Line data Source code
1 : /*-------------------------------------------------------------------------
2 : *
3 : * nodeLockRows.c
4 : * Routines to handle FOR UPDATE/FOR SHARE row locking
5 : *
6 : * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
7 : * Portions Copyright (c) 1994, Regents of the University of California
8 : *
9 : *
10 : * IDENTIFICATION
11 : * src/backend/executor/nodeLockRows.c
12 : *
13 : *-------------------------------------------------------------------------
14 : */
15 : /*
16 : * INTERFACE ROUTINES
17 : * ExecLockRows - fetch locked rows
18 : * ExecInitLockRows - initialize node and subnodes..
19 : * ExecEndLockRows - shutdown node and subnodes
20 : */
21 :
22 : #include "postgres.h"
23 :
24 : #include "access/tableam.h"
25 : #include "access/xact.h"
26 : #include "executor/executor.h"
27 : #include "executor/nodeLockRows.h"
28 : #include "foreign/fdwapi.h"
29 : #include "miscadmin.h"
30 : #include "utils/rel.h"
31 :
32 :
33 : /* ----------------------------------------------------------------
34 : * ExecLockRows
35 : * ----------------------------------------------------------------
36 : */
37 : static TupleTableSlot * /* return: a tuple or NULL */
38 86104 : ExecLockRows(PlanState *pstate)
39 : {
40 86104 : LockRowsState *node = castNode(LockRowsState, pstate);
41 : TupleTableSlot *slot;
42 : EState *estate;
43 : PlanState *outerPlan;
44 : bool epq_needed;
45 : ListCell *lc;
46 :
47 86104 : CHECK_FOR_INTERRUPTS();
48 :
49 : /*
50 : * get information from the node
51 : */
52 86104 : estate = node->ps.state;
53 86104 : outerPlan = outerPlanState(node);
54 :
55 : /*
56 : * Get next tuple from subplan, if any.
57 : */
58 57 : lnext:
59 86161 : slot = ExecProcNode(outerPlan);
60 :
61 86161 : if (TupIsNull(slot))
62 : {
63 : /* Release any resources held by EPQ mechanism before exiting */
64 4466 : EvalPlanQualEnd(&node->lr_epqstate);
65 4466 : return NULL;
66 : }
67 :
68 : /* We don't need EvalPlanQual unless we get updated tuple version(s) */
69 81695 : epq_needed = false;
70 :
71 : /*
72 : * Attempt to lock the source tuple(s). (Note we only have locking
73 : * rowmarks in lr_arowMarks.)
74 : */
75 163510 : foreach(lc, node->lr_arowMarks)
76 : {
77 81902 : ExecAuxRowMark *aerm = (ExecAuxRowMark *) lfirst(lc);
78 81902 : ExecRowMark *erm = aerm->rowmark;
79 : Datum datum;
80 : bool isNull;
81 : ItemPointerData tid;
82 : TM_FailureData tmfd;
83 : LockTupleMode lockmode;
84 81902 : int lockflags = 0;
85 : TM_Result test;
86 : TupleTableSlot *markSlot;
87 :
88 : /* clear any leftover test tuple for this rel */
89 81902 : markSlot = EvalPlanQualSlot(&node->lr_epqstate, erm->relation, erm->rti);
90 81902 : ExecClearTuple(markSlot);
91 :
92 : /* if child rel, must check whether it produced this row */
93 81902 : if (erm->rti != erm->prti)
94 : {
95 : Oid tableoid;
96 :
97 781 : datum = ExecGetJunkAttribute(slot,
98 781 : aerm->toidAttNo,
99 : &isNull);
100 : /* shouldn't ever get a null result... */
101 781 : if (isNull)
102 0 : elog(ERROR, "tableoid is NULL");
103 781 : tableoid = DatumGetObjectId(datum);
104 :
105 : Assert(OidIsValid(erm->relid));
106 781 : if (tableoid != erm->relid)
107 : {
108 : /* this child is inactive right now */
109 158 : erm->ermActive = false;
110 158 : ItemPointerSetInvalid(&(erm->curCtid));
111 158 : continue;
