Mariadb

Somewhere in your monitoring there is a panel built on a status counter you picked because of its name. Maybe the query came from a dashboard written for another database, or for another fork of the same one. Have you ever sampled that counter by hand, next to one you already understand, to check that the two move the way you think? I picked Innodb_os_log_written for a measurement because its name says exactly what I wanted: bytes of redo log written. On MySQL 8.4 it agreed with the crash results. On MariaDB 11.8 it said the redo log left the process every 5.6 ms. A crash test on the same server, earlier that day, had lost 9,123 acknowledged commits, which only happens if the log sits in memory for most of a second. I had measured both numbers myself, and they could not both be true. ...

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. ...