Reading WALs

On my built in logical replication I see that sometimes it tooks a long time
to be updated with master. The question is how can I see what is being done
on replica ? I know I can have a WAL reader, I tried WAL2JSON, it listen all
data which comes from master, but as I understood when I use that plugin
that data is discarded, so, not replicated. 

Is that correct ? Can I see what is coming to replica server and apply that
change to server as usual ?



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