Re: lazy_scan_heap() forgets to mark buffer dirty when setting all frozen?

On Mon, Apr 8, 2019 at 12:49 PM Andres Freund <andres@anarazel.de> wrote:
>
> Hi,
>
> lazy_scan_heap() contains the following block:
>
>                 /*
>                  * If the all-visible page is turned out to be all-frozen but not
>                  * marked, we should so mark it.  Note that all_frozen is only valid
>                  * if all_visible is true, so we must check both.
>                  */
>                 else if (all_visible_according_to_vm && all_visible && all_frozen &&
>                                  !VM_ALL_FROZEN(onerel, blkno, &vmbuffer))
>                 {
>                         /*
>                          * We can pass InvalidTransactionId as the cutoff XID here,
>                          * because setting the all-frozen bit doesn't cause recovery
>                          * conflicts.
>                          */
>                         visibilitymap_set(onerel, blkno, buf, InvalidXLogRecPtr,
>                                                           vmbuffer, InvalidTransactionId,
>                                                           VISIBILITYMAP_ALL_FROZEN);
>                 }
>
> but I'm afraid that's not quite enough. As an earlier comment explains:
>
>
>                          * NB: If the heap page is all-visible but the VM bit is not set,
>                          * we don't need to dirty the heap page.  However, if checksums
>                          * are enabled, we do need to make sure that the heap page is
>                          * dirtied before passing it to visibilitymap_set(), because it
>                          * may be logged.  Given that this situation should only happen in
>                          * rare cases after a crash, it is not worth optimizing.
>                          */
>                         PageSetAllVisible(page);
>                         MarkBufferDirty(buf);
>                         visibilitymap_set(onerel, blkno, buf, InvalidXLogRecPtr,
>                                                           vmbuffer, visibility_cutoff_xid, flags);
>
> don't we need to do that here too?

Thank you for pointing out. I think that the same things are necessary
here. Otherwise does it lead the case that the visibility map page is
set while the heap page bit is cleared?

Regards,

--
Masahiko Sawada
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center