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1 : : /*-------------------------------------------------------------------------
2 : : *
3 : : * constraint.c
4 : : * PostgreSQL CONSTRAINT support code.
5 : : *
6 : : * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
7 : : * Portions Copyright (c) 1994, Regents of the University of California
8 : : *
9 : : * IDENTIFICATION
10 : : * src/backend/commands/constraint.c
11 : : *
12 : : *-------------------------------------------------------------------------
13 : : */
14 : : #include "postgres.h"
15 : :
16 : : #include "access/genam.h"
17 : : #include "access/tableam.h"
18 : : #include "catalog/index.h"
19 : : #include "commands/trigger.h"
20 : : #include "executor/executor.h"
21 : : #include "utils/fmgrprotos.h"
22 : : #include "utils/snapmgr.h"
23 : :
24 : :
25 : : /*
26 : : * unique_key_recheck - trigger function to do a deferred uniqueness check.
27 : : *
28 : : * This now also does deferred exclusion-constraint checks, so the name is
29 : : * somewhat historical.
30 : : *
31 : : * This is invoked as an AFTER ROW trigger for both INSERT and UPDATE,
32 : : * for any rows recorded as potentially violating a deferrable unique
33 : : * or exclusion constraint.
34 : : *
35 : : * This may be an end-of-statement check, a commit-time check, or a
36 : : * check triggered by a SET CONSTRAINTS command.
37 : : */
38 : : Datum
39 : 20 : unique_key_recheck(PG_FUNCTION_ARGS)
40 : : {
41 : 20 : TriggerData *trigdata = (TriggerData *) fcinfo->context;
42 : 20 : const char *funcname = "unique_key_recheck";
43 : 20 : ItemPointerData checktid;
44 : 20 : ItemPointerData tmptid;
45 : 20 : Relation indexRel;
46 : 20 : IndexInfo *indexInfo;
47 : 20 : EState *estate;
48 : 20 : ExprContext *econtext;
49 : 20 : TupleTableSlot *slot;
50 : 20 : Datum values[INDEX_MAX_KEYS];
51 : 20 : bool isnull[INDEX_MAX_KEYS];
52 : :
53 : : /*
54 : : * Make sure this is being called as an AFTER ROW trigger. Note:
55 : : * translatable error strings are shared with ri_triggers.c, so resist the
56 : : * temptation to fold the function name into them.
57 : : */
58 [ + - ]: 20 : if (!CALLED_AS_TRIGGER(fcinfo))
59 [ # # # # ]: 0 : ereport(ERROR,
60 : : (errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
61 : : errmsg("function \"%s\" was not called by trigger manager",
62 : : funcname)));
63 : :
64 [ + - ]: 20 : if (!TRIGGER_FIRED_AFTER(trigdata->tg_event) ||
65 : 20 : !TRIGGER_FIRED_FOR_ROW(trigdata->tg_event))
66 [ # # # # ]: 0 : ereport(ERROR,
67 : : (errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
68 : : errmsg("function \"%s\" must be fired AFTER ROW",
69 : : funcname)));
70 : :
71 : : /*
72 : : * Get the new data that was inserted/updated.
73 : : */
74 [ + + ]: 20 : if (TRIGGER_FIRED_BY_INSERT(trigdata->tg_event))
75 : 14 : checktid = trigdata->tg_trigslot->tts_tid;
76 [ + - ]: 6 : else if (TRIGGER_FIRED_BY_UPDATE(trigdata->tg_event))
77 : 6 : checktid = trigdata->tg_newslot->tts_tid;
78 : : else
79 : : {
80 [ # # # # ]: 0 : ereport(ERROR,
81 : : (errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
82 : : errmsg("function \"%s\" must be fired for INSERT or UPDATE",
83 : : funcname)));
84 : 0 : ItemPointerSetInvalid(&checktid); /* keep compiler quiet */
85 : : }
86 : :
87 : 20 : slot = table_slot_create(trigdata->tg_relation, NULL);
88 : :
89 : : /*
90 : : * If the row pointed at by checktid is now dead (ie, inserted and then
91 : : * deleted within our transaction), we can skip the check. However, we
92 : : * have to be careful, because this trigger gets queued only in response
93 : : * to index insertions; which means it does not get queued e.g. for HOT
94 : : * updates. The row we are called for might now be dead, but have a live
95 : : * HOT child, in which case we still need to make the check ---
96 : : * effectively, we're applying the check against the live child row,
97 : : * although we can use the values from this row since by definition all
98 : : * columns of interest to us are the same.
