal users reporting higher satisfaction compared to off-the-shelf tools like GitHub Copilot. ## Quantifying Quality in Generative AI A significant portion of the technical discussion centered on moving away from subjective "vibes-based" assessments toward rigorous, multi-faceted evaluation of AI outputs. * To measure the quality of generated images, developers utilized traditional metrics like Fréchet Inception Distance (FID) and Inception Score (IS) alongside LAION’s Aesthetic Score. * Advanced evaluation techniques were introduced, including CLIP-IQA, Q-Align, and Visual Question Answering (VQA) based on video-language models to analyze image accuracy. * Technical challenges in image translation and inpainting were highlighted, specifically the difficulty of restoring layout and text structures naturally after optical character recognition (OCR) and translation. ## Global Technical Exchange and Implementation The conference served as a collaborative hub for engineers across Japan, Taiwan, and Korea to discuss the implementation of emerging standards like the Model Context Protocol (MCP). * Sessions emphasized the "how-to" of overcoming deployment hurdles rather than just following technical trends. * Poster sessions (Product Street) and interactive Q&A segments allowed developers to share localized insights on LLM agent performance and agentic workflows. * The recurring theme across diverse teams was that the "evaluation and verification" stage is now the primary driver of quality in generative AI services. For organizations looking to scale AI, the key recommendation is to move beyond simple implementation and invest in "evaluation-driven development." By building internal tools that leverage graph-based context and quantitative metrics like Aesthetic Scores and VQA, teams can ensure that generative outputs meet professional service standards.

AILarge Language ModelsModel Context ProtocolRAG+5

line·Aug 8, 2025Original article

Sharing the workflow of a 3rd (opens in new tab)

This blog post outlines a structured nine-step workflow designed to enhance development efficiency and improve the code review experience within a collaborative team environment. By emphasizing pre-implementation simulation, task visualization through Jira, and proactive self-feedback, the author demonstrates how breaking work into manageable, reviewer-friendly units leads to more predictable and reliable software delivery. The core conclusion is that prioritizing "reviewability" through small, logical increments fosters team trust and reduces technical debt. ### Strategic Planning and Simulation * Begin by thoroughly reviewing requirements and simulating the feature’s behavior, focusing specifically on data flow, state management, and edge cases. * Proactively communicate with stakeholders to clarify ambiguities and suggest user experience improvements before any code is written. * Draft high-level diagrams or flowcharts to map out how data points interact and where specific logic should reside, ensuring a solid architectural foundation. ### Task Visualization and Collaborative Alignment * Organize features into Jira Epics and decompose them into granular tickets that include estimated effort and dependencies. * Sync with teammates early—specifically between workflow design and ticket creation—to align on technical direction and prevent significant rework during the final review stage. * Ensure ticket titles are concise and descriptive to allow teammates to understand the project's progress at a glance. ### PoC-Driven Iteration and Self-Feedback * Conduct Proof of Concept (PoC) or prototyping to validate assumptions and identify unforeseen technical challenges before committing to a final implementation. * Perform self-feedback by checking the volume of code changes; the author suggests a 400-line threshold, beyond which a ticket should be split into sub-tasks to maintain clarity. * Use tools like `git diff` or temporary PR branches to review your own work from the perspective of a reviewer, identifying parts of the code that may be difficult to digest. ### Implementation and Documentation for Reviewers * Commit code in small, meaningful increments with clear messages, following a logical sequence such as defining interfaces before their actual implementations. * Draft Pull Requests (PRs) using standardized templates that include the purpose of the change, affected features, and developer test results. * Include visual aids, such as videos or screenshots, for complex UI changes or intricate workflows to reduce the cognitive load on the reviewer. ### Future Process Refinement * Improve the accuracy of project timelines by strictly recording actual time spent on tickets compared to original estimates in Jira. * Analyze the delta between "Estimated" and "Actual" time to better understand personal development velocity and refine future scheduling. Adopting this systematic approach helps developers transition from simply "writing code" to managing a complete technical lifecycle. For teams prioritizing code quality, implementing a line-count threshold for PRs and scheduling early-stage technical alignment sessions can significantly reduce "review fatigue" and streamline the path to production.

