On Tue, 2010-07-27 at 15:50 -0400, Robert Haas wrote:
> > 1. Have log_newpage() and heap_xlog_newpage() only call PageSetLSN() and
> > PageSetTLI() if the page is not new. This seems slightly awkward because
> > most WAL replay stuff doesn't have to worry about zero pages, but in
> > this case I think it does.
> >
> > 2. Have copy_relation_data() initialize new pages. I don't like this
> > because (a) it's not really the job of SET TABLESPACE to clean up zero
> > pages; and (b) it could be an index with different special size, etc.,
> > and it doesn't seem like a good place to figure that out.
>
> It appears to me that all of the callers of log_newpage() other than
> copy_relation_data() do so with pages that they've just constructed,
> and which therefore can't be new. So maybe we could just modify
> copy_relation_data to check PageIsNew(buf), or something like that,
> and only call log_newpage() if that returns true.
My first concern with that idea was that it may create an inconsistency
between the primary and the standby. The primary could have a bunch of
zero pages that never make it to the standby.
However, it looks like all WAL recovery stuff passes true for "init"
when calling XLogReadBuffer(), so I think it's safe.
I'll test it and submit a patch.
Regards,Jeff Davis