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1 : /*-------------------------------------------------------------------------
2 : *
3 : * transam.h
4 : * postgres transaction access method support code
5 : *
6 : *
7 : * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
8 : * Portions Copyright (c) 1994, Regents of the University of California
9 : *
10 : * src/include/access/transam.h
11 : *
12 : *-------------------------------------------------------------------------
13 : */
14 : #ifndef TRANSAM_H
15 : #define TRANSAM_H
16 :
17 : #include "access/xlogdefs.h"
18 :
19 :
20 : /* ----------------
21 : * Special transaction ID values
22 : *
23 : * BootstrapTransactionId is the XID for "bootstrap" operations, and
24 : * FrozenTransactionId is used for very old tuples. Both should
25 : * always be considered valid.
26 : *
27 : * FirstNormalTransactionId is the first "normal" transaction id.
28 : * Note: if you need to change it, you must change pg_class.h as well.
29 : * ----------------
30 : */
31 : #define InvalidTransactionId ((TransactionId) 0)
32 : #define BootstrapTransactionId ((TransactionId) 1)
33 : #define FrozenTransactionId ((TransactionId) 2)
34 : #define FirstNormalTransactionId ((TransactionId) 3)
35 : #define MaxTransactionId ((TransactionId) 0xFFFFFFFF)
36 :
37 : /* ----------------
38 : * transaction ID manipulation macros
39 : * ----------------
40 : */
41 : #define TransactionIdIsValid(xid) ((xid) != InvalidTransactionId)
42 : #define TransactionIdIsNormal(xid) ((xid) >= FirstNormalTransactionId)
43 : #define TransactionIdEquals(id1, id2) ((id1) == (id2))
44 : #define TransactionIdStore(xid, dest) (*(dest) = (xid))
45 : #define StoreInvalidTransactionId(dest) (*(dest) = InvalidTransactionId)
46 :
47 : #define EpochFromFullTransactionId(x) ((uint32) ((x).value >> 32))
48 : #define XidFromFullTransactionId(x) ((uint32) (x).value)
49 : #define U64FromFullTransactionId(x) ((x).value)
50 : #define FullTransactionIdEquals(a, b) ((a).value == (b).value)
51 : #define FullTransactionIdPrecedes(a, b) ((a).value < (b).value)
52 : #define FullTransactionIdPrecedesOrEquals(a, b) ((a).value <= (b).value)
53 : #define FullTransactionIdFollows(a, b) ((a).value > (b).value)
54 : #define FullTransactionIdFollowsOrEquals(a, b) ((a).value >= (b).value)
55 : #define FullTransactionIdIsValid(x) TransactionIdIsValid(XidFromFullTransactionId(x))
56 : #define InvalidFullTransactionId FullTransactionIdFromEpochAndXid(0, InvalidTransactionId)
57 : #define FirstNormalFullTransactionId FullTransactionIdFromEpochAndXid(0, FirstNormalTransactionId)
58 : #define FullTransactionIdIsNormal(x) FullTransactionIdFollowsOrEquals(x, FirstNormalFullTransactionId)
59 :
60 : /*
61 : * A 64 bit value that contains an epoch and a TransactionId. This is
62 : * wrapped in a struct to prevent implicit conversion to/from TransactionId.
63 : * Not all values represent valid normal XIDs.
64 : */
65 : typedef struct FullTransactionId
66 : {
67 : uint64 value;
68 : } FullTransactionId;
69 :
70 : static inline FullTransactionId
71 2705218 : FullTransactionIdFromEpochAndXid(uint32 epoch, TransactionId xid)
72 : {
73 : FullTransactionId result;
74 :
75 2705218 : result.value = ((uint64) epoch) << 32 | xid;
76 :
77 2705218 : return result;
78 : }
79 :
80 : static inline FullTransactionId
81 15886908 : FullTransactionIdFromU64(uint64 value)
82 : {
83 : FullTransactionId result;
84 :
85 15886908 : result.value = value;
86 :
87 15886908 : return result;
88 : }
89 :
90 : /* advance a transaction ID variable, handling wraparound correctly */
91 : #define TransactionIdAdvance(dest) \
92 : do { \
93 : (dest)++; \
94 : if ((dest) < FirstNormalTransactionId) \
95 : (dest) = FirstNormalTransactionId; \
96 : } while(0)
97 :
98 : /*
99 : * Retreat a FullTransactionId variable, stepping over xids that would appear
100 : * to be special only when viewed as 32bit XIDs.
