From 6a6f956884d09a58a834c964f4a7d9d7016f0a05 Mon Sep 17 00:00:00 2001
From: skrzypo987 <krzysztof.skrzypczynski@starburstdata.com>
Date: Wed, 20 Apr 2022 14:42:06 +0200
Subject: [PATCH] Add a comment to an interface method

---
 .../src/main/java/io/trino/operator/GroupByHash.java       | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/core/trino-main/src/main/java/io/trino/operator/GroupByHash.java b/core/trino-main/src/main/java/io/trino/operator/GroupByHash.java
index 5ca6fdcfcb93..d0a477a12062 100644
--- a/core/trino-main/src/main/java/io/trino/operator/GroupByHash.java
+++ b/core/trino-main/src/main/java/io/trino/operator/GroupByHash.java
@@ -72,6 +72,13 @@ static GroupByHash createGroupByHash(
 
     Work<?> addPage(Page page);
 
+    /**
+     * The order of new group ids need to be the same as the order of incoming rows,
+     * i.e. new group ids should be assigned in rows iteration order
+     * Example:
+     * rows:      A B C B D A E
+     * group ids: 1 2 3 2 4 1 5
+     */
     Work<GroupByIdBlock> getGroupIds(Page page);
 
     boolean contains(int position, Page page, int[] hashChannels);