Re: Phantom segment upon promotion causing troubles.

Hi,

On 2017-06-19 00:30:26 -0700, Andres Freund wrote:
> There seems to be a larger question ehre though: Why does
> XLogFileReadAnyTLI() probe all timelines even if they weren't a parent
> at that period?  That seems like a bad idea, especially in more
> complicated scenarios where some precursor timeline might live for
> longer than it was a parent?  ISTM XLogFileReadAnyTLI() should check
> which timeline a segment ought to come from, based on the historY?

One thing that I blamed first, before debunking it, is that after
promotion we do:

	/*
	 * Preallocate additional log files, if wanted.
	 */
	PreallocXlogFiles(EndOfLog);

where EndOfLog points to the last replayed record, rather than last
record(s).  I think that's currently harmless, but it's certainly
fragile.  Given the uselessness of PreallocXlogFiles() calls, I'm
inclined to just remove it here...

- Andres