lmdb.h Caveats: Reserved vs. actual mem/disk usage

libraries/liblmdb/lmdb.h

@@ -78,6 +78,11 @@
  *	  access to locks and lock file. Exceptions: On read-only filesystems
  *	  or with the #MDB_NOLOCK flag described under #mdb_env_open().
  *
+ *	- An LMDB configuration will often reserve considerable \b unused
+ *	  memory address space and maybe file size for future growth.
+ *	  This does not use actual memory or disk space, but users may need
+ *	  to understand the difference so they won't be scared off.
+ *
  *	- By default, in versions before 0.9.10, unused portions of the data
  *	  file might receive garbage data from memory freed by other code.
  *	  (This does not happen when using the #MDB_WRITEMAP flag.) As of