diff --git a/default.yaml b/default.yaml
index 50425552..d4e5cbd0 100644
--- a/default.yaml
+++ b/default.yaml
@@ -950,7 +950,9 @@ history:
 
     # options to store history messages in a persistent database (currently only MySQL).
     # in order to enable any of this functionality, you must configure a MySQL server
-    # in the `datastore.mysql` section.
+    # in the `datastore.mysql` section. enabling persistence overrides the history
+    # size limits above (`channel-length`, `client-length`, etc.); persistent
+    # history has no limits other than those imposed by expire-time.
     persistent:
         enabled: false
 
diff --git a/traditional.yaml b/traditional.yaml
index 3ea879ae..21e46945 100644
--- a/traditional.yaml
+++ b/traditional.yaml
@@ -922,7 +922,9 @@ history:
 
     # options to store history messages in a persistent database (currently only MySQL).
     # in order to enable any of this functionality, you must configure a MySQL server
-    # in the `datastore.mysql` section.
+    # in the `datastore.mysql` section. enabling persistence overrides the history
+    # size limits above (`channel-length`, `client-length`, etc.); persistent
+    # history has no limits other than those imposed by expire-time.
     persistent:
         enabled: false