Merge branch 'stable-3.9' into stable-3.10

* stable-3.9:
  Specify cache.threads = 0 in the multi-site config documentation

Change-Id: I8d52110a924d808ffdf77537cf11e1c8919267d5

src/main/resources/Documentation/config.md

diff --git a/src/main/resources/Documentation/config.md b/src/main/resources/Documentation/config.md
index 3baa911..0485d5b 100644
--- a/src/main/resources/Documentation/config.md
+++ b/src/main/resources/Documentation/config.md
@@ -13,6 +13,9 @@
 ```cache.synchronize```
 :   Whether to synchronize cache evictions. Set to false when relying on
     low cache TTLs and therefore cache eviction is not strictly needed.
+    It requires disabling the background cache evictions notifications in
+    `gerrit.config` by setting `cache.threads = 0`.
+
     Defaults to true.
 
 ```cache.threadPoolSize```