On 12/17/19, 2:26 AM, "Kyotaro Horiguchi" <horikyota....@gmail.com> wrote: > But I think I found a corner case where the patch doesn't work. As I > mentioned in another message, if WAL buffer was full, > AdvanceXLInsertBuffer calls XLogWrite to write out the victim buffer > regardless whether the last record in the page was the first half of a > continuation record. XLogWrite can mark the segment as .ready even > with the patch. > > Is that correct? And do you think the corner case is worth amending?
I certainly think it is worth trying to prevent potential WAL archive corruption in known corner cases. Your comment highlights a potential shortcoming of my patch. AFAICT there is no guarantee that XLogWrite() is called with a complete WAL record. Even if that assumption is true at the moment, it might not hold up over time. > If so, we could amend also that case by marking the last segment as > .ready when XLogWrite writes the first bytes of the next segment. (As > the further corner-case, it still doesn't work if a contination record > spans over trhee or more segments.. But I don't (or want not to) think > we don't need to consider that case..) I'm working on a new version of the patch that will actually look at the WAL page metadata to determine when it is safe to mark a segment as ready for archival. It seems relatively easy to figure out whether a page is the last one for the current WAL record. Nathan
