graphql-exporter: implement caching

README.md

@@ -47,3 +47,4 @@ graphql_exporter_custom_fields_price{name="server",order_contract_id="contract-n
 ```
 
 API token can be overridden with `GRAPHQLAPITOKEN` env variable.
+`CacheExpire` configuration parameter defines cache validity period. Value of `0` disables caching.

config_example.json

@@ -1,6 +1,7 @@
 {
   "GraphqlURL": "http://localhost:8090/graphql/",
   "GraphqlAPIToken": "Token SECRET",
+  "CacheExpire": 0,
   "queries":[
     {
       "query": "query {device_list {name serial custom_fields}}",

pkg/config/config.go

@@ -9,6 +9,7 @@ import (
 type Cfg struct {
 	GraphqlURL      string
 	GraphqlAPIToken string
+	CacheExpire     int64
 	Queries         []Query
 }
 

pkg/prometheus/prometheus.go

@@ -13,6 +13,8 @@ import (
 	"reflect"
 	"strconv"
 	"strings"
+	"sync"
+	"time"
 )
 
 type Graphql struct {
@@ -32,6 +34,12 @@ type Label struct {
 	Value string
 }
 
+var (
+	metrics_cache []Metric
+	cache_time    = int64(0)
+	mutex         = sync.RWMutex{}
+)
+
 const metric_prepend = "graphql_exporter_"
 
 func buildValueData(val_hash map[string]interface{}, m string) (string, string, error) {
@@ -152,11 +160,17 @@ func buildPromDesc(name string, description string, labels map[string]string) *p
 }
 
 func (collector *graphqlCollector) Collect(ch chan<- prometheus.Metric) {
-	metrics, err := getMetrics()
+	var err error
+	mutex.Lock()
+	if time.Now().Unix()-cache_time > config.Config.CacheExpire {
+		metrics_cache, err = getMetrics()
+		cache_time = time.Now().Unix()
+	}
+	mutex.Unlock()
 	if err != nil {
 		log.Printf("%s", err)
 	}
-	for _, metric := range metrics {
+	for _, metric := range metrics_cache {
 		var desc *prometheus.Desc
 		if value, err := strconv.ParseFloat(metric.Value, 64); err == nil {
 			desc = buildPromDesc(metric.Name, metric.Description, metric.Labels)