dynstream, metrics: add batch metrics #4014
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Summary of ChangesHello @3AceShowHand, I'm Gemini Code Assist1! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed! This pull request significantly enhances the observability of the dynamic stream component by introducing detailed batch-level metrics. It adds new Prometheus histograms to track the count of events, total bytes, and processing duration for each batch. These additions provide critical insights into the performance and efficiency of event handling, facilitating better monitoring and debugging of the dynamic stream's operational characteristics. Highlights
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Code Review
This pull request adds batch metrics to dynstream. The changes are generally good, but I've found a critical issue that could cause a panic due to a nil pointer dereference, as well as an issue with an incorrect time unit for a duration metric. Additionally, there's a minor inconsistency in metric labeling that should be addressed for better clarity. My detailed feedback and suggestions are in the comments below.
utils/dynstream/stream.go
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| metrics.DynamicStreamBatchDuration.WithLabelValues(path.areaStr).Observe(float64(time.Since(start))) | ||
| metrics.DynamicStreamBatchCount.WithLabelValues(path.areaStr).Observe(float64(len(eventBuf))) | ||
| metrics.DynamicStreamBatchBytes.WithLabelValues(path.areaStr).Observe(float64(nBytes)) | ||
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| if len(eventBuf) == 0 { | ||
| eventQueueEmpty = true | ||
| continue Loop |
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There are two critical issues in this block:
-
Nil Pointer Dereference:
s.eventQueue.popEventscan return anilpath if the event queue is empty. The current code attempts to record metrics usingpath.areaStrbefore checking if a batch was actually returned (len(eventBuf) == 0). This will cause a panic ifpathisnil. -
Incorrect Metric Unit: The
DynamicStreamBatchDurationhistogram expects a value in seconds (as indicated by its buckets), butfloat64(time.Since(start))provides nanoseconds. You should usetime.Since(start).Seconds()to report the duration correctly.
I've provided a suggestion to fix both issues by checking the batch size before recording metrics and using the correct unit for the duration.
if len(eventBuf) == 0 {
eventQueueEmpty = true
continue Loop
}
metrics.DynamicStreamBatchDuration.WithLabelValues(path.areaStr).Observe(time.Since(start).Seconds())
metrics.DynamicStreamBatchCount.WithLabelValues(path.areaStr).Observe(float64(len(eventBuf)))
metrics.DynamicStreamBatchBytes.WithLabelValues(path.areaStr).Observe(float64(nBytes))| DynamicStreamBatchCount = prometheus.NewHistogramVec( | ||
| prometheus.HistogramOpts{ | ||
| Namespace: "ticdc", | ||
| Subsystem: "dynamic_stream", | ||
| Name: "batch_count", | ||
| Help: "The number of events in each batch processed by dynamic stream", | ||
| Buckets: prometheus.ExponentialBuckets(1, 2, 15), // 1 ~ 16384 | ||
| }, []string{"module"}) | ||
| DynamicStreamBatchBytes = prometheus.NewHistogramVec( | ||
| prometheus.HistogramOpts{ | ||
| Namespace: "ticdc", | ||
| Subsystem: "dynamic_stream", | ||
| Name: "batch_bytes", | ||
| Help: "The total bytes in each batch processed by dynamic stream", | ||
| Buckets: prometheus.ExponentialBuckets(1024, 2, 18), // 1KB ~ 128MB | ||
| }, []string{"module"}) | ||
| DynamicStreamBatchDuration = prometheus.NewHistogramVec( | ||
| prometheus.HistogramOpts{ | ||
| Namespace: "ticdc", | ||
| Subsystem: "dynamic_stream", | ||
| Name: "batch_duration", | ||
| Help: "The duration of batch each batch in dynamic stream", | ||
| Buckets: prometheus.ExponentialBuckets(0.00004, 2.0, 19), // 40us to 10s | ||
| }, []string{"module"}) |
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The new batch metrics are defined with the label module, but they are used with path.areaStr in stream.go. For consistency with other metrics like DynamicStreamMemoryUsage and to accurately reflect what is being measured, the label should be area.
Additionally, the help text for DynamicStreamBatchDuration is slightly ungrammatical. I've included a fix for that as well.
// Other metrics like DynamicStreamMemoryUsage use "area" as a label.
DynamicStreamMemoryUsage = prometheus.NewGaugeVec(
...
[]string{"module", "type", getKeyspaceLabel(), "area"})
// The new metrics are used with area string.
metrics.DynamicStreamBatchDuration.WithLabelValues(path.areaStr).Observe(...)
DynamicStreamBatchCount = prometheus.NewHistogramVec(
prometheus.HistogramOpts{
Namespace: "ticdc",
Subsystem: "dynamic_stream",
Name: "batch_count",
Help: "The number of events in each batch processed by dynamic stream",
Buckets: prometheus.ExponentialBuckets(1, 2, 15), // 1 ~ 16384
}, []string{"area"})
DynamicStreamBatchBytes = prometheus.NewHistogramVec(
prometheus.HistogramOpts{
Namespace: "ticdc",
Subsystem: "dynamic_stream",
Name: "batch_bytes",
Help: "The total bytes in each batch processed by dynamic stream",
Buckets: prometheus.ExponentialBuckets(1024, 2, 18), // 1KB ~ 128MB
}, []string{"area"})
DynamicStreamBatchDuration = prometheus.NewHistogramVec(
prometheus.HistogramOpts{
Namespace: "ticdc",
Subsystem: "dynamic_stream",
Name: "batch_duration",
Help: "The duration of each batch processed by dynamic stream",
Buckets: prometheus.ExponentialBuckets(0.00004, 2.0, 19), // 40us to 10s
}, []string{"area"})
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What problem does this PR solve?
Issue Number: close #xxx
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