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Move pg_multixact SLRU page format definitions to a separate header

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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 <orlovmg@gmail.com>
Discussion: https://www.postgresql.org/message-id/CACG%3DezbZo_3_fnx%3DS5BfepwRftzrpJ%2B7WET4EkTU6wnjDTsnjg@mail.gmail.com
pull/256/head
Heikki Linnakangas 1 week ago
parent e9443a5526
commit bb3b1c4f64
2 changed files with 141 additions and 119 deletions
Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL
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  1. 120
      src/backend/access/transam/multixact.c
  2. 140
      src/include/access/multixact_internal.h

120
src/backend/access/transam/multixact.c
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@ -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 \

140
src/include/access/multixact_internal.h
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@ -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 */
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