101 : */
102 : static inline void
103 1508 : FullTransactionIdRetreat(FullTransactionId *dest)
104 : {
105 1508 : dest->value--;
106 :
107 : /*
108 : * In contrast to 32bit XIDs don't step over the "actual" special xids.
109 : * For 64bit xids these can't be reached as part of a wraparound as they
110 : * can in the 32bit case.
111 : */
112 1508 : if (FullTransactionIdPrecedes(*dest, FirstNormalFullTransactionId))
113 808 : return;
114 :
115 : /*
116 : * But we do need to step over XIDs that'd appear special only for 32bit
117 : * XIDs.
118 : */
119 700 : while (XidFromFullTransactionId(*dest) < FirstNormalTransactionId)
120 0 : dest->value--;
121 : }
122 :
123 : /*
124 : * Advance a FullTransactionId variable, stepping over xids that would appear
125 : * to be special only when viewed as 32bit XIDs.
126 : */
127 : static inline void
128 933692 : FullTransactionIdAdvance(FullTransactionId *dest)
129 : {
130 933692 : dest->value++;
131 :
132 : /* see FullTransactionIdAdvance() */
133 933692 : if (FullTransactionIdPrecedes(*dest, FirstNormalFullTransactionId))
134 0 : return;
135 :
136 933692 : while (XidFromFullTransactionId(*dest) < FirstNormalTransactionId)
137 0 : dest->value++;
138 : }
139 :
140 : /* back up a transaction ID variable, handling wraparound correctly */
141 : #define TransactionIdRetreat(dest) \
142 : do { \
143 : (dest)--; \
144 : } while ((dest) < FirstNormalTransactionId)
145 :
146 : /* compare two XIDs already known to be normal; this is a macro for speed */
147 : #define NormalTransactionIdPrecedes(id1, id2) \
148 : (AssertMacro(TransactionIdIsNormal(id1) && TransactionIdIsNormal(id2)), \
149 : (int32) ((id1) - (id2)) < 0)
150 :
151 : /* compare two XIDs already known to be normal; this is a macro for speed */
152 : #define NormalTransactionIdFollows(id1, id2) \
153 : (AssertMacro(TransactionIdIsNormal(id1) && TransactionIdIsNormal(id2)), \
154 : (int32) ((id1) - (id2)) > 0)
155 :
156 : /* ----------
157 : * Object ID (OID) zero is InvalidOid.
158 : *
159 : * OIDs 1-9999 are reserved for manual assignment (see .dat files in
160 : * src/include/catalog/). Of these, 8000-9999 are reserved for
161 : * development purposes (such as in-progress patches and forks);
162 : * they should not appear in released versions.
163 : *
164 : * OIDs 10000-11999 are reserved for assignment by genbki.pl, for use
165 : * when the .dat files in src/include/catalog/ do not specify an OID
166 : * for a catalog entry that requires one.
167 : *
168 : * OIDS 12000-16383 are reserved for assignment during initdb
169 : * using the OID generator. (We start the generator at 12000.)
170 : *
171 : * OIDs beginning at 16384 are assigned from the OID generator
172 : * during normal multiuser operation. (We force the generator up to
173 : * 16384 as soon as we are in normal operation.)
174 : *
175 : * The choices of 8000, 10000 and 12000 are completely arbitrary, and can be
176 : * moved if we run low on OIDs in any category. Changing the macros below,
177 : * and updating relevant documentation (see bki.sgml and RELEASE_CHANGES),
178 : * should be sufficient to do this. Moving the 16384 boundary between
179 : * initdb-assigned OIDs and user-defined objects would be substantially
180 : * more painful, however, since some user-defined OIDs will appear in
181 : * on-disk data; such a change would probably break pg_upgrade.
