6 files changed, 40 insertions, 7 deletions
diff --git a/src/backend/commands/indexcmds.c b/src/backend/commands/indexcmds.c
index 5712fac3697..a8033be4bff 100644
--- a/src/backend/commands/indexcmds.c
+++ b/src/backend/commands/indexcmds.c
@@ -1789,6 +1789,7 @@ DefineIndex(Oid tableId,
 	 * before the reference snap was taken, we have to wait out any
 	 * transactions that might have older snapshots.
 	 */
+	INJECTION_POINT("define-index-before-set-valid", NULL);
 	pgstat_progress_update_param(PROGRESS_CREATEIDX_PHASE,
 								 PROGRESS_CREATEIDX_PHASE_WAIT_3);
 	WaitForOlderSnapshots(limitXmin, true);
@@ -4229,6 +4230,7 @@ ReindexRelationConcurrently(const ReindexStmt *stmt, Oid relationOid, const Rein
 	 * indexes with the correct names.
 	 */
 
+	INJECTION_POINT("reindex-relation-concurrently-before-swap", NULL);
 	StartTransactionCommand();
 
 	/*
@@ -4307,6 +4309,7 @@ ReindexRelationConcurrently(const ReindexStmt *stmt, Oid relationOid, const Rein
 	 * index_drop() for more details.
 	 */
 
+	INJECTION_POINT("reindex-relation-concurrently-before-set-dead", NULL);
 	pgstat_progress_update_param(PROGRESS_CREATEIDX_PHASE,
 								 PROGRESS_CREATEIDX_PHASE_WAIT_4);
 	WaitForLockersMultiple(lockTags, AccessExclusiveLock, true);
diff --git a/src/backend/executor/execIndexing.c b/src/backend/executor/execIndexing.c
index 401606f840a..d1cbab58799 100644
--- a/src/backend/executor/execIndexing.c
+++ b/src/backend/executor/execIndexing.c
@@ -114,6 +114,7 @@
 #include "executor/executor.h"
 #include "nodes/nodeFuncs.h"
 #include "storage/lmgr.h"
+#include "utils/injection_point.h"
 #include "utils/multirangetypes.h"
 #include "utils/rangetypes.h"
 #include "utils/snapmgr.h"
@@ -943,6 +944,13 @@ retry:
 
 	ExecDropSingleTupleTableSlot(existing_slot);
 
+#ifdef USE_INJECTION_POINTS
+	if (conflict)
+		INJECTION_POINT("check-exclusion-or-unique-constraint-conflict", NULL);
+	else
+		INJECTION_POINT("check-exclusion-or-unique-constraint-no-conflict", NULL);
+#endif
+
 	return !conflict;
 }
 
diff --git a/src/backend/executor/execPartition.c b/src/backend/executor/execPartition.c
index aa12e9ad2ea..0dcce181f09 100644
--- a/src/backend/executor/execPartition.c
+++ b/src/backend/executor/execPartition.c
@@ -722,8 +722,9 @@ ExecInitPartitionInfo(ModifyTableState *mtstate, EState *estate,
 
 		/*
 		 * If the resulting lists are of inequal length, something is wrong.
-		 * (This shouldn't happen, since arbiter index selection should not
-		 * pick up an invalid index.)
+		 * XXX This may happen because we don't match the lists correctly when
+		 * a partitioned index is being processed by REINDEX CONCURRENTLY.
+		 * FIXME later.
 		 */
 		if (list_length(rootResultRelInfo->ri_onConflictArbiterIndexes) !=
 			list_length(arbiterIndexes))
diff --git a/src/backend/executor/nodeModifyTable.c b/src/backend/executor/nodeModifyTable.c
index 00429326c34..e44f1223886 100644
--- a/src/backend/executor/nodeModifyTable.c
+++ b/src/backend/executor/nodeModifyTable.c
@@ -68,6 +68,7 @@
 #include "storage/lmgr.h"
 #include "utils/builtins.h"
 #include "utils/datum.h"
+#include "utils/injection_point.h"
 #include "utils/rel.h"
 #include "utils/snapmgr.h"
 
@@ -1186,6 +1187,7 @@ ExecInsert(ModifyTableContext *context,
 			 * if we're going to go ahead with the insertion, instead of
 			 * waiting for the whole transaction to complete.
 			 */
+			INJECTION_POINT("exec-insert-before-insert-speculative", NULL);
 			specToken = SpeculativeInsertionLockAcquire(GetCurrentTransactionId());
 
 			/* insert the tuple, with the speculative token */
diff --git a/src/backend/optimizer/util/plancat.c b/src/backend/optimizer/util/plancat.c
index d950bd93002..7af9a2064e3 100644
--- a/src/backend/optimizer/util/plancat.c
+++ b/src/backend/optimizer/util/plancat.c
@@ -814,6 +814,7 @@ infer_arbiter_indexes(PlannerInfo *root)
 
 	/* Results */
 	List	   *results = NIL;
+	bool		foundValid = false;
 
 	/*
 	 * Quickly return NIL for ON CONFLICT DO NOTHING without an inference
@@ -907,7 +908,22 @@ infer_arbiter_indexes(PlannerInfo *root)
 		idxRel = index_open(indexoid, rte->rellockmode);
 		idxForm = idxRel->rd_index;
 
-		if (!idxForm->indisvalid)
+		/*
+		 * Ignore indexes that aren't indisready, because we cannot trust
+		 * their catalog structure yet.  However, if any indexes are marked
+		 * indisready but not yet indisvalid, we still consider them, because
+		 * they might turn valid while we're running.  Doing it this way
+		 * allows a concurrent transaction with a slightly later catalog
+		 * snapshot infer the same set of indexes, which is critical to
+		 * prevent spurious 'duplicate key' errors.
+		 *
+		 * However, another critical aspect is that a unique index that isn't
+		 * yet marked indisvalid=true might not be complete yet, meaning it
+		 * wouldn't detect possible duplicate rows.  In order to prevent false
+		 * negatives, we require that we include in the set of inferred
+		 * indexes at least one index that is marked valid.
+		 */
+		if (!idxForm->indisready)
 			goto next;
 
 		/*
@@ -929,10 +945,9 @@ infer_arbiter_indexes(PlannerInfo *root)
 						 errmsg("ON CONFLICT DO UPDATE not supported with exclusion constraints")));
 
 			results = lappend_oid(results, idxForm->indexrelid);
-			list_free(indexList);
+			foundValid |= idxForm->indisvalid;
 			index_close(idxRel, NoLock);
-			table_close(relation, NoLock);
-			return results;
+			break;
 		}
 		else if (indexOidFromConstraint != InvalidOid)
 		{
@@ -1033,6 +1048,7 @@ infer_arbiter_indexes(PlannerInfo *root)
 			goto next;
 
 		results = lappend_oid(results, idxForm->indexrelid);
+		foundValid |= idxForm->indisvalid;
 next:
 		index_close(idxRel, NoLock);
 	}
@@ -1040,7 +1056,8 @@ next:
 	list_free(indexList);
 	table_close(relation, NoLock);
 
-	if (results == NIL)
+	/* We require at least one indisvalid index */
+	if (results == NIL || !foundValid)
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
 				 errmsg("there is no unique or exclusion constraint matching the ON CONFLICT specification")));
diff --git a/src/backend/utils/time/snapmgr.c b/src/backend/utils/time/snapmgr.c
index 65561cc6bc3..24f73a49d27 100644
--- a/src/backend/utils/time/snapmgr.c
+++ b/src/backend/utils/time/snapmgr.c
@@ -119,6 +119,7 @@
 #include "storage/proc.h"
 #include "storage/procarray.h"
 #include "utils/builtins.h"
+#include "utils/injection_point.h"
 #include "utils/memutils.h"
 #include "utils/resowner.h"
 #include "utils/snapmgr.h"
@@ -458,6 +459,7 @@ InvalidateCatalogSnapshot(void)
 		pairingheap_remove(&RegisteredSnapshots, &CatalogSnapshot->ph_node);
 		CatalogSnapshot = NULL;
 		SnapshotResetXmin();
+		INJECTION_POINT("invalidate-catalog-snapshot-end", NULL);
 	}
 }