From: Heikki Linnakangas Date: Tue, 9 Dec 2025 11:45:01 +0000 (+0200) Subject: Move pg_multixact SLRU page format definitions to a separate header X-Git-Url: http://git.postgresql.org/gitweb/static/gitweb.js?a=commitdiff_plain;h=bb3b1c4f64620ca05d86a20a26c8fa4ca1cf7b78;p=postgresql.git Move pg_multixact SLRU page format definitions to a separate header This makes them accessible from pg_upgrade, needed by the next commit. I'm doing this mechanical move as a separate commit to make the next commit's changes to these definitions more obvious. Author: Maxim Orlov Discussion: https://www.postgresql.org/message-id/CACG%3DezbZo_3_fnx%3DS5BfepwRftzrpJ%2B7WET4EkTU6wnjDTsnjg@mail.gmail.com --- diff --git a/src/backend/access/transam/multixact.c b/src/backend/access/transam/multixact.c index 8ed3fd9d071..14d46fb761b 100644 --- a/src/backend/access/transam/multixact.c +++ b/src/backend/access/transam/multixact.c @@ -69,6 +69,7 @@ #include "postgres.h" #include "access/multixact.h" +#include "access/multixact_internal.h" #include "access/slru.h" #include "access/twophase.h" #include "access/twophase_rmgr.h" @@ -88,125 +89,6 @@ #include "utils/memutils.h" -/* - * 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 */ -#define MULTIXACT_OFFSETS_PER_PAGE (BLCKSZ / sizeof(MultiXactOffset)) - -static inline int64 -MultiXactIdToOffsetPage(MultiXactId multi) -{ - return multi / MULTIXACT_OFFSETS_PER_PAGE; -} - -static inline int -MultiXactIdToOffsetEntry(MultiXactId multi) -{ - return multi % MULTIXACT_OFFSETS_PER_PAGE; -} - -static inline int64 -MultiXactIdToOffsetSegment(MultiXactId multi) -{ - return MultiXactIdToOffsetPage(multi) / SLRU_PAGES_PER_SEGMENT; -} - -/* - * The situation for members is a bit more complex: we store one byte of - * additional flag bits for each TransactionId. To do this without getting - * into alignment issues, we store four bytes of flags, and then the - * corresponding 4 Xids. Each such 5-word (20-byte) set we call a "group", and - * are stored as a whole in pages. Thus, with 8kB BLCKSZ, we keep 409 groups - * per page. This wastes 12 bytes per page, but that's OK -- simplicity (and - * performance) trumps space efficiency here. - * - * Note that the "offset" macros work with byte offset, not array indexes, so - * arithmetic must be done using "char *" pointers. - */ -/* We need eight bits per xact, so one xact fits in a byte */ -#define MXACT_MEMBER_BITS_PER_XACT 8 -#define MXACT_MEMBER_FLAGS_PER_BYTE 1 -#define MXACT_MEMBER_XACT_BITMASK ((1 << MXACT_MEMBER_BITS_PER_XACT) - 1) - -/* how many full bytes of flags are there in a group? */ -#define MULTIXACT_FLAGBYTES_PER_GROUP 4 -#define MULTIXACT_MEMBERS_PER_MEMBERGROUP \ - (MULTIXACT_FLAGBYTES_PER_GROUP * MXACT_MEMBER_FLAGS_PER_BYTE) -/* size in bytes of a complete group */ -#define MULTIXACT_MEMBERGROUP_SIZE \ - (sizeof(TransactionId) * MULTIXACT_MEMBERS_PER_MEMBERGROUP + MULTIXACT_FLAGBYTES_PER_GROUP) -#define MULTIXACT_MEMBERGROUPS_PER_PAGE (BLCKSZ / MULTIXACT_MEMBERGROUP_SIZE) -#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) -{ - return offset / MULTIXACT_MEMBERS_PER_PAGE; -} - -static inline int64 -MXOffsetToMemberSegment(MultiXactOffset offset) -{ - return MXOffsetToMemberPage(offset) / SLRU_PAGES_PER_SEGMENT; -} - -/* Location (byte offset within page) of flag word for a given member */ -static inline int -MXOffsetToFlagsOffset(MultiXactOffset offset) -{ - MultiXactOffset group = offset / MULTIXACT_MEMBERS_PER_MEMBERGROUP; - int grouponpg = group % MULTIXACT_MEMBERGROUPS_PER_PAGE; - int byteoff = grouponpg * MULTIXACT_MEMBERGROUP_SIZE; - - return byteoff; -} - -static inline int -MXOffsetToFlagsBitShift(MultiXactOffset offset) -{ - int member_in_group = offset % MULTIXACT_MEMBERS_PER_MEMBERGROUP; - int bshift = member_in_group * MXACT_MEMBER_BITS_PER_XACT; - - return bshift; -} - -/* Location (byte offset within page) of TransactionId of given member */ -static inline int -MXOffsetToMemberOffset(MultiXactOffset offset) -{ - int member_in_group = offset % MULTIXACT_MEMBERS_PER_MEMBERGROUP; - - return MXOffsetToFlagsOffset(offset) + - MULTIXACT_FLAGBYTES_PER_GROUP + - member_in_group * sizeof(TransactionId); -} - /* Multixact members wraparound thresholds. */ #define MULTIXACT_MEMBER_SAFE_THRESHOLD (MaxMultiXactOffset / 2) #define MULTIXACT_MEMBER_DANGER_THRESHOLD \ diff --git a/src/include/access/multixact_internal.h b/src/include/access/multixact_internal.h new file mode 100644 index 00000000000..f711f0a81eb --- /dev/null +++ b/src/include/access/multixact_internal.h @@ -0,0 +1,140 @@ +/* + * multixact_internal.h + * + * PostgreSQL multi-transaction-log manager internal declarations + * + * These functions and definitions are for dealing with pg_multixact SLRU + * pages. They are internal to multixact.c, but they are exported here to + * allow pg_upgrade to write pg_multixact files directly. + * + * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group + * Portions Copyright (c) 1994, Regents of the University of California + * + * src/include/access/multixact_internal.h + */ +#ifndef MULTIXACT_INTERNAL_H +#define MULTIXACT_INTERNAL_H + +#include "access/multixact.h" + + +/* + * 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 */ +#define MULTIXACT_OFFSETS_PER_PAGE (BLCKSZ / sizeof(MultiXactOffset)) + +static inline int64 +MultiXactIdToOffsetPage(MultiXactId multi) +{ + return multi / MULTIXACT_OFFSETS_PER_PAGE; +} + +static inline int +MultiXactIdToOffsetEntry(MultiXactId multi) +{ + return multi % MULTIXACT_OFFSETS_PER_PAGE; +} + +static inline int64 +MultiXactIdToOffsetSegment(MultiXactId multi) +{ + return MultiXactIdToOffsetPage(multi) / SLRU_PAGES_PER_SEGMENT; +} + +/* + * The situation for members is a bit more complex: we store one byte of + * additional flag bits for each TransactionId. To do this without getting + * into alignment issues, we store four bytes of flags, and then the + * corresponding 4 Xids. Each such 5-word (20-byte) set we call a "group", and + * are stored as a whole in pages. Thus, with 8kB BLCKSZ, we keep 409 groups + * per page. This wastes 12 bytes per page, but that's OK -- simplicity (and + * performance) trumps space efficiency here. + * + * Note that the "offset" macros work with byte offset, not array indexes, so + * arithmetic must be done using "char *" pointers. + */ +/* We need eight bits per xact, so one xact fits in a byte */ +#define MXACT_MEMBER_BITS_PER_XACT 8 +#define MXACT_MEMBER_FLAGS_PER_BYTE 1 +#define MXACT_MEMBER_XACT_BITMASK ((1 << MXACT_MEMBER_BITS_PER_XACT) - 1) + +/* how many full bytes of flags are there in a group? */ +#define MULTIXACT_FLAGBYTES_PER_GROUP 4 +#define MULTIXACT_MEMBERS_PER_MEMBERGROUP \ + (MULTIXACT_FLAGBYTES_PER_GROUP * MXACT_MEMBER_FLAGS_PER_BYTE) +/* size in bytes of a complete group */ +#define MULTIXACT_MEMBERGROUP_SIZE \ + (sizeof(TransactionId) * MULTIXACT_MEMBERS_PER_MEMBERGROUP + MULTIXACT_FLAGBYTES_PER_GROUP) +#define MULTIXACT_MEMBERGROUPS_PER_PAGE (BLCKSZ / MULTIXACT_MEMBERGROUP_SIZE) +#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) +{ + return offset / MULTIXACT_MEMBERS_PER_PAGE; +} + +static inline int64 +MXOffsetToMemberSegment(MultiXactOffset offset) +{ + return MXOffsetToMemberPage(offset) / SLRU_PAGES_PER_SEGMENT; +} + +/* Location (byte offset within page) of flag word for a given member */ +static inline int +MXOffsetToFlagsOffset(MultiXactOffset offset) +{ + MultiXactOffset group = offset / MULTIXACT_MEMBERS_PER_MEMBERGROUP; + int grouponpg = group % MULTIXACT_MEMBERGROUPS_PER_PAGE; + int byteoff = grouponpg * MULTIXACT_MEMBERGROUP_SIZE; + + return byteoff; +} + +static inline int +MXOffsetToFlagsBitShift(MultiXactOffset offset) +{ + int member_in_group = offset % MULTIXACT_MEMBERS_PER_MEMBERGROUP; + int bshift = member_in_group * MXACT_MEMBER_BITS_PER_XACT; + + return bshift; +} + +/* Location (byte offset within page) of TransactionId of given member */ +static inline int +MXOffsetToMemberOffset(MultiXactOffset offset) +{ + int member_in_group = offset % MULTIXACT_MEMBERS_PER_MEMBERGROUP; + + return MXOffsetToFlagsOffset(offset) + + MULTIXACT_FLAGBYTES_PER_GROUP + + member_in_group * sizeof(TransactionId); +} + +#endif /* MULTIXACT_INTERNAL_H */