RocksJava - FindBugs issues

Addressed some FindBugs issues.
[RocksJava] Remove obsolete dbFolder cleanup
[RocksJava] Comparator tests for CF

- Added AbstractComparatorTest.
- Fixed a bug in the JNI Part about Java comparators
[RocksJava] Quality improvements

Summary:
- Addressed some FindBugs issues.
- Remove obsolete dbFolder cleanup
- Comparator tests for CF
 - Added AbstractComparatorTest.
 - Fixed a bug in the JNI Part about Java comparators
- Minor test improvements

Test Plan:
make rocksdbjava
make jtest
mvn -f rocksjni.pom package

Reviewers: adamretter, yhchiang, ankgup87

Subscribers: dhruba

Differential Revision: https://reviews.facebook.net/D29571
Fixed a Lint problem
Integrated changes from D29571
Bump version to 3.9
Replace exception by abort() in dummy HdfsEnv implementation.

Summary: Replace exception by abort() in dummy HdfsEnv implementation.

Test Plan: make dbg -j32

Reviewers: sdong, igor

Reviewed By: igor

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D29895
Provide mechanism to restart tests from previous error

Summary:
While running rocksdb tests, we sometimes encounter errors and
the test run stops. We now provide a new make target call check_some
which restarts the test run from a specific test and continues from
there depending on the value of the environment variable ROCKSDBTESTS_START

Test Plan:
Run make check_some with different values of
ROCKSDBTESTS_START.

Reviewers: igor

Reviewed By: igor

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D29913
Add DBProperty to return number of snapshots and time for oldest snapshot

Summary:
Add a counter in SnapshotList to show number of snapshots. Also a unix timestamp in every snapshot.
Add two DB Properties to return number of snapshots and timestamp of the oldest one.

Test Plan: Add unit test checking

Reviewers: yhchiang, rven, igor

Reviewed By: igor

Subscribers: leveldb, dhruba, MarkCallaghan

Differential Revision: https://reviews.facebook.net/D29919
Add -fno-exceptions flag to ROCKSDB_LITE.

Summary: Add -fno-exceptions flag to ROCKSDB_LITE.

Test Plan: make OPT=-DROCKSDB_LITE shared_lib -j32

Reviewers: sdong, igor

Reviewed By: igor

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D29901
Merge pull request #422 from fyrz/RocksJava-Quality-Improvements

Rocks java quality improvements
Fix problem with create_if_missing option when wal_dir is used

Summary: When wal_dir is used, DestroyDB is not passed the wal_dir option and so we get a Corruption exception.

Test Plan:
Verified manually that the following command line works now:
./db_bench --db=/mnt/db/rocksdb ... --disable_wal=0 --wal_dir=/data/users/rocksdb/WAL... --benchmarks=filluniquerandom --use_existing_db=0...

Reviewers: sdong

Reviewed By: sdong

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D29859
Update HISTORY.md for release 3.9
Fix calculation of max_total_wal_size in db_options_.max_total_wal_size == 0 case

Summary: This is a regression bug introduced by https://reviews.facebook.net/D24729 . max_total_wal_size would be off the target it should be more and more in the case that the a user holds the current super version after flush or compaction. This patch fixes it

Test Plan: make all check

Reviewers: yhchiang, rven, igor

Reviewed By: igor

Subscribers: ljin, yoshinorim, MarkCallaghan, hermanlee4, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D29961
Fix #434

Summary: Why do we assert here? This doesn't seem like user friendly thing to do :)

Test Plan: none

Reviewers: sdong, yhchiang, rven

Reviewed By: rven

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D30027
add range scan test to benchmark script

Summary: as title

Test Plan: ran it

Reviewers: yhchiang, igor, sdong, MarkCallaghan

Reviewed By: MarkCallaghan

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D25563
VersionBuilder to use unordered set and map to store added and deleted files

Summary: Set operations in VerisonBuilder is shown as a performance bottleneck of restarting DB when there are lots of files. Make both of added_files and deleted_files use unordered set or map. Only when adding the files, sort the added files.

Test Plan: make all check

Reviewers: yhchiang, rven, igor

Reviewed By: igor

Subscribers: hermanlee4, leveldb, dhruba, ljin

Differential Revision: https://reviews.facebook.net/D30051
Modifed the LRU cache eviction code so that it doesn't evict blocks which have exteranl references

Summary:
Currently, blocks which have more than one reference (ie referenced by something other than cache itself) are evicted from cache. This doesn't make much sense:
- blocks are still in RAM, so the RAM usage reported by the cache is incorrect
- if the same block is needed by another iterator, it will be loaded and decompressed again

This diff changes the reference counting scheme a bit. Previously, if the cache contained the block, this was accounted for in its refcount. After this change, the refcount is only used to track external references. There is a boolean flag which indicates whether or not the block is contained in the cache.
This diff also changes how LRU list is used. Previously, both hashtable and the LRU list contained all blocks. After this change, the LRU list contains blocks with the refcount==0, ie those which can be evicted from the cache.

Note that this change still allows for cache to grow beyond its capacity. This happens when all blocks are pinned (ie refcount>0). This is consistent with the current behavior. The cache's insert function never fails. I spent lots of time trying to make table_reader and other places work with the insert which might failed. It turned out to be pretty hard. It might really destabilize some customers, so finally, I decided against doing this.

table_cache_remove_scan_count_limit option will be unneeded after this change, but I will remove it in the following diff, if this one gets approved

Test Plan: Ran tests, made sure they pass

Reviewers: sdong, ljin

Differential Revision: https://reviews.facebook.net/D25503
Improve scalability of DB::GetSnapshot()

Summary: Now DB::GetSnapshot() doesn't scale to more column families, as it needs to go through all the column families to find whether snapshot is supported. This patch optimizes it.

Test Plan:
Add unit tests to cover negative cases.
make all check

Reviewers: yhchiang, rven, igor

Reviewed By: igor

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D30093