From cca60a5e487090252dddd515c716272786841c5e Mon Sep 17 00:00:00 2001 From: Maxim Orlov Date: Wed, 6 Mar 2024 11:11:33 +0300 Subject: [PATCH v4 2/4] Use 64-bit multixact offsets. Author: Maxim Orlov --- src/backend/access/transam/multixact.c | 172 +------------------------ src/bin/pg_resetwal/pg_resetwal.c | 2 +- src/bin/pg_resetwal/t/001_basic.pl | 2 +- src/include/access/multixact.h | 2 +- src/include/c.h | 2 +- 5 files changed, 11 insertions(+), 169 deletions(-) diff --git a/src/backend/access/transam/multixact.c b/src/backend/access/transam/multixact.c index ab90912ed3..c51e03e832 100644 --- a/src/backend/access/transam/multixact.c +++ b/src/backend/access/transam/multixact.c @@ -96,14 +96,6 @@ /* * Defines for MultiXactOffset page sizes. A page is the same BLCKSZ as is * used everywhere else in Postgres. - * - * Note: because MultiXactOffsets are 32 bits and wrap around at 0xFFFFFFFF, - * MultiXact page numbering also wraps around at - * 0xFFFFFFFF/MULTIXACT_OFFSETS_PER_PAGE, and segment numbering at - * 0xFFFFFFFF/MULTIXACT_OFFSETS_PER_PAGE/SLRU_PAGES_PER_SEGMENT. We need - * take no explicit notice of that fact in this module, except when comparing - * segment and page numbers in TruncateMultiXact (see - * MultiXactOffsetPagePrecedes). */ /* We need four bytes per offset */ @@ -272,9 +264,6 @@ typedef struct MultiXactStateData MultiXactId multiStopLimit; MultiXactId multiWrapLimit; - /* support for members anti-wraparound measures */ - MultiXactOffset offsetStopLimit; /* known if oldestOffsetKnown */ - /* * This is used to sleep until a multixact offset is written when we want * to create the next one. @@ -409,8 +398,6 @@ static bool MultiXactOffsetPrecedes(MultiXactOffset offset1, MultiXactOffset offset2); static void ExtendMultiXactOffset(MultiXactId multi); static void ExtendMultiXactMember(MultiXactOffset offset, int nmembers); -static bool MultiXactOffsetWouldWrap(MultiXactOffset boundary, - MultiXactOffset start, uint32 distance); static bool SetOffsetVacuumLimit(bool is_startup); static bool find_multixact_start(MultiXactId multi, MultiXactOffset *result); static void WriteMZeroPageXlogRec(int64 pageno, uint8 info); @@ -1164,78 +1151,6 @@ GetNewMultiXactId(int nmembers, MultiXactOffset *offset) else *offset = nextOffset; - /*---------- - * Protect against overrun of the members space as well, with the - * following rules: - * - * If we're past offsetStopLimit, refuse to generate more multis. - * If we're close to offsetStopLimit, emit a warning. - * - * Arbitrarily, we start emitting warnings when we're 20 segments or less - * from offsetStopLimit. - * - * Note we haven't updated the shared state yet, so if we fail at this - * point, the multixact ID we grabbed can still be used by the next guy. - * - * Note that there is no point in forcing autovacuum runs here: the - * multixact freeze settings would have to be reduced for that to have any - * effect. - *---------- - */ -#define OFFSET_WARN_SEGMENTS 20 - if (MultiXactState->oldestOffsetKnown && - MultiXactOffsetWouldWrap(MultiXactState->offsetStopLimit, nextOffset, - nmembers)) - { - /* see comment in the corresponding offsets wraparound case */ - SendPostmasterSignal(PMSIGNAL_START_AUTOVAC_LAUNCHER); - - ereport(ERROR, - (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED), - errmsg("multixact \"members\" limit exceeded"), - errdetail_plural("This command would create a multixact with %u members, but the remaining space is only enough for %u member.", - "This command would create a multixact with %u members, but the remaining space is only enough for %u members.", - MultiXactState->offsetStopLimit - nextOffset - 1, - nmembers, - MultiXactState->offsetStopLimit - nextOffset - 1), - errhint("Execute a database-wide VACUUM in database with OID %u with reduced \"vacuum_multixact_freeze_min_age\" and \"vacuum_multixact_freeze_table_age\" settings.", - MultiXactState->oldestMultiXactDB))); - } - - /* - * Check whether we should kick autovacuum into action, to prevent members - * wraparound. NB we use a much larger window to trigger autovacuum than - * just the warning limit. The warning is just a measure of last resort - - * this is in line with GetNewTransactionId's behaviour. - */ - if (!MultiXactState->oldestOffsetKnown || - (MultiXactState->nextOffset - MultiXactState->oldestOffset - > MULTIXACT_MEMBER_SAFE_THRESHOLD)) - { - /* - * To avoid swamping the postmaster with signals, we issue the autovac - * request only when crossing a segment boundary. With default - * compilation settings that's roughly after 50k members. This still - * gives plenty of chances before we get into real trouble. - */ - if ((MXOffsetToMemberPage(nextOffset) / SLRU_PAGES_PER_SEGMENT) != - (MXOffsetToMemberPage(nextOffset + nmembers) / SLRU_PAGES_PER_SEGMENT)) - SendPostmasterSignal(PMSIGNAL_START_AUTOVAC_LAUNCHER); - } - - if (MultiXactState->oldestOffsetKnown && - MultiXactOffsetWouldWrap(MultiXactState->offsetStopLimit, - nextOffset, - nmembers + MULTIXACT_MEMBERS_PER_PAGE * SLRU_PAGES_PER_SEGMENT * OFFSET_WARN_SEGMENTS)) - ereport(WARNING, - (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED), - errmsg_plural("database with OID %u must be vacuumed before %d more multixact member is used", - "database with OID %u must be vacuumed before %d more multixact members are used", - MultiXactState->offsetStopLimit - nextOffset + nmembers, - MultiXactState->oldestMultiXactDB, - MultiXactState->offsetStopLimit - nextOffset + nmembers), - errhint("Execute a database-wide VACUUM in that database with reduced \"vacuum_multixact_freeze_min_age\" and \"vacuum_multixact_freeze_table_age\" settings."))); - ExtendMultiXactMember(nextOffset, nmembers); /* @@ -1976,7 +1891,7 @@ MultiXactShmemInit(void) "pg_multixact/offsets", LWTRANCHE_MULTIXACTOFFSET_BUFFER, LWTRANCHE_MULTIXACTOFFSET_SLRU, SYNC_HANDLER_MULTIXACT_OFFSET, - false); + true); SlruPagePrecedesUnitTests(MultiXactOffsetCtl, MULTIXACT_OFFSETS_PER_PAGE); SimpleLruInit(MultiXactMemberCtl, "multixact_member", multixact_member_buffers, 0, @@ -2721,8 +2636,6 @@ SetOffsetVacuumLimit(bool is_startup) MultiXactOffset nextOffset; bool oldestOffsetKnown = false; bool prevOldestOffsetKnown; - MultiXactOffset offsetStopLimit = 0; - MultiXactOffset prevOffsetStopLimit; /* * NB: Have to prevent concurrent truncation, we might otherwise try to @@ -2737,7 +2650,6 @@ SetOffsetVacuumLimit(bool is_startup) nextOffset = MultiXactState->nextOffset; prevOldestOffsetKnown = MultiXactState->oldestOffsetKnown; prevOldestOffset = MultiXactState->oldestOffset; - prevOffsetStopLimit = MultiXactState->offsetStopLimit; Assert(MultiXactState->finishedStartup); LWLockRelease(MultiXactGenLock); @@ -2768,11 +2680,7 @@ SetOffsetVacuumLimit(bool is_startup) oldestOffsetKnown = find_multixact_start(oldestMultiXactId, &oldestOffset); - if (oldestOffsetKnown) - ereport(DEBUG1, - (errmsg_internal("oldest MultiXactId member is at offset %u", - oldestOffset))); - else + if (!oldestOffsetKnown) ereport(LOG, (errmsg("MultiXact member wraparound protections are disabled because oldest checkpointed MultiXact %u does not exist on disk", oldestMultiXactId))); @@ -2785,24 +2693,7 @@ SetOffsetVacuumLimit(bool is_startup) * overrun of old data in the members SLRU area. We can only do so if the * oldest offset is known though. */ - if (oldestOffsetKnown) - { - /* move back to start of the corresponding segment */ - offsetStopLimit = oldestOffset - (oldestOffset % - (MULTIXACT_MEMBERS_PER_PAGE * SLRU_PAGES_PER_SEGMENT)); - - /* always leave one segment before the wraparound point */ - offsetStopLimit -= (MULTIXACT_MEMBERS_PER_PAGE * SLRU_PAGES_PER_SEGMENT); - - if (!prevOldestOffsetKnown && !is_startup) - ereport(LOG, - (errmsg("MultiXact member wraparound protections are now enabled"))); - - ereport(DEBUG1, - (errmsg_internal("MultiXact member stop limit is now %u based on MultiXact %u", - offsetStopLimit, oldestMultiXactId))); - } - else if (prevOldestOffsetKnown) + if (prevOldestOffsetKnown) { /* * If we failed to get the oldest offset this time, but we have a @@ -2812,14 +2703,12 @@ SetOffsetVacuumLimit(bool is_startup) */ oldestOffset = prevOldestOffset; oldestOffsetKnown = true; - offsetStopLimit = prevOffsetStopLimit; } /* Install the computed values */ LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE); MultiXactState->oldestOffset = oldestOffset; MultiXactState->oldestOffsetKnown = oldestOffsetKnown; - MultiXactState->offsetStopLimit = offsetStopLimit; LWLockRelease(MultiXactGenLock); /* @@ -2829,54 +2718,6 @@ SetOffsetVacuumLimit(bool is_startup) (nextOffset - oldestOffset > MULTIXACT_MEMBER_SAFE_THRESHOLD); } -/* - * Return whether adding "distance" to "start" would move past "boundary". - * - * We use this to determine whether the addition is "wrapping around" the - * boundary point, hence the name. The reason we don't want to use the regular - * 2^31-modulo arithmetic here is that we want to be able to use the whole of - * the 2^32-1 space here, allowing for more multixacts than would fit - * otherwise. - */ -static bool -MultiXactOffsetWouldWrap(MultiXactOffset boundary, MultiXactOffset start, - uint32 distance) -{ - MultiXactOffset finish; - - /* - * Note that offset number 0 is not used (see GetMultiXactIdMembers), so - * if the addition wraps around the UINT_MAX boundary, skip that value. - */ - finish = start + distance; - if (finish < start) - finish++; - - /*----------------------------------------------------------------------- - * When the boundary is numerically greater than the starting point, any - * value numerically between the two is not wrapped: - * - * <----S----B----> - * [---) = F wrapped past B (and UINT_MAX) - * [---) = F not wrapped - * [----] = F wrapped past B - * - * When the boundary is numerically less than the starting point (i.e. the - * UINT_MAX wraparound occurs somewhere in between) then all values in - * between are wrapped: - * - * <----B----S----> - * [---) = F not wrapped past B (but wrapped past UINT_MAX) - * [---) = F wrapped past B (and UINT_MAX) - * [----] = F not wrapped - *----------------------------------------------------------------------- - */ - if (start < boundary) - return finish >= boundary || finish < start; - else - return finish >= boundary && finish < start; -} - /* * Find the starting offset of the given MultiXactId. * @@ -2998,8 +2839,9 @@ MultiXactMemberFreezeThreshold(void) * we try to eliminate from the system is based on how far we are past * MULTIXACT_MEMBER_SAFE_THRESHOLD. */ - fraction = (double) (members - MULTIXACT_MEMBER_SAFE_THRESHOLD) / - (MULTIXACT_MEMBER_DANGER_THRESHOLD - MULTIXACT_MEMBER_SAFE_THRESHOLD); + fraction = (double) (members - MULTIXACT_MEMBER_SAFE_THRESHOLD); + fraction /= (double) (MULTIXACT_MEMBER_DANGER_THRESHOLD - MULTIXACT_MEMBER_SAFE_THRESHOLD); + victim_multixacts = multixacts * fraction; /* fraction could be > 1.0, but lowest possible freeze age is zero */ @@ -3345,7 +3187,7 @@ MultiXactIdPrecedesOrEquals(MultiXactId multi1, MultiXactId multi2) static bool MultiXactOffsetPrecedes(MultiXactOffset offset1, MultiXactOffset offset2) { - int32 diff = (int32) (offset1 - offset2); + int64 diff = (int64) (offset1 - offset2); return (diff < 0); } diff --git a/src/bin/pg_resetwal/pg_resetwal.c b/src/bin/pg_resetwal/pg_resetwal.c index 985cd06802..1af2ce4b93 100644 --- a/src/bin/pg_resetwal/pg_resetwal.c +++ b/src/bin/pg_resetwal/pg_resetwal.c @@ -264,7 +264,7 @@ main(int argc, char *argv[]) case 'O': errno = 0; - set_mxoff = strtoul(optarg, &endptr, 0); + set_mxoff = strtou64(optarg, &endptr, 0); if (endptr == optarg || *endptr != '\0' || errno != 0) { pg_log_error("invalid argument for option %s", "-O"); diff --git a/src/bin/pg_resetwal/t/001_basic.pl b/src/bin/pg_resetwal/t/001_basic.pl index 9829e48106..f8a8eef44d 100644 --- a/src/bin/pg_resetwal/t/001_basic.pl +++ b/src/bin/pg_resetwal/t/001_basic.pl @@ -206,7 +206,7 @@ push @cmd, sprintf("%d,%d", hex($files[0]) == 0 ? 3 : hex($files[0]), hex($files[-1])); @files = get_slru_files('pg_multixact/offsets'); -$mult = 32 * $blcksz / 4; +$mult = 32 * $blcksz / 8; # -m argument is "new,old" push @cmd, '-m', sprintf("%d,%d", diff --git a/src/include/access/multixact.h b/src/include/access/multixact.h index 7ffd256c74..90583634ec 100644 --- a/src/include/access/multixact.h +++ b/src/include/access/multixact.h @@ -27,7 +27,7 @@ #define MultiXactIdIsValid(multi) ((multi) != InvalidMultiXactId) -#define MaxMultiXactOffset ((MultiXactOffset) 0xFFFFFFFF) +#define MaxMultiXactOffset UINT64CONST(0xFFFFFFFFFFFFFFFF) /* * Possible multixact lock modes ("status"). The first four modes are for diff --git a/src/include/c.h b/src/include/c.h index 55dec71a6d..556fffa333 100644 --- a/src/include/c.h +++ b/src/include/c.h @@ -652,7 +652,7 @@ typedef uint32 SubTransactionId; /* MultiXactId must be equivalent to TransactionId, to fit in t_xmax */ typedef TransactionId MultiXactId; -typedef uint32 MultiXactOffset; +typedef uint64 MultiXactOffset; typedef uint32 CommandId; -- 2.43.0