diff --git a/sql/postgres_tables_cache_hit_ratio.sql b/sql/postgres_tables_cache_hit_ratio.sql
index d3212514..9de06e51 100644
--- a/sql/postgres_tables_cache_hit_ratio.sql
+++ b/sql/postgres_tables_cache_hit_ratio.sql
@@ -15,7 +15,7 @@
 
 -- PostgreSQL Tables Cache-hit Ratio
 --
--- should be closer to 1, eg. 0.99
+-- should be closer to 1, eg. 0.99, at least 0.90
 
 SELECT
   SUM(heap_blks_read) AS heap_blks_read,