db_bench: measure the real latency of write/delete
db_bench: measure the real latency of write/delete

Summary: as title

Test Plan: make release

Reviewers: haobo, sdong, yhchiang

Reviewed By: yhchiang

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19227

fengshao0907/rocksdb,wat-ze-hex/rocksdb,zhangpng/rocksdb,sorphi/rocksdb,tizzybec/rocksdb,Andymic/rocksdb,ryneli/rocksdb,temicai/rocksdb,NickCis/rocksdb,caijieming-baidu/rocksdb,sorphi/rocksdb,OverlordQ/rocksdb,siddhartharay007/rocksdb,lgscofield/rocksdb,Applied-Duality/rocksdb,ylong/rocksdb,rDSN-Projects/rocksdb.replicated,SunguckLee/RocksDB,zhangpng/rocksdb,kaschaeffer/rocksdb,rDSN-Projects/rocksdb.replicated,skunkwerks/rocksdb,wenduo/rocksdb,lgscofield/rocksdb,zhangpng/rocksdb,wenduo/rocksdb,jalexanderqed/rocksdb,temicai/rocksdb,SunguckLee/RocksDB,ylong/rocksdb,fengshao0907/rocksdb,luckywhu/rocksdb,tizzybec/rocksdb,amyvmiwei/rocksdb,Andymic/rocksdb,alihalabyah/rocksdb,JoeWoo/rocksdb,dkorolev/rocksdb,bbiao/rocksdb,biddyweb/rocksdb,RyanTech/rocksdb,mbarbon/rocksdb,rDSN-Projects/rocksdb.replicated,tizzybec/rocksdb,JohnPJenkins/rocksdb,tsheasha/rocksdb,dkorolev/rocksdb,vmx/rocksdb,tizzybec/rocksdb,makelivedotnet/rocksdb,geraldoandradee/rocksdb,bbiao/rocksdb,vashstorm/rocksdb,siddhartharay007/rocksdb,siddhartharay007/rocksdb,virtdb/rocksdb,facebook/rocksdb,alihalabyah/rocksdb,anagav/rocksdb,JohnPJenkins/rocksdb,anagav/rocksdb,geraldoandradee/rocksdb,SunguckLee/RocksDB,Vaisman/rocksdb,JoeWoo/rocksdb,msb-at-yahoo/rocksdb,amyvmiwei/rocksdb,geraldoandradee/rocksdb,jalexanderqed/rocksdb,wskplho/rocksdb,zhangpng/rocksdb,facebook/rocksdb,IMCG/RcoksDB,JackLian/rocksdb,tsheasha/rocksdb,anagav/rocksdb,anagav/rocksdb,JohnPJenkins/rocksdb,virtdb/rocksdb,vashstorm/rocksdb,jalexanderqed/rocksdb,skunkwerks/rocksdb,luckywhu/rocksdb,ryneli/rocksdb,skunkwerks/rocksdb,NickCis/rocksdb,JoeWoo/rocksdb,wskplho/rocksdb,mbarbon/rocksdb,makelivedotnet/rocksdb,tsheasha/rocksdb,anagav/rocksdb,Andymic/rocksdb,virtdb/rocksdb,Applied-Duality/rocksdb,JoeWoo/rocksdb,flabby/rocksdb,RyanTech/rocksdb,kaschaeffer/rocksdb,virtdb/rocksdb,tsheasha/rocksdb,facebook/rocksdb,biddyweb/rocksdb,tschottdorf/rocksdb,JackLian/rocksdb,JohnPJenkins/rocksdb,makelivedotnet/rocksdb,JackLian/rocksdb,wskplho/rocksdb,luckywhu/rocksdb,OverlordQ/rocksdb,lgscofield/rocksdb,ryneli/rocksdb,ylong/rocksdb,kaschaeffer/rocksdb,wenduo/rocksdb,NickCis/rocksdb,hobinyoon/rocksdb,jalexanderqed/rocksdb,bbiao/rocksdb,IMCG/RcoksDB,wlqGit/rocksdb,msb-at-yahoo/rocksdb,dkorolev/rocksdb,SunguckLee/RocksDB,hobinyoon/rocksdb,makelivedotnet/rocksdb,hobinyoon/rocksdb,NickCis/rocksdb,jalexanderqed/rocksdb,tizzybec/rocksdb,vmx/rocksdb,wenduo/rocksdb,JackLian/rocksdb,wskplho/rocksdb,Andymic/rocksdb,caijieming-baidu/rocksdb,biddyweb/rocksdb,Vaisman/rocksdb,wskplho/rocksdb,RyanTech/rocksdb,facebook/rocksdb,Applied-Duality/rocksdb,flabby/rocksdb,vashstorm/rocksdb,caijieming-baidu/rocksdb,zhangpng/rocksdb,lgscofield/rocksdb,Andymic/rocksdb,facebook/rocksdb,sorphi/rocksdb,wenduo/rocksdb,amyvmiwei/rocksdb,wat-ze-hex/rocksdb,NickCis/rocksdb,JackLian/rocksdb,amyvmiwei/rocksdb,alihalabyah/rocksdb,wat-ze-hex/rocksdb,temicai/rocksdb,wat-ze-hex/rocksdb,facebook/rocksdb,RyanTech/rocksdb,fengshao0907/rocksdb,Andymic/rocksdb,alihalabyah/rocksdb,geraldoandradee/rocksdb