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New pixa_ metrics, none with labels: - source cache hits and misses, counted once per variant made or checked; a source whose cached file cannot be used is a miss - cache usage and limit gauges; usage is set each time eviction reads it - eviction count and bytes, from the size_bytes the deleted row returns - upstream fetch duration histogram and fetch error counter - transform duration histogram and an in-progress gauge, both including the wait for a processing slot Removing a damaged file during reconciliation is not counted as an eviction. README lists every metric; the metrics config comment now says the pixa_ metrics are measured whether or not /metrics is served. Model: opus-5-5
89 lines
2.8 KiB
Go
89 lines
2.8 KiB
Go
package imgcache
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import (
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"fmt"
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"github.com/prometheus/client_golang/prometheus"
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)
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// registerMetrics makes the cache's metrics and registers them on
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// metricsRegistry. The metrics are kept in memory, so updating one waits
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// for nothing and makes no database call. It fails when metricsRegistry
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// already holds metrics of the same names.
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func (c *Cache) registerMetrics(metricsRegistry prometheus.Registerer) error {
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c.cacheHits = prometheus.NewCounter(prometheus.CounterOpts{
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Name: "pixa_cache_hits_total",
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Help: "Image requests served from the cache.",
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})
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c.cacheMisses = prometheus.NewCounter(prometheus.CounterOpts{
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Name: "pixa_cache_misses_total",
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Help: "Image requests not served from the cache.",
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})
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c.sourceCacheHits = prometheus.NewCounter(prometheus.CounterOpts{
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Name: "pixa_source_cache_hits_total",
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Help: "Variants made or checked whose source was in the cache.",
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})
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c.sourceCacheMisses = prometheus.NewCounter(prometheus.CounterOpts{
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Name: "pixa_source_cache_misses_total",
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Help: "Variants made or checked whose source was not in the cache.",
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})
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c.usageBytes = prometheus.NewGauge(prometheus.GaugeOpts{
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Name: "pixa_cache_usage_bytes",
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Help: "Bytes of sources and variants in the cache, as eviction last read them.",
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})
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c.maxBytes = prometheus.NewGauge(prometheus.GaugeOpts{
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Name: "pixa_cache_max_bytes",
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Help: "The disk cache limit in bytes, cache_max_bytes.",
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})
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c.evictions = prometheus.NewCounter(prometheus.CounterOpts{
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Name: "pixa_cache_evictions_total",
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Help: "Sources and variants removed by eviction.",
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})
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c.evictedBytes = prometheus.NewCounter(prometheus.CounterOpts{
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Name: "pixa_cache_evicted_bytes_total",
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Help: "Bytes of the sources and variants removed by eviction.",
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})
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c.maxBytes.Set(float64(c.config.MaxBytes))
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for _, metric := range []prometheus.Collector{
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c.cacheHits, c.cacheMisses, c.sourceCacheHits, c.sourceCacheMisses,
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c.usageBytes, c.maxBytes, c.evictions, c.evictedBytes,
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} {
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err := metricsRegistry.Register(metric)
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if err != nil {
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return fmt.Errorf("failed to register the cache's metrics: %w", err)
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}
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}
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return nil
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}
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// IncrementStats counts a cache hit or miss of an image request. It only
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// adds to the cache's counters in memory, so it never waits for the
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// database or fails.
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func (c *Cache) IncrementStats(hit bool) {
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if hit {
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c.cacheHits.Inc()
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} else {
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c.cacheMisses.Inc()
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}
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}
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// IncrementSourceStats counts whether a variant being made or checked found
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// its source in the cache. Like IncrementStats, it never waits or fails.
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func (c *Cache) IncrementSourceStats(hit bool) {
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if hit {
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c.sourceCacheHits.Inc()
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} else {
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c.sourceCacheMisses.Inc()
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}
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}
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// countEviction counts one source or variant of sizeBytes bytes removed by
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// eviction.
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func (c *Cache) countEviction(sizeBytes int64) {
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c.evictions.Inc()
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c.evictedBytes.Add(float64(sizeBytes))
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}
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