What would be the effect of suddenly introducing a 1-2 GB of WAL archives to the WAL restore folder on the slave? Would there be a big performance effect on the incoming queries to the slave? Would the slave be available for queries while the WAL logs are restored into the DB?
If the Queries are running on slave whilst WAL archives are being applied, there is a bright chance that, queries would encounter a conflict with the recovery and would eventually get cancelled. You can see messages in the PostgreSQL logfiles. The recommended approach would be to apply WALs when queries are being executed on slave.