GithubCode ReviewGitJira+4

line·Aug 7, 2025Original article

Flexible Multi-site Architecture Designed with N (opens in new tab)

LINE NEXT optimized its web server infrastructure by transitioning from fragmented, manual Nginx setups to a centralized native Nginx multi-site architecture. By integrating global configurations and automating the deployment pipeline with Ansible, the team successfully reduced service launch lead times by over 80% while regaining the ability to use advanced features like GeoIP and real client IP tracking. This evolution ensures that the infrastructure can scale to support over 100 subdomains across diverse global services with high reliability and minimal manual overhead. ## Evolution of Nginx Infrastructure * **PMC-based Structure**: The initial phase relied on a Project Management Console using `rsync` via SSH; this created security risks and led to fragmented, siloed configurations that were difficult to maintain. * **Ingress Nginx Structure**: To improve speed, the team moved to Kubernetes-based Ingress using Helm charts, which automated domain and certificate settings but limited the use of native Nginx modules and complicated the retrieval of real client IP addresses. * **Native Nginx Multi-site Structure**: The current hybrid approach utilizes native Nginx managed by Ansible, combining the speed of configuration-driven setups with the flexibility to use advanced modules like GeoIP and Loki for log collection. ## Configuration Integration and Multi-site Management * **Master Configuration Extraction**: Common directives such as `timeouts`, `keep-alive` settings, and `log formats` were extracted into a master Nginx configuration file to eliminate redundancy across services. * **Hierarchical Directory Structure**: Inspired by Apache, the team adopted a `sites-available` structure where individual `server` blocks for different services (alpha, beta, production) are managed in separate files. * **Operational Efficiency**: This integrated structure allows a single Nginx instance to serve multiple sites simultaneously, significantly reducing the time required to add and deploy new service domains. ## Automated Deployment with Ansible * **Standardized Workflow**: The team replaced manual processes with Ansible playbooks that handle everything from cloning the latest configuration from Git to extracting environment-specific files. * **Safety and Validation**: The automated pipeline includes mandatory Nginx syntax verification (`nginx -t`) and process status checks to ensure stability before a deployment is finalized. * **Rolling Deployments**: To minimize service impact, updates are pushed sequentially across servers; the process automatically halts if an error is detected at any stage of the rollout. To effectively manage a rapidly expanding portfolio of global services, infrastructure teams should move toward a "configuration-as-code" model that separates common master settings from service-specific logic. Leveraging automation tools like Ansible alongside a native Nginx multi-site structure provides the necessary balance between rapid deployment and the granular control required for complex logging and security requirements.

KubernetesNginxAnsibleInfrastructure Automation+4

line·Aug 7, 2025Original article

Hey, won't you become a (opens in new tab)

