From b35b0aa849a16a9f71ba615c8134fe74db37d088 Mon Sep 17 00:00:00 2001 From: Heikki Linnakangas Date: Wed, 18 Dec 2024 11:57:06 +0200 Subject: [PATCH v10 06/14] Remove some dead code related to handling members wraparound Now that offsets are 64-bit, we assume members never wrap around. Start the offset counter from 1 so that we don't need the special case for starting from 0. --- src/backend/access/transam/multixact.c | 42 +++----------------------- src/backend/access/transam/xlog.c | 2 +- 2 files changed, 5 insertions(+), 39 deletions(-) diff --git a/src/backend/access/transam/multixact.c b/src/backend/access/transam/multixact.c index 3d27995a299..737154814a8 100644 --- a/src/backend/access/transam/multixact.c +++ b/src/backend/access/transam/multixact.c @@ -147,19 +147,6 @@ MultiXactIdToOffsetSegment(MultiXactId multi) #define MULTIXACT_MEMBERS_PER_PAGE \ (MULTIXACT_MEMBERGROUPS_PER_PAGE * MULTIXACT_MEMBERS_PER_MEMBERGROUP) -/* - * Because the number of items per page is not a divisor of the last item - * number (member 0xFFFFFFFF), the last segment does not use the maximum number - * of pages, and moreover the last used page therein does not use the same - * number of items as previous pages. (Another way to say it is that the - * 0xFFFFFFFF member is somewhere in the middle of the last page, so the page - * has some empty space after that item.) - * - * This constant is the number of members in the last page of the last segment. - */ -#define MAX_MEMBERS_IN_LAST_MEMBERS_PAGE \ - ((uint32) ((0xFFFFFFFF % MULTIXACT_MEMBERS_PER_PAGE) + 1)) - /* page in which a member is to be found */ static inline int64 MXOffsetToMemberPage(MultiXactOffset offset) @@ -1140,18 +1127,10 @@ GetNewMultiXactId(int nmembers, MultiXactOffset *offset) ExtendMultiXactOffset(result); /* - * Reserve the members space, similarly to above. Also, be careful not to - * return zero as the starting offset for any multixact. See - * GetMultiXactIdMembers() for motivation. + * Reserve the members space, similarly to above. */ nextOffset = MultiXactState->nextOffset; - if (nextOffset == 0) - { - *offset = 1; - nmembers++; /* allocate member slot 0 too */ - } - else - *offset = nextOffset; + *offset = nextOffset; ExtendMultiXactMember(nextOffset, nmembers); @@ -2537,22 +2516,9 @@ ExtendMultiXactMember(MultiXactOffset offset, int nmembers) } /* - * Compute the number of items till end of current page. Careful: if - * addition of unsigned ints wraps around, we're at the last page of - * the last segment; since that page holds a different number of items - * than other pages, we need to do it differently. + * Compute the number of items till end of current page. */ - if (offset + MAX_MEMBERS_IN_LAST_MEMBERS_PAGE < offset) - { - /* - * This is the last page of the last segment; we can compute the - * number of items left to allocate in it without modulo - * arithmetic. - */ - difference = MaxMultiXactOffset - offset + 1; - } - else - difference = MULTIXACT_MEMBERS_PER_PAGE - offset % MULTIXACT_MEMBERS_PER_PAGE; + difference = MULTIXACT_MEMBERS_PER_PAGE - offset % MULTIXACT_MEMBERS_PER_PAGE; /* * Advance to next page, taking care to properly handle the wraparound diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index 6f58412bcab..067cb70938a 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -5083,7 +5083,7 @@ BootStrapXLOG(uint32 data_checksum_version) FullTransactionIdFromEpochAndXid(0, FirstNormalTransactionId); checkPoint.nextOid = FirstGenbkiObjectId; checkPoint.nextMulti = FirstMultiXactId; - checkPoint.nextMultiOffset = 0; + checkPoint.nextMultiOffset = 1; checkPoint.oldestXid = FirstNormalTransactionId; checkPoint.oldestXidDB = Template1DbOid; checkPoint.oldestMulti = FirstMultiXactId; -- 2.39.5