support max_source_resolution param for instant queries

This adds support for the ?max_source_resolution query
param for instant queries.

Instant queries had the issue that when there was a subquery requesting wide
data ranges e.g. sum_over_time(metric_name[30d])) and the retention of raw data
was for example only 7d, the query would (silently) only take data from the last
7 days into account (ignoring the downsampled 5m and 1h timeseries that were
available with longer retention).

We default to 1h max_source_resolution for now as this will cover
the highest/broadest resolution available and should include
all retention. It is configurable per query (although no known
clients send it).

Signed-off-by: Tim Reddehase <tim.reddehase@xing.com>

pkg/query/api/v1.go

@@ -183,13 +183,18 @@ func (api *API) parseEnableDedupParam(r *http.Request) (enableDeduplication bool
 }
 
 func (api *API) parseDownsamplingParamMillis(r *http.Request, step time.Duration) (maxResolutionMillis int64, _ *ApiError) {
+	// If no max_source_resolution is specified fit at least 5 samples between steps.
+	return api.parseDownsamplingParamMillisWithDefault(r, step/5)
+}
+
+func (api *API) parseDownsamplingParamMillisWithDefault(r *http.Request, defaultVal time.Duration) (maxResolutionMillis int64, _ *ApiError) {
 	const maxSourceResolutionParam = "max_source_resolution"
 	maxSourceResolution := 0 * time.Second
 
 	if api.enableAutodownsampling {
-		// If no max_source_resolution is specified fit at least 5 samples between steps.
-		maxSourceResolution = step / 5
+		maxSourceResolution = defaultVal
 	}
+
 	if val := r.FormValue(maxSourceResolutionParam); val != "" {
 		var err error
 		maxSourceResolution, err = parseDuration(val)
@@ -257,11 +262,17 @@ func (api *API) query(r *http.Request) (interface{}, []error, *ApiError) {
 		return nil, nil, apiErr
 	}
 
+	const defaultMaxSourceResolution = 3600 * time.Second
+	maxSourceResolution, apiErr := api.parseDownsamplingParamMillisWithDefault(r, defaultMaxSourceResolution)
+	if apiErr != nil {
+		return nil, nil, apiErr
+	}
+
 	// We are starting promQL tracing span here, because we have no control over promQL code.
 	span, ctx := tracing.StartSpan(ctx, "promql_instant_query")
 	defer span.Finish()
 
-	qry, err := api.queryEngine.NewInstantQuery(api.queryableCreate(enableDedup, 0, enablePartialResponse), r.FormValue("query"), ts)
+	qry, err := api.queryEngine.NewInstantQuery(api.queryableCreate(enableDedup, maxSourceResolution, enablePartialResponse), r.FormValue("query"), ts)
 	if err != nil {
 		return nil, nil, &ApiError{errorBadData, err}
 	}