Cluster: send a ping to every node we never contacted in timeout/2 seconds.
Cluster: send a ping to every node we never contacted in timeout/2 seconds.

Usually we try to send just 1 ping every second, however when we detect
we are going to have unreliable failure detection because we can't ping
some node in time, send an additional ping.

This should only happen with very large clusters or when the the node
timeout is set to a very low value.

LongXQ/redis,gilala/bjredis,atreeyang/redis,MasahikoSawada/redis,Soledad89/redis,miaoyc1989/redis-3.0-annotated,fankeke/redis-3.0-annotated,charsyam/redis,mcanthony/redis,jbochi/redis,huangz1990/experiment-redis,yuhc/redis-benchmark-enhanced,arijitvt/redis,mgk/redis,ipmobiletech/redis,itugs/redis,weizijun/redis,hornen/redis,modulexcite/redis,PKRoma/redis,a-pavlov/redis,ramonsnir/redis,colstrom/redis,idning/redis,twskipper/redis,cusspvz/redis,spinlock/redis,roth1002/redis,magastzheng/redis-3.0-annotated,izhoujie/redis,kaushik94/redis,unasm/redis-3.0-annotated,hornen/redis,whille/redis-3.0-annotated,nuxeh/redis,jacklee0810/redis-3.0-annotated,itugs/redis,rogerchina/redis,devaos/redis,tjschuck/redis,Markgorden/redis,Soledad89/redis,july2993/redis,mverrilli/redis,seppo0010/redis,pietern/redis,pmem/redis,SummonY/redis,Sciumo/redis,nilyang/redis-tdd-annotation,jasonkying/redis,ytjiang/redis,jbochi/parallel_redis,soveran/redis,nnog/redis,wprice/redis,slfs007/mk-redis,gilala/hbjredis,blackmady/redis,kensou97/redis,antirez/redis,healerkx/redis,unasm/redis-3.0-annotated,wuyu201321060203/redis-3.0-annotated,xujunhai1991/redis,Aliceljm1/redis,shreesundara/redis,spearhead-ea/redis,StevenTsai/redis,supasate/redis,elkingtonmcb/redis,sunlianqiang/redis-3.0-annotated,duanx/redis,ipmobiletech/redis,brg-liuwei/redis,z-fork/redis,zy416548283/redis-3.0-annotated,mpalmer/redis,badboy/redis,ketor/redis,allengaller/redis,pedigree/redis,wuyu201321060203/redis-3.0-annotated,CodeJuan/redis,qiyang0221/redis,gilala/hbjredis,cusspvz/redis,GrimDerp/redis,nuxeh/redis,charsyam/redis,haima-zju/redis-3.0-annotated,clamoriniere1A/redis,wangyikai/redis,Aliceljm1/redis,Wangyao14cyy/redis,NBSW/redis,Aaron1992/redis,sunheehnus/redis,csuhawk/redis,ReadCode/redis-3.0-annotated,onlymellb/redis-3.0-annotated,gilala/bjredis,soveran/redis,yuhc/redis-benchmark-enhanced,GitHubMota/redis,valdsJohn/redis,zhoudayang/redis,ksarch-saas/redis,0x20h/redis,oranagra/redis,takeshineshiro/redis,itamarhaber/redis,jingjidejuren/redis,wujf/redis,mcanthony/redis,drinkthere/redis-3.0-annotated,francischan714/redis,pietern/redis,xuguruogu/redis,YongMan/redis,badboy/redis,pcarrier/redis,kensou97/redis,0x55/redis-3.0-annotated,seppo0010/redis,neomantra/redis,clamoriniere1A/redis,hawkchch/redis,YuanZhewei/redis,huangz1990/redis-3.0-annotated,tanghaodong25/redis,july2993/redis,darksideofthemoo/redis-histogram,mengyou0304/redis,tellapart/redis,alenslan/redis,rogerlz/redis,jingjidejuren/redis,colstrom/redis,zhaobo1023/redis-3.0-annotated,ttuna/msot-redis,wprice/redis,YuanZhewei/redis,MSOpenTech/redis,spearhead-ea/redis,iandyh/redis,cloudrain21/redis,ouyangkongtong/redis,riyan8250/redis,ttuna/msot-redis,gechong/redis-3.0-annotated,sunheehnus/redis,mumingv/redis,mingyaaaa/redis,tanghaodong25/redis,ctripcorp/redis,yuzhangjob/redis-3.0-annotated-unstable,ksarch-saas/redis,linfangrong/redis,hgl888/redis,neomantra/redis,Markgorden/redis,universsky/redis,louisliangjun/redis,itamarhaber/redis,HunanTV/redis,gilala/redis,mpalmer/redis,YuraLukashik/redis,ncopa/redis,Hailei/redis,weizijun/redis,Wangyao14cyy/redis,Aaron1992/redis,pcarrier/redis,modulexcite/redis,MSOpenTech/redis,shshlzh/redis-3.0-annotated,hornen/redis,holstvoogd/redis,elkingtonmcb/redis,zczhuohuo/redis,gaoxianglong/redis,pkdevbox/redis,neomantra/redis,HeartSaVioR/redis,francischan714/redis,harrisonfeng/redis,ofirluzon/redis,YongMan/redis,mumingv/redis-3.0-annotated,zguangyu/redis,WorkingOfTimtohyZhang/redis-3.0-annotated,universsky/redis,cusspvz/redis,qiyang0221/redis,pcarrier/redis,timothyohare/3rdPartySrc-redis,NBSW/redis,iandyh/redis,wujf/redis,shshlzh/redis-3.0-annotated,atreeyang/redis,4396/redis,j0hnma/hszredis,pedigree/redis,soveran/redis,GitHubMota/redis,weizijun/redis,linfangrong/redis,janekmi/redis,AplayER/redis,ytjiang/redis,0x20h/redis,guker/redis,thomasdarimont/redis,ofirluzon/redis,linfangrong/redis,RepmujNetsik/redis,4396/redis,CodeJuan/redis,jackyan/redis,HeartSaVioR/redis,ErikDubbelboer/redis,davidradunz/redis,hornen/redis,yuhc/redis-benchmark-enhanced,sunlianqiang/redis-3.0-annotated,a-pavlov/redis,josiahcarlson/redis,aim-for-better/redis,twskipper/redis,himoca/redis,YongMan/redis,wuyu201321060203/redis-3.0-annotated,jackyan/redis,wangyikai/redis,harrisonfeng/redis,hgl888/redis,tellapart/redis,ctripcorp/redis,jbochi/parallel_redis,SyntaxStacks/redis,jbochi/redis,nilyang/redis-tdd-annotation,PKRoma/redis,magastzheng/redis-3.0-annotated,YuanZhewei/redis,taoguan/redis,OmarQunsul/graph-redis,honestme/redis,sunheehnus/redis,maodeyi/redis_lua,Aliceljm1/redis-3.0-annotated,aim-for-better/redis,citusdata/redis,charsyam/redis,ketor/redis,ncopa/redis,Soledad89/redis,shining-yang/redis,yossigo/redis,SummonY/redis,PradheepShrinivasan/redis,maodeyi/redis_lua,flashbuckets/redis,YuraLukashik/redis,soloestoy/redis,AALEKH/redis,holstvoogd/redis,h0x91b/redis,seppo0010/rlite-server,rogerlz/redis,mengyou0304/redis,YongMan/redis,dongqifan2/redis-3.0-annotated,josiahcarlson/redis,abhiklodh/redis,programmecat/redis,universsky/redis,onlymellb/redis-3.0-annotated,moonbingbing/redis-3.0-annotated,LongXQ/redis,wenxueliu/redis_comment,GrimDerp/redis,ketor/redis,NBSW/redis,citusdata/redis,antirez/redis,Soledad89/redis,RepmujNetsik/redis,nuxeh/redis,alenslan/redis,alenslan/redis,rouzier/redis,RepmujNetsik/redis,Wangyao14cyy/redis,idning/redis,ctripcorp/redis,mengzhejin/RedisStudy,flashbuckets/redis,guker/redis,izhoujie/redis,ttuna/msot-redis,zhiliaoniu/redis,Hailei/redis,seppo0010/rlite-server,Aaron1992/redis,janekmi/redis,blackmady/redis,GrimDerp/redis,buobao/redis-3.0-annotated,ouyangkongtong/redis,dayuoba/redis,neomantra/redis,MSOpenTech/redis,ofirluzon/redis,huyuezheng/redis,SyntaxStacks/redis,GitHubMota/redis,xuzhezhaozhao/redis_reading,shreesundara/redis,4396/redis,tellapart/redis,mgk/redis,shshlzh/redis-3.0-annotated,Hailei/redis,programmecat/redis,miaoyc1989/redis-3.0-annotated,kmiku7/redis,