diff options
Diffstat (limited to 'src/backend/commands/vacuumlazy.c')
| -rw-r--r-- | src/backend/commands/vacuumlazy.c | 34 |
1 files changed, 29 insertions, 5 deletions
diff --git a/src/backend/commands/vacuumlazy.c b/src/backend/commands/vacuumlazy.c index 0e0193d40e1..3ff56a73664 100644 --- a/src/backend/commands/vacuumlazy.c +++ b/src/backend/commands/vacuumlazy.c @@ -419,6 +419,15 @@ lazy_scan_heap(Relation onerel, LVRelStats *vacrelstats, * Note: if scan_all is true, we won't actually skip any pages; but we * maintain next_not_all_visible_block anyway, so as to set up the * all_visible_according_to_vm flag correctly for each page. + * + * Note: The value returned by visibilitymap_test could be slightly + * out-of-date, since we make this test before reading the corresponding + * heap page or locking the buffer. This is OK. If we mistakenly think + * that the page is all-visible when in fact the flag's just been cleared, + * we might fail to vacuum the page. But it's OK to skip pages when + * scan_all is not set, so no great harm done; the next vacuum will find + * them. If we make the reverse mistake and vacuum a page unnecessarily, + * it'll just be a no-op. */ for (next_not_all_visible_block = 0; next_not_all_visible_block < nblocks; @@ -852,22 +861,37 @@ lazy_scan_heap(Relation onerel, LVRelStats *vacrelstats, freespace = PageGetHeapFreeSpace(page); /* mark page all-visible, if appropriate */ - if (all_visible && !all_visible_according_to_vm) + if (all_visible) { if (!PageIsAllVisible(page)) { PageSetAllVisible(page); MarkBufferDirty(buf); + visibilitymap_set(onerel, blkno, InvalidXLogRecPtr, vmbuffer, + visibility_cutoff_xid); + } + else if (!all_visible_according_to_vm) + { + /* + * It should never be the case that the visibility map page + * is set while the page-level bit is clear, but the reverse + * is allowed. Set the visibility map bit as well so that + * we get back in sync. + */ + visibilitymap_set(onerel, blkno, InvalidXLogRecPtr, vmbuffer, + visibility_cutoff_xid); } - visibilitymap_set(onerel, blkno, InvalidXLogRecPtr, vmbuffer, - visibility_cutoff_xid); } /* * As of PostgreSQL 9.2, the visibility map bit should never be set if - * the page-level bit is clear. + * the page-level bit is clear. However, it's possible that the bit + * got cleared after we checked it and before we took the buffer + * content lock, so we must recheck before jumping to the conclusion + * that something bad has happened. */ - else if (all_visible_according_to_vm && !PageIsAllVisible(page)) + else if (all_visible_according_to_vm && !PageIsAllVisible(page) + && visibilitymap_test(onerel, blkno, &vmbuffer)) { elog(WARNING, "page is not marked all-visible but visibility map bit is set in relation \"%s\" page %u", relname, blkno); |