WARM can do WARM update 50% of time, indirect index can do HOT update 100% of time (provided the column is not changed), I don't see why we could not have both solutions.
I think the reason why I restricted WARM to one update per chain, also applies to indirect index. For example, if a indirect column value is changed from 'a' to 'b' and back to 'a', there will be two pointers from 'a' to the PK and AFAICS that would lead to the same duplicate scan issue.
We have a design to convert WARM chains back to HOT and that will increase the percentage of WARM updates much beyond 50%. I was waiting for feedback on the basic patch before putting in more efforts, but it went unnoticed last CF.
That all being said, it would be interesting to hear Álvaro's thoughts about which use-cases he expects indirect indexes to work better than WARM.
Yes, will be interesting to see that comparison. May be we need both or may be just one. Even better may be they complement each other.. I'll also put in some thoughts in this area.