func NewQueryEngine(query *parser.SelectQuery, responseChan chan *protocol.Response) (*QueryEngine, error) {
limit := query.Limit
queryEngine := &QueryEngine{
query: query,
where: query.GetWhereCondition(),
limiter: NewLimiter(limit),
responseChan: responseChan,
seriesToPoints: make(map[string]*protocol.Series),
// stats stuff
explain: query.IsExplainQuery(),
runStartTime: 0,
runEndTime: 0,
pointsRead: 0,
pointsWritten: 0,
shardId: 0,
shardLocal: false, //that really doesn't matter if it is not EXPLAIN query
duration: nil,
seriesStates: make(map[string]*SeriesState),
}
if queryEngine.explain {
queryEngine.runStartTime = float64(time.Now().UnixNano()) / float64(time.Millisecond)
}
yield := func(series *protocol.Series) error {
var response *protocol.Response
queryEngine.limiter.calculateLimitAndSlicePoints(series)
if len(series.Points) == 0 {
return nil
}
if queryEngine.explain {
//TODO: We may not have to send points, just count them
queryEngine.pointsWritten += int64(len(series.Points))
}
response = &protocol.Response{Type: &queryResponse, Series: series}
responseChan <- response
return nil
}
var err error
if query.HasAggregates() {
err = queryEngine.executeCountQueryWithGroupBy(query, yield)
} else if containsArithmeticOperators(query) {
err = queryEngine.executeArithmeticQuery(query, yield)
} else {
err = queryEngine.distributeQuery(query, yield)
}
if err != nil {
return nil, err
}
return queryEngine, nil
}