Hack Day 2025 serves as a cornerstone of LY Corporation’s engineering culture, bringing together diverse global teams to innovate beyond their daily operational scopes. By fostering a high-intensity environment focused on creative freedom, the event facilitates technical growth and strengthens interpersonal bonds across international branches. This 19th edition demonstrated how rapid prototyping and cross-functional collaboration can transform abstract ideas into functional AI-driven prototypes within a strict 24-hour window. ### Structure and Participation Dynamics * The hackathon follows a "9 to 9" format, providing exactly 24 hours of development time followed by a day for presentations and awards. * Participation is inclusive of all roles, including developers, designers, planners, and HR staff, allowing for holistic product development. * Teams can be "General Teams" from the same legal entity or "Global Mixed Teams" comprising members from different regions like Korea, Japan, Taiwan, and Vietnam. * The Developer Relations (DevRel) team facilitates team building for remote employees using digital collaboration tools like Zoom and Miro. ### AI-Powered Personality Analysis Project * The author's team developed a "Scouter" program inspired by Dragon Ball, designed to measure professional "combat power" based on communication history. * The system utilizes Slack bots and AI models to analyze message logs and map them to the Big 5 Personality traits (Openness, Conscientiousness, Extraversion, Agreeableness, and Neuroticism). * Professional metrics are visualized as game-like character statistics to make personality insights engaging and less intimidating. * While the original plan involved using AI to generate and print physical character cards, hardware failures with photo printers forced a technical pivot to digital file downloads. ### High-Pressure Presentation and Networking * Every team is allotted a strict 90-second window to pitch their product and demonstrate a live demo. * The "90-second rule" includes a mandatory microphone cutoff to maintain momentum and keep the large-scale event engaging for all attendees. * Dedicated booth sessions follow the presentations, allowing participants to provide hands-on experiences to colleagues and judges. * The event emphasizes "Perfect the Details," a core company value, by encouraging teams to utilize all available resources—from whiteboards to AI image generators—within the time limit. ### Environmental Support and Culture * The event occupies an entire office floor, providing a high-density yet comfortable environment designed to minimize distractions during the "Hack Time." * Cultural exchange is encouraged through "humanity snacks," where participants from different global offices share local treats in dedicated rest areas. * Strategic scheduling, such as "Travel Days" for international participants, ensures that teams can focus entirely on technical execution once the event begins. Participating in internal hackathons provides a vital platform for testing new technologies—like LLMs and personality modeling—that may not fit into immediate product roadmaps. For organizations with hybrid work models, these intensive in-person events are highly recommended to bridge the communication gap and build lasting trust between global teammates.

AIGenerative AIPrompt EngineeringRedis+5

line·Aug 1, 2025Original article

Replacing the Payment System DB Handling (opens in new tab)

The LINE Billing Platform successfully migrated its large-scale payment database from Nbase-T to Vitess to handle high-traffic global transactions. While initially exploring gRPC for its performance reputation, the team transitioned to the MySQL protocol to ensure stability and reduce CPU overhead within their Java-based environment. This implementation demonstrates how Vitess can manage complex sharding requirements while maintaining high availability through automated recovery tools. ### Protocol Selection and Implementation - The team initially attempted to use the gRPC protocol but encountered `http2: frame too large` errors and significant CPU overhead during performance testing. - Manual mapping of query results to Java objects proved cumbersome with the Vitess gRPC client, leading to a shift toward the more mature and recommended MySQL protocol. - Using the MySQL protocol allowed the team to leverage standard database drivers while benefiting from Vitess's routing capabilities via VTGate. ### Keyspace Architecture and Data Routing - The system utilizes a dual-keyspace strategy: a "Global Keyspace" for unsharded metadata and a "Service Keyspace" for sharded transaction data. - The Global Keyspace manages sharding keys using a "sequence" table type to ensure unique, auto-incrementing identifiers across the platform. - The Service Keyspace is partitioned into $N$ shards using a hash-based Vindex, which distributes coin balances and transaction history. - VTGate automatically routes queries to the correct shard by analyzing the sharding key in the `WHERE` clause or `INSERT` statement, minimizing cross-shard overhead. ### MySQL Compatibility and Transaction Logic - Vitess maintains `REPEATABLE READ` isolation for single-shard transactions, while multi-shard transactions default to `READ COMMITTED`. - Advanced features like Two-Phase Commit (2PC) are available for handling distributed transactions across multiple shards. - Query execution plans are analyzed using `VEXPLAIN` and `VTEXPLAIN`, often managed through the VTAdmin web interface for better visibility. - Certain limitations apply, such as temporary tables only being supported in unsharded keyspaces and specific unsupported SQL cases documented in the Vitess core. ### Automated Operations and Monitoring - The team employs VTOrc (based on Orchestrator) to automatically detect and repair database failures, such as unreachable primaries or replication stops. - Monitoring is centralized via Prometheus, which scrapes metrics from VTOrc, VTGate, and VTTablet components at dedicated ports (e.g., 16000). - Real-time alerts are routed through Slack and email, using `tablet_alias` to specifically identify which MySQL node or VTTablet is experiencing issues. - A web-based recovery dashboard provides a history of automated fixes, allowing operators to track the health of the cluster over time. For organizations migrating high-traffic legacy systems to a cloud-native sharding solution, prioritizing the MySQL protocol over gRPC is recommended for better compatibility with existing application frameworks and reduced operational complexity.

