From c27436eaeedbc1551072922d92460ca1c30ed116 Mon Sep 17 00:00:00 2001 From: Melanie Plageman Date: Sat, 30 Dec 2023 16:22:12 -0500 Subject: [PATCH v5a 2/7] Add lazy_scan_skip unskippable state to LVRelState Future commits will remove all skipping logic from lazy_scan_heap() and confine it to lazy_scan_skip(). To make those commits more clear, first introduce add a struct to LVRelState containing variables needed to skip ranges less than SKIP_PAGES_THRESHOLD. lazy_scan_prune() and lazy_scan_new_or_empty() can now access the buffer containing the relevant block of the visibility map through the LVRelState.skip, so it no longer needs to be a separate function parameter. While we are at it, add additional information to the lazy_scan_skip() comment, including descriptions of the role and expectations for its function parameters. --- src/backend/access/heap/vacuumlazy.c | 154 ++++++++++++++++----------- 1 file changed, 90 insertions(+), 64 deletions(-) diff --git a/src/backend/access/heap/vacuumlazy.c b/src/backend/access/heap/vacuumlazy.c index 1dc6cc8e4db..0ddb986bc03 100644 --- a/src/backend/access/heap/vacuumlazy.c +++ b/src/backend/access/heap/vacuumlazy.c @@ -204,6 +204,22 @@ typedef struct LVRelState int64 live_tuples; /* # live tuples remaining */ int64 recently_dead_tuples; /* # dead, but not yet removable */ int64 missed_dead_tuples; /* # removable, but not removed */ + + /* + * Parameters maintained by lazy_scan_skip() to manage skipping ranges of + * pages greater than SKIP_PAGES_THRESHOLD. + */ + struct + { + /* Next unskippable block */ + BlockNumber next_unskippable_block; + /* Buffer containing next unskippable block's visibility info */ + Buffer vmbuffer; + /* Next unskippable block's visibility status */ + bool next_unskippable_allvis; + /* Whether or not skippable blocks should be skipped */ + bool skipping_current_range; + } skip; } LVRelState; /* Struct for saving and restoring vacuum error information. */ @@ -214,19 +230,15 @@ typedef struct LVSavedErrInfo VacErrPhase phase; } LVSavedErrInfo; - /* non-export function prototypes */ static void lazy_scan_heap(LVRelState *vacrel); -static BlockNumber lazy_scan_skip(LVRelState *vacrel, Buffer *vmbuffer, - BlockNumber next_block, - bool *next_unskippable_allvis, - bool *skipping_current_range); +static void lazy_scan_skip(LVRelState *vacrel, BlockNumber next_block); static bool lazy_scan_new_or_empty(LVRelState *vacrel, Buffer buf, BlockNumber blkno, Page page, - bool sharelock, Buffer vmbuffer); + bool sharelock); static void lazy_scan_prune(LVRelState *vacrel, Buffer buf, BlockNumber blkno, Page page, - Buffer vmbuffer, bool all_visible_according_to_vm, + bool all_visible_according_to_vm, bool *has_lpdead_items); static bool lazy_scan_noprune(LVRelState *vacrel, Buffer buf, BlockNumber blkno, Page page, @@ -803,12 +815,8 @@ lazy_scan_heap(LVRelState *vacrel) { BlockNumber rel_pages = vacrel->rel_pages, blkno, - next_unskippable_block, next_fsm_block_to_vacuum = 0; VacDeadItems *dead_items = vacrel->dead_items; - Buffer vmbuffer = InvalidBuffer; - bool next_unskippable_allvis, - skipping_current_range; const int initprog_index[] = { PROGRESS_VACUUM_PHASE, PROGRESS_VACUUM_TOTAL_HEAP_BLKS, @@ -822,10 +830,9 @@ lazy_scan_heap(LVRelState *vacrel) initprog_val[2] = dead_items->max_items; pgstat_progress_update_multi_param(3, initprog_index, initprog_val); + vacrel->skip.vmbuffer = InvalidBuffer; /* Set up an initial range of skippable blocks using the visibility map */ - next_unskippable_block = lazy_scan_skip(vacrel, &vmbuffer, 0, - &next_unskippable_allvis, - &skipping_current_range); + lazy_scan_skip(vacrel, 0); for (blkno = 0; blkno < rel_pages; blkno++) { Buffer buf; @@ -834,26 +841,23 @@ lazy_scan_heap(LVRelState *vacrel) bool has_lpdead_items; bool