Re: foreign key locks

On 2013-01-18 15:37:47 -0500, Tom Lane wrote:
> Alvaro Herrera <alvherre@2ndquadrant.com> writes:
> > The reason is that there is an (unknown to me) rule that there must be
> > some data not associated with a buffer:
> 
> >     /*
> >      * NOTE: We disallow len == 0 because it provides a useful bit of extra
> >      * error checking in ReadRecord.  This means that all callers of
> >      * XLogInsert must supply at least some not-in-a-buffer data. [...]
> >      */
> 
> > This seems pretty strange to me.  And having the rule be spelled out
> > only in a comment within XLogInsert and not at its top, and not nearby
> > the XLogRecData struct definition either, seems pretty strange to me.
> > I wonder how come every PG hacker except me knows this.
> 
> I doubt it ever came up before.  What use is logging only the content of
> a buffer page?  Surely you'd need to know, for example, which relation
> and page number it is from.

It only got to be a length of 0 because the the data got removed due to
a logged full page write. And the backup block contains the data about
which blocks it is logging in itself.
I wonder if the check shouldn't just check write_len instead, directly
below the loop that ads backup blocks.

Greetings,

Andres Freund

-- Andres Freund                       http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training &
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