How to increase Postgres WAL size?
max_wal_size controls the total size of all WAL segments, not the size of each segment. 

So with a value of 2GB, you are saying that about 128 of those segments can be created before they get re-used. 

The hint is about increasing the total number of files (hence the mentioning of max_wal_size), it's not about the size of each segment (file).



Up to Postgres 10, the size of each segment is fixed to 16MB

Starting with Postgres 11, you can change the size of each segment but only when you initialize a new database cluster (but again: that's not what that hint is about).