The below issue was caused by a change in domain controller for the Portal's IWA identity store config.
"Wal files size exceeded the maximum size"
These errors occur in the portal logs every minute and began to occur at the same timestamp as the IWA config change. No other change occured on the Portal machine at this time.
Despite these errors, the ArcGIS Enterprise (10.6) is functioning as normal and the underlying postgres db seems to be behaving fine. The walarchive is consistently increasing as per the 60 minute archive setting in postgresql.conf. These archive dumps are all 16,384 KB and have modified dates AFTER the above change and errors began to occur.
Therefore, I do not believe anyting is actually going wrong and impacting users, but there is clearly a config/setting somewhere which is tied to the old domain controller. Any thoughts as to where I can investigate further? The underlying postgres logs indicate no issues in this space.
FYI, we do not use webgis DR and do not plan on using this as a solution moving forward due to the scale of our deployment (some incremental backups took 7+ hours to complete).
The reason why the "Wal files size exceeded the maximum size" error is getting written to the logs is because the total file sizes of the walarchive logs under the C:\arcgisportal\backups\walarchive folder, (or wherever your default content directory was set to during the install) is more than 5 GB.
Before you run the DR tool, the total size is capped at 5 GB and the logs rollover. After you run the DR tool, the limit is removed so they can grow unbounded. If you run the DR tool again, then it deletes all walarchive logs in the directory.
This doesn't have anything to do with IWA/authentication settings.