Greetings, * Tom Lane (t...@sss.pgh.pa.us) wrote: > Chapman Flack <c...@anastigmatix.net> writes: > > On 03/27/18 22:10, Michael Paquier wrote: > >> Here you go for one example: > >> https://sourceforge.net/projects/pglesslog/ > > > In any case, from my study of the commit, it is hard for me to see an issue. > > The code comment says: "mark the header to indicate that WAL records > > beginning in this page have removable backup blocks." > > Yeah, that commit just moved a flag from individual WAL records to page > headers, arguing that it was okay to assume that the same flag value > applies to all records on a page. If there are no records in the page, > it doesn't matter what you think the flag value is. > > A potentially stronger complaint is that WAL-reading tools might fail > outright on a page with an invalid header, but I'd say that's a robustness > issue that they'd need to address anyway. There's never been any > guarantee that the trailing pages of a WAL segment are valid.
Agreed, I don't buy off that tools which fall apart when reading a page with an invalid header should block this from moving forward- those tools need to be fixed to not rely on trailing/unused WAL pages to be valid. Thanks! Stephen
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