Eliminate use of cached VM value in lazy_scan_prune() lazy_scan_prune() takes a parameter from lazy_scan_heap() indicating whether the page was marked all-visible in the VM at the time it was last checked in find_next_unskippable_block(). This behavior is historical, dating back to commit 608195a3a365, when we did not pin the VM page until deciding we must read it. Now that the VM page is already pinned, there is no meaningful benefit to relying on a cached VM status.
Removing this cached value simplifies the logic in both lazy_scan_heap() and lazy_scan_prune(). It also clarifies future work that will set the visibility map on-access: such paths will not have a cached value available, which would make the logic harder to reason about. And eliminating it enables us to detect and repair VM corruption on-access. Along with removing the cached value and unconditionally checking the visibility status of the heap page, this commit also moves the VM corruption handling to occur first. This reordering should have no performance impact, since the checks are inexpensive and performed only once per page. It does, however, make the control flow easier to understand. The new restructuring also makes it possible to set the VM after fixing corruption (if pruning found the page all-visible). Now that no callers of visibilitymap_set() use its return value, change its (and visibilitymap_set_vmbits()) return type to void. Author: Melanie Plageman <[email protected]> Reviewed-by: Andres Freund <[email protected]> Reviewed-by: Kirill Reshke <[email protected]> Reviewed-by: Chao Li <[email protected]> Reviewed-by: Andrey Borodin <[email protected]> Reviewed-by: Xuneng Zhou <[email protected]> Discussion: https://postgr.es/m/5CEAA162-67B1-44DA-B60D-8B65717E8B05%40gmail.com Branch ------ master Details ------- https://git.postgresql.org/pg/commitdiff/648a7e28d7c28754ca46caa09864435bc45e543d Modified Files -------------- src/backend/access/heap/vacuumlazy.c | 180 ++++++++++++++------------------ src/backend/access/heap/visibilitymap.c | 9 +- src/include/access/visibilitymap.h | 18 ++-- 3 files changed, 92 insertions(+), 115 deletions(-)
