We're having the same issue: After stopping/starting the Portal for ArcGIS Windows service, not all java executables were started, the postgres.exe process is not running on the machine, and the portal (including the portaladmin endpoint) became unresponsive. The java.exe process was started (I'm guessing this is the Windows service), but no javaw.exe processes. Eventually the indexer javaw.exe process started (after a few minutes).
The portal logs contained serveral instances of this error:
The portal has been initialized and configured but is not accessible. The internal portal database does not appear to be running or accepting connections. Restart the portal machine or machines and if the problem persists, contact Esri technical support (U.S.) ...
And the Windows Event Viewer had half a dozen PostgreSQL errors of two different variations...
1)
The description for Event ID 0 from source PostgreSQL cannot be found. Either the component that raises this event is not installed on your local computer or the installation is corrupted. You can install or repair the component on the local computer.
If the event originated on another computer, the display information had to be saved with the event.
The following information was included with the event:
pg_ctl: PID file "E:/arcgisportal/db/postmaster.pid" does not exist
2)
The description for Event ID 0 from source PostgreSQL cannot be found. Either the component that raises this event is not installed on your local computer or the installation is corrupted. You can install or repair the component on the local computer.
If the event originated on another computer, the display information had to be saved with the event.
The following information was included with the event:
Is server running?
... both of which we've been told to ignore in the previous post.
The same conditions persisted after rebooting the machine.
As the local PostgreSQL db is installed as an Esri component of the portal and is software-managed without the usual PostgreSQL client applications, perhaps Esri could provide additional feedback on how to troubleshoot this issue.