Epplus

He’d written this C# console app three years ago. Back then, it was a scrappy script using EPPlus 4.5, just to save his team two hours of manual copying and pasting. Now, the system had metastasized. It pulled from three APIs, two SQL databases, and a CSV vomited out by a legacy mainframe in the basement.

Arjun needed a different pattern.

EPPlus, like all great libraries, had taught him a deeper lesson: EPPlus abstracts away the horror of Open XML’s SharedStringTable and CellValue types, but it cannot abstract away memory. The “deep story” isn’t about Excel—it’s about the gap between what we ask computers to hold and what they can actually hold. epplus

EPPlus, he remembered from the documentation, wasn’t just a writer. It maintained a full object model of the spreadsheet in RAM: styles, formulas, comments, hidden rows. Every cell you touched became a ExcelRangeBase object, a tiny ghost in memory. After three years of patches and feature creep, his app was loading the entire source template—all forty-two sheets, all conditional formatting, all pivot caches—just to write a single new column of data. He’d written this C# console app three years ago

But Arjun knew.

He opened Task Manager. 1.8 GB of RAM. Garbage collection was running every few seconds, like a frantic housekeeper at a frat party. It pulled from three APIs, two SQL databases,

He added a comment to the new codebase, right above the using statement: