Fix progress reporting of REINDEX CONCURRENTLY

This addresses a couple of issues with the so-said subject:
- Report the correct parent relation with the index actually being
rebuilt or validated.  Previously, the command status remained set to
the last index created for the progress of the index build and
validation, which would be incorrect when working on a table that has
more than one index.
- Use the correct phase when waiting before the drop of the old
indexes.  Previously, this was reported with the same status as when
waiting before the old indexes are marked as dead.

Author: Matthias van de Meent, Michael Paquier
Discussion: https://postgr.es/m/CAEze2WhqFgcwe1_tv=sFYhLWV2AdpfukumotJ6JNcAOQs3jufg@mail.gmail.com
Backpatch-through: 12

src/backend/commands/indexcmds.c

@@ -2837,6 +2837,13 @@ ReindexRelationConcurrently(Oid relationOid, int options)
 	char	   *relationName = NULL;
 	char	   *relationNamespace = NULL;
 	PGRUsage	ru0;
+	const int	progress_index[] = {
+		PROGRESS_CREATEIDX_COMMAND,
+		PROGRESS_CREATEIDX_PHASE,
+		PROGRESS_CREATEIDX_INDEX_OID,
+		PROGRESS_CREATEIDX_ACCESS_METHOD_OID
+	};
+	int64		progress_vals[4];
 
 	/*
 	 * Create a memory context that will survive forced transaction commits we
@@ -3079,12 +3086,11 @@ ReindexRelationConcurrently(Oid relationOid, int options)
 
 		pgstat_progress_start_command(PROGRESS_COMMAND_CREATE_INDEX,
 									  RelationGetRelid(heapRel));
-		pgstat_progress_update_param(PROGRESS_CREATEIDX_COMMAND,
+		progress_vals[0] = PROGRESS_CREATEIDX_COMMAND_REINDEX_CONCURRENTLY;
-									 PROGRESS_CREATEIDX_COMMAND_REINDEX_CONCURRENTLY);
+		progress_vals[1] = 0;	/* initializing */
-		pgstat_progress_update_param(PROGRESS_CREATEIDX_INDEX_OID,
+		progress_vals[2] = indexId;
-									 indexId);
+		progress_vals[3] = indexRel->rd_rel->relam;
-		pgstat_progress_update_param(PROGRESS_CREATEIDX_ACCESS_METHOD_OID,
+		pgstat_progress_update_multi_param(4, progress_index, progress_vals);
-									 indexRel->rd_rel->relam);
 
 		/* Choose a temporary relation name for the new index */
 		concurrentName = ChooseRelationName(get_rel_name(indexId),
@@ -3188,12 +3194,12 @@ ReindexRelationConcurrently(Oid relationOid, int options)
 	WaitForLockersMultiple(lockTags, ShareLock, true);
 	CommitTransactionCommand();
 
-	forboth(lc, indexIds, lc2, newIndexIds)
+	foreach(lc, newIndexIds)
 	{
-		Relation	indexRel;
+		Relation	newIndexRel;
-		Oid			oldIndexId = lfirst_oid(lc);
+		Oid			newIndexId = lfirst_oid(lc);
-		Oid			newIndexId = lfirst_oid(lc2);
 		Oid			heapId;
+		Oid			indexam;
 
 		/* Start new transaction for this index's concurrent build */
 		StartTransactionCommand();
@@ -3212,9 +3218,21 @@ ReindexRelationConcurrently(Oid relationOid, int options)
 		 * Index relation has been closed by previous commit, so reopen it to
 		 * get its information.
 		 */
-		indexRel = index_open(oldIndexId, ShareUpdateExclusiveLock);
+		newIndexRel = index_open(newIndexId, ShareUpdateExclusiveLock);
-		heapId = indexRel->rd_index->indrelid;
+		heapId = newIndexRel->rd_index->indrelid;
-		index_close(indexRel, NoLock);
+		indexam = newIndexRel->rd_rel->relam;
+		index_close(newIndexRel, NoLock);
+
+		/*
+		 * Update progress for the index to build, with the correct parent
+		 * table involved.
+		 */
+		pgstat_progress_start_command(PROGRESS_COMMAND_CREATE_INDEX, heapId);
+		progress_vals[0] = PROGRESS_CREATEIDX_COMMAND_REINDEX_CONCURRENTLY;
+		progress_vals[1] = PROGRESS_CREATEIDX_PHASE_BUILD;
+		progress_vals[2] = newIndexId;
+		progress_vals[3] = indexam;
+		pgstat_progress_update_multi_param(4, progress_index, progress_vals);
 
 		/* Perform concurrent build of new index */
 		index_concurrently_build(heapId, newIndexId);
@@ -3243,6 +3261,8 @@ ReindexRelationConcurrently(Oid relationOid, int options)
 		Oid			heapId;
 		TransactionId limitXmin;
 		Snapshot	snapshot;
+		Relation	newIndexRel;
+		Oid			indexam;
 
 		StartTransactionCommand();
 
@@ -3253,8 +3273,6 @@ ReindexRelationConcurrently(Oid relationOid, int options)
 		 */
 		CHECK_FOR_INTERRUPTS();
 
-		heapId = IndexGetRelation(newIndexId, false);
-
 		/*
 		 * Take the "reference snapshot" that will be used by validate_index()
 		 * to filter candidate tuples.
@@ -3262,6 +3280,26 @@ ReindexRelationConcurrently(Oid relationOid, int options)
 		snapshot = RegisterSnapshot(GetTransactionSnapshot());
 		PushActiveSnapshot(snapshot);
 
+		/*
+		 * Index relation has been closed by previous commit, so reopen it to
+		 * get its information.
+		 */
+		newIndexRel = index_open(newIndexId, ShareUpdateExclusiveLock);
+		heapId = newIndexRel->rd_index->indrelid;
+		indexam = newIndexRel->rd_rel->relam;
+		index_close(newIndexRel, NoLock);
+
+		/*
+		 * Update progress for the index to build, with the correct parent
+		 * table involved.
+		 */
+		pgstat_progress_start_command(PROGRESS_COMMAND_CREATE_INDEX, heapId);
+		progress_vals[0] = PROGRESS_CREATEIDX_COMMAND_REINDEX_CONCURRENTLY;
+		progress_vals[1] = PROGRESS_CREATEIDX_PHASE_VALIDATE_IDXSCAN;
+		progress_vals[2] = newIndexId;
+		progress_vals[3] = indexam;
+		pgstat_progress_update_multi_param(4, progress_index, progress_vals);
+
 		validate_index(heapId, newIndexId, snapshot);
 
 		/*
@@ -3396,7 +3434,7 @@ ReindexRelationConcurrently(Oid relationOid, int options)
 	 */
 
 	pgstat_progress_update_param(PROGRESS_CREATEIDX_PHASE,
-								 PROGRESS_CREATEIDX_PHASE_WAIT_4);
+								 PROGRESS_CREATEIDX_PHASE_WAIT_5);
 	WaitForLockersMultiple(lockTags, AccessExclusiveLock, true);
 
 	PushActiveSnapshot(GetTransactionSnapshot());