From 57e817b71490c808e471705687c9104e8d8fbe1e Mon Sep 17 00:00:00 2001
From: alexey-milovidov <milovidov@yandex-team.ru>
Date: Thu, 19 Aug 2021 11:47:59 +0300
Subject: [PATCH] Update CHANGELOG.md

---
 CHANGELOG.md | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 103d8e40fd9..71cdac17825 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,8 @@
 ### ClickHouse release v21.8, 2021-08-12
 
+#### Upgrade Notes
+* New version is using `Map` data type for system logs tables (`system.query_log`, `system.query_thread_log`, `system.processes`, `system.opentelemetry_span_log`). These tables will be auto-created with new data types. Virtual columns are created to support old queries. Closes [#18698](https://github.com/ClickHouse/ClickHouse/issues/18698). [#23934](https://github.com/ClickHouse/ClickHouse/pull/23934), [#25773](https://github.com/ClickHouse/ClickHouse/pull/25773) ([hexiaoting](https://github.com/hexiaoting), [sundy-li](https://github.com/sundy-li), [Maksim Kita](https://github.com/kitaisreal)). If you want to *downgrade* from version 21.8 to older versions, you will need to cleanup system tables with logs manually. Look at `/var/lib/clickhouse/data/system/*_log`.
+
 #### New Features
 
 * Add support for a part of SQL/JSON standard. [#24148](https://github.com/ClickHouse/ClickHouse/pull/24148) ([l1tsolaiki](https://github.com/l1tsolaiki), [Kseniia Sumarokova](https://github.com/kssenii)).