Re: [bug fix] pg_rewind creates corrupt WAL files, and the standby cannot catch up the primary

On Thu, Mar 01, 2018 at 01:26:32AM +0000, Tsunakawa, Takayuki wrote:
> BTW, should pg_rewind really copy WAL files from the primary? If the
> sole purpose of pg_rewind is to recover an instance to use as a
> standby, can pg_rewind just remove all WAL files in the target
> directory, because the standby can get WAL files from the primary
> and/or archive?

Yes, it should not copy those WAL files. Most of the time they are going
to be meaningless. See this recent thread:
https://www.postgresql.org/message-id/20180126023609.GH17847%40paquier.xyz
So I would rather go this way instead of having to worry about
manipulating those WAL segments as you do. Depending on the needs, I
think that even a backpatch could be considered.

> Related to this, shouldn't pg_rewind avoid copying more files and
> directories like pg_basebackup? Currently, pg_rewind doesn't copy
> postmaster.pid, postmaster.opts, and temporary files/directories
> (pg_sql_tmp/).

Yes, it should not copy those files. I have a patch in the current CF
to do that:
https://commitfest.postgresql.org/17/1507/
--
Michael