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/*-------------------------------------------------------------------------
*
* constraint.c
* PostgreSQL CONSTRAINT support code.
*
* Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* src/backend/commands/constraint.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "access/genam.h"
#include "access/heapam.h"
#include "access/tableam.h"
#include "catalog/index.h"
#include "commands/trigger.h"
#include "executor/executor.h"
#include "utils/builtins.h"
#include "utils/rel.h"
#include "utils/snapmgr.h"
/*
* unique_key_recheck - trigger function to do a deferred uniqueness check.
*
* This now also does deferred exclusion-constraint checks, so the name is
* somewhat historical.
*
* This is invoked as an AFTER ROW trigger for both INSERT and UPDATE,
* for any rows recorded as potentially violating a deferrable unique
* or exclusion constraint.
*
* This may be an end-of-statement check, a commit-time check, or a
* check triggered by a SET CONSTRAINTS command.
*/
Datum
unique_key_recheck(PG_FUNCTION_ARGS)
{
TriggerData *trigdata = (TriggerData *) fcinfo->context;
const char *funcname = "unique_key_recheck";
ItemPointerData checktid;
ItemPointerData tmptid;
Relation indexRel;
IndexInfo *indexInfo;
EState *estate;
ExprContext *econtext;
TupleTableSlot *slot;
Datum values[INDEX_MAX_KEYS];
bool isnull[INDEX_MAX_KEYS];
/*
* Make sure this is being called as an AFTER ROW trigger. Note:
* translatable error strings are shared with ri_triggers.c, so resist the
* temptation to fold the function name into them.
*/
if (!CALLED_AS_TRIGGER(fcinfo))
ereport(ERROR,
(errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
errmsg("function \"%s\" was not called by trigger manager",
funcname)));
if (!TRIGGER_FIRED_AFTER(trigdata->tg_event) ||
!TRIGGER_FIRED_FOR_ROW(trigdata->tg_event))
ereport(ERROR,
(errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
errmsg("function \"%s\" must be fired AFTER ROW",
funcname)));
/*
* Get the new data that was inserted/updated.
*/
if (TRIGGER_FIRED_BY_INSERT(trigdata->tg_event))
checktid = trigdata->tg_trigslot->tts_tid;
else if (TRIGGER_FIRED_BY_UPDATE(trigdata->tg_event))
checktid = trigdata->tg_newslot->tts_tid;
else
{
ereport(ERROR,
(errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
errmsg("function \"%s\" must be fired for INSERT or UPDATE",
funcname)));
ItemPointerSetInvalid(&checktid); /* keep compiler quiet */
}
slot = table_slot_create(trigdata->tg_relation, NULL);
/*
* If the row pointed at by checktid is now dead (ie, inserted and then
* deleted within our transaction), we can skip the check. However, we
* have to be careful, because this trigger gets queued only in response
* to index insertions; which means it does not get queued e.g. for HOT
* updates. The row we are called for might now be dead, but have a live
* HOT child, in which case we still need to make the check ---
* effectively, we're applying the check against the live child row,
* although we can use the values from this row since by definition all
* columns of interest to us are the same.
*
* This might look like just an optimization, because the index AM will
* make this identical test before throwing an error. But it's actually
* needed for correctness, because the index AM will also throw an error
* if it doesn't find the index entry for the row. If the row's dead then
* it's possible the index entry has also been marked dead, and even
* removed.
*/
tmptid = checktid;
{
IndexFetchTableData *scan = table_index_fetch_begin(trigdata->tg_relation);
bool call_again = false;
if (!table_index_fetch_tuple(scan, &tmptid, SnapshotSelf, slot,
&call_again, NULL))
{
/*
* All rows referenced by the index entry are dead, so skip the
* check.
*/
ExecDropSingleTupleTableSlot(slot);
table_index_fetch_end(scan);
return PointerGetDatum(NULL);
}
table_index_fetch_end(scan);
}
/*
* Open the index, acquiring a RowExclusiveLock, just as if we were going
* to update it. (This protects against possible changes of the index
* schema, not against concurrent updates.)
*/
indexRel = index_open(trigdata->tg_trigger->tgconstrindid,
RowExclusiveLock);
indexInfo = BuildIndexInfo(indexRel);
/*
* Typically the index won't have expressions, but if it does we need an
* EState to evaluate them. We need it for exclusion constraints too,
* even if they are just on simple columns.
*/
if (indexInfo->ii_Expressions != NIL ||
indexInfo->ii_ExclusionOps != NULL)
{
estate = CreateExecutorState();
econtext = GetPerTupleExprContext(estate);
econtext->ecxt_scantuple = slot;
}
else
estate = NULL;
/*
* Form the index values and isnull flags for the index entry that we need
* to check.
*
* Note: if the index uses functions that are not as immutable as they are
* supposed to be, this could produce an index tuple different from the
* original. The index AM can catch such errors by verifying that it
* finds a matching index entry with the tuple's TID. For exclusion
* constraints we check this in check_exclusion_constraint().
*/
FormIndexDatum(indexInfo, slot, estate, values, isnull);
/*
* Now do the appropriate check.
*/
if (indexInfo->ii_ExclusionOps == NULL)
{
/*
* Note: this is not a real insert; it is a check that the index entry
* that has already been inserted is unique. Passing the tuple's tid
* (i.e. unmodified by table_index_fetch_tuple()) is correct even if
* the row is now dead, because that is the TID the index will know
* about.
*/
index_insert(indexRel, values, isnull, &checktid,
trigdata->tg_relation, UNIQUE_CHECK_EXISTING,
false, indexInfo);
}
else
{
/*
* For exclusion constraints we just do the normal check, but now it's
* okay to throw error. In the HOT-update case, we must use the live
* HOT child's TID here, else check_exclusion_constraint will think
* the child is a conflict.
*/
check_exclusion_constraint(trigdata->tg_relation, indexRel, indexInfo,
&tmptid, values, isnull,
estate, false);
}
/*
* If that worked, then this index entry is unique or non-excluded, and we
* are done.
*/
if (estate != NULL)
FreeExecutorState(estate);
ExecDropSingleTupleTableSlot(slot);
index_close(indexRel, RowExclusiveLock);
return PointerGetDatum(NULL);
}
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