From c77b90409ae204e8b58e0c54ddac1b8d4479fe79 Mon Sep 17 00:00:00 2001
From: Dirkjan Bussink <d.bussink@gmail.com>
Date: Mon, 23 Oct 2023 09:33:34 +0200
Subject: [PATCH] Fix hang on error

Signed-off-by: Dirkjan Bussink <d.bussink@gmail.com>
---
 go/vt/vtgate/engine/concatenate.go | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/go/vt/vtgate/engine/concatenate.go b/go/vt/vtgate/engine/concatenate.go
index 04d08245b0e..2692f34695d 100644
--- a/go/vt/vtgate/engine/concatenate.go
+++ b/go/vt/vtgate/engine/concatenate.go
@@ -310,8 +310,15 @@ func (c *Concatenate) parallelStreamExec(inCtx context.Context, vcursor VCursor,
 				return callback(resultChunk, currIndex)
 			})
 			if err != nil {
+				muFields.Lock()
+				if rest[currIndex] == nil {
+					// In case we haven't received any fields yet, we need to set it
+					// empty, or otherwise we will keep waiting forever.
+					rest[currIndex] = &sqltypes.Result{}
+				}
 				cancel()
 				condFields.Broadcast()
+				muFields.Unlock()
 			}
 			return err
 		})