# Postmortem: Biased Model Training with EEG Signals ## Persistent model bias observed during training on EEG dataset for wheelchair navigation commands: – Models consistently best identified `stop/neutral` → moderately performed on `forward/left` → consistently failed on `right` – Observed across MATLAB Classification Learner models and custom – Best outcomes: ~50% accuracy for problematic classes … Read more
# The Cache Miss Illusion: When Out-of-Order Execution Masks Real ## We investigated the misconception that cache misses consistently cause severe pipeline stalls in out-of-order (OOO) CPUs. While cache misses do incur latency, OOO execution often hides this cost by continuing unrelated work—misleading profiling tools and engineers into misidentifying optimization targets. ## Root – **Misinterpretation … Read more
# Postmortem: Performance Bottleneck in Repeated Python Function Calls from ## A performance-critical data processing pipeline experienced significant slowdowns when integrating Python-calculated variables into an R dataframe using reticulate and dplyr. The implementation repeatedly called the same Python function 7 times per group to extract individual output elements, leading to unnecessary computation. ## Root – … Read more
Postmortem: UI Reactivity Breakdown in Vue 3 Notification System Summary When users clicked new notifications in a Vue 3 application, some notifications failed to immediately disappear visually after backend updates. Despite successful backend updates via Axios, frontend state changes didn’t trigger reactive UI updates consistently, requiring page reloads to reflect changes. Root Cause Non-reactive parent … Read more
Production Incident: Flash Memory Performance Degradation Due to Disabled ART Prefetch on STM32F4 Summary During hardware initialization, prefetching was inadvertently disabled in the STM32F4 memory subsystem. This caused severe performance degradation during peak traffic when instruction fetches from Flash couldn’t be anticipated by the ART Accelerator, leading to CPU stalls and unresponsive systems. Root Cause … Read more
Postmortem: Avoiding OUTER APPLY for Retrieving Latest Rows in SQL Server Summary A developer needed to fetch the latest attendance record per employee after a specific timestamp but inadvertently retrieved all matching records. The initial solution used OUTER APPLY, which caused performance issues in a complex production query. This postmortem explains the optimization strategy replacing … Read more
Technical Postmortem: Unmanaged Object Lifetimes Causing Performance Degradation in p5.js Traffic Simulation Summary Implementation failed to manage dynamically spawned road markings, causing unbounded memory growth due to unremoved off-canvas objects and ineffective virtualization. Root Cause Declared roadLinesArray was never populated or utilized RoadLine class permanently maintained two static instances that reset vertically without deletion No … Read more
Why does my linked list node occupies 16 bytes yet malloc reports 24 bytes? Summary A developer implemented a linked list node (struct Node) in C using manual memory allocation. While sizeof(struct Node) returned 16 bytes, malloc_usable_size() reported 24 bytes for an allocated node. Additionally, observed memory addresses between consecutive nodes differed by 32 bytes. … Read more
# Why Removing Mutexes Reduces Latency in Low-Contention Multithreaded Systems ## Summary A low-contention multithreaded application using mutexes exhibited higher-than-expected latency. Replacing mutexes with lighter synchronization mechanisms (like atomic operations) reduced latency despite minimal lock contention. This occurs because mutex operations incur non-negligible overhead even without blocking due to hardware/system-level interactions. ## Root Cause – … Read more
# Why is my Python multiprocessing code slower than single-thread execution? ## Summary Multiprocessing implementations in Python can run slower than single-threaded versions when: – High inter-process communication (IPC) overhead exists – The computational payload per process is insufficiently large – System resource constraints limit parallel scaling The provided example exhibits these characteristics due to … Read more