I am a junior developer in a small team of about 20 people, I have been working at this job for about 1 year so far. Every now and then I have to ask a question to my senior coworkers. Those questions are unavoidable.
I do have a pretty good relation with this coworker, I really value his experience and opinion and he always treats me respectful and tries to help and educate me whenever he gets the chance.
The problem is: If I ask something about topic A he will quickly explain things to me, but then proceed to give me useful information about topic B and C which are somehow related to A - so far so good. Sadly he won't stop there, he will explain to me how the company solved problem D back in 1990 and then switched to use design pattern E in 2003. After that he also wants to let me know about the completely unrelated things F and G and will finish off with his personal story H.
Obviously I (only) need an explaination A to solve my problem, B and C usually are also helpful but at this point he already talked for 10-15 minutes and will proceed for at least another 15-20 minutes. This does not cause 'real' trouble for me, since I am still new and don't have strict deadlines to meet but I still want to meet my manager's expectations about my performance(and my own expectations aswell).
How could I stop those conversations at point 'D' which is not related to my question any more without being unpolite and maintaining a good relationship with my coworker in a professional manner?
Some more information:
What did I do already?
I did not talk to talk to my coworker about this problem, however I found out that sending him mails works fine (His answers are really on point then). The problem is that my desk is about 3 steps away from his and when he has office time it would be akward/strange/unusual to send him mails.
I have also tried to ask other coworkers about problems, but I usually get pointed back to the person this question is about.
I tried to find solutions for my problems online, however there are some questions that noone but this guy can answer ( For example: I could not access a folder called 'templates' simply because the - to me not visible - apache settings denied the access, the 403-error was not helpful in order to find out this detail...)
What do I want to avoid?
I don't want my coworker to feel bad about the care he puts in my education/our relationship. I would also like to keep hearing about the related facts B and C .
Thank you for your help in advance.