From 58b3187b1bb54585c5b81e261678fb448ad9cea0 Mon Sep 17 00:00:00 2001 From: Melanie Plageman Date: Tue, 2 Dec 2025 15:07:42 -0500 Subject: [PATCH v43 03/10] WAL log VM setting during vacuum phase I in XLOG_HEAP2_PRUNE_VACUUM_SCAN Vacuum no longer emits a separate WAL record for each page set all-visible or all-frozen during phase I. Instead, visibility map updates are now included in the XLOG_HEAP2_PRUNE_VACUUM_SCAN record that is already emitted for pruning and freezing. Previously, heap_page_prune_and_freeze() determined whether a page was all-visible, but the corresponding VM bits were only set later in lazy_scan_prune(). Now the VM is updated immediately in heap_page_prune_and_freeze(), at the same time as the heap modifications. For now, this change applies only to vacuum phase I, not to pruning performed during normal page access. Author: Melanie Plageman Reviewed-by: Andres Freund Reviewed-by: Robert Haas Reviewed-by: Kirill Reshke Reviewed-by: Chao Li Discussion: https://postgr.es/m/flat/CAAKRu_ZMw6Npd_qm2KM%2BFwQ3cMOMx1Dh3VMhp8-V7SOLxdK9-g%40mail.gmail.com --- src/backend/access/heap/pruneheap.c | 245 +++++++++++++++++++-------- src/backend/access/heap/vacuumlazy.c | 113 ++---------- src/include/access/heapam.h | 37 ++-- 3 files changed, 205 insertions(+), 190 deletions(-) diff --git a/src/backend/access/heap/pruneheap.c b/src/backend/access/heap/pruneheap.c index cebd78603cb..c43b192b163 100644 --- a/src/backend/access/heap/pruneheap.c +++ b/src/backend/access/heap/pruneheap.c @@ -72,6 +72,21 @@ typedef struct OffsetNumber nowunused[MaxHeapTuplesPerPage]; HeapTupleFreeze frozen[MaxHeapTuplesPerPage]; + /* + * set_all_visible and set_all_frozen indicate if the all-visible and + * all-frozen bits in the visibility map can be set for this page after + * pruning. + * + * NOTE: set_all_visible and set_all_frozen initially don't include + * LP_DEAD items. That's convenient for heap_page_prune_and_freeze() to + * use them to decide whether to opportunistically freeze the page or not. + * The set_all_visible and set_all_frozen values ultimately used to set + * the VM are adjusted to include LP_DEAD items after we determine whether + * or not to opportunistically freeze. + */ + bool set_all_visible; + bool set_all_frozen; + /*------------------------------------------------------- * Working state for HOT chain processing *------------------------------------------------------- @@ -122,12 +137,16 @@ typedef struct /* * Caller must provide a pinned vmbuffer corresponding to the heap block * passed to heap_page_prune_and_freeze(). We will fix any corruption - * found in the VM. + * found in the VM and set the VM if the page is all-visible/all-frozen. */ Buffer vmbuffer; - /* Bits in the vmbuffer for this heap page */ + /* + * The state of the VM bits at the beginning of pruning and the state they + * will be in at the end. + */ uint8 old_vmbits; + uint8 new_vmbits; /* The newest xmin of live tuples on the page */ TransactionId newest_live_xid; @@ -157,21 +176,6 @@ typedef struct */ int lpdead_items; /* number of items in the array */ OffsetNumber *deadoffsets; /* points directly to presult->deadoffsets */ - - /* - * set_all_visible and set_all_frozen indicate if the all-visible and - * all-frozen bits in the visibility map can be set for this page after - * pruning. - * - * NOTE: set_all_visible and set_all_frozen initially don't include - * LP_DEAD items. That's convenient for heap_page_prune_and_freeze() to - * use them to decide whether to freeze the page or not. The - * set_all_visible and set_all_frozen values returned to the caller are - * adjusted to include LP_DEAD items after we determine whether to - * opportunistically freeze. - */ - bool set_all_visible; - bool