Couchbase 4.5 Order by diffrence in performnace for ASC and DESC even query covered

Couchbase Server
61

{
“plan”: {
“#operator”: “Sequence”,
“~children”: [
{
“#operator”: “Sequence”,
“~children”: [
{
“#operator”: “IntersectScan”,
“scans”: [
{
“#operator”: “IndexScan2”,
“index”: “Ottoman__type”,
“index_id”: “3d174a8be03093df”,
“index_projection”: {
“primary_key”: true
},
“keyspace”: “appsec”,
“namespace”: “default”,
“spans”: [
{
“exact”: true,
“range”: [
{
“high”: ““event””,
“inclusion”: 3,
“low”: ““event””
}
]
}
],
“using”: “gsi”
},
{
“#operator”: “IndexScan2”,
“index”: “event_index”,
“index_id”: “a952594212eb0de6”,
“index_projection”: {
“primary_key”: true
},
“keyspace”: “appsec”,
“namespace”: “default”,
“spans”: [
{
“exact”: true,
“range”: [
{
“high”: ““event””,
“inclusion”: 3,
“low”: ““event””
}
]
}
],
“using”: “gsi”
}
]
},
{
“#operator”: “Fetch”,
“keyspace”: “appsec”,
“namespace”: “default”
},
{
“#operator”: “Parallel”,
“~child”: {
“#operator”: “Sequence”,
“~children”: [
{
“#operator”: “Filter”,
“condition”: “(((appsec._type) = “event”) and ((((appsec.event).categoryParams).severity) = “High”))”
},
{
“#operator”: “InitialProject”,
“result_terms”: [
{
“expr”: “self”,
“star”: true
}
]
}
]
}
}
]
},
{
“#operator”: “Order”,
“limit”: “3”,
“sort_terms”: [
{
“expr”: “((appsec.event).eventTimeInGmt)”
}
]
},
{
“#operator”: “Limit”,
“expr”: “3”
},
{
“#operator”: “FinalProject”
}
]
},
“text”: “select * from appsec where _type=‘event’ and event.categoryParams.severity = ‘High’ ORDER BY event.eventTimeInGmt ASC LIMIT 3”
}

62

create index ix1 on appsec(event.categoryParams.severity, event.eventTimeInGmt) where _type=‘event’ ;