182 : *
183 : * NOTE: if the OID generator wraps around, we skip over OIDs 0-16383
184 : * and resume with 16384. This minimizes the odds of OID conflict, by not
185 : * reassigning OIDs that might have been assigned during initdb.
186 : * ----------
187 : */
188 : #define FirstGenbkiObjectId 10000
189 : #define FirstBootstrapObjectId 12000
190 : #define FirstNormalObjectId 16384
191 :
192 : /*
193 : * VariableCache is a data structure in shared memory that is used to track
194 : * OID and XID assignment state. For largely historical reasons, there is
195 : * just one struct with different fields that are protected by different
196 : * LWLocks.
197 : *
198 : * Note: xidWrapLimit and oldestXidDB are not "active" values, but are
199 : * used just to generate useful messages when xidWarnLimit or xidStopLimit
200 : * are exceeded.
201 : */
202 : typedef struct VariableCacheData
203 : {
204 : /*
205 : * These fields are protected by OidGenLock.
206 : */
207 : Oid nextOid; /* next OID to assign */
208 : uint32 oidCount; /* OIDs available before must do XLOG work */
209 :
210 : /*
211 : * These fields are protected by XidGenLock.
212 : */
213 : FullTransactionId nextXid; /* next XID to assign */
214 :
215 : TransactionId oldestXid; /* cluster-wide minimum datfrozenxid */
216 : TransactionId xidVacLimit; /* start forcing autovacuums here */
217 : TransactionId xidWarnLimit; /* start complaining here */
218 : TransactionId xidStopLimit; /* refuse to advance nextXid beyond here */
219 : TransactionId xidWrapLimit; /* where the world ends */
220 : Oid oldestXidDB; /* database with minimum datfrozenxid */
221 :
222 : /*
223 : * These fields are protected by CommitTsLock
224 : */
225 : TransactionId oldestCommitTsXid;
226 : TransactionId newestCommitTsXid;
227 :
228 : /*
229 : * These fields are protected by ProcArrayLock.
230 : */
231 : FullTransactionId latestCompletedXid; /* newest full XID that has
232 : * committed or aborted */
233 :
234 : /*
235 : * Number of top-level transactions with xids (i.e. which may have
236 : * modified the database) that completed in some form since the start of
237 : * the server. This currently is solely used to check whether
238 : * GetSnapshotData() needs to recompute the contents of the snapshot, or
239 : * not. There are likely other users of this. Always above 1.
240 : */
241 : uint64 xactCompletionCount;
242 :
243 : /*
244 : * These fields are protected by XactTruncationLock
245 : */
246 : TransactionId oldestClogXid; /* oldest it's safe to look up in clog */
247 :
248 : } VariableCacheData;
249 :
250 : typedef VariableCacheData *VariableCache;
251 :
252 :
253 : /* ----------------
254 : * extern declarations
255 : * ----------------
256 : */
257 :
258 : /* in transam/xact.c */
259 : extern bool TransactionStartedDuringRecovery(void);
260 :
261 : /* in transam/varsup.c */
262 : extern PGDLLIMPORT VariableCache ShmemVariableCache;
263 :
264 : /*
265 : * prototypes for functions in transam/transam.c
266 : */
267 : extern bool TransactionIdDidCommit(TransactionId transactionId);
268 : extern bool TransactionIdDidAbort(TransactionId transactionId);
269 : extern bool TransactionIdIsKnownCompleted(TransactionId transactionId);
270 : extern void TransactionIdCommitTree(TransactionId xid, int nxids, TransactionId *xids);
271 : extern void TransactionIdAsyncCommitTree(TransactionId xid, int nxids, TransactionId *xids, XLogRecPtr lsn);
272 : extern void TransactionIdAbortTree(TransactionId xid, int nxids, TransactionId *xids);