set_all_frozen; } PruneState; /* @@ -228,6 +232,7 @@ static void page_verify_redirects(Page page); static bool heap_page_will_freeze(bool did_tuple_hint_fpi, bool do_prune, bool do_hint_prune, PruneState *prstate); +static bool heap_page_will_set_vm(PruneState *prstate, PruneReason reason); /* @@ -395,6 +400,7 @@ prune_freeze_setup(PruneFreezeParams *params, Assert(BufferIsValid(params->vmbuffer)); prstate->vmbuffer = params->vmbuffer; + prstate->new_vmbits = 0; prstate->old_vmbits = visibilitymap_get_status(prstate->relation, prstate->block, &prstate->vmbuffer); @@ -906,6 +912,42 @@ heap_page_fix_vm_corruption(PruneState *prstate, OffsetNumber offnum, } } +/* + * Decide whether to set the visibility map bits (all-visible and all-frozen) + * for heap_blk using information from the PruneState and VM. + * + * This function does not actually set the VM bits or page-level visibility + * hint, PD_ALL_VISIBLE. + * + * Returns true if one or both VM bits should be set and false otherwise. + */ +static bool +heap_page_will_set_vm(PruneState *prstate, PruneReason reason) +{ + /* + * Though on-access pruning maintains prstate->set_all_visible, we don't + * set the VM for now. + */ + if (reason == PRUNE_ON_ACCESS) + return false; + + if (!prstate->set_all_visible) + return false; + + prstate->new_vmbits = VISIBILITYMAP_ALL_VISIBLE; + + if (prstate->set_all_frozen) + prstate->new_vmbits |= VISIBILITYMAP_ALL_FROZEN; + + if (prstate->new_vmbits == prstate->old_vmbits) + { + prstate->new_vmbits = 0; + return false; + } + + return true; +} + /* * If the page is already all-frozen, or already all-visible and freezing * won't be attempted, there is no remaining work and we can use the fast path @@ -939,8 +981,6 @@ prune_freeze_fast_path(PruneState *prstate, PruneFreezeResult *presult) /* We'll fill in presult for the caller */ memset(presult, 0, sizeof(PruneFreezeResult)); - presult->old_vmbits = prstate->old_vmbits; - /* Clear any stale prune hint */ if (TransactionIdIsValid(PageGetPruneXid(page))) { @@ -975,7 +1015,8 @@ prune_freeze_fast_path(PruneState *prstate, PruneFreezeResult *presult) /* * Prune and repair fragmentation and potentially freeze tuples on the - * specified page. + * specified page. If the page's visibility status has changed, update it in + * the VM. * * Caller must have pin and buffer cleanup lock on the page. Note that we * don't update the FSM information for page on caller's behalf. Caller might @@ -990,12 +1031,10 @@ prune_freeze_fast_path(PruneState *prstate, PruneFreezeResult *presult) * tuples if it's required in order to advance relfrozenxid / relminmxid, or * if it's considered advantageous for overall system performance to do so * now. The 'params.cutoffs', 'presult', 'new_relfrozen_xid' and - * 'new_relmin_mxid' arguments are required when freezing. When - * HEAP_PAGE_PRUNE_FREEZE option is passed, we also set - * presult->set_all_visible and presult->set_all_frozen after determining - * whether or not to opportunistically freeze, to indicate if the VM bits can - * be set. 'all-frozen' is always set to false when the HEAP_PAGE_PRUNE_FREEZE - * option is not passed. + * 'new_relmin_mxid' arguments are required when freezing. + * + * A vmbuffer corresponding to the heap page is also passed and if the page is + * found to be all-visible/all-frozen, we will set it in the VM. * * presult contains output parameters needed by callers, such as the number of * tuples removed and the offsets of dead items on the page after pruning. @@ -1023,8 +1062,10 @@ heap_page_prune_and_freeze(PruneFreezeParams *params, bool do_freeze; bool do_prune; bool do_hint_prune; + bool do_set_vm; bool did_tuple_hint_fpi; int64 fpi_before = pgWalUsage.wal_fpi; + TransactionId conflict_xid; /* Initialize