Age Owner TLA Line data Source code
1 : /*
2 : * multixact_internal.h
3 : *
4 : * PostgreSQL multi-transaction-log manager internal declarations
5 : *
6 : * These functions and definitions are for dealing with pg_multixact SLRU
7 : * pages. They are internal to multixact.c, but they are exported here to
8 : * allow pg_upgrade to write pg_multixact files directly.
9 : *
10 : * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
11 : * Portions Copyright (c) 1994, Regents of the University of California
12 : *
13 : * src/include/access/multixact_internal.h
14 : */
15 : #ifndef MULTIXACT_INTERNAL_H
16 :
17 : /*
18 : * Note: This is not only to prevent including this file twice.
19 : * MULTIXACT_INTERNAL_H is checked explicitly in multixact_read_v18.c.
20 : */
21 : #define MULTIXACT_INTERNAL_H
22 :
23 : #include "access/multixact.h"
24 :
25 :
26 : /*
27 : * Defines for MultiXactOffset page sizes. A page is the same BLCKSZ as is
28 : * used everywhere else in Postgres.
29 : */
30 :
31 : /* We need 8 bytes per offset */
32 : #define MULTIXACT_OFFSETS_PER_PAGE (BLCKSZ / sizeof(MultiXactOffset))
33 :
34 : static inline int64
7 heikki.linnakangas@i 35 GNC 195899 : MultiXactIdToOffsetPage(MultiXactId multi)
36 : {
37 195899 : return multi / MULTIXACT_OFFSETS_PER_PAGE;
38 : }
39 :
40 : static inline int
41 200267 : MultiXactIdToOffsetEntry(MultiXactId multi)
42 : {
43 200267 : return multi % MULTIXACT_OFFSETS_PER_PAGE;
44 : }
45 :
46 : static inline int64
7 heikki.linnakangas@i 47 UNC 0 : MultiXactIdToOffsetSegment(MultiXactId multi)
48 : {
49 0 : return MultiXactIdToOffsetPage(multi) / SLRU_PAGES_PER_SEGMENT;
50 : }
51 :
52 : /*
53 : * The situation for members is a bit more complex: we store one byte of
54 : * additional flag bits for each TransactionId. To do this without getting
55 : * into alignment issues, we store four bytes of flags, and then the
56 : * corresponding 4 Xids. Each such 5-word (20-byte) set we call a "group", and
57 : * are stored as a whole in pages. Thus, with 8kB BLCKSZ, we keep 409 groups
58 : * per page. This wastes 12 bytes per page, but that's OK -- simplicity (and
59 : * performance) trumps space efficiency here.
60 : *
61 : * Note that the "offset" macros work with byte offset, not array indexes, so
62 : * arithmetic must be done using "char *" pointers.
63 : */
64 : /* We need eight bits per xact, so one xact fits in a byte */
65 : #define MXACT_MEMBER_BITS_PER_XACT 8
66 : #define MXACT_MEMBER_FLAGS_PER_BYTE 1
67 : #define MXACT_MEMBER_XACT_BITMASK ((1 << MXACT_MEMBER_BITS_PER_XACT) - 1)
68 :
69 : /* how many full bytes of flags are there in a group? */
70 : #define MULTIXACT_FLAGBYTES_PER_GROUP 4
71 : #define MULTIXACT_MEMBERS_PER_MEMBERGROUP \
72 : (MULTIXACT_FLAGBYTES_PER_GROUP * MXACT_MEMBER_FLAGS_PER_BYTE)
73 : /* size in bytes of a complete group */
74 : #define MULTIXACT_MEMBERGROUP_SIZE \
75 : (sizeof(TransactionId) * MULTIXACT_MEMBERS_PER_MEMBERGROUP + MULTIXACT_FLAGBYTES_PER_GROUP)
76 : #define MULTIXACT_MEMBERGROUPS_PER_PAGE (BLCKSZ / MULTIXACT_MEMBERGROUP_SIZE)
77 : #define MULTIXACT_MEMBERS_PER_PAGE \
78 : (MULTIXACT_MEMBERGROUPS_PER_PAGE * MULTIXACT_MEMBERS_PER_MEMBERGROUP)
79 :
80 : /* page in which a member is to be found */
81 : static inline int64
7 heikki.linnakangas@i 82 GNC 1832752 : MXOffsetToMemberPage(MultiXactOffset offset)
83 : {
84 1832752 : return offset / MULTIXACT_MEMBERS_PER_PAGE;
85 : }
86 :
87 : static inline int64
7 heikki.linnakangas@i 88 UNC 0 : MXOffsetToMemberSegment(MultiXactOffset offset)
89 : {
90 0 : return MXOffsetToMemberPage(offset) / SLRU_PAGES_PER_SEGMENT;
91 : }
92 :
93 : /* Location (byte offset within page) of flag word for a given member */
94 : static inline int
7 heikki.linnakangas@i 95 GNC 3668038 : MXOffsetToFlagsOffset(MultiXactOffset offset)
96 : {
97 3668038 : MultiXactOffset group = offset / MULTIXACT_MEMBERS_PER_MEMBERGROUP;
98 3668038 : int grouponpg = group % MULTIXACT_MEMBERGROUPS_PER_PAGE;
99 3668038 : int byteoff = grouponpg * MULTIXACT_MEMBERGROUP_SIZE;
100 :
101 3668038 : return byteoff;
102 : }
103 :
104 : static inline int
105 1836252 : MXOffsetToFlagsBitShift(MultiXactOffset offset)
106 : {
107 1836252 : int member_in_group = offset % MULTIXACT_MEMBERS_PER_MEMBERGROUP;
108 1836252 : int bshift = member_in_group * MXACT_MEMBER_BITS_PER_XACT;
109 :
110 1836252 : return bshift;
111 : }
112 :
113 : /* Location (byte offset within page) of TransactionId of given member */
114 : static inline int
115 1830916 : MXOffsetToMemberOffset(MultiXactOffset offset)
116 : {
117 1830916 : int member_in_group = offset % MULTIXACT_MEMBERS_PER_MEMBERGROUP;
118 :
119 1830916 : return MXOffsetToFlagsOffset(offset) +
120 1830916 : MULTIXACT_FLAGBYTES_PER_GROUP +
121 : member_in_group * sizeof(TransactionId);
122 : }
123 :
124 : #endif /* MULTIXACT_INTERNAL_H */
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