Database DesignGrpcMysqlDatabase Migration+4

line·Jul 28, 2025Original article

Introducing a case of utilizing DDD in (opens in new tab)

LY Corporation’s ABC Studio developed a specialized retail Merchant system by leveraging Domain-Driven Design (DDD) to overcome the functional limitations of a legacy food-delivery infrastructure. The project demonstrates that the primary value of DDD lies not just in technical implementation, but in aligning organizational structures and team responsibilities with domain boundaries. By focusing on the roles and responsibilities of the system rather than just the code, the team created a scalable platform capable of supporting diverse consumer interfaces. ### Redefining the Retail Domain * The legacy system treated retail items like restaurant entries, creating friction for specialized retail services; the new system was built to be a standalone platform. * The team narrowed the domain focus to five core areas: Shop, Item, Category, Inventory, and Order. * Sales-specific logic, such as coupons and promotions, was delegated to external "Consumer Platforms," allowing the Merchant system to serve as a high-performance information provider. ### Clean Architecture and Modular Composition * The system utilizes Clean Architecture to ensure domain entities remain independent of external frameworks, which also provided a manageable learning curve for new team members. * Services are split into two distinct modules: "API" modules for receiving external requests and "Engine" modules for processing business logic. * Communication between these modules is handled asynchronously via gRPC and Apache Kafka, using the Decaton library to increase throughput while maintaining a low partition count. * The architecture prioritizes eventual consistency, allowing for high responsiveness and scalability across the platform. ### Global Collaboration and Conway’s Law * Development was split between teams in Korea (Core Domain) and Japan (System Integration and BFF), requiring a shared understanding of domain boundaries. * Architectural Decision Records (ADR) were implemented to document critical decisions and prevent "knowledge drift" during long-term collaboration. * The organizational structure was intentionally designed to mirror the system architecture, with specific teams (Core, Link, BFF, and Merchant Link) assigned to distinct domain layers. * This alignment, reflecting Conway’s Law, ensures that changes to external consumer platforms have minimal impact on the stable core domain logic. Successful DDD adoption requires moving beyond technical patterns like hexagonal architecture and focusing on establishing a shared understanding of roles across the organization. By structuring teams to match domain boundaries, companies can build resilient systems where the core business logic remains protected even as the external service ecosystem evolves.

Apache KafkaSoftware DesignGrpcEventual Consistency+4

line·Jul 23, 2025Original article

Milvus: Building a Large-Scale (opens in new tab)

LINE VOOM transitioned its recommendation system from a batch-based offline process to a real-time infrastructure to solve critical content freshness issues. By adopting Milvus, an open-source vector database, the team enabled the immediate indexing and searching of new video content as soon as it is uploaded. This implementation ensures that time-sensitive posts are recommended to users without the previous 24-hour delay, significantly enhancing user engagement. ### Limitations of the Legacy Recommendation System * The original system relied on daily offline batch processing for embedding generation and similarity searches. * New content, such as holiday greetings or trending sports clips, suffered from a "lack of immediacy," often taking up to a full day to appear in user feeds. * To improve user experience, the team needed to shift from offline candidate pools to an online system capable of real-time Approximate Nearest Neighbor (ANN) searches. ### Selecting Milvus as the Vector Database * The team evaluated Milvus and Qdrant based on performance, open-source status, and on-premise compatibility. * Milvus was selected due to its superior performance, handling 2,406 requests per second compared to Qdrant's 326, with lower query latency (1ms vs 4ms). * Key architectural advantages of Milvus included the separation of storage and computing, support for both stream and batch inserts, and a diverse range of supported in-memory index types. ### Reliability Verification via Chaos Testing * Given the complexity of Milvus clusters, the team performed chaos testing by intentionally injecting failures like pod kills and scaling events. * Tests revealed critical vulnerabilities: killing the `Querycoord` led to collection release and search failure, while losing the `Etcd` quorum caused total metadata loss. * These findings highlighted the need for robust high-availability (HA) configurations to prevent service interruptions during component failures. ### High Availability (HA) Implementation Strategies * **Collection-Level HA:** To prevent search failures during coordinator issues, the team implemented a dual-writing system where embeddings are recorded in two separate collections simultaneously. * **Alias Switching:** Client applications use an "alias" to reference collections; if the primary collection becomes unavailable, the system instantly switches the alias to the backup collection to minimize downtime. * **Coordinator-Level HA:** To eliminate single points of failure, coordinators (such as `Indexcoord`) were configured in an Active-Standby mode, ensuring a backup is always ready to take over management tasks. To successfully deploy a large-scale real-time recommendation engine, it is critical to select a vector database that decouples storage from compute and to implement multi-layered high-availability strategies, such as dual-collection writing and active-standby coordinators, to ensure production stability.

