Only

sum

,

max

,

min

supported as for today for realtimetoofflineSegmentsTask, right?

For roll up, yes

Will offline table saves more disk space compared to realtime table if mergeType=concat?

It will share dictionary, so yes overall size will be less.

But I need to use percentile function in select query.

Sure, you can do that with concat

So should I use star tree to pre-aggregate percentile if most select queries will use percentile function?

Yes you can do that. But that makes sense with rollup only. Note, you can still do percentile tdigest during query on raw data

ok