prstate */ prune_freeze_setup(params, @@ -1122,6 +1163,31 @@ heap_page_prune_and_freeze(PruneFreezeParams *params, prstate.set_all_visible = prstate.set_all_frozen = false; Assert(!prstate.set_all_frozen || prstate.set_all_visible); + Assert(!prstate.set_all_visible || (prstate.lpdead_items == 0)); + + do_set_vm = heap_page_will_set_vm(&prstate, params->reason); + + /* + * new_vmbits should be 0 regardless of whether or not the page is + * all-visible if we do not intend to set the VM. + */ + Assert(do_set_vm || prstate.new_vmbits == 0); + + /* + * The snapshot conflict horizon for the whole record is the most + * conservative (newest) horizon required by any change in the record. + */ + conflict_xid = InvalidTransactionId; + if (do_set_vm) + conflict_xid = prstate.newest_live_xid; + if (do_freeze && TransactionIdFollows(prstate.pagefrz.FreezePageConflictXid, conflict_xid)) + conflict_xid = prstate.pagefrz.FreezePageConflictXid; + if (do_prune && TransactionIdFollows(prstate.latest_xid_removed, conflict_xid)) + conflict_xid = prstate.latest_xid_removed; + + /* Lock vmbuffer before entering a critical section */ + if (do_set_vm) + LockBuffer(prstate.vmbuffer, BUFFER_LOCK_EXCLUSIVE); /* Any error while applying the changes is critical */ START_CRIT_SECTION(); @@ -1143,14 +1209,17 @@ heap_page_prune_and_freeze(PruneFreezeParams *params, /* * If that's all we had to do to the page, this is a non-WAL-logged - * hint. If we are going to freeze or prune the page, we will mark - * the buffer dirty below. + * hint. If we are going to freeze or prune the page or set + * PD_ALL_VISIBLE, we will mark the buffer dirty below. + * + * Setting PD_ALL_VISIBLE is fully WAL-logged because it is forbidden + * for the VM to be set and PD_ALL_VISIBLE to be clear. */ - if (!do_freeze && !do_prune) + if (!do_freeze && !do_prune && !do_set_vm) MarkBufferDirtyHint(prstate.buffer, true); } - if (do_prune || do_freeze) + if (do_prune || do_freeze || do_set_vm) { /* Apply the planned item changes and repair page fragmentation. */ if (do_prune) @@ -1164,6 +1233,27 @@ heap_page_prune_and_freeze(PruneFreezeParams *params, if (do_freeze) heap_freeze_prepared_tuples(prstate.buffer, prstate.frozen, prstate.nfrozen); + /* Set the visibility map and page visibility hint */ + if (do_set_vm) + { + /* + * While it is valid for PD_ALL_VISIBLE to be set when the + * corresponding VM bit is clear, we strongly prefer to keep them + * in sync. + * + * The heap buffer must be marked dirty before adding it to the + * WAL chain when setting the VM. We don't worry about + * unnecessarily dirtying the heap buffer if PD_ALL_VISIBLE is + * already set, though. It is extremely rare to have a clean heap + * buffer with PD_ALL_VISIBLE already set and the VM bits clear, + * so there is no point in optimizing it. + */ + PageSetAllVisible(prstate.page); + PageClearPrunable(prstate.page); + visibilitymap_set_vmbits(prstate.block, prstate.vmbuffer, prstate.new_vmbits, + prstate.relation->rd_locator); + } + MarkBufferDirty(prstate.buffer); /* @@ -1171,29 +1261,12 @@ heap_page_prune_and_freeze(PruneFreezeParams *params, */ if (RelationNeedsWAL(prstate.relation)) { - /* - * The snapshotConflictHorizon for the whole record should be the - * most conservative of all the horizons calculated for any of the - * possible modifications. If this record will prune tuples, any - * queries on the standby older than the newest xid of the most - * recently removed tuple this record will prune will conflict. If - * this record will freeze tuples, any queries on the standby with - * xids older than the newest tuple this record will freeze will - * conflict. - */ - TransactionId conflict_xid; - - if (TransactionIdFollows(prstate.pagefrz.FreezePageConflictXid, - prstate.latest_xid_removed)) - conflict_xid = prstate.pagefrz.FreezePageConflictXid; - else - conflict_xid = prstate.latest_xid_removed; - log_heap_prune_and_freeze(prstate.relation, prstate.buffer, - InvalidBuffer, /* vmbuffer */ - 0, /* vmflags */ + do_set_vm ? prstate.vmbuffer : InvalidBuffer, + do_set_vm ? prstate.new_vmbits : 0, conflict_xid, - true, params->reason, + true, /* cleanup lock */ + params->reason, prstate.frozen, prstate.nfrozen, prstate.redirected, prstate.nredirected, prstate.nowdead, prstate.ndead, @@ -1203,33 +1276,71 @@ heap_page_prune_and_freeze(PruneFreezeParams *params, END_CRIT_SECTION(); + if (do_set_vm) + LockBuffer(prstate.vmbuffer, BUFFER_LOCK_UNLOCK); + + /* + * During its second pass over the heap, VACUUM calls + * heap_page_would_be_all_visible() to determine whether a page is + * all-visible and all-frozen. The logic here is similar. After completing + * pruning and freezing, use an assertion to verify that our results + * remain consistent with heap_page_would_be_all_visible(). It's also a + * valuable cross-check of the page state after pruning and freezing. + */ +#ifdef USE_ASSERT_CHECKING + if (prstate.set_all_visible) + { + TransactionId debug_cutoff; + bool debug_all_frozen; + + Assert(prstate.lpdead_items == 0); + + Assert(heap_page_is_all_visible(prstate.relation, prstate.buffer, + prstate.vistest, + &debug_all_frozen, + &debug_cutoff, off_loc)); + + Assert(!TransactionIdIsValid(debug_cutoff) || + debug_cutoff == prstate.newest_live_xid); + + /* + * It's possible the page is composed entirely of frozen tuples but is + * not set all-frozen in the VM and did not pass + * HEAP_PAGE_PRUNE_FREEZE. In this case, it's possible + * heap_page_is_all_visible() finds the page completely frozen, even + * though prstate.set_all_frozen is false. + */ + Assert(!prstate.set_all_frozen || debug_all_frozen); + } +#endif + /* Copy information back for caller */ presult->ndeleted = prstate.ndeleted; presult->nnewlpdead = prstate.ndead; presult->nfrozen = prstate.nfrozen; presult->live_tuples = prstate.live_tuples; presult->recently_dead_tuples = prstate.recently_dead_tuples; - presult->set_all_visible = prstate.set_all_visible; - presult->set_all_frozen = prstate.set_all_frozen; presult->hastup = prstate.hastup; - presult->old_vmbits = prstate.old_vmbits; - - /* - * For callers planning to update the visibility map, the conflict horizon - * for that record must be the newest xmin on the page. However, if the - * page is completely frozen, there can be no conflict and the - * vm_conflict_horizon should remain InvalidTransactionId. This includes - * the case that we just froze all the tuples; the prune-freeze record - * included the conflict XID already so the caller doesn't need it. - */ - if (presult->set_all_frozen) - presult->vm_conflict_horizon = InvalidTransactionId; - else - presult->vm_conflict_horizon = prstate.newest_live_xid; presult->lpdead_items = prstate.lpdead_items; /* the presult->deadoffsets array was already filled in */ + presult->newly_all_visible = false; + presult->newly_all_frozen = false; + presult->newly_all_visible_frozen = false; + if (do_set_vm) + { + if ((prstate.old_vmbits & VISIBILITYMAP_ALL_VISIBLE) == 0) + { + presult->newly_all_visible = true; + if (prstate.set_all_frozen) + presult->newly_all_visible_frozen = true; + } + else if ((prstate.old_vmbits & VISIBILITYMAP_ALL_FROZEN) == 0 && + prstate.set_all_frozen) + presult->newly_all_frozen = true; + } + if (prstate.attempt_freeze) { if (presult->nfrozen > 0) diff --git a/src/backend/access/heap/vacuumlazy.c b/src/backend/access/heap/vacuumlazy.c index 696919e35dd..23deabd8c01 100644 --- a/src/backend/access/heap/vacuumlazy.c +++ b/src/backend/access/heap/vacuumlazy.c @@ -466,13 +466,6 @@ static void dead_items_add(LVRelState *vacrel, BlockNumber blkno, OffsetNumber * static void dead_items_reset(LVRelState *vacrel); static void dead_items_cleanup(LVRelState *vacrel); -#ifdef USE_ASSERT_CHECKING -static bool heap_page_is_all_visible(Relation rel, Buffer buf, - GlobalVisState *vistest, - bool *all_frozen, - TransactionId *newest_live_xid, - OffsetNumber *logging_offnum); -#endif static bool heap_page_would_be_all_visible(Relation rel, Buffer buf, GlobalVisState *vistest, bool allow_update_vistest, @@ -2022,8 +2015,6 @@ lazy_scan_prune(LVRelState *vacrel, .vistest = vacrel->vistest, .cutoffs = &vacrel->cutoffs, }; - uint8 old_vmbits = 0; - uint8 new_vmbits = 0; Assert(BufferGetBlockNumber(buf) == blkno); @@ -2074,32 +2065,6 @@ lazy_scan_prune(LVRelState *vacrel, vacrel->new_frozen_tuple_pages++; } - /* - * VACUUM will call heap_page_is_all_visible() during the second pass over - * the heap to determine all_visible and all_frozen for the page -- this - * is a specialized version of the logic from this function. Now that - * we've finished pruning and freezing, make sure that we're in total - * agreement with heap_page_is_all_visible() using an assertion. - */ -#ifdef USE_ASSERT_CHECKING - if (presult.set_all_visible) - { - TransactionId debug_cutoff; - bool debug_all_frozen; - - Assert(presult.lpdead_items == 0); - - Assert(heap_page_is_all_visible(vacrel->rel, buf, - vacrel->vistest, &debug_all_frozen, - &debug_cutoff, &vacrel->offnum)); - - Assert(presult.set_all_frozen == debug_all_frozen); - - Assert(!TransactionIdIsValid(debug_cutoff) || - debug_cutoff == presult.vm_conflict_horizon); - } -#endif - /* * Now save details of the LP_DEAD items from the page in vacrel */ @@ -2120,6 +2085,17 @@ lazy_scan_prune(LVRelState *vacrel, } /* Finally, add page-local counts to whole-VACUUM counts */ + if (presult.newly_all_visible) + vacrel->new_all_visible_pages++; + if (presult.newly_all_visible_frozen) + vacrel->new_all_visible_all_frozen_pages++; + if (presult.newly_all_frozen) + vacrel->new_all_frozen_pages++; + + /* Capture if the page was newly set frozen */ + *vm_page_frozen = presult.newly_all_visible_frozen || + presult.newly_all_frozen; + vacrel->tuples_deleted += presult.ndeleted; vacrel->tuples_frozen += presult.nfrozen; vacrel->lpdead_items += presult.lpdead_items; @@ -2133,71 +2109,6 @@ lazy_scan_prune(LVRelState *vacrel, /* Did we find LP_DEAD items? */ *has_lpdead_items = (presult.lpdead_items > 0); - Assert(!presult.set_all_visible || !(*has_lpdead_items)); - Assert(!presult.set_all_frozen || presult.set_all_visible); - - if (!presult.set_all_visible) - return presult.ndeleted; - - /* Set the visibility map and page visibility hint */ - old_vmbits = presult.old_vmbits; - new_vmbits = VISIBILITYMAP_ALL_VISIBLE; - if (presult.set_all_frozen) - new_vmbits |= VISIBILITYMAP_ALL_FROZEN; - - /* Nothing to do */ - if (old_vmbits == new_vmbits) - return presult.ndeleted; - - /* - * It should never be the case that the visibility map page is set while - * the page-level bit is clear (and if so, we cleared it above), but the - * reverse is allowed (if checksums are not enabled). Regardless, set both - * bits so that we get back in sync. - * - * The heap buffer must be marked dirty before adding it to the WAL chain - * when setting the VM. We don't worry about unnecessarily dirtying the - * heap buffer if PD_ALL_VISIBLE is already set, though. It is extremely - * rare to have a clean heap buffer with PD_ALL_VISIBLE already set and - * the VM bits clear, so there is no point in optimizing it. - */ - PageSetAllVisible(page); - PageClearPrunable(page); - MarkBufferDirty(buf); - - /* - * If the page is being set all-frozen, we pass