gilala/hredis,wbailey5/redis,timothyohare/3rdPartySrc-redis,soloestoy/redis,ituncle/redis,ttuna/msot-redis,holstvoogd/redis,moonbingbing/redis-3.0-annotated,soloestoy/redis,ytjiang/redis,charsyam/redis,kmiku7/redis,spinlock/redis,PKRoma/redis,hedisdb/hedis,ituncle/redis,ouyangkongtong/redis,timothyohare/3rdPartySrc-redis,fengshao0907/redis-3.0-annotated,simplestbest/redis,vincent-vivian-liu/redis,ramonsnir/redis,miaoyc1989/redis-3.0-annotated,OmarQunsul/graph-redis,clamoriniere1A/redis,spinlock/redis,cnbin/redis,idning/redis,MSOpenTech/redis,pkdevbox/redis,seandsky/redis,huangz1990/redis-3.0-annotated,splitice/redis,roth1002/redis,AplayER/redis,rogerchina/redis,wbailey5/redis,oranagra/redis,yybirdcf/learn-redis,AALEKH/redis,mengzhejin/RedisStudy,huangz1990/experiment-redis,jxwr/redis,a-pavlov/redis,onlymellb/redis-3.0-annotated,gilala/hredis,modulexcite/redis,rrsean/redis-3.0-annotated,jackyan/redis,190235047/redis,saisai/redis,thomasdarimont/redis,MOON-CLJ/redis,mcanthony/redis,shining-yang/redis,jingjidejuren/redis,atreeyang/redis,splitice/redis,davidradunz/redis,simplestbest/redis,janekmi/redis,cusspvz/redis,shreesundara/redis,nilyang/redis-tdd-annotation,pedigree/redis,vincent-vivian-liu/redis,ncopa/redis,wujf/redis,riyan8250/redis,allengaller/redis,yybirdcf/learn-redis,qiyang0221/redis,RepmujNetsik/redis,kmiku7/redis,huangz1990/experiment-redis,dayuoba/redis,Aaron1992/redis,shining-yang/redis,duanx/redis,xuzhezhaozhao/redis_reading,cloudrain21/redis,Wangyao14cyy/redis,programmecat/redis,PKRoma/redis,thomasdarimont/redis,zy416548283/redis-3.0-annotated,dongqifan2/redis-3.0-annotated,PKRoma/redis,SummonY/redis,dreamquster/redis,simplestbest/redis,tanghaodong25/redis,h0x91b/redis,PradheepShrinivasan/redis,zhoudayang/redis,rrsean/redis-3.0-annotated,ErikDubbelboer/redis,spearhead-ea/redis,GitHubMota/redis,zhcy/redis,ton31337/redis,seppo0010/rlite-server,haima-zju/redis-3.0-annotated,arijitvt/redis,gechong/redis-3.0-annotated,fengshao0907/redis,seandsky/redis,gilala/redis,jackyan/redis,NBSW/redis,supasate/redis,fankeke/redis-3.0-annotated,gilala/redis,tjschuck/redis,z-fork/redis,roth1002/redis,j0hnma/hszredis,SyntaxStacks/redis,brg-liuwei/redis,devaos/redis,itamarhaber/redis,jxwr/redis,tanghaodong25/redis,zczhuohuo/redis,ouyangkongtong/redis,Aliceljm1/redis-3.0-annotated,darksideofthemoo/redis-histogram,HouKangkang/redis-3.0-annotated,SummonY/redis,huangz1990/experiment-redis,Markgorden/redis,wangyikai/redis,mpalmer/redis,saisai/redis,zhoudayang/redis,charsyam/redis,wuyu201321060203/redis-3.0-annotated,kaushik94/redis,aim-for-better/redis,fengshao0907/redis-3.0-annotated,izhoujie/redis,maodeyi/redis_lua,WorkingOfTimtohyZhang/redis-3.0-annotated,miaoyc1989/redis-3.0-annotated,takeshineshiro/redis,yuzhangjob/redis-3.0-annotated-unstable,netroby/redis,duanx/redis,h0x91b/redis,fengshao0907/redis,supasate/redis,abhiklodh/redis,nnog/redis,whille/redis-3.0-annotated,a-pavlov/redis,tellapart/redis,ErikDubbelboer/redis,hedisdb/hedis,slfs007/mk-redis,rouzier/redis,j0hnma/szredis,ReadCode/redis-3.0-annotated,brg-liuwei/redis,190235047/redis,elkingtonmcb/redis,healerkx/redis,YuraLukashik/redis,supasate/redis,zguangyu/redis,gilala/bjredis,july2993/redis,alenslan/redis,MasahikoSawada/redis,unasm/redis-3.0-annotated,buobao/redis-3.0-annotated,gongice/redis-3.0-annotated,zhiliaoniu/redis,Aliceljm1/redis-3.0-annotated,vincent-vivian-liu/redis,mumingv/redis-3.0-annotated,iandyh/redis,adamweixuan/redis-3.0-annotated,sunheehnus/redis,dongqifan2/redis-3.0-annotated,netroby/redis,fengshao0907/redis,HunanTV/redis,zhcy/redis,rrsean/redis-3.0-annotated,splitice/redis,riyan8250/redis,cloudrain21/redis,StevenTsai/redis,cloudrain21/redis,louisliangjun/redis,huyuezheng/redis,mingyaaaa/redis,AplayER/redis,jacklee0810/redis-3.0-annotated,shshlzh/redis-3.0-annotated,jasonkying/redis,mumingv/redis-3.0-annotated,davidradunz/redis,mengzhejin/RedisStudy,Aliceljm1/redis,WorkingOfTimtohyZhang/redis-3.0-annotated,xujunhai1991/redis,valdsJohn/redis,adamweixuan/redis-3.0-annotated,nnog/redis,allengaller/redis,mcanthony/redis,oranagra/redis,francischan714/redis,drinkthere/redis-3.0-annotated,nilyang/redis-tdd-annotation,holstvoogd/redis,yuhc/redis-benchmark-enhanced,fengshao0907/redis,gilala/bjredis,yybirdcf/learn-redis,tjschuck/redis,wprice/redis,mingyaaaa/redis,xuzhezhaozhao/redis_reading,hgl888/redis,whille/redis-3.0-annotated,haima-zju/redis-3.0-annotated,netroby/redis,devaos/redis,MasahikoSawada/redis,Markgorden/redis,colstrom/redis,huyuezheng/redis,wujf/redis,itamarhaber/redis,devaos/redis,gongice/redis-3.0-annotated,0x20h/redis,jxwr/redis,yossigo/redis,yybirdcf/learn-redis,rouzier/redis,xuguruogu/redis,guker/redis,mgk/redis,zhoudayang/redis,twskipper/redis,taoguan/redis,StevenTsai/redis,fankeke/redis-3.0-annotated,sunlianqiang/redis-3.0-annotated,SyntaxStacks/redis,zguangyu/redis,z-fork/redis,fengshao0907/redis-3.0-annotated,idning/redis,jingjidejuren/redis,universsky/redis,adamweixuan/redis-3.0-annotated,msn217/redis-3.0-annotated,nnog/redis,healerkx/redis,gaoxianglong/redis,190235047/redis,josiahcarlson/redis,honestme/redis,mumingv/redis,shining-yang/redis,msn217/redis-3.0-annotated,darksideofthemoo/redis-histogram,pietern/redis,honestme/redis,clamoriniere1A/redis,badboy/redis,soveran/redis,nuxeh/redis,mverrilli/redis,jbochi/parallel_redis,pmem/redis,neomantra/redis,mattsta/redis,mengyou0304/redis,AALEKH/redis,thomasdarimont/redis,louisliangjun/redis,csuhawk/redis,ramonsnir/redis,zhaobo1023/redis-3.0-annotated,jbochi/redis,JoeWoo/redis,gilala/hredis,LongXQ/redis,seandsky/redis,guker/redis,xujunhai1991/redis,xuguruogu/redis,pcarrier/redis,CodeJuan/redis,valdsJohn/redis,AplayER/redis,badboy/redis,louisliangjun/redis,wenxueliu/redis_comment,gongice/redis-3.0-annotated,tzq668766/redis-3.0-annotated,hawkchch/redis,gilala/hbjredis,ofirluzon/redis,csuhawk/redis,pkdevbox/redis,HouKangkang/redis-3.0-annotated,PradheepShrinivasan/redis,kensou97/redis,kaushik94/redis,oranagra/redis,timothyohare/3rdPartySrc-redis,zy416548283/redis-3.0-annotated,ipmobiletech/redis,ofirluzon/redis,moonbingbing/redis-3.0-annotated,zhcy/redis,ReadCode/redis-3.0-annotated,kmiku7/redis,mattsta/redis,wbailey5/redis,healerkx/redis,wenxueliu/redis_comment,JoeWoo/redis,dayuoba/redis,zguangyu/redis,allengaller/redis,jasonkying/redis,xlzhan/redis,zhcy/redis,ton31337/redis,dreamquster/