Additional features in innodb have added new variables in memory
structures which increases the total memory usage. In dict_index_t
in-memory structure which is allocated for each index these three
additional members are added in mysql-5.7.


last_ops_cur_t* last_ins_cur :- cache the last insert position.
last_ops_cur_t* last_sel_cur :- cache the last selected position
rec_cache_t     rec_cache    :- cache the field that needs to be
                                re-computed on each insert.

These three caches are only used for temporary or intrinsic tables
but memory for them is allocated for all tables which increases
the overall usage of memory

Fix
---
This fix optimizes the memory usage by allocating memory for these
caches only when they are used .