We had seen that changefeed catchup scans can be disruptive to upgrades (internal), including affecting foreground traffic, due to consuming a lot of IOPS. We have consensus that kv.rangefeed.separated_intent_scan.enabled is safe and beneficial.

I think we've gained enough confidence in separated intents that it's safe to enable kv.rangefeed.separated_intent_scan.enabled, at least. To put it another way, if we didn't have a cluster setting for it, I wouldn't hesitate to backport a change to only scan separated intents.

Let’s default kv.rangefeed.separated_intent_scan.enabled to true in the next patch releases of v21.2. This will reduce likelihood of upgrade problems and support issues.

Notes from this discussion:

PS: we'd have to make sure these new default settings respect the relevant version gates, if they don't already, to avoid breakage in mixed-version 21.1/21.2 clusters.

We respect a cluster setting for the intent scanner. I don't think there are any cluster settings we need to worry about for catchup-scans, but if I'm wrong there let me know.

Related work:

• changefeedccl: default kv.rangefeed.catchup_scan_iterator_optimization.enabled to true in 21.2 #79727
• changefeedccl: make recommended cluster setttings default #76508
• settings: retire kv.rangefeed.separated_intent_scan.enabled  #78246
• kvserver: default kv.rangefeed.catchup_scan_iterator_optimization.enabled to true #73473