,flabby/rocksdb,OverlordQ/rocksdb,makelivedotnet/rocksdb,lgscofield/rocksdb,Applied-Duality/rocksdb,ylong/rocksdb,Andymic/rocksdb,JoeWoo/rocksdb,RyanTech/rocksdb,skunkwerks/rocksdb,facebook/rocksdb,siddhartharay007/rocksdb,wskplho/rocksdb,norton/rocksdb,hobinyoon/rocksdb,wlqGit/rocksdb,tizzybec/rocksdb,tsheasha/rocksdb,kaschaeffer/rocksdb,alihalabyah/rocksdb,fengshao0907/rocksdb,Vaisman/rocksdb,bbiao/rocksdb,geraldoandradee/rocksdb,lgscofield/rocksdb,geraldoandradee/rocksdb,sorphi/rocksdb,vashstorm/rocksdb,sorphi/rocksdb,facebook/rocksdb,kaschaeffer/rocksdb,vashstorm/rocksdb,Applied-Duality/rocksdb,sorphi/rocksdb,ylong/rocksdb,norton/rocksdb,hobinyoon/rocksdb,RyanTech/rocksdb,OverlordQ/rocksdb,mbarbon/rocksdb,tsheasha/rocksdb,tsheasha/rocksdb,caijieming-baidu/rocksdb,wenduo/rocksdb,ryneli/rocksdb,msb-at-yahoo/rocksdb,IMCG/RcoksDB,mbarbon/rocksdb,hobinyoon/rocksdb,ylong/rocksdb,msb-at-yahoo/rocksdb,JohnPJenkins/rocksdb,virtdb/rocksdb,tsheasha/rocksdb,norton/rocksdb,wat-ze-hex/rocksdb,NickCis/rocksdb,luckywhu/rocksdb,biddyweb/rocksdb,siddhartharay007/rocksdb,jalexanderqed/rocksdb,SunguckLee/RocksDB,rDSN-Projects/rocksdb.replicated,Vaisman/rocksdb,alihalabyah/rocksdb,wat-ze-hex/rocksdb,wat-ze-hex/rocksdb,fengshao0907/rocksdb,vmx/rocksdb,kaschaeffer/rocksdb,caijieming-baidu/rocksdb,tschottdorf/rocksdb,msb-at-yahoo/rocksdb,dkorolev/rocksdb,vmx/rocksdb,dkorolev/rocksdb,IMCG/RcoksDB,vmx/rocksdb,fengshao0907/rocksdb,siddhartharay007/rocksdb,bbiao/rocksdb,temicai/rocksdb,JoeWoo/rocksdb,wenduo/rocksdb,wlqGit/rocksdb,Applied-Duality/rocksdb,temicai/rocksdb,vmx/rocksdb,temicai/rocksdb,flabby/rocksdb,NickCis/rocksdb,wlqGit/rocksdb,makelivedotnet/rocksdb,kaschaeffer/rocksdb,luckywhu/rocksdb,makelivedotnet/rocksdb,ryneli/rocksdb,OverlordQ/rocksdb,mbarbon/rocksdb,virtdb/rocksdb,biddyweb/rocksdb,JackLian/rocksdb,JoeWoo/rocksdb,RyanTech/rocksdb,luckywhu/rocksdb,alihalabyah/rocksdb,caijieming-baidu/rocksdb,rDSN-Projects/rocksdb.replicated,ylong/rocksdb,zhangpng/rocksdb,skunkwerks/rocksdb,JohnPJenkins/rocksdb,Andymic/rocksdb,lgscofield/rocksdb,OverlordQ/rocksdb,SunguckLee/RocksDB,amyvmiwei/rocksdb,norton/rocksdb,caijieming-baidu/rocksdb,biddyweb/rocksdb,IMCG/RcoksDB,zhangpng/rocksdb,luckywhu/rocksdb,anagav/rocksdb,rDSN-Projects/rocksdb.replicated,norton/rocksdb,amyvmiwei/rocksdb,JohnPJenkins/rocksdb,norton/rocksdb,IMCG/RcoksDB,Applied-Duality/rocksdb,tschottdorf/rocksdb,virtdb/rocksdb,dkorolev/rocksdb,bbiao/rocksdb,mbarbon/rocksdb,tizzybec/rocksdb,flabby/rocksdb,SunguckLee/RocksDB,rDSN-Projects/rocksdb.replicated,flabby/rocksdb,hobinyoon/rocksdb,siddhartharay007/rocksdb,JackLian/rocksdb,vashstorm/rocksdb,vashstorm/rocksdb,msb-at-yahoo/rocksdb,vmx/rocksdb,sorphi/rocksdb,Vaisman/rocksdb,skunkwerks/rocksdb,dkorolev/rocksdb,jalexanderqed/rocksdb,OverlordQ/rocksdb,amyvmiwei/rocksdb,flabby/rocksdb,wskplho/rocksdb,norton/rocksdb,tschottdorf/rocksdb,IMCG/RcoksDB,vmx/rocksdb,tschottdorf/rocksdb,Vaisman/rocksdb,wat-ze-hex/rocksdb,ryneli/rocksdb,wlqGit/rocksdb,wenduo/rocksdb,wlqGit/rocksdb,temicai/rocksdb,wlqGit/rocksdb,SunguckLee/RocksDB,hobinyoon/rocksdb,bbiao/rocksdb,tschottdorf/rocksdb,fengshao0907/rocksdb,anagav/rocksdb,bbiao/rocksdb,skunkwerks/rocksdb,geraldoandradee/rocksdb,norton/rocksdb,mbarbon/rocksdb,ryneli/rocksdb,biddyweb/rocksdb,Vaisman/rocksdb