Hi,

*1. Current problem.*
 1.There is more size taking on java heap to create Btree for index file.
It is because we create multiple objects for each leaf node so it takes
more memory inside heap than actual size of index file. while doing LRU
cache also we are considering only index file size instead of objects size
so it impacts the eviction process of LRU cache.
 2. Currently we load one btree on driver side to find the blocks and load
another btree on executor side to find the blocklets. After we have
increased the blocklet size to 128 mb and decrease the table_block size to
256 mb the number of nodes inside driver side btree and executor side btree
is not much different. So it would be overhead to read the same information
twice.
And also chances of loading btree on each executor is more for every query
because there is no guarantee that same block goes to same executor every
time. It will be worse in case of dynamic containers.

*2. Proposed solution.*
 1. To reduce the java heap for Btree , we can remove the Btree data
structure and use simple single array and do binary search on it. And also
we should move this cached arrays to unsafe (offheap/onheap) to reduce the
burden on GC.
 2. Unify the btree to single Btree instead of 2 and load at driver side.
So that only one lookup can be done to find the blocklets directly. And
executors are not required to load the btree for every query.
    We can consider moving this to separate metadata service eventually
once the memory footprint get reduced.

First I will consider point 1 reduce the btree size after that I consider
merging of btrees.

Please comment on it.

-- 
Thanks & Regards,
Ravindra.

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