Don't overflow size_t in mac
RocksDB 2.8 to be able to read files generated by 2.6

Summary:
From 2.6 to 2.7, property block name is renamed from rocksdb.stats to rocksdb.properties. Older properties were not able to be loaded. In 2.8, we seem to have added some logic that uses property block without checking null pointers, which create segment faults.

In this patch, we fix it by:
(1) try rocksdb.stats if rocksdb.properties is not found
(2) add some null checking before consuming rep->table_properties

Test Plan: make sure a file generated in 2.7 couldn't be opened now can be opened.

Reviewers: haobo, igor, yhchiang

Reviewed By: igor

CC: ljin, xjin, dhruba, kailiu, leveldb

Differential Revision: https://reviews.facebook.net/D17961
Don't compile sync_point if NDEBUG

Summary:
We don't really need sync_point.o if we're compiling with NDEBUG.

This diff depends on D17823

Test Plan: compiles

Reviewers: haobo, ljin, sdong

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17829
Index type doesn't have to be persisted

Summary:

With the recent changes, there is no need to check the property block about the index block type.
If user want to use it, they don't really need any disk format change; everything happens in the fly.

Also another team encountered an error while reading the index type from properties.

Test Plan:

ran all the tests

Reviewers: sdong

CC:

Task ID: #

Blame Rev:
Minimize accessing multiple objects in Version::Get()

Summary:
One of our profilings shows that Version::Get() sometimes is slow when getting pointer of user comparators or other global objects. In this patch:
(1) we keep pointers of immutable objects in Version to avoid accesses them though option objects or cfd objects
(2) table_reader is directly cached in FileMetaData so that table cache don't have to go through handle first to fetch it
(3) If level 0 has less than 3 files, skip the filtering logic based on SST tables' key range. Smallest and largest key are stored in separated memory locations, which has potential cache misses

Test Plan: make all check

Reviewers: haobo, ljin

Reviewed By: haobo

CC: igor, yhchiang, nkg-, leveldb

Differential Revision: https://reviews.facebook.net/D17739
Fix ifdef NDEBUG
Nuke tools/shell

Summary: We don't use or build this code

Test Plan: builds

Reviewers: dhruba

Reviewed By: dhruba

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17979