Queries slow down as more indexes are added

I have noticed that query times increase significantly as I add more indexes to my bucket. I observe this with my own data, as well as travel-sample (as a control).

With 1 index, a query takes 8ms to execute. With around 20, it jumps to 50ms. A 6-fold increase in execution is not trivial.

I am using 4.5.1 CE. Is this expected behavior? If I invoke the USE INDEX statement, then query time drops back to 8ms.

Size of bucket does not matter, here. The slow-down occurs even if I only have about 10 documents.

Planner has to consider all the indexes and decide one of the index. To reduce planner time use prepared statements (prepare once and execute multiple times). This has been improved in 5.0.0