kv: update comments
kv: update comments

silenceper/tidb,astaxie/tidb,andelf/tidb,ming-relax/tidb,c4pt0r/tidb,cosmtrek/tidb,zimulala/tidb,qhsong/tidb,simon-xia/tidb,silenceper/tidb,yangwenmai/tidb,yuanwhy/tidb,Nify/tidb,pingcap/tidb,ngaut/tidb,tiancaiamao/tidb,ming-relax/tidb,CodeRushing/tidb,JinheLin/tidb,zimulala/tidb,ngaut/tidb,tiancaiamao/tidb,ngaut/tidb,anywhy/tidb,kyle-wang/tidb,Cofyc/tidb,zs634134578/tidb,andelf/tidb,8cbx/tidb,kyle-wang/tidb,mccxj/tidb,coocood/tidb,silentred/tidb,ngaut/tidb,mccxj/tidb,ueizhou/tidb,c4pt0r/tidb,qiuyesuifeng/tidb,astaxie/tidb,XuHuaiyu/tidb,EvilMcJerkface/tidb,qhsong/tidb,kyle-wang/tidb,Nify/tidb,spongedu/tidb,pingcap/tidb,kyle-wang/tidb,cosmtrek/tidb,EvilMcJerkface/tidb,liyu4/tidb,8cbx/tidb,yangwenmai/tidb,c4pt0r/tidb,gaocegege/tidb,simon-xia/tidb,louishust/tidb,wusphinx/tidb,anywhy/tidb,louishust/tidb,JinheLin/tidb,gaocegege/tidb,c4pt0r/tidb,spongedu/tidb,pingcap/tidb,XuHuaiyu/tidb,coocood/tidb,qiuyesuifeng/tidb,wusphinx/tidb,liyu4/tidb,zs634134578/tidb,Cofyc/tidb,pingcap/tidb,pingcap/tidb,kyle-wang/tidb,ngaut/tidb,ngaut/tidb,myrice/tidb,pingcap/tidb,kyle-wang/tidb,c4pt0r/tidb,c4pt0r/tidb,CodeRushing/tidb,yuanwhy/tidb,ueizhou/tidb,silentred/tidb,myrice/tidb