it was awful at first. Ds1 (2.7 when DS2 was born) was a very tantrummy, melt-downy toddler, and was very thrown and angry about the birth of his brother.
They were very physical with each other as they got older - lots of pushing, biting, pinching. But also friendly wrestling.
DS1 would be quite verbally negative about the existence of his brother, and I despaired that they'd get on because DS1 didn't "love his little brother" like some of my friends DCs did (although actually, a lot of them either had more subtle upset reactions - regression, sly violence whereas his was more overt and easier to deal with)
HOWEVER
They get on really well now (13 and nearly-11). They are very different and this helps - very little competition between them. I know there's a theory that siblings do tend to emphasise their differences. There's none of the tale-telling I see between siblings with a bigger gap. They are mates and I love to see them supporting each other and giving each other advice.
DS2 gave his first smile and his first laugh to his brother.
For a few years I wished for a bigger gap but actually I think I got the (IME) harder baby and toddler bit over in a concentrated period of time.
MY advice - don't push your older one to be the big one. Remember how little they are. Encourage kindness but don't expect them to be best mates. That will come later if you don't get too stressed.