backupccl: fix scheduled backup pts pushing race

Informs #128013

Epic: none

pkg/ccl/backupccl/backup_job.go

@@ -617,6 +617,21 @@ func (b *backupResumer) Resume(ctx context.Context, execCtx interface{}) error {
 	defaultURI := details.URI
 	var backupDest backupdest.ResolvedDestination
 	if details.URI == "" {
+		// Choose which scheduled backup pts we will update at the the end of the
+		// backup _before_ we resolve the destination of the backup. This avoids a
+		// race with inc backups where backup destination resolution leads this backup
+		// to extend a chain that is about to be superseded by a new full backup
+		// chain, which could cause this inc to accidentally push the pts for the
+		// _new_ chain instead of the old chain it is apart of. By choosing the pts to
+		// move before we resolve the destination, we guarantee that we push the old
+		// chain.
+		insqlDB := p.ExecCfg().InternalDB
+		if err := insqlDB.Txn(ctx, func(ctx context.Context, txn isql.Txn) error {
+			return planSchedulePTSChaining(ctx, p.ExecCfg().JobsKnobs(), txn, &details, b.job.CreatedBy())
+		}); err != nil {
+			return err
+		}
+
 		var err error
 		backupDest, err = backupdest.ResolveDest(ctx, p.User(), details.Destination, details.EndTime,
 			details.IncrementalFrom, p.ExecCfg())
@@ -727,12 +742,6 @@ func (b *backupResumer) Resume(ctx context.Context, execCtx interface{}) error {
 			return err
 		}
 
-		if err := insqlDB.Txn(ctx, func(ctx context.Context, txn isql.Txn) error {
-			return planSchedulePTSChaining(ctx, p.ExecCfg().JobsKnobs(), txn, &details, b.job.CreatedBy())
-		}); err != nil {
-			return err
-		}
-
 		// The description picked during original planning might still say "LATEST",
 		// if resolving that to the actual directory only just happened above here.
 		// Ideally we'd re-render the description now that we know the subdir, but