+ * <li>#MDB_CLEANMEM
+ * Don't write uninitialized memory to unused spaces in the datafile.
+ * By default, memory for pages written to the datafile is obtained
+ * using malloc, and only the portions that LMDB uses are modified.
+ * Unused portions of a page may contain leftover data from other
+ * code that used the heap and subsequently freed that memory.
+ * That can be a problem for applications which handle sensitive data
+ * like passwords, and it makes memory checkers like Valgrind noisy.
+ * With this flag, unused portions of pages will be initialized to
+ * zero. This flag is not needed with #MDB_WRITEMAP, which writes
+ * directly to the mmap instead of using malloc for pages. The
+ * initialization is also skipped if #MDB_RESERVE is used; the
+ * caller is expected to overwrite all of the memory that was
+ * reserved in that case.
+ * This flag may be changed at any time using #mdb_env_set_flags().
+ * It comes at some performance cost.