BTreeMap: small perf improvements
BTreeMap: small perf improvements

jankotek/mapdb,sumit784/mapdb,cocosli/mapdb,jankotek/mapdb,morfeo8marc/mapdb,ffjiao/mapdb,hangum/mapdb,binarytemple/mapdb,pettermahlen/mapdb,SleimanJneidi/mapdb,lamfire/mapdb,ringoluo/mapdb,jankotek/MapDB,jankotek/MapDB,codeaudit/mapdb