got_cleanup_lock = false; - if (blkno == next_unskippable_block) + if (blkno == vacrel->skip.next_unskippable_block) { /* * Can't skip this page safely. Must scan the page. But * determine the next skippable range after the page first. */ - all_visible_according_to_vm = next_unskippable_allvis; - next_unskippable_block = lazy_scan_skip(vacrel, &vmbuffer, - blkno + 1, - &next_unskippable_allvis, - &skipping_current_range); + all_visible_according_to_vm = vacrel->skip.next_unskippable_allvis; + lazy_scan_skip(vacrel, blkno + 1); - Assert(next_unskippable_block >= blkno + 1); + Assert(vacrel->skip.next_unskippable_block >= blkno + 1); } else { /* Last page always scanned (may need to set nonempty_pages) */ Assert(blkno < rel_pages - 1); - if (skipping_current_range) + if (vacrel->skip.skipping_current_range) continue; /* Current range is too small to skip -- just scan the page */ @@ -896,10 +900,10 @@ lazy_scan_heap(LVRelState *vacrel) * correctness, but we do it anyway to avoid holding the pin * across a lengthy, unrelated operation. */ - if (BufferIsValid(vmbuffer)) + if (BufferIsValid(vacrel->skip.vmbuffer)) { - ReleaseBuffer(vmbuffer); - vmbuffer = InvalidBuffer; + ReleaseBuffer(vacrel->skip.vmbuffer); + vacrel->skip.vmbuffer = InvalidBuffer; } /* Perform a round of index and heap vacuuming */ @@ -924,7 +928,7 @@ lazy_scan_heap(LVRelState *vacrel) * all-visible. In most cases this will be very cheap, because we'll * already have the correct page pinned anyway. */ - visibilitymap_pin(vacrel->rel, blkno, &vmbuffer); + visibilitymap_pin(vacrel->rel, blkno, &vacrel->skip.vmbuffer); buf = ReadBufferExtended(vacrel->rel, MAIN_FORKNUM, blkno, RBM_NORMAL, vacrel->bstrategy); @@ -942,8 +946,7 @@ lazy_scan_heap(LVRelState *vacrel) LockBuffer(buf, BUFFER_LOCK_SHARE); /* Check for new or empty pages before lazy_scan_[no]prune call */ - if (lazy_scan_new_or_empty(vacrel, buf, blkno, page, !got_cleanup_lock, - vmbuffer)) + if (lazy_scan_new_or_empty(vacrel, buf, blkno, page, !got_cleanup_lock)) { /* Processed as new/empty page (lock and pin released) */ continue; @@ -985,7 +988,7 @@ lazy_scan_heap(LVRelState *vacrel) */ if (got_cleanup_lock) lazy_scan_prune(vacrel, buf, blkno, page, - vmbuffer, all_visible_according_to_vm, + all_visible_according_to_vm, &has_lpdead_items); /* @@ -1035,8 +1038,11 @@ lazy_scan_heap(LVRelState *vacrel) } vacrel->blkno = InvalidBlockNumber; - if (BufferIsValid(vmbuffer)) - ReleaseBuffer(vmbuffer); + if (BufferIsValid(vacrel->skip.vmbuffer)) + { + ReleaseBuffer(vacrel->skip.vmbuffer); + vacrel->skip.vmbuffer = InvalidBuffer; + } /* report that everything is now scanned */ pgstat_progress_update_param(PROGRESS_VACUUM_HEAP_BLKS_SCANNED, blkno); @@ -1080,15 +1086,34 @@ lazy_scan_heap(LVRelState *vacrel) * lazy_scan_skip() -- set up range of skippable blocks using visibility map. * * lazy_scan_heap() calls here every time it needs to set up a new range of - * blocks to skip via the visibility map. Caller passes the next block in - * line. We return a next_unskippable_block for this range. When there are - * no skippable blocks we just return caller's next_block. The all-visible - * status of the returned block is set in *next_unskippable_allvis for caller, - * too. Block usually won't be all-visible (since it's unskippable), but it - * can be during aggressive VACUUMs (as well as in certain edge cases). + * blocks to skip via the visibility map. Caller passes next_block, the next + * block in line. The parameters of the skipped range are recorded in skip. + * vacrel is an in/out parameter here; vacuum options and information about the + * relation are read and vacrel->skippedallvis is set to ensure we don't + * advance relfrozenxid when we have skipped vacuuming all visible blocks. + * + * skip->vmbuffer will