The following bug has been logged on the website:
Bug reference: 14774
Logged by: Jym Morton
Email address: jym(at)outlook(dot)com
PostgreSQL version: 9.6.3
Operating system: Windows 10
Description:
I've noticed that if there's a conflict the sequence still adds 1 even if
the INSERT is a conflict.
i.e. INSERT INTO foo(bar) VALUES ('test') ON CONFLICT bar = EXCLUDE.bar
returning foopk
bar has a UNIQUE constraint, doing this 10 times you see the Next serial in
foopk is 10 even though there is only 1 row in the table.