Re: Online base backup from the hot-standby

On 24.10.2011 15:29, Fujii Masao wrote:
> In your patch, FPW is always WAL-logged at startup even when FPW has
> not been changed since last shutdown. I don't think that's required.
> I changed the recovery code so that it keeps track of last FPW indicated
> by WAL record. Then, at end of startup, if that FPW is equal to FPW
> specified in postgresql.conf (which means that FPW has not been changed
> since last shutdown or crash), WAL-logging of FPW is skipped. This change
> prevents unnecessary WAL-logging. Thought?

One problem with this whole FPW-tracking is that pg_lesslog makes it
fail. I'm not sure what we need to do about that - maybe just add a
warning to the docs. But it leaves a bit bad feeling in my mouth.
Usually we try to make features work orthogonally, without dependencies
to other settings. Now this feature requires that full_page_writes is
turned on in the master, and also that you don't use pg_lesslog to
compress the WAL segments or your base backup might be corrupt. The
procedure to take a backup from the standby seems more complicated than
taking it on the master - there are more steps to follow.

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com