redis,JoeWoo/redis,kaushik94/redis,valdsJohn/redis,slfs007/mk-redis,darksideofthemoo/redis-histogram,blackmady/redis,Sciumo/redis,vincent-vivian-liu/redis,YuanZhewei/redis,rogerchina/redis,huyuezheng/redis,soloestoy/redis,josiahcarlson/redis,abhiklodh/redis,takeshineshiro/redis,xuguruogu/redis,mverrilli/redis,ytjiang/redis,mengyou0304/redis,cnbin/redis,twskipper/redis,davidradunz/redis,aim-for-better/redis,dreamquster/redis,taoguan/redis,elkingtonmcb/redis,ituncle/redis,rogerlz/redis,pmem/redis,wprice/redis,Aliceljm1/redis,abhiklodh/redis,roth1002/redis,xlzhan/redis,0x55/redis-3.0-annotated,modulexcite/redis,harrisonfeng/redis,msn217/redis-3.0-annotated,j0hnma/szredis,ksarch-saas/redis,hgl888/redis,citusdata/redis,gilala/hbjredis,jasonkying/redis,mumingv/redis,mgk/redis,h0x91b/redis,narma/redis,pedigree/redis,MOON-CLJ/redis,buobao/redis-3.0-annotated,mattsta/redis,mengzhejin/RedisStudy,iandyh/redis,zczhuohuo/redis,zczhuohuo/redis,itugs/redis,zhiliaoniu/redis,jacklee0810/redis-3.0-annotated,netroby/redis,rogerlz/redis,drinkthere/redis-3.0-annotated,j0hnma/hszredis,AALEKH/redis,oranagra/redis,arijitvt/redis,j0hnma/szredis,pietern/redis,citusdata/redis,tjschuck/redis,HeartSaVioR/redis,HunanTV/redis,mumingv/redis,gaoxianglong/redis,yossigo/redis,dreamquster/redis,xlzhan/redis,riyan8250/redis,xuzhezhaozhao/redis_reading,huangz1990/redis-3.0-annotated,gechong/redis-3.0-annotated,StevenTsai/redis,Hailei/redis,LongXQ/redis,CodeJuan/redis,qiyang0221/redis,rogerchina/redis,wangyikai/redis,shreesundara/redis,JoeWoo/redis,ttuna/msot-redis,OmarQunsul/graph-redis,hedisdb/hedis,magastzheng/redis-3.0-annotated,ErikDubbelboer/redis,gaoxianglong/redis,janekmi/redis,rouzier/redis,MOON-CLJ/redis,pmem/redis,antirez/redis,0x55/redis-3.0-annotated,190235047/redis,HeartSaVioR/redis,honestme/redis,colstrom/redis,HunanTV/redis,july2993/redis,francischan714/redis,narma/redis,xujunhai1991/redis,ctripcorp/redis,gilala/redis,ncopa/redis,taoguan/redis,narma/redis,YuraLukashik/redis,z-fork/redis,duanx/redis,HouKangkang/redis-3.0-annotated,yuzhangjob/redis-3.0-annotated-unstable,wenxueliu/redis_comment,Sciumo/redis,saisai/redis,yossigo/redis,hedisdb/hedis,Sciumo/redis,brg-liuwei/redis,saisai/redis,mpalmer/redis,ituncle/redis,yossigo/redis,j0hnma/hszredis,0x55/redis-3.0-annotated,dayuoba/redis,simplestbest/redis,itugs/redis,arijitvt/redis,izhoujie/redis,j0hnma/szredis,seppo0010/redis,mverrilli/redis,splitice/redis,seppo0010/rlite-server,programmecat/redis,mingyaaaa/redis,zhaobo1023/redis-3.0-annotated,wbailey5/redis,himoca/redis,antirez/redis,4396/redis,spinlock/redis,weizijun/redis,hawkchch/redis,tzq668766/redis-3.0-annotated,ton31337/redis,blackmady/redis,tzq668766/redis-3.0-annotated,pkdevbox/redis,xlzhan/redis,cnbin/redis,GrimDerp/redis,gilala/hredis,0x20h/redis,OmarQunsul/graph-redis,soloestoy/redis,hawkchch/redis,MasahikoSawada/redis,PradheepShrinivasan/redis,ipmobiletech/redis,kensou97/redis,himoca/redis,takeshineshiro/redis,seppo0010/redis,flashbuckets/redis,zhiliaoniu/redis,seandsky/redis,flashbuckets/redis,ksarch-saas/redis,ton31337/redis,linfangrong/redis,atreeyang/redis,harrisonfeng/redis,cnbin/redis,csuhawk/redis,MSOpenTech/redis