Couchbase metrics

I wanted to get some more information on the below Couchbase metrics. Was not able to find it out from the documentation

The definition of this says “Total size in bytes of the DCP backlog for XDCR”.
So, what happens if the size in bytes increases or decreases. Does this mean that XDCR is not able to keep up with the amount of changes being collected by DCP?
This says Number of internal XDCR DCP connections in this bucket. What is the default count? If we increase this, will XDCR be faster? Where do we change this number(if it is possible to change)

This says “Number bytes per second being sent for replica DCP connections”. What does this mean? Is it the speed in which replication is happening for the vbuckets

This says “Number of replication senders for this bucket”. Does this mean if we have more senders, replication will be faster. What is the default value? And where is this value set? Should this be changed by user?