On 2013-01-18 15:37:47 -0500, Tom Lane wrote: > Alvaro Herrera <alvhe...@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 & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
