Discussion
We had a very slow operation involving using an API to verify data in uploaded user CSV files. Taking 3–7m on average.
Juniors looked at it, concluded “API is slow, can’t make this faster”.
Seniors looked at it, came to same conclusion, also asked AI for ideas. After a week of poking and testing: “no optimization improves performance by more than 2%, not worth the risk”.
1/3
One of my fellow leads and I took a look today. A couple hours of reading and discussing and diagramming later, and we noted that records were being sent to the API one at a time, but the API provides a batch endpoint that allows batches of up to 100 records per query.
Flipped to using that and went async (one thread to make queries, one to receive and process responses).
Average is now 7–20s. Yes, _seconds_. 
2/3
Just goes to show that despite profilers and other quite nice tooling, there really is no substitute for systems analysis done by a few experts.
And that the answer isn’t always just in the code in front of you; sometimes it comes from understanding the whole system.
3/3
@calcifer
The best part is how much this fix will impact your salary review and bonus.
I mean, I hope it does, but...
@xinit @calcifer I once saved a company's 5-year multimillion dollar contract, allowing them to meet the deadline in two weeks after picking up someone else's code who they'd just fired. I worked nights, weekends, and basically slept in the office, but I got it done. We're talking tens of millions of dollars.
I come in Monday and the boss calls me into his office. CEO of the company. Says I did a really great job and he was really impressed and wanted to thank me for my help.
In an envelope was a $50 Target gift card.
I'll never forget what he said to me, with a wink, as I left.
"Don't spend it all in one place."
I was gone from there two weeks later.
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