1 files changed, 205 insertions, 0 deletions
diff --git a/src/backend/commands/constraint.c b/src/backend/commands/constraint.c
new file mode 100644
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+++ b/src/backend/commands/constraint.c
@@ -0,0 +1,205 @@
+/*-------------------------------------------------------------------------
+ *
+ * constraint.c
+ *	  PostgreSQL CONSTRAINT support code.
+ *
+ * Portions Copyright (c) 1996-2021, 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);
+}