112 : }
113 : }
114 81744 : erm->ermActive = true;
115 :
116 : /* fetch the tuple's ctid */
117 81744 : datum = ExecGetJunkAttribute(slot,
118 81744 : aerm->ctidAttNo,
119 : &isNull);
120 : /* shouldn't ever get a null result... */
121 81744 : if (isNull)
122 0 : elog(ERROR, "ctid is NULL");
123 :
124 : /* requests for foreign tables must be passed to their FDW */
125 81744 : if (erm->relation->rd_rel->relkind == RELKIND_FOREIGN_TABLE)
126 0 : {
127 : FdwRoutine *fdwroutine;
128 0 : bool updated = false;
129 :
130 0 : fdwroutine = GetFdwRoutineForRelation(erm->relation, false);
131 : /* this should have been checked already, but let's be safe */
132 0 : if (fdwroutine->RefetchForeignRow == NULL)
133 0 : ereport(ERROR,
134 : (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
135 : errmsg("cannot lock rows in foreign table \"%s\"",
136 : RelationGetRelationName(erm->relation))));
137 :
138 0 : fdwroutine->RefetchForeignRow(estate,
139 : erm,
140 : datum,
141 : markSlot,
142 : &updated);
143 0 : if (TupIsNull(markSlot))
144 : {
145 : /* couldn't get the lock, so skip this row */
146 0 : goto lnext;
147 : }
148 :
149 : /*
150 : * if FDW says tuple was updated before getting locked, we need to
151 : * perform EPQ testing to see if quals are still satisfied
152 : */
153 0 : if (updated)
154 0 : epq_needed = true;
155 :
156 0 : continue;
157 : }
158 :
159 : /* okay, try to lock (and fetch) the tuple */
160 81744 : tid = *((ItemPointer) DatumGetPointer(datum));
161 81744 : switch (erm->markType)
162 : {
163 3931 : case ROW_MARK_EXCLUSIVE:
164 3931 : lockmode = LockTupleExclusive;
165 3931 : break;
166 39 : case ROW_MARK_NOKEYEXCLUSIVE:
167 39 : lockmode = LockTupleNoKeyExclusive;
168 39 : break;
169 1159 : case ROW_MARK_SHARE:
170 1159 : lockmode = LockTupleShare;
171 1159 : break;
172 76615 : case ROW_MARK_KEYSHARE:
173 76615 : lockmode = LockTupleKeyShare;
174 76615 : break;
175 0 : default:
176 0 : elog(ERROR, "unsupported rowmark type");
177 : lockmode = LockTupleNoKeyExclusive; /* keep compiler quiet */
178 : break;
179 : }
180 :
181 81744 : lockflags = TUPLE_LOCK_FLAG_LOCK_UPDATE_IN_PROGRESS;
182 81744 : if (!IsolationUsesXactSnapshot())
183 78025 : lockflags |= TUPLE_LOCK_FLAG_FIND_LAST_VERSION;
184 :
185 81744 : test = table_tuple_lock(erm->relation, &tid, estate->es_snapshot,
186 : markSlot, estate->es_output_cid,
187 : lockmode, erm->waitPolicy,
188 : lockflags,
189 : &tmfd);
190 :
191 81727 : switch (test)
192 : {
193 37 : case TM_WouldBlock:
194 : /* couldn't lock tuple in SKIP LOCKED mode */
195 37 : goto lnext;
196 :
197 3 : case TM_SelfModified:
198 :
199 : /*
200 : * The target tuple was already updated or deleted by the
201 : * current command, or by a later command in the current
202 : * transaction. We *must* ignore the tuple in the former
203 : * case, so as to avoid the "Halloween problem" of repeated
204 : * update attempts. In the latter case it might be sensible
205 : * to fetch the updated tuple instead, but doing so would
206 : * require changing heap_update and heap_delete to not
207 : * complain about updating "invisible" tuples, which seems
208 : * pretty scary (table_tuple_lock will not complain, but few
209 : * callers expect TM_Invisible, and we're not one of them). So
210 : * for now, treat the tuple as deleted and do not process.
