运行db.exec("select * from $SNAPSHOT_CATA where MainCLName='monitordb.processlistfromtop'")命令，其中的一条数据如下：
{
"Attribute": 9,
"AttributeDesc": "Compressed | StrictDataMode",
"AutoIncrement": [
{
"SequenceName": "SYS_4294968858_id_SEQ",
"Field": "id",
"Generated": "default",
"SequenceID": 1680
}
],
"CataInfo": [
{
"GroupID": 1000,
"GroupName": "DataGroup1",
"LowBound": {
"monitortime": {
"$minKey": 1
}
},
"UpBound": {
"monitortime": {
"$maxKey": 1
}
}
}
],
"CompressionType": 1,
"CompressionTypeDesc": "lzw",
"EnsureShardingIndex": true,
"MainCLName": "monitordb.processlistfromtop",
"Name": "monitordb.processlistfromtop_subp_20221029",
"ReplSize": 1,
"ShardingKey": {
"monitortime": 1
},
"ShardingType": "range",
"UniqueID": 4294968858,
"Version": 2,
"_id": {
"$oid": "635959be0b182ab0471da676"
}
}
请问其中的$minKey、$maxKey代表什么意思？您能通俗的解释一下吗
