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0 pointslathiat9y ago0 comments

> If you read the MySQL manual, it's absolutely littered with sloppy little breakages throughout its history: Like how, until 5.0.something, when comparing a "date" value with a "datetime" value, the time portion would be silently ignored and ('2017-04-08 14:04' = '2017-04-08') would return true; but they fixed that, and broke a lot of client code because they didn't stop to realize that a lot of developers depended on that behaviour.

This is an interesting comment for two reasons. Firstly because a lot of people also complain about MySQL's archaic defaults which often stay too long because of upgrade concerns (though they fortunately are fixing a lot of them already or for MySQL 8.0 - hooray).

But also because it speaks volumes, in my opinion, about the MySQL documentation that these are documented in the first place. I worked at MySQL for 9 years and though it was always clear our manual was always a good source of information, now that I am working on Ubuntu & OpenStack it is painfully obvious just how good the MySQL documentation team and processes were compared to many other projects. Even just the version ChangeLog.

I'm not saying other projects don't get it right (and have no opinion at all about postgresql's documentation state), but MySQL seems to get it pretty right in general.

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lobster_johnson9y ago

But MySQL's problem is that those "archaic defaults" shouldn't have happened in the first place.

No matter how good MySQL is good at documenting their bugginess, weirdness, flakiness and overall history of legacy warts, the point was PostgreSQL eliminates pretty much all of this through promoting, at every single stage of the development process, the same strict, uncompromising QA principles. By doing this, legacy behaviour generally disappears.

Postgres isn't bug-free, of course. But they take great care to not be continually chased by a tsunami of technical debt. If you build a house on a crappy foundation, you get a crappy house, so it's a good idea to spend time on the foundation before building the house. The Postgres team spent years on the foundation, before building the higher-level parts, and the rewards are obvious.

Meanwhile, MySQL has spent years and years slowly mopping up tech debt. Things have gotten a lot better with the tighter semantics, such as preventing "February 29th" from being inserted, or rejecting "0000-00-00" as a date, or silently ignoring data coercion errors, and so on. But those things shouldn't have happened in the first place if the developers had been better at QA. So while you're right that the documentation is decent at describing various legacy semantics, it's also encodes a history of carelessness that's rather embarrassing reading.

By the way, date/datetime regression I mention isn't in the documentation at all. It's in their bug tracker.