[DOC-12004] Add a note about completed_requests eviction order behavior (#641)

Author: rakhi-prathap

modules/n1ql/pages/n1ql-manage/monitoring-n1ql-query.adoc

@@ -822,6 +822,10 @@ curl $BASE_URL/admin/settings -u $USER:$PASSWORD \
   -d '{"completed-limit":1000}'
 ----
 
+NOTE: To optimize performance, the completed requests catalog uses a generic cache that does not guarantee a strict eviction order.
+When the catalog reaches the specified limit, it evicts requests based on when they complete, and not when they start. 
+As a result, it may remove a request with a later start time (`requestTime`) that completes quickly before it removes a long-running request with an earlier start time that completes later.
+
 [[sys-history]]
 == Stream Completed Requests