doc: add note on the hashsize recommendation for datasets

(cherry picked from commit 3045e75ee1d8196e8bcdb346bfad3b84b851d51a)

diff --git a/doc/userguide/rules/datasets.rst b/doc/userguide/rules/datasets.rst
index b248fe3f91611bef3ea41123d3d18f8adf7db2ba..29696e7b2df16f634859284c52f9af6d67e88b1b 100644 (file)
--- a/doc/userguide/rules/datasets.rst
+++ b/doc/userguide/rules/datasets.rst
@@ -62,6 +62,7 @@ Example::
         memcap: 10mb
         hashsize: 1024
 
+.. note:: The `hashsize` should be close to the amount of entries in the dataset to avoid collisions. If it's set too low, this could result in rather long startup time.
 
 Rule keywords
 -------------