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Refactor lazy_scan_prune() VM clear logic into helper
Encapsulating the cases that clear the visibility map after vacuum phase I, when corruption is detected, into in a helper makes the code cleaner and enables further refactoring in future commits. Author: Melanie Plageman <melanieplageman@gmail.com> Reviewed-by: Andres Freund <andres@anarazel.de> Reviewed-by: Kirill Reshke <reshkekirill@gmail.com> Reviewed-by: Chao Li <li.evan.chao@gmail.com> Reviewed-by: Andrey Borodin <x4mmm@yandex-team.ru> Discussion: https://postgr.es/m/7ib3sa55sapwjlaz4sijbiq7iezna27kjvvvar4dpgkmadml6t%40gfpkkwmdnepx
This commit is contained in:
Melanie Plageman
parent
648a7e28d7
commit
19af794b66
1 changed files with 83 additions and 48 deletions
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@ -422,6 +422,11 @@ static void find_next_unskippable_block(LVRelState *vacrel, bool *skipsallvis);
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static bool lazy_scan_new_or_empty(LVRelState *vacrel, Buffer buf,
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BlockNumber blkno, Page page,
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bool sharelock, Buffer vmbuffer);
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static void identify_and_fix_vm_corruption(Relation rel, Buffer heap_buffer,
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BlockNumber heap_blk, Page heap_page,
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int nlpdead_items,
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Buffer vmbuffer,
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uint8 *vmbits);
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static int lazy_scan_prune(LVRelState *vacrel, Buffer buf,
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BlockNumber blkno, Page page,
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Buffer vmbuffer,
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@ -1955,6 +1960,81 @@ cmpOffsetNumbers(const void *a, const void *b)
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return pg_cmp_u16(*(const OffsetNumber *) a, *(const OffsetNumber *) b);
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}
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/*
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* Helper to correct any corruption detected on a heap page and its
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* corresponding visibility map page after pruning but before setting the
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* visibility map. It examines the heap page, the associated VM page, and the
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* number of dead items previously identified.
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*
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* This function must be called while holding an exclusive lock on the heap
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* buffer, and the dead items must have been discovered under that same lock.
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* The provided vmbits must reflect the current state of the VM block
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* referenced by vmbuffer. Although we do not hold a lock on the VM buffer, it
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* is pinned, and the heap buffer is exclusively locked, ensuring that no
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* other backend can update the VM bits corresponding to this heap page.
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*
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* If it clears corruption, it will zero out vmbits.
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*/
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static void
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identify_and_fix_vm_corruption(Relation rel, Buffer heap_buffer,
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BlockNumber heap_blk, Page heap_page,
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int nlpdead_items,
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Buffer vmbuffer,
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uint8 *vmbits)
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{
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Assert(visibilitymap_get_status(rel, heap_blk, &vmbuffer) == *vmbits);
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Assert(BufferIsLockedByMeInMode(heap_buffer, BUFFER_LOCK_EXCLUSIVE));
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/*
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* As of PostgreSQL 9.2, the visibility map bit should never be set if the
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* page-level bit is clear. However, it's possible that the bit got
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* cleared after heap_vac_scan_next_block() was called, so we must recheck
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* with buffer lock before concluding that the VM is corrupt.
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*/
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if (!PageIsAllVisible(heap_page) &&
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((*vmbits & VISIBILITYMAP_VALID_BITS) != 0))
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{
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ereport(WARNING,
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(errcode(ERRCODE_DATA_CORRUPTED),
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errmsg("page is not marked all-visible but visibility map bit is set in relation \"%s\" page %u",
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RelationGetRelationName(rel), heap_blk)));
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visibilitymap_clear(rel, heap_blk, vmbuffer,
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VISIBILITYMAP_VALID_BITS);
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*vmbits = 0;
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}
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/*
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* It's possible for the value returned by
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* GetOldestNonRemovableTransactionId() to move backwards, so it's not
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* wrong for us to see tuples that appear to not be visible to everyone
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* yet, while PD_ALL_VISIBLE is already set. The real safe xmin value
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* never moves backwards, but GetOldestNonRemovableTransactionId() is
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* conservative and sometimes returns a value that's unnecessarily small,
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* so if we see that contradiction it just means that the tuples that we
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* think are not visible to everyone yet actually are, and the
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* PD_ALL_VISIBLE flag is correct.
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*
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* There should never be LP_DEAD items on a page with PD_ALL_VISIBLE set,
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* however.
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*/
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else if (PageIsAllVisible(heap_page) && nlpdead_items > 0)
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{
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ereport(WARNING,
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(errcode(ERRCODE_DATA_CORRUPTED),
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errmsg("page containing LP_DEAD items is marked as all-visible in relation \"%s\" page %u",
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RelationGetRelationName(rel), heap_blk)));
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PageClearAllVisible(heap_page);
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MarkBufferDirty(heap_buffer);
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visibilitymap_clear(rel, heap_blk, vmbuffer,
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VISIBILITYMAP_VALID_BITS);
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*vmbits = 0;
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}
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}
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/*
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* lazy_scan_prune() -- lazy_scan_heap() pruning and freezing.
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*
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@ -2097,54 +2177,9 @@ lazy_scan_prune(LVRelState *vacrel,
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old_vmbits = visibilitymap_get_status(vacrel->rel, blkno, &vmbuffer);
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/*
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* As of PostgreSQL 9.2, the visibility map bit should never be set if the
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* page-level bit is clear. However, it's possible that the bit got
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* cleared after heap_vac_scan_next_block() was called, so we must recheck
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* with buffer lock before concluding that the VM is corrupt.
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*/
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if (!PageIsAllVisible(page) &&
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(old_vmbits & VISIBILITYMAP_VALID_BITS) != 0)
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{
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ereport(WARNING,
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(errcode(ERRCODE_DATA_CORRUPTED),
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errmsg("page is not marked all-visible but visibility map bit is set in relation \"%s\" page %u",
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vacrel->relname, blkno)));
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visibilitymap_clear(vacrel->rel, blkno, vmbuffer,
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VISIBILITYMAP_VALID_BITS);
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/* VM bits are now clear */
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old_vmbits = 0;
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}
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/*
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* It's possible for the value returned by
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* GetOldestNonRemovableTransactionId() to move backwards, so it's not
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* wrong for us to see tuples that appear to not be visible to everyone
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* yet, while PD_ALL_VISIBLE is already set. The real safe xmin value
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* never moves backwards, but GetOldestNonRemovableTransactionId() is
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* conservative and sometimes returns a value that's unnecessarily small,
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* so if we see that contradiction it just means that the tuples that we
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* think are not visible to everyone yet actually are, and the
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* PD_ALL_VISIBLE flag is correct.
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*
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* There should never be LP_DEAD items on a page with PD_ALL_VISIBLE set,
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* however.
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*/
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else if (presult.lpdead_items > 0 && PageIsAllVisible(page))
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{
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ereport(WARNING,
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(errcode(ERRCODE_DATA_CORRUPTED),
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errmsg("page containing LP_DEAD items is marked as all-visible in relation \"%s\" page %u",
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vacrel->relname, blkno)));
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PageClearAllVisible(page);
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MarkBufferDirty(buf);
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visibilitymap_clear(vacrel->rel, blkno, vmbuffer,
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VISIBILITYMAP_VALID_BITS);
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/* VM bits are now clear */
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old_vmbits = 0;
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}
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identify_and_fix_vm_corruption(vacrel->rel, buf, blkno, page,
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presult.lpdead_items, vmbuffer,
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&old_vmbits);
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if (!presult.all_visible)
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return presult.ndeleted;
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