Vector DbHigh AvailabilityEmbeddingChaos Testing+3

line·Jul 18, 2025Original article

Making the Most of Flutter (opens in new tab)

Riverpod is a powerful state management library for Flutter designed to overcome the limitations of its predecessor, Provider, by offering a more flexible and robust framework. By decoupling state from the widget tree and providing built-in support for asynchronous data, it significantly reduces boilerplate code and improves application reliability. Ultimately, it allows developers to focus on logic rather than the complexities of manual state synchronization and resource management. ### Modern State Management Architecture Riverpod introduces a streamlined approach to state by separating the logic into Models, Providers, and Views. Unlike the standard `setState` approach, Riverpod manages the lifecycle of state automatically, ensuring resources are allocated and disposed of efficiently. * **Providers as Logic Hubs:** Providers define how state is built and updated, supporting synchronous data, Futures, and Streams. * **Consumer Widgets:** Views use `ref.watch` to subscribe to data and `ref.read` to trigger actions, creating a clear reactive loop. * **Global Access:** Because providers are not tied to the widget hierarchy, they can be accessed from anywhere in the app without passing context through multiple layers. ### Optimization for Server Data and Asynchronous Logic One of Riverpod's strongest advantages is its native handling of server-side data, which typically requires manual logic in other libraries. It simplifies the user experience during network requests by providing built-in states for loading and error handling. * **Resource Cleanup:** Using `ref.onDispose`, developers can automatically cancel active API calls when a provider is no longer needed, preventing memory leaks and unnecessary network usage. * **State Management Utilities:** It natively supports "pull-to-refresh" functionality through `ref.refresh` and allows for custom data expiration settings. * **AsyncValue Integration:** Riverpod wraps asynchronous data in an `AsyncValue` object, making it easy to check if a provider `hasValue`, `hasError`, or `isLoading` directly within the UI. ### Advanced State Interactions and Caching Beyond basic data fetching, Riverpod allows providers to interact with each other to create complex, reactive workflows. This is particularly useful for features like search filters or multi-layered data displays. * **Cross-Provider Subscriptions:** A provider can "watch" another provider; for example, a `PostList` provider can automatically rebuild itself whenever a `Filter` provider's state changes. * **Strategic Caching:** Developers can implement "instant" page transitions by yielding cached data from a list provider to a detail provider immediately, then updating the UI once the full network request completes. * **Offline-First Capabilities:** By combining local database streams with server-side Futures, Riverpod can display local data first to ensure a seamless user experience regardless of network connectivity. ### Seamless Data Synchronization Maintaining consistency across different screens is simplified through Riverpod's centralized state. When a user interacts with a data point on one screen—such as "starring" a post on a detail page—the change can be propagated globally so that the main list view is updated instantly without additional manual refreshes. This synchronization ensures the UI remains a "single source of truth" across the entire application. For developers building data-intensive Flutter applications, Riverpod is a highly recommended choice. Its ability to handle complex asynchronous states and inter-provider dependencies with minimal code makes it an essential tool for creating scalable, maintainable, and high-performance mobile apps.

CachingState ManagementFlutterDependency Injection+3