From be0aae7467bb95a8e8f1f3909464408c20432729 Mon Sep 17 00:00:00 2001
From: Patrik Oldsberg <poldsberg@gmail.com>
Date: Tue, 17 Dec 2024 12:43:36 +0100
Subject: [PATCH] catalog-backend: better concurrency and more eager response
 writing

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>
---
 .changeset/silly-bottles-raise.md                   |  5 +++++
 plugins/catalog-backend/src/service/createRouter.ts | 13 ++++++++++---
 2 files changed, 15 insertions(+), 3 deletions(-)
 create mode 100644 .changeset/silly-bottles-raise.md

diff --git a/.changeset/silly-bottles-raise.md b/.changeset/silly-bottles-raise.md
new file mode 100644
index 0000000000..880d976680
--- /dev/null
+++ b/.changeset/silly-bottles-raise.md
@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-catalog-backend': patch
+---
+
+Improved concurrency of the `entities` endpoint when using the streamed query mode behind the `catalog.disableRelationsCompatibility` flag.
diff --git a/plugins/catalog-backend/src/service/createRouter.ts b/plugins/catalog-backend/src/service/createRouter.ts
index 404d201a44..f0b6793c3f 100644
--- a/plugins/catalog-backend/src/service/createRouter.ts
+++ b/plugins/catalog-backend/src/service/createRouter.ts
@@ -181,6 +181,7 @@ export async function createRouter(
         let cursor: Cursor | undefined;
 
         try {
+          let currentWrite: Promise<boolean> | undefined = undefined;
           do {
             const result = await entitiesCatalog.queryEntities(
               !cursor
@@ -195,15 +196,21 @@ export async function createRouter(
                 : { credentials, fields, limit, cursor },
             );
 
+            // Wait for previous write to complete
+            if (await currentWrite) {
+              return; // Client closed connection
+            }
+
             if (result.items.entities.length) {
-              if (await responseStream.send(result.items)) {
-                return; // Client closed connection
-              }
+              currentWrite = responseStream.send(result.items);
             }
 
             cursor = result.pageInfo?.nextCursor;
           } while (cursor);
 
+          // Wait for last write to complete
+          await currentWrite;
+
           responseStream.complete();
         } finally {
           responseStream.close();