273 : extern bool TransactionIdPrecedes(TransactionId id1, TransactionId id2);
274 : extern bool TransactionIdPrecedesOrEquals(TransactionId id1, TransactionId id2);
275 : extern bool TransactionIdFollows(TransactionId id1, TransactionId id2);
276 : extern bool TransactionIdFollowsOrEquals(TransactionId id1, TransactionId id2);
277 : extern TransactionId TransactionIdLatest(TransactionId mainxid,
278 : int nxids, const TransactionId *xids);
279 : extern XLogRecPtr TransactionIdGetCommitLSN(TransactionId xid);
280 :
281 : /* in transam/varsup.c */
282 : extern FullTransactionId GetNewTransactionId(bool isSubXact);
283 : extern void AdvanceNextFullTransactionIdPastXid(TransactionId xid);
284 : extern FullTransactionId ReadNextFullTransactionId(void);
285 : extern void SetTransactionIdLimit(TransactionId oldest_datfrozenxid,
286 : Oid oldest_datoid);
287 : extern void AdvanceOldestClogXid(TransactionId oldest_datfrozenxid);
288 : extern bool ForceTransactionIdLimitUpdate(void);
289 : extern Oid GetNewObjectId(void);
290 :
291 : #ifdef USE_ASSERT_CHECKING
292 : extern void AssertTransactionIdInAllowableRange(TransactionId xid);
293 : #else
294 : #define AssertTransactionIdInAllowableRange(xid) ((void)true)
295 : #endif
296 :
297 : /*
298 : * Some frontend programs include this header. For compilers that emit static
299 : * inline functions even when they're unused, that leads to unsatisfied
300 : * external references; hence hide them with #ifndef FRONTEND.
301 : */
302 : #ifndef FRONTEND
303 :
304 : /*
305 : * For callers that just need the XID part of the next transaction ID.
306 : */
307 : static inline TransactionId
308 115138 : ReadNewTransactionId(void)
309 : {
310 115138 : return XidFromFullTransactionId(ReadNextFullTransactionId());
311 : }
312 :
313 : /* return transaction ID backed up by amount, handling wraparound correctly */
314 : static inline TransactionId
315 1350042 : TransactionIdRetreatedBy(TransactionId xid, uint32 amount)
316 : {
317 1350042 : xid -= amount;
318 :
319 1350042 : while (xid < FirstNormalTransactionId)
320 0 : xid--;
321 :
322 1350042 : return xid;
323 : }
324 :
325 : /* return the older of the two IDs */
326 : static inline TransactionId
327 4268996 : TransactionIdOlder(TransactionId a, TransactionId b)
328 : {
329 4268996 : if (!TransactionIdIsValid(a))
330 924312 : return b;
331 :
332 3344684 : if (!TransactionIdIsValid(b))
333 1786934 : return a;
334 :
335 1557750 : if (TransactionIdPrecedes(a, b))
336 153852 : return a;
337 1403898 : return b;
338 : }
339 :
340 : /* return the older of the two IDs, assuming they're both normal */
341 : static inline TransactionId
342 : NormalTransactionIdOlder(TransactionId a, TransactionId b)
343 : {
344 : Assert(TransactionIdIsNormal(a));
345 : Assert(TransactionIdIsNormal(b));
346 : if (NormalTransactionIdPrecedes(a, b))
347 : return a;
348 : return b;
349 : }
350 :
351 : /* return the newer of the two IDs */
352 : static inline FullTransactionId
353 4771986 : FullTransactionIdNewer(FullTransactionId a, FullTransactionId b)
354 : {
355 4771986 : if (!FullTransactionIdIsValid(a))
356 37284 : return b;
357 :
358 4734702 : if (!FullTransactionIdIsValid(b))
359 38598 : return a;
360 :
361 4696104 : if (FullTransactionIdFollows(a, b))
362 2795096 : return a;
363 1901008 : return b;
364 : }
365 :
366 : #endif /* FRONTEND */
367 :
368 : #endif /* TRANSAM_H */
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