Re: Potential G2-item cycles under serializable isolation

On 6/1/20 12:20 AM, Peter Geoghegan wrote:
> It's confusing because the standard only requires that the isolation > levels avoid certain read phenomena, but implementations are free to > go above and beyond. For example, you can ask Postgres for READ > UNCOMMITTED, but you'll get READ COMMITTED. (So RC, RR, and SI each > provide distinct behavior.)
Right, right. I was thinking "Oh, repeatable read is incomparable with snapshot, so it must be that read committed is snapshot, and repeatable is serializable." This way around, Postgres "repeatable read" actually gives you behavior that violates repeatable read! But I understand the pragmatic rationale of "we need 3 levels, and this is the closest mapping we could get to the ANSI SQL names". :)

--Kyle