On Fri, Oct 13, 2017 at 10:32 AM, Michael Paquier <michael.paqu...@gmail.com> wrote: > On Thu, Oct 12, 2017 at 10:47 PM, Amit Kapila <amit.kapil...@gmail.com> wrote: >> Today, I was trying to think about cases when we can return BLK_DONE >> in XLogReadBufferForRedoExtended. One thing that occurred to me is >> that it can happen during the replay of WAL if the full_page_writes is >> off. Basically, when the full_page_writes is on, then during crash >> recovery, it will always first restore the full page image of page and >> then apply the WAL corresponding to that page, so we will never hit >> the case where the lsn of the page is greater than lsn of WAL record. >> >> Are there other cases for which we can get BLK_DONE state? Is it >> mentioned somewhere in code/comments which I am missing? > > Remember the thread about meta page optimization... Some index AMs use > XLogInitBufferForRedo() to redo their meta pages and those don't have > a FPW so when doing crash recovery you may finish by not replaying a > meta page if its LSN on the page header is newer than what's being > replayed. >
I think for metapage usage, it will anyway apply the changes. See _bt_restore_page. > That's another case where BLK_DONE can be reached, even if > full_page_writes is on. > Yeah and probably if someone uses REGBUF_NO_IMAGE. However, I was mainly thinking about cases where caller is not doing anything to prevent full_page_image explicitly. -- With Regards, Amit Kapila. EnterpriseDB: http://www.enterprisedb.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
