I Wrote the Index Escalation Threshold as a Number, Then Measured It and Found It Off by 15x to 100x
Somewhere in a design document you have signed off on, there is a sentence of the form “when it passes X, we will do Y.” Has anyone ever generated X rows to check that the number means what it says? At the end of last month I signed off on a design that runs a lookup against a column with no index, on a table my team does not own, and wrote the condition for fixing it as a sentence with two numbers in it: “when the table passes about 1,000,000 rows or the p95 of the voucher filter passes 300 ms, request a non-unique index from the owning team.” The sentence had one job: get the option “ship without the index” through design review, with “we will add it later” turned into something a reviewer could sign. It did that job. ...