Re: unite recovery.conf and postgresql.conf

Robert,

> In most cases we either break backwards compatibility or require some
> type of switch to turn on backwards compatibility for those who want
> it. While the above plan tries to do one better, it leaves me feeling
> that the thing I don't like about this is that it sounds like you are
> forcing backwards compatibility on people who would much rather just
> do things the new way. Given that, I foresee a whole new generation
> of
> confused users who end up setting their configs one way only to have
> someone else set the same config in the other file, or some tool dump
> out some config file, overriding what was really intended. This will
> also make things *harder* for those tool providers you are trying to
> help, as they will be forced to support the behavior *both ways*. I'd
> much rather see some type of switch which turns on the old behavior
> for those who really want it, because while you can teach the new
> behavior, if you can't prevent the old behavior, you're creating
> operational headaches for yourself.

This is a good point.  There's also the second drawback, which is complexity of code, which I believe that Tom Lane has brought up before; having two separate-but-equal paths for configuration is liable to lead to a lot of bugs.

So, we have four potential paths regarding recovery.conf:

1) Break backwards compatibility entirely, and stop supporting recovery.conf as a trigger file at all.

2) Offer backwards compatibility only if "recovery_conf='filename'" is set in postgresql.conf, then behave like Simon's compromise.

3) Simon's compromise.

4) Don't ever change how recovery.conf works.

The only two of the above I see as being real options are (1) and (2).  (3) would, as Robert points out, cause DBAs to have unpleasant surprises when some third-party tool creates a recovery.conf they weren't expecting. So:

(1) pros:
   * new, clean API
   * makes everyone update their tools
   * no confusion on "how to do failover"
   * code simplicity
 cons:
   * breaks a bunch of 3rd-party tools
   * or forces them to maintain separate 9.1 and 9.2 branches

(2) pros:
   * allows people to use only new API if they want
   * allows gradual update of tools
   * can also lump in relocatable recovery.conf as feature
  cons:
   * puts off the day when vendors pay attention to the new API
     (and even more kicking & screaming when that day comes)
   * confusion about "how to do failover"
   * code complexity