app/vmselect: mention command-line flag, which could be used for adjusting query timeouts, in timeout errors

app/vmselect/netstorage/netstorage.go

@@ -101,7 +101,7 @@ func (rss *Results) RunParallel(f func(rs *Result, workerID uint)) error {
 			rowsProcessed := 0
 			for pts := range workCh {
 				if time.Until(rss.deadline.Deadline) < 0 {
-					err = fmt.Errorf("timeout exceeded during query execution: %s", rss.deadline.Timeout)
+					err = fmt.Errorf("timeout exceeded during query execution: %s", rss.deadline.String())
 					break
 				}
 				if err = pts.Unpack(rss.tbf, rs, rss.tr, rss.fetchData, rss.at, maxWorkersCount); err != nil {
@@ -1010,7 +1010,7 @@ func (sn *storageNode) execOnConn(rpcName string, f func(bc *handshake.BufferedC
 			// since it may be broken.
 			_ = bc.Close()
 		}
-		return fmt.Errorf("cannot execute rpcName=%q on vmstorage %q with timeout %s: %s", rpcName, remoteAddr, deadline.Timeout, err)
+		return fmt.Errorf("cannot execute rpcName=%q on vmstorage %q with timeout %s: %s", rpcName, remoteAddr, deadline.String(), err)
 	}
 	// Return the connection back to the pool, assuming it is healthy.
 	sn.connPool.Put(bc)
@@ -1406,13 +1406,24 @@ var rsPool sync.Pool
 // Deadline contains deadline with the corresponding timeout for pretty error messages.
 type Deadline struct {
 	Deadline time.Time
-	Timeout  time.Duration
+
+	timeout  time.Duration
+	flagHint string
 }
 
 // NewDeadline returns deadline for the given timeout.
-func NewDeadline(timeout time.Duration) Deadline {
+//
+// flagHint must contain a hit for command-line flag, which could be used
+// in order to increase timeout.
+func NewDeadline(timeout time.Duration, flagHint string) Deadline {
 	return Deadline{
 		Deadline: time.Now().Add(timeout),
-		Timeout:  timeout,
+		timeout:  timeout,
+		flagHint: flagHint,
 	}
 }
+
+// String returns human-readable string representation for d.
+func (d *Deadline) String() string {
+	return fmt.Sprintf("%.3f seconds; the timeout can be adjusted with `%s` command-line flag", d.timeout.Seconds(), d.flagHint)
+}

app/vmselect/prometheus/prometheus.go

@@ -953,15 +953,15 @@ func getMaxLookback(r *http.Request) (int64, error) {
 
 func getDeadlineForQuery(r *http.Request) netstorage.Deadline {
 	dMax := int64(maxQueryDuration.Seconds() * 1e3)
-	return getDeadlineWithMaxDuration(r, dMax)
+	return getDeadlineWithMaxDuration(r, dMax, "-search.maxQueryDuration")
 }
 
 func getDeadlineForExport(r *http.Request) netstorage.Deadline {
 	dMax := int64(maxExportDuration.Seconds() * 1e3)
-	return getDeadlineWithMaxDuration(r, dMax)
+	return getDeadlineWithMaxDuration(r, dMax, "-search.maxExportDuration")
 }
 
-func getDeadlineWithMaxDuration(r *http.Request, dMax int64) netstorage.Deadline {
+func getDeadlineWithMaxDuration(r *http.Request, dMax int64, flagHint string) netstorage.Deadline {
 	d, err := getDuration(r, "timeout", 0)
 	if err != nil {
 		d = 0
@@ -970,7 +970,7 @@ func getDeadlineWithMaxDuration(r *http.Request, dMax int64) netstorage.Deadline
 		d = dMax
 	}
 	timeout := time.Duration(d) * time.Millisecond
-	return netstorage.NewDeadline(timeout)
+	return netstorage.NewDeadline(timeout, flagHint)
 }
 
 func getBool(r *http.Request, argKey string) bool {

app/vmselect/promql/exec_test.go

@@ -31,7 +31,7 @@ func TestExecSuccess(t *testing.T) {
 			Start:    start,
 			End:      end,
 			Step:     step,
-			Deadline: netstorage.NewDeadline(time.Minute),
+			Deadline: netstorage.NewDeadline(time.Minute, ""),
 		}
 		for i := 0; i < 5; i++ {
 			result, err := Exec(ec, q, false)
@@ -5243,7 +5243,7 @@ func TestExecError(t *testing.T) {
 			Start:    1000,
 			End:      2000,
 			Step:     100,
-			Deadline: netstorage.NewDeadline(time.Minute),
+			Deadline: netstorage.NewDeadline(time.Minute, ""),
 		}
 		for i := 0; i < 4; i++ {
 			rv, err := Exec(ec, q, false)