PouchDB slow on insert when I have 4k+ items in DB

I have an app that based on ionic2 and uses PouchDB for saving and sync data.

In the case when I have 4k+ items in DB, sometimes new post cat take 20+ seconds.

The issue reproduces only on iOS devices but works perfectly in Chrome on the laptop.

Platform: iOS
Ionic: 2
PouchDB: 6.1.1
Adapter: websql
App use about: 30 MB RAM based on XCode

What part can I check for improving performance?

Should PouchDB be able to handle that?
On what device are you testing? Real device or emulator?
What about Android?

I think yes, I saw posts where it manages much more data with PouchDB.

“On what device are you testing? Real device or emulator?” real device iPhone 6S and iOS 10.3.3.

“What about Android?” not tested and that platform not required currently.

Does the response time depend on the number of items in the database? Does it “scale” with the number of entries? What about 8k? 20k? 100k? 0?

No difference between 8k and 20k but not tried 100k.

That issue does not happen constantly, sometimes it takes 20 sec, sometimes less than 1 sec. I am suspecting GC, but can’t debug it with Safari profiles, after 10 sec profiling my app closing.