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Add timeout to endpointset metric collector #7336

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May 21, 2024
Merged

Add timeout to endpointset metric collector #7336

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13 changes: 10 additions & 3 deletions pkg/query/endpointset.go
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Original file line number Diff line number Diff line change
Expand Up @@ -202,15 +202,17 @@ type endpointSetNodeCollector struct {
storeNodes map[component.Component]map[string]int
storePerExtLset map[string]int

logger log.Logger
connectionsDesc *prometheus.Desc
labels []string
}

func newEndpointSetNodeCollector(labels ...string) *endpointSetNodeCollector {
func newEndpointSetNodeCollector(logger log.Logger, labels ...string) *endpointSetNodeCollector {
if len(labels) == 0 {
labels = []string{string(ExternalLabels), string(StoreType)}
}
return &endpointSetNodeCollector{
logger: logger,
storeNodes: map[component.Component]map[string]int{},
connectionsDesc: prometheus.NewDesc(
"thanos_store_nodes_grpc_connections",
Expand Down Expand Up @@ -277,7 +279,12 @@ func (c *endpointSetNodeCollector) Collect(ch chan<- prometheus.Metric) {
lbls = append(lbls, storeTypeStr)
}
}
ch <- prometheus.MustNewConstMetric(c.connectionsDesc, prometheus.GaugeValue, float64(occurrences), lbls...)
select {
case ch <- prometheus.MustNewConstMetric(c.connectionsDesc, prometheus.GaugeValue, float64(occurrences), lbls...):
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Why this can take even 1 second? 🤔

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I don't yet understand why the send would block forever here, the only explanation is that the caller does not read from the channel. The 1s timeout is arbitrary though, it's there to make sure we do not end up in a deadlock.

We noticed queriers getting stuck occasionally and the goroutine profile showed that the mutex in this function was constantly locked.

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I think something else might be at play here, e.g., this goroutine is starved of CPU resources. Do you have a lot of goroutines running when this happens?

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@fpetkovski fpetkovski May 9, 2024 •
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There is only 1 goroutine here but there are new goroutines constantly piling up here. That is because the mutex for the collector is locked, which causes the call here to hang so this mutex also is locked.

I do not yet understand why the channel reader would stop or block though.

case <-time.After(1 * time.Second):
level.Warn(c.logger).Log("msg", "failed to collect endpointset metrics", "timeout", 1*time.Second)
return
}
}
}
}
Expand Down Expand Up @@ -319,7 +326,7 @@ func NewEndpointSet(
endpointInfoTimeout time.Duration,
endpointMetricLabels ...string,
) *EndpointSet {
endpointsMetric := newEndpointSetNodeCollector(endpointMetricLabels...)
endpointsMetric := newEndpointSetNodeCollector(logger, endpointMetricLabels...)
if reg != nil {
reg.MustRegister(endpointsMetric)
}
Expand Down