contain the block from the VM containing visibility + * information for the next unskippable heap block. We may end up needed a + * different block from the VM (if we decide not to skip a skippable block). + * This is okay; visibilitymap_pin() will take care of this while processing + * the block. + * + * A block is unskippable if it is not all visible according to the visibility + * map. It is also unskippable if it is the last block in the relation, if the + * vacuum is an aggressive vacuum, or if DISABLE_PAGE_SKIPPING was passed to + * vacuum. * - * Sets *skipping_current_range to indicate if caller should skip this range. - * Costs and benefits drive our decision. Very small ranges won't be skipped. + * Even if a block is skippable, we may choose not to skip it if the range of + * skippable blocks is too small (below SKIP_PAGES_THRESHOLD). As a + * consequence, we must keep track of the next truly unskippable block and its + * visibility status along with whether or not we are skipping the current + * range of skippable blocks. This can be used to derive the next block + * lazy_scan_heap() must process and its visibility status. + * + * The block number and visibility status of the next unskippable block are set + * in skip->next_unskippable_block and next_unskippable_allvis. + * skip->skipping_current_range indicates to the caller whether or not it is + * processing a skippable (and thus all-visible) block. * * Note: our opinion of which blocks can be skipped can go stale immediately. * It's okay if caller "misses" a page whose all-visible or all-frozen marking @@ -1098,25 +1123,26 @@ lazy_scan_heap(LVRelState *vacrel) * older XIDs/MXIDs. The vacrel->skippedallvis flag will be set here when the * choice to skip such a range is actually made, making everything safe.) */ -static BlockNumber -lazy_scan_skip(LVRelState *vacrel, Buffer *vmbuffer, BlockNumber next_block, - bool *next_unskippable_allvis, bool *skipping_current_range) +static void +lazy_scan_skip(LVRelState *vacrel, BlockNumber next_block) { + /* Use local variables for better optimized loop code */ BlockNumber rel_pages = vacrel->rel_pages, next_unskippable_block = next_block; + bool skipsallvis = false; - *next_unskippable_allvis = true; + vacrel->skip.next_unskippable_allvis = true; while (next_unskippable_block < rel_pages) { uint8 mapbits = visibilitymap_get_status(vacrel->rel, next_unskippable_block, - vmbuffer); + &vacrel->skip.vmbuffer); if ((mapbits & VISIBILITYMAP_ALL_VISIBLE) == 0) { Assert((mapbits & VISIBILITYMAP_ALL_FROZEN) == 0); - *next_unskippable_allvis = false; + vacrel->skip.next_unskippable_allvis = false; break; } @@ -1137,7 +1163,7 @@ lazy_scan_skip(LVRelState *vacrel, Buffer *vmbuffer, BlockNumber next_block, if (!vacrel->skipwithvm) { /* Caller shouldn't rely on all_visible_according_to_vm */ - *next_unskippable_allvis = false; + vacrel->skip.next_unskippable_allvis = false; break; } @@ -1162,6 +1188,8 @@ lazy_scan_skip(LVRelState *vacrel, Buffer *vmbuffer, BlockNumber next_block, next_unskippable_block++; } + vacrel->skip.next_unskippable_block = next_unskippable_block; + /* * We only skip a range with at least SKIP_PAGES_THRESHOLD consecutive * pages. Since we're reading sequentially, the OS should be doing @@ -1172,16 +1200,14 @@ lazy_scan_skip(LVRelState *vacrel, Buffer *vmbuffer, BlockNumber next_block, * non-aggressive VACUUMs. If the range has any all-visible pages then * skipping makes updating relfrozenxid unsafe, which is a real downside. */ - if (next_unskippable_block - next_block < SKIP_PAGES_THRESHOLD) - *skipping_current_range = false; + if (vacrel->skip.next_unskippable_block - next_block < SKIP_PAGES_THRESHOLD) + vacrel->skip.skipping_current_range = false; else { - *skipping_current_range = true; + vacrel->skip.skipping_current_range = true; if (skipsallvis) vacrel->skippedallvis = true; } - - return next_unskippable_block; } /* @@ -1214,7 +1240,7 @@ lazy_scan_skip(LVRelState *vacrel, Buffer *vmbuffer, BlockNumber next_block, */ static bool lazy_scan_new_or_empty(LVRelState *vacrel, Buffer buf, BlockNumber blkno, - Page page, bool sharelock, Buffer vmbuffer) + Page page, bool sharelock) { Size freespace; @@ -1300,7 +1326,7 @@ lazy_scan_new_or_empty(LVRelState *vacrel, Buffer buf, BlockNumber blkno, PageSetAllVisible(page); visibilitymap_set(vacrel->rel, blkno, buf, InvalidXLogRecPtr, - vmbuffer, InvalidTransactionId, + vacrel->skip.vmbuffer, InvalidTransactionId, VISIBILITYMAP_ALL_VISIBLE | VISIBILITYMAP_ALL_FROZEN); END_CRIT_SECTION(); } @@ -1336,10 +1362,11 @@ lazy_scan_new_or_empty(LVRelState *vacrel, Buffer buf, BlockNumber blkno, * any tuple that becomes dead after the call to heap_page_prune() can't need to * be frozen, because it was visible to another session when vacuum started. * - * vmbuffer is the buffer containing the VM block with visibility information - * for the heap block, blkno. all_visible_according_to_vm is the saved - * visibility status of the heap block looked up earlier by the caller. We - * won't rely entirely on this status, as it may be out of date. + * vacrel->skipstate.vmbuffer is the buffer containing the VM block with + * visibility information for the heap block, blkno. + * all_visible_according_to_vm is the saved visibility status of the heap block + * looked up earlier by the caller. We won't rely entirely on this status, as + * it may be out of date. * * *has_lpdead_items is set to true or false depending on whether, upon return * from this function, any LP_DEAD items are still present on the page. @@ -1349,7 +1376,6 @@ lazy_scan_prune(LVRelState *vacrel, Buffer buf, BlockNumber blkno, Page page, - Buffer vmbuffer, bool all_visible_according_to_vm, bool *has_lpdead_items) { @@ -1783,7 +1809,7 @@ lazy_scan_prune(LVRelState *vacrel, PageSetAllVisible(page); MarkBufferDirty(buf); visibilitymap_set(vacrel->rel, blkno, buf, InvalidXLogRecPtr, - vmbuffer, visibility_cutoff_xid, + vacrel->skip.vmbuffer, visibility_cutoff_xid, flags); } @@ -1794,11 +1820,11 @@ lazy_scan_prune(LVRelState *vacrel, * buffer lock before concluding that the VM is corrupt. */ else if (all_visible_according_to_vm && !PageIsAllVisible(page) && - visibilitymap_get_status(vacrel->rel, blkno, &vmbuffer) != 0) + visibilitymap_get_status(vacrel->rel, blkno, &vacrel->skip.vmbuffer) != 0) { elog(WARNING, "page is not marked all-visible but visibility map bit is set in relation \"%s\" page %u", vacrel->relname, blkno); - visibilitymap_clear(vacrel->rel, blkno, vmbuffer, + visibilitymap_clear(vacrel->rel, blkno, vacrel->skip.vmbuffer, VISIBILITYMAP_VALID_BITS); } @@ -1822,7 +1848,7 @@ lazy_scan_prune(LVRelState *vacrel, vacrel->relname, blkno); PageClearAllVisible(page); MarkBufferDirty(buf); - visibilitymap_clear(vacrel->rel, blkno, vmbuffer, + visibilitymap_clear(vacrel->rel, blkno, vacrel->skip.vmbuffer, VISIBILITYMAP_VALID_BITS); } @@ -1832,7 +1858,7 @@ lazy_scan_prune(LVRelState *vacrel, * true, so we must check both all_visible and all_frozen. */ else if (all_visible_according_to_vm && all_visible && - all_frozen && !VM_ALL_FROZEN(vacrel->rel, blkno, &vmbuffer)) + all_frozen && !VM_ALL_FROZEN(vacrel->rel, blkno, &vacrel->skip.vmbuffer)) { /* * Avoid relying on all_visible_according_to_vm as a proxy for the @@ -1854,7 +1880,7 @@ lazy_scan_prune(LVRelState *vacrel, */ Assert(!TransactionIdIsValid(visibility_cutoff_xid)); visibilitymap_set(vacrel->rel, blkno, buf, InvalidXLogRecPtr, - vmbuffer, InvalidTransactionId, + vacrel->skip.vmbuffer, InvalidTransactionId, VISIBILITYMAP_ALL_VISIBLE | VISIBILITYMAP_ALL_FROZEN); } -- 2.40.1