ddl: address comment.
ddl: address comment.

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