Here is an excellent article written by Chris Nauroth on how to tune GC.
Here is another guide that explains the relative file objects size and GC settings.
Since you mentioned pause as an issue, this might help you.
Hi Hadoop experts,
We are getting continuous Pause duration alert from Standby NN.
Current configuration for Java heap size of NN : 7.8 GB
When we checked NN webUI heap memory used 7.5 GB of 7.8 GB heap memory.
Please suggest how to fix this.