[GENERAL] Refresh Materialized View

[Jayadevan M]

Hello all,
A few questions about materialized views.
When I refresh a materialized view, is it a DELETE/INSERT behind the
scenes?
Do we need to vacuum to reclaim space?
If a query is executed against the view when the refresh is happening, will
the query see the data before the refresh started?
Does the refresh result in exclusive locking?
Regards,
Jayadevan