on a reserve connection retry ignore the existing shard session

Signed-off-by: Harshit Gangal <harshit@planetscale.com>

go/vt/vtgate/scatter_conn.go

@@ -222,6 +222,7 @@ func (stc *ScatterConn) ExecuteMultiShard(
 					retryRequest(func() {
 						// we seem to have lost our connection. it was a reserved connection, let's try to recreate it
 						info.actionNeeded = reserve
+						info.ignoreOldSession = true
 						var state queryservice.ReservedState
 						state, innerqr, err = qs.ReserveExecute(ctx, rs.Target, session.SetPreQueries(), queries[i].Sql, queries[i].BindVariables, 0 /*transactionId*/, opts)
 						reservedID = state.ReservedID
@@ -237,6 +238,7 @@ func (stc *ScatterConn) ExecuteMultiShard(
 					retryRequest(func() {
 						// we seem to have lost our connection. it was a reserved connection, let's try to recreate it
 						info.actionNeeded = reserveBegin
+						info.ignoreOldSession = true
 						var state queryservice.ReservedTransactionState
 						state, innerqr, err = qs.ReserveBeginExecute(ctx, rs.Target, session.SetPreQueries(), session.SavePoints(), queries[i].Sql, queries[i].BindVariables, opts)
 						transactionID = state.TransactionID
@@ -670,16 +672,19 @@ func (stc *ScatterConn) multiGoTransaction(
 		if err != nil {
 			return
 		}
-		updated, err := action(rs, i, info)
-		if updated == nil {
+		info, err = action(rs, i, info)
+		if info == nil {
 			return
 		}
-		if shardSession != nil && updated.rowsAffected {
+		if info.ignoreOldSession {
+			shardSession = nil
+		}
+		if shardSession != nil && info.rowsAffected {
 			// We might not always update or append in the session.
 			// We need to track if rows were affected in the transaction.
-			shardSession.RowsAffected = updated.rowsAffected
+			shardSession.RowsAffected = info.rowsAffected
 		}
-		if updated.actionNeeded != nothing && (updated.transactionID != 0 || updated.reservedID != 0) {
+		if info.actionNeeded != nothing && (info.transactionID != 0 || info.reservedID != 0) {
 			appendErr := session.AppendOrUpdate(rs.Target, info, shardSession, stc.txConn.mode)
 			if appendErr != nil {
 				err = appendErr
@@ -901,6 +906,7 @@ type shardActionInfo struct {
 	actionNeeded              actionNeeded
 	reservedID, transactionID int64
 	alias                     *topodatapb.TabletAlias
+	ignoreOldSession          bool
 	rowsAffected              bool
 }