I contacted microsoft support, but haven't got a concrete answer yet. Basically we use Azure sql P range with GEO replication, one primary one secondary readonly.
As it is P range, we have the read only replica on primary and secondary as well. So in total 4 servers: Primary, Primary - readonly repilca, secondary readonly and secondary readonly replica.
What we saw was that the queries on primary are fairly quick, but really slows down on other three instances.
We found this article that gives out one reason:
Our db's index is rather fragmented, and we do use nolock quite frequently. Unfortunately our db is also quite big, and we will have to find a maintenance window to rebuild indexes and stats.
I would like to be sure that azure geo replication does have the same problem as above article as I can only rebuild index 2 weeks later. Anyone has similar experience?