Function processQuery

edgraph/server.go:1566–1719

(ctx context.Context, qc *queryContext)

}

func processQuery(ctx context.Context, qc *queryContext) (*api.Response, error) {
	resp := &api.Response{}
	if qc.req.Query == "" {
		// No query, so make the query cost 0.
		resp.Metrics = &api.Metrics{
			NumUids: map[string]uint64{"_total": 0},
		}
		return resp, nil
	}
	if ctx.Err() != nil {
		return resp, ctx.Err()
	}
	qr := query.Request{
		Latency:  qc.latency,
		DqlQuery: &qc.dqlRes,
	}

	// Here we try our best effort to not contact Zero for a timestamp. If we succeed,
	// then we use the max known transaction ts value (from ProcessDelta) for a read-only query.
	// If we haven't processed any updates yet then fall back to getting TS from Zero.
	switch {
	case qc.req.BestEffort:
		qc.span.AddEvent("", trace.WithAttributes(attribute.Bool("be", true)))
	case qc.req.ReadOnly:
		qc.span.AddEvent("", trace.WithAttributes(attribute.Bool("ro", true)))
	default:
		qc.span.AddEvent("", trace.WithAttributes(attribute.Bool("no", true)))
	}

	if qc.req.BestEffort {
		// Sanity: check that request is read-only too.
		if !qc.req.ReadOnly {
			return resp, errors.Errorf("A best effort query must be read-only.")
		}
		if qc.req.StartTs == 0 {
			qc.req.StartTs = posting.Oracle().MaxAssigned()
		}
		qr.Cache = worker.NoCache
	}

	if qc.req.StartTs == 0 {
		assignTimestampStart := time.Now()
		qc.req.StartTs = worker.State.GetTimestamp(qc.req.ReadOnly)
		qc.latency.AssignTimestamp = time.Since(assignTimestampStart)
	}

	qr.ReadTs = qc.req.StartTs
	resp.Txn = &api.TxnContext{StartTs: qc.req.StartTs}

	// Core processing happens here.
	er, err := qr.Process(ctx)

	if bool(glog.V(3)) || worker.LogDQLRequestEnabled() {
		glog.Infof("Finished a query that started at: %+v",
			qr.Latency.Start.Format(time.RFC3339))
	}

	if err != nil {