Remove malloc from FormatFileNumber

Summary: Replace unnecessary malloc with stack allocation

Test Plan: make all check

Reviewers: sdong

Reviewed By: sdong

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D21771
log db path info before open

Summary: 1. write db MANIFEST, CURRENT, IDENTITY, sst files, log files to log before open

Test Plan: run db and check LOG file

Reviewers: ljin, yhchiang, igor, dhruba, sdong

Reviewed By: sdong

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D21459
Add histogram for DB_SEEK

Summary: as title

Test Plan: make release

Reviewers: sdong, yhchiang

Reviewed By: yhchiang

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D21717
print compaction_filter name in Options.Dump

Summary:
Was looking at an issue. All options are the same except
compaction_filter was missed from a newer package. Our option dump does
not capture that

Test Plan: make release

Reviewers: sdong, igor, yhchiang

Reviewed By: yhchiang

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D21765
fix_valgrind_error_caused_in_db_info_dummper

Summary: 1. add default value to FileType type, thus avoid valgrind error

Test Plan: valgrind ./db_test

Reviewers: sdong

Reviewed By: sdong

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D21807
Allow env_posix to lower background thread IO priority

Summary: This is a linux-specific system call.

Test Plan: ran db_bench

Reviewers: igor, yhchiang, sdong

Reviewed By: sdong

Subscribers: haobo, leveldb

Differential Revision: https://reviews.facebook.net/D21183