99 : : *
100 : : * This might look like just an optimization, because the index AM will
101 : : * make this identical test before throwing an error. But it's actually
102 : : * needed for correctness, because the index AM will also throw an error
103 : : * if it doesn't find the index entry for the row. If the row's dead then
104 : : * it's possible the index entry has also been marked dead, and even
105 : : * removed.
106 : : */
107 : 20 : tmptid = checktid;
108 : : {
109 : 20 : IndexFetchTableData *scan = table_index_fetch_begin(trigdata->tg_relation);
110 : 20 : bool call_again = false;
111 : :
112 [ + - ]: 20 : if (!table_index_fetch_tuple(scan, &tmptid, SnapshotSelf, slot,
113 : : &call_again, NULL))
114 : : {
115 : : /*
116 : : * All rows referenced by the index entry are dead, so skip the
117 : : * check.
118 : : */
119 : 0 : ExecDropSingleTupleTableSlot(slot);
120 : 0 : table_index_fetch_end(scan);
121 : 0 : return PointerGetDatum(NULL);
122 : : }
123 : 20 : table_index_fetch_end(scan);
124 [ - + ]: 20 : }
125 : :
126 : : /*
127 : : * Open the index, acquiring a RowExclusiveLock, just as if we were going
128 : : * to update it. (This protects against possible changes of the index
129 : : * schema, not against concurrent updates.)
130 : : */
131 : 20 : indexRel = index_open(trigdata->tg_trigger->tgconstrindid,
132 : : RowExclusiveLock);
133 : 20 : indexInfo = BuildIndexInfo(indexRel);
134 : :
135 : : /*
136 : : * Typically the index won't have expressions, but if it does we need an
137 : : * EState to evaluate them. We need it for exclusion constraints too,
138 : : * even if they are just on simple columns.
139 : : */
140 [ + - + + ]: 20 : if (indexInfo->ii_Expressions != NIL ||
141 : 20 : indexInfo->ii_ExclusionOps != NULL)
142 : : {
143 : 4 : estate = CreateExecutorState();
144 [ - + ]: 4 : econtext = GetPerTupleExprContext(estate);
145 : 4 : econtext->ecxt_scantuple = slot;
146 : 4 : }
147 : : else
148 : 16 : estate = NULL;
149 : :
150 : : /*
151 : : * Form the index values and isnull flags for the index entry that we need
152 : : * to check.
153 : : *
154 : : * Note: if the index uses functions that are not as immutable as they are
155 : : * supposed to be, this could produce an index tuple different from the
156 : : * original. The index AM can catch such errors by verifying that it
157 : : * finds a matching index entry with the tuple's TID. For exclusion
158 : : * constraints we check this in check_exclusion_constraint().
159 : : */
160 : 20 : FormIndexDatum(indexInfo, slot, estate, values, isnull);
161 : :
162 : : /*
163 : : * Now do the appropriate check.
164 : : */
165 [ + + ]: 20 : if (indexInfo->ii_ExclusionOps == NULL)
166 : : {
167 : : /*
168 : : * Note: this is not a real insert; it is a check that the index entry
169 : : * that has already been inserted is unique. Passing the tuple's tid
170 : : * (i.e. unmodified by table_index_fetch_tuple()) is correct even if
171 : : * the row is now dead, because that is the TID the index will know
172 : : * about.
173 : : */
174 : 32 : index_insert(indexRel, values, isnull, &checktid,
175 : 16 : trigdata->tg_relation, UNIQUE_CHECK_EXISTING,
176 : 16 : false, indexInfo);
177 : :
178 : : /* Cleanup cache possibly initialized by index_insert. */
179 : 16 : index_insert_cleanup(indexRel, indexInfo);
180 : 16 : }
181 : : else
182 : : {
183 : : /*
184 : : * For exclusion constraints we just do the normal check, but now it's
185 : : * okay to throw error. In the HOT-update case, we must use the live
186 : : * HOT child's TID here, else check_exclusion_constraint will think
187 : : * the child is a conflict.
188 : : */
189 : 8 : check_exclusion_constraint(trigdata->tg_relation, indexRel, indexInfo,
190 : 4 : &tmptid, values, isnull,
191 : 4 : estate, false);
192 : : }
193 : :
194 : : /*
195 : : * If that worked, then this index entry is unique or non-excluded, and we
196 : : * are done.
197 : : */
198 [ + + ]: 20 : if (estate != NULL)
199 : 1 : FreeExecutorState(estate);
200 : :
201 : 20 : ExecDropSingleTupleTableSlot(slot);
202 : :
203 : 20 : index_close(indexRel, RowExclusiveLock);
204 : :
205 : 20 : return PointerGetDatum(NULL);
206 : 20 : }
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