211 : */
212 3 : goto lnext;
213 :
214 81657 : case TM_Ok:
215 :
216 : /*
217 : * Got the lock successfully, the locked tuple saved in
218 : * markSlot for, if needed, EvalPlanQual testing below.
219 : */
220 81657 : if (tmfd.traversed)
221 35 : epq_needed = true;
222 81657 : break;
223 :
224 16 : case TM_Updated:
225 16 : if (IsolationUsesXactSnapshot())
226 16 : ereport(ERROR,
227 : (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
228 : errmsg("could not serialize access due to concurrent update")));
229 0 : elog(ERROR, "unexpected table_tuple_lock status: %u",
230 : test);
231 : break;
232 :
233 14 : case TM_Deleted:
234 14 : if (IsolationUsesXactSnapshot())
235 6 : ereport(ERROR,
236 : (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
237 : errmsg("could not serialize access due to concurrent update")));
238 : /* tuple was deleted so don't return it */
239 8 : goto lnext;
240 :
241 0 : case TM_Invisible:
242 0 : elog(ERROR, "attempted to lock invisible tuple");
243 : break;
244 :
245 0 : default:
246 0 : elog(ERROR, "unrecognized table_tuple_lock status: %u",
247 : test);
248 : }
249 :
250 : /* Remember locked tuple's TID for EPQ testing and WHERE CURRENT OF */
251 81657 : erm->curCtid = tid;
252 : }
253 :
254 : /*
255 : * If we need to do EvalPlanQual testing, do so.
256 : */
257 81608 : if (epq_needed)
258 : {
259 : /* Initialize EPQ machinery */
260 34 : EvalPlanQualBegin(&node->lr_epqstate);
261 :
262 : /*
263 : * To fetch non-locked source rows the EPQ logic needs to access junk
264 : * columns from the tuple being tested.
265 : */
266 34 : EvalPlanQualSetSlot(&node->lr_epqstate, slot);
267 :
268 : /*
269 : * And finally we can re-evaluate the tuple.
270 : */
271 34 : slot = EvalPlanQualNext(&node->lr_epqstate);
272 34 : if (TupIsNull(slot))
273 : {
274 : /* Updated tuple fails qual, so ignore it and go on */
275 9 : goto lnext;
276 : }
277 : }
278 :
279 : /* Got all locks, so return the current tuple */
280 81599 : return slot;
281 : }
282 :
283 : /* ----------------------------------------------------------------
284 : * ExecInitLockRows
285 : *
286 : * This initializes the LockRows node state structures and
287 : * the node's subplan.
288 : * ----------------------------------------------------------------
289 : */
290 : LockRowsState *
291 7018 : ExecInitLockRows(LockRows *node, EState *estate, int eflags)
292 : {
293 : LockRowsState *lrstate;
294 7018 : Plan *outerPlan = outerPlan(node);
295 : List *epq_arowmarks;
296 : ListCell *lc;
297 :
298 : /* check for unsupported flags */
299 : Assert(!(eflags & EXEC_FLAG_MARK));
300 :
301 : /*
302 : * create state structure
303 : */
304 7018 : lrstate = makeNode(LockRowsState);
305 7018 : lrstate->ps.plan = (Plan *) node;
306 7018 : lrstate->ps.state = estate;
307 7018 : lrstate->ps.ExecProcNode = ExecLockRows;
308 :
309 : /*
310 : * Miscellaneous initialization
311 : *
312 : * LockRows nodes never call ExecQual or ExecProject, therefore no
313 : * ExprContext is needed.
314 : */
315 :
316 : /*
317 : * Initialize result type.
