ctiy:PRIMARY> use local
switched to db local
ctiy:PRIMARY>  db.oplog.rs.stats().maxSize   //查看大小
NumberLong("53687091200")   //这里为50G，单位为B
ctiy:PRIMARY>  use local
switched to db local
ctiy:PRIMARY> db.adminCommand({replSetResizeOplog:1,size:5120}) //修改为5G，
{  //修改  这里单位 为 M
	"ok" : 1,
	"operationTime" : Timestamp(1595321857, 1),
	"$clusterTime" : {
		"clusterTime" : Timestamp(1595321857, 1),
		"signature" : {
			"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
			"keyId" : NumberLong(0)
		}
	}
}
ctiy:PRIMARY> db.oplog.rs.stats().maxSize
NumberLong("5368709120")

    ctiy:SECONDARY> rs.printReplicationInfo()  // 另一种查看方法
configured oplog size:   51200MB
log length start to end: 2580359secs (716.77hrs)
oplog first event time:  Sun Jun 21 2020 20:01:51 GMT+0800 (CST)
oplog last event time:   Tue Jul 21 2020 16:47:50 GMT+0800 (CST)
now:                     Tue Jul 21 2020 16:47:54 GMT+0800 (CST)