collector.postmaster is disabled by default

[duj4]

What did you do?
Download postgres_exporter with version 0.13.2 and run "./postgres_exporter --help", noticed:

--[no-]collector.postmaster Enable the postmaster collector (default: disabled)

What did you expect to see?
[no-]collector.postmaster Enable the postmaster collector (default: enabled).

What did you see instead? Under which circumstances?
--[no-]collector.postmaster Enable the postmaster collector (default: disabled)

Environment
postgres_exporter 0.13.2

• System information:
  Linux 4.18.0-477.15.1.el8_8.x86_64 x86_64

• postgres_exporter version:
  0.13.2

• postgres_exporter flags:

--help

• PostgreSQL version:
  Did not run yet

• Logs:
  Did not run yet

[yanghu5]

I also encountered a this problem， so when i check the source code found

const postmasterSubsystem = "postmaster"
func init() {
registerCollector(postmasterSubsystem, defaultDisabled, NewPGPostmasterCollector)
}
but the wiki says
[no-]collector.postmaster Enable the postmaster collector (default: enabled).

[Sayrus]

Behavior was explicitly changed on 8d087f2 but the README was not updated.

[salzig]

I'm unable to find a note why it is disabled by default. Can someone give me a hint?

[sysadmind]

We have #830 open to track improvements to the postmaster collector. The original implementation had some problems so we disabled it while it was so unstable. It is probably close to stable at this point, but we could probably use more tests and more documentation around what columns can be NULL and how those are handled.