According to the documentation,
The address (LSN) of oldest WAL which still might be required by the consumer of this slot and thus won't be automatically removed during checkpoints...
This is not very clear. The oldest LSN required by the consumer should be
confirm_flush, because that is the point upto which the client has seen the data in a durable way. So my questions are
- How is restart_lsn initialized?
- When is it updated? and with what value?
- How is it used?