PostgreSQL - Base Backups and PITR

Question

According to the PostgreSQL documentation for producing Standalone Hot Backups:

These are backups that cannot be used for point-in-time recovery, yet are typically much faster to backup and restore than pg_dump dumps.

It seems that all that is required to produce these kinds of backups is to use pg_basebackup utility and include the -X option, which essentially includes the required WAL files necessary to start the cluster. Why can't these backups be used for PITR? If I don't start this backup immediately, shouldn't I be able to place it in recovery mode and allow it to restore up to any point after the backup was created?

Answer 1

I agree that the wording is confusing.

A pg_basebackup taken with -X stream can of course be taken as a basis for point-in-time recovery.

I think the assumption here is that you take a pg_basebackup but do not have WAL archiving configured. Then the backup contains just the WAL segments required to recover to the end of the backup and reach a consistent state, but you don't have the WAL required to recover beyond that point.

Answer 2

That seems like a doc bug, in that -X needs an argument, and it doesn't clarify what options you are supposedly using for it. The description it gives would seem to apply to either fetch or to stream, but not apply to none.

You can use such a basebackup generated with -X stream or -X fetch for PITR as long as also have a WAL archive. I think the assumption here is that you would not use those options if you were keeping a wal archive anyway. I think that is a bad assumption. I like my backups to be as flexible as possible. If your backup includes the minimal set of its own WAL, then you can either restore it standalone for a single time point, or you can use it to seed PITR with the wal archive. This seems useful to me. Actually this is your bad assumption, not the doc's. You have juxtaposed two different parts of the docs, talking about two different things (pg_dump and pg_basebackup), as if they were talking about the same thing.