[bjacokes]

For Aurora MySQL, the default for read-only replicas is repeatable read. As we mentioned towards the end of the post, read committed support appears to have been introduced to Aurora MySQL just last year. But you're right – now that it's supported, switching to read committed is by far the easiest fix.

No idea why people would be using serializable reads for ETL jobs though! :O

[slownews45]

My own guess was that some ETL jobs were really data integrity jobs - in which case folks got used to higher levels of isolation being necessary across many reads to avoid false positives on their cross check stuff maybe.