InvalidTransactionId as - * the cutoff_xid, since a snapshot conflict horizon sufficient to make - * everything safe for REDO was logged when the page's tuples were frozen. - */ - Assert(!presult.set_all_frozen || - !TransactionIdIsValid(presult.vm_conflict_horizon)); - - visibilitymap_set(vacrel->rel, blkno, buf, - InvalidXLogRecPtr, - vmbuffer, presult.vm_conflict_horizon, - new_vmbits); - - /* - * If the page wasn't already set all-visible and/or all-frozen in the VM, - * count it as newly set for logging. - */ - if ((old_vmbits & VISIBILITYMAP_ALL_VISIBLE) == 0) - { - vacrel->new_all_visible_pages++; - if (presult.set_all_frozen) - { - vacrel->new_all_visible_all_frozen_pages++; - *vm_page_frozen = true; - } - } - else if ((old_vmbits & VISIBILITYMAP_ALL_FROZEN) == 0 && - presult.set_all_frozen) - { - vacrel->new_all_frozen_pages++; - *vm_page_frozen = true; - } - return presult.ndeleted; } @@ -3613,7 +3524,7 @@ dead_items_cleanup(LVRelState *vacrel) * that expect no LP_DEAD on the page. Currently assert-only, but there is no * reason not to use it outside of asserts. */ -static bool +bool heap_page_is_all_visible(Relation rel, Buffer buf, GlobalVisState *vistest, bool *all_frozen, diff --git a/src/include/access/heapam.h b/src/include/access/heapam.h index 8815acccafb..e123dda090f 100644 --- a/src/include/access/heapam.h +++ b/src/include/access/heapam.h @@ -265,7 +265,8 @@ typedef struct PruneFreezeParams /* * Callers should provide a pinned vmbuffer corresponding to the heap - * block in buffer. We will check for and repair any corruption in the VM. + * block in buffer. We will check for and repair any corruption in the VM + * and set the VM after pruning if the page is all-visible/all-frozen. */ Buffer vmbuffer; @@ -281,8 +282,7 @@ typedef struct PruneFreezeParams * HEAP_PAGE_PRUNE_MARK_UNUSED_NOW indicates that dead items can be set * LP_UNUSED during pruning. * - * HEAP_PAGE_PRUNE_FREEZE indicates that we will also freeze tuples, and - * will return 'all_visible', 'all_frozen' flags to the caller. + * HEAP_PAGE_PRUNE_FREEZE indicates that we will also freeze tuples. */ int options; @@ -316,26 +316,12 @@ typedef struct PruneFreezeResult int recently_dead_tuples; /* - * set_all_visible and set_all_frozen indicate if the all-visible and - * all-frozen bits in the visibility map should be set for this page after - * pruning. - * - * vm_conflict_horizon is the newest xmin of live tuples on the page. The - * caller can use it as the conflict horizon when setting the VM bits. It - * is only valid if we froze some tuples (nfrozen > 0), and set_all_frozen - * is true. - * - * These are only set if the HEAP_PAGE_PRUNE_FREEZE option is set. - */ - bool set_all_visible; - bool set_all_frozen; - TransactionId vm_conflict_horizon; - - /* - * The value of the vmbuffer's vmbits at the beginning of pruning. It is - * cleared if VM corruption is found and corrected. + * Whether or not the page was newly set all-visible and all-frozen during + * phase I of vacuuming. */ - uint8 old_vmbits; + bool newly_all_visible; + bool newly_all_visible_frozen; + bool newly_all_frozen; /* * Whether or not the page makes rel truncation unsafe. This is set to @@ -472,6 +458,13 @@ extern void log_heap_prune_and_freeze(Relation relation, Buffer buffer, /* in heap/vacuumlazy.c */ extern void heap_vacuum_rel(Relation rel, const VacuumParams params, BufferAccessStrategy bstrategy); +#ifdef USE_ASSERT_CHECKING +extern bool heap_page_is_all_visible(Relation rel, Buffer buf, + GlobalVisState *vistest, + bool *all_frozen, + TransactionId *visibility_cutoff_xid, + OffsetNumber *logging_offnum); +#endif /* in heap/heapam_visibility.c */ extern bool HeapTupleSatisfiesVisibility(HeapTuple htup, Snapshot snapshot, -- 2.43.0