DOCS-580 first draft of changes

Author: Bob Grabar

source/faq/fundamentals.txt

@@ -135,22 +135,20 @@ in RAM, MongoDB serves all queries from memory.
 MongoDB does not implement a query cache: MongoDB serves all queries
 directly from the indexes and/or data files.
 
-Does MongoDB require a separate object-caching layer?
------------------------------------------------------
-
-No. MongoDB integrates databases with object caches such that an
-object's representation in the database is very close to its
-representation in memory. Retrieval from RAM is a far less expensive
-operation for MongoDB than it is for a traditional RDMS. For an RDMS, a
-high expense is incurred when data must be transformed into an object
-representation when transferred to RAM.
-
-Additionally, MongoDB's integration of databases with memory means there
-is no risk of retrieving stale data from the cache.
-
-Keep in mind, though, that in MongoDB retrieving from RAM is always
-faster than from disk, and it is best to have enough memory to fit all
-of your working data set.
+Does MongoDB require a separate caching layer for application-level caching?
+----------------------------------------------------------------------------
+
+No. In MongoDB, a document's representation in the database is similar
+to its representation in application memory. This means the database
+already stores the usable form of data, making the data usable in both
+the persistent store and in the application cache. This eliminates the
+need for a separate caching layer in the application.
+
+This differs from relational databases, where caching data is more
+expensive. Relational databases must transform data into object
+representations that applications can read and must store the
+transformed data in a separate cache. If joins are required that adds to
+the overhead.
 
 What language is MongoDB written in?
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