Metric to calculate WAL size left to transfer to Standby

[Viral Shah <vshah@xxxxxxxxxxxxxxxxx>]

Hello All,

We have a PostgreSQL 10.12 cluster of servers in two different data centers. Off lately, in the case of a large WAL generation, we are seeing replication delay between the master and the standby server. These delays have off lately been there for an unusually long time. I was wondering if we have any metric that can calculate the amount (size) of WAL transfer left between master and standby?

PS: We have ensured we have upgraded our firewalls for better speed transfer.

Any help on how to figure out the slowness in the WAL transfer would be much appreciated.

Thanks,

Viral Shah