n1ql "max()" is much slower than "min()" operation

n1ql "max()" is much slower than "min()" operation on couchbase 4.5 preview edition.

the detail:

SELECT min(time_first) FROM statis_user_success
{{{
"requestID": "c5e8b6df-9f0e-4690-b3a7-350d07b1e2e4",
"signature":

{ "$1": "json" }

,
"results":
{
"0":

{ "$1": 1465663242 }

},
"status": "success",
"metrics":

{ "elapsedTime": "7.153457ms", "executionTime": "7.100002ms", "resultCount": 1, "resultSize": 40 }

}}}

SELECT max(time_first) FROM statis_user_success
{{{
"requestID": "c5e8b6df-9f0e-4690-b3a7-350d07b1e2e4",
"signature":

{ "$1": "json" }

,
"results":
{
"0":

{ "$1": 1465663242 }

},
"status": "success",
"metrics":

{ "elapsedTime": "43860.153457ms", "executionTime": "43860.100002ms", "resultCount": 1, "resultSize": 40 }

}}}

SELECT * FROM statis_user_success limit 3
{{[
{
"statis_user_success":

{ "uid": "EZS108-02", "time_first": 1465678128 }

},
{
"statis_user_success":

{ "uid": "PZM215-02", "time_first": 1465722317 }

},
{
"statis_user_success":

{ "uid": "H03217-02", "time_first": 1465678130 }

}
]}}

SELECT * FROM system:indexes where keyspace_id='statis_user_success' and name='idx_time_first'
{{[
{
"indexes":

{ "datastore_id": "http://127.0.0.1:8091", "id": "9d8f7238fa7276a5", "index_key": [ "`time_first`" ], "keyspace_id": "statis_user_success", "name": "idx_time_first", "namespace_id": "default", "state": "online", "using": "gsi" }

}
]}}

explain select min(time_first) from statis_user_success
{{[
{
"plan": {
"#operator": "Sequence",
"~children": [
{
"#operator": "IndexScan",
"covers": [
"cover ((`statis_user_success`.`time_first`))",
"cover ((meta(`statis_user_success`).`id`))"
],
"index": "idx_time_first",
"index_id": "9d8f7238fa7276a5",
"keyspace": "statis_user_success",
"limit": "1",
"namespace": "default",
"spans": [
{
"Range":

{ "Inclusion": 0, "Low": [ "null" ] }

}
],
"using": "gsi"
},
{
"#operator": "Parallel",
"maxParallelism": 1,
"~child": {
"#operator": "Sequence",
"~children": [

{ "#operator": "InitialGroup", "aggregates": [ "min(cover ((`statis_user_success`.`time_first`)))" ], "group_keys": [] }

]
}
},

{ "#operator": "IntermediateGroup", "aggregates": [ "min(cover ((`statis_user_success`.`time_first`)))" ], "group_keys": [] }

,

{ "#operator": "FinalGroup", "aggregates": [ "min(cover ((`statis_user_success`.`time_first`)))" ], "group_keys": [] }

,
{
"#operator": "Parallel",
"maxParallelism": 1,
"~child": {
"#operator": "Sequence",
"~children": [
{
"#operator": "InitialProject",
"result_terms": [

{ "expr": "min(cover ((`statis_user_success`.`time_first`)))" }

]
},

{ "#operator": "FinalProject" }

]
}
}
]
},
"text": "select min(time_first) from statis_user_success"
}
]}}

explain select max(time_first) from statis_user_success
{{[
{
"plan": {
"#operator": "Sequence",
"~children": [
{
"#operator": "IndexScan",
"covers": [
"cover ((`statis_user_success`.`time_first`))",
"cover ((meta(`statis_user_success`).`id`))"
],
"index": "idx_time_first",
"index_id": "9d8f7238fa7276a5",
"keyspace": "statis_user_success",
"namespace": "default",
"spans": [
{
"Range":

{ "Inclusion": 0, "Low": [ "null" ] }

}
],
"using": "gsi"
},
{
"#operator": "Parallel",
"~child": {
"#operator": "Sequence",
"~children": [

{ "#operator": "InitialGroup", "aggregates": [ "max(cover ((`statis_user_success`.`time_first`)))" ], "group_keys": [] }

]
}
},

{ "#operator": "IntermediateGroup", "aggregates": [ "max(cover ((`statis_user_success`.`time_first`)))" ], "group_keys": [] }

,

{ "#operator": "FinalGroup", "aggregates": [ "max(cover ((`statis_user_success`.`time_first`)))" ], "group_keys": [] }

,
{
"#operator": "Parallel",
"~child": {
"#operator": "Sequence",
"~children": [
{
"#operator": "InitialProject",
"result_terms": [

{ "expr": "max(cover ((`statis_user_success`.`time_first`)))" }

]
},

{ "#operator": "FinalProject" }

]
}
}
]
},
"text": "statis_user_success"
}
]}}