c# - Delay on first call on DataReader.Read() -

i have odp connection oracle database.

var reader = command.executereader(); whild (reader.read()) {     //... } 

in situations first call reader.read() take more usual time (3 10 sectonds).

next calls ok. not next calls ok of time closing application , re-running ok too!

what parameters affect reader.read() take time more usual?

update1: clarify situation consider situations:

1. the application runs.
2. lots of queries execute during application.
3. user decides run report specific query tables
4. execurereader called in proer time.
5. now it's time read via reader. takes unusual time.
6. user runs application again.
7. it doesn't happen again.

i guess caching mechanism on database. if database caching executereader() should have variant execution times.