318 : */
319 7018 : ExecInitResultTypeTL(&lrstate->ps);
320 :
321 : /*
322 : * then initialize outer plan
323 : */
324 7018 : outerPlanState(lrstate) = ExecInitNode(outerPlan, estate, eflags);
325 :
326 : /* node returns unmodified slots from the outer plan */
327 7018 : lrstate->ps.resultopsset = true;
328 7018 : lrstate->ps.resultops = ExecGetResultSlotOps(outerPlanState(lrstate),
329 : &lrstate->ps.resultopsfixed);
330 :
331 : /*
332 : * LockRows nodes do no projections, so initialize projection info for
333 : * this node appropriately
334 : */
335 7018 : lrstate->ps.ps_ProjInfo = NULL;
336 :
337 : /*
338 : * Locate the ExecRowMark(s) that this node is responsible for, and
339 : * construct ExecAuxRowMarks for them. (InitPlan should already have
340 : * built the global list of ExecRowMarks.)
341 : */
342 7018 : lrstate->lr_arowMarks = NIL;
343 7018 : epq_arowmarks = NIL;
344 15258 : foreach(lc, node->rowMarks)
345 : {
346 8240 : PlanRowMark *rc = lfirst_node(PlanRowMark, lc);
347 8240 : RangeTblEntry *rte = exec_rt_fetch(rc->rti, estate);
348 : ExecRowMark *erm;
349 : ExecAuxRowMark *aerm;
350 :
351 : /* ignore "parent" rowmarks; they are irrelevant at runtime */
352 8240 : if (rc->isParent)
353 923 : continue;
354 :
355 : /*
356 : * Also ignore rowmarks belonging to child tables that have been
357 : * pruned in ExecDoInitialPruning().
358 : */
359 7317 : if (rte->rtekind == RTE_RELATION &&
360 7316 : !bms_is_member(rc->rti, estate->es_unpruned_relids))
361 36 : continue;
362 :
363 : /* find ExecRowMark and build ExecAuxRowMark */
364 7281 : erm = ExecFindRowMark(estate, rc->rti, false);
365 7281 : aerm = ExecBuildAuxRowMark(erm, outerPlan->targetlist);
366 :
367 : /*
368 : * Only locking rowmarks go into our own list. Non-locking marks are
369 : * passed off to the EvalPlanQual machinery. This is because we don't
370 : * want to bother fetching non-locked rows unless we actually have to
371 : * do an EPQ recheck.
372 : */
373 7281 : if (RowMarkRequiresRowShareLock(erm->markType))
374 7119 : lrstate->lr_arowMarks = lappend(lrstate->lr_arowMarks, aerm);
375 : else
376 162 : epq_arowmarks = lappend(epq_arowmarks, aerm);
377 : }
378 :
379 : /* Now we have the info needed to set up EPQ state */
380 7018 : EvalPlanQualInit(&lrstate->lr_epqstate, estate,
381 : outerPlan, epq_arowmarks, node->epqParam, NIL);
382 :
383 7018 : return lrstate;
384 : }
385 :
386 : /* ----------------------------------------------------------------
387 : * ExecEndLockRows
388 : *
389 : * This shuts down the subplan and frees resources allocated
390 : * to this node.
391 : * ----------------------------------------------------------------
392 : */
393 : void
394 6959 : ExecEndLockRows(LockRowsState *node)
395 : {
396 : /* We may have shut down EPQ already, but no harm in another call */
397 6959 : EvalPlanQualEnd(&node->lr_epqstate);
398 6959 : ExecEndNode(outerPlanState(node));
399 6959 : }
400 :
401 :
402 : void
403 8 : ExecReScanLockRows(LockRowsState *node)
404 : {
405 8 : PlanState *outerPlan = outerPlanState(node);
406 :
407 : /*
408 : * if chgParam of subnode is not null then plan will be re-scanned by
409 : * first ExecProcNode.
410 : */
411 8 : if (outerPlan->chgParam == NULL)
412 0 : ExecReScan(outerPlan);
413 8 : }
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