Fix: clickhousesystemtablesreceiver: fix scraper waiting forever afte…

…r ch downtime (#407)

fixes #406

receiver/clickhousesystemtablesreceiver/receiver.go

@@ -156,7 +156,12 @@ func (r *systemTablesReceiver) scrapeQueryLogIfReady(ctx context.Context) (
  // For example, this can happen if this was the first successful scrape
  // after several failed attempts and subsequent waits for r.ScrapeIntervalSeconds
  nextScrapeMinServerTs := r.nextScrapeIntervalStartTs + r.scrapeIntervalSeconds + r.scrapeDelaySeconds
- nextWaitSeconds := max(0, nextScrapeMinServerTs-serverTsNow)
+
+ nextWaitSeconds := uint32(0)
+ if nextScrapeMinServerTs > serverTsNow {
+ // Do the subtraction only if it will not lead to an overflow/wrap around
+ nextWaitSeconds = nextScrapeMinServerTs - serverTsNow
+ }
 
  return nextWaitSeconds, nil
 }

receiver/clickhousesystemtablesreceiver/receiver_test.go

@@ -127,4 +127,14 @@ func TestReceiver(t *testing.T) {
  et, exists := lr.Attributes().Get("event_time")
  require.True(exists)
  require.Equal(et.Str(), testQlEventTime.Format(time.RFC3339))
+
+ // should scrape again immediately if scrape is too far behind the server ts
+ // for example: this can happen if clickhouse goes down for some time
+ mockQuerrier.tsNow += 10 * testScrapeIntervalSeconds
+ testQl4 := makeTestQueryLog("host-4", time.Now(), "test query 4")
+ mockQuerrier.nextScrapeResult = []QueryLog{testQl4}
+
+ waitSeconds, err = testReceiver.scrapeQueryLogIfReady(context.Background())
+ require.Nil(err)
+ require.Equal(uint32(0), waitSeconds)
 }