Optimization

Hi,
The ES version I 'm using is 15.0 and found some issues are displayed
here.
Day 1 :I had ported the data and the indexing is completed . I had
also optimized the database manually.
Day 2 : We were working in the data and made some searches , the
database was working fine .
Suddenly the optimization tooks place without any intimation .On
that time the database was closed and we weren't able to get DB
access .
Day 3 : After optimization process , the same database was working
fine.
Question 1 : Is there any method, that we need to configure to get
the
information when the optimization is going to start for that
particular DB ?
Question 2 : Is there any settings to schedule the time for this
process to be happened ?
Question 3 : Is there any predefined rule for optimization?
Question 4 : Why the index are getting optimized very often?

Thanks
---Gloria