dd9fc8962c
* Improve plugin/cache metrics * Add coredns_cache_prefetch_total metric to track number of prefetches. * Remove unnecessary Cache.get() call which would incorrectly increment cache counters. * Initialize all counters and gauges at zero. * Allow prefetching of a single request per ttl The original implementation didn't allow prefetching queries which are only requested once during the duration of a TTL. The minimum amount of queries which had to be seen was therefore capped at 2. This change also implements a real prefetch test. The existing test was a noop and always passed regardless of any prefetch implementation. * Fix prefetching for items with a short TTL The default prefetch threshold (percentage) is 10% of the lifetime of a cache item. With the previous implementation, this disabled prefetching for all items with a TTL < 10s (the resulting percentage would be 0, at which point a cached item is already discarded). This change uses a time based threshold calculation and ensures that a prefetch is triggered at a TTL of 1 at the latest. * Fix wrong duration reporting of cached responses The logging and metrics plugins (among others) included the duration of a cache prefetch in the request latency of client request. This change fixes this wrong reporting and executes the prefetch request in a goroutine in the background.
132 lines
3.4 KiB
Go
132 lines
3.4 KiB
Go
package cache
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import (
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"math"
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"sync"
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"time"
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"github.com/coredns/coredns/plugin"
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"github.com/coredns/coredns/request"
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"github.com/miekg/dns"
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"github.com/prometheus/client_golang/prometheus"
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"golang.org/x/net/context"
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)
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// ServeDNS implements the plugin.Handler interface.
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func (c *Cache) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
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state := request.Request{W: w, Req: r}
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qname := state.Name()
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qtype := state.QType()
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zone := plugin.Zones(c.Zones).Matches(qname)
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if zone == "" {
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return plugin.NextOrFailure(c.Name(), c.Next, ctx, w, r)
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}
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do := state.Do() // TODO(): might need more from OPT record? Like the actual bufsize?
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now := c.now().UTC()
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i, ttl := c.get(now, qname, qtype, do)
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if i != nil && ttl > 0 {
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resp := i.toMsg(r, now)
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state.SizeAndDo(resp)
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resp, _ = state.Scrub(resp)
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w.WriteMsg(resp)
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if c.prefetch > 0 {
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i.Freq.Update(c.duration, now)
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threshold := int(math.Ceil(float64(c.percentage) / 100 * float64(i.origTTL)))
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if i.Freq.Hits() >= c.prefetch && ttl <= threshold {
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go func() {
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cachePrefetches.Inc()
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// When prefetching we loose the item i, and with it the frequency
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// that we've gathered sofar. See we copy the frequencies info back
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// into the new item that was stored in the cache.
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prr := &ResponseWriter{ResponseWriter: w, Cache: c, prefetch: true}
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plugin.NextOrFailure(c.Name(), c.Next, ctx, prr, r)
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if i1 := c.exists(qname, qtype, do); i1 != nil {
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i1.Freq.Reset(now, i.Freq.Hits())
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}
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}()
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}
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}
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return dns.RcodeSuccess, nil
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}
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crr := &ResponseWriter{ResponseWriter: w, Cache: c}
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return plugin.NextOrFailure(c.Name(), c.Next, ctx, crr, r)
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}
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// Name implements the Handler interface.
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func (c *Cache) Name() string { return "cache" }
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func (c *Cache) get(now time.Time, qname string, qtype uint16, do bool) (*item, int) {
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k := hash(qname, qtype, do)
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if i, ok := c.ncache.Get(k); ok {
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cacheHits.WithLabelValues(Denial).Inc()
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return i.(*item), i.(*item).ttl(now)
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}
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if i, ok := c.pcache.Get(k); ok {
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cacheHits.WithLabelValues(Success).Inc()
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return i.(*item), i.(*item).ttl(now)
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}
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cacheMisses.Inc()
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return nil, 0
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}
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func (c *Cache) exists(qname string, qtype uint16, do bool) *item {
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k := hash(qname, qtype, do)
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if i, ok := c.ncache.Get(k); ok {
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return i.(*item)
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}
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if i, ok := c.pcache.Get(k); ok {
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return i.(*item)
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}
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return nil
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}
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var (
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cacheSize = prometheus.NewGaugeVec(prometheus.GaugeOpts{
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Namespace: plugin.Namespace,
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Subsystem: "cache",
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Name: "size",
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Help: "The number of elements in the cache.",
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}, []string{"type"})
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cacheCapacity = prometheus.NewGaugeVec(prometheus.GaugeOpts{
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Namespace: plugin.Namespace,
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Subsystem: "cache",
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Name: "capacity",
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Help: "The cache's capacity.",
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}, []string{"type"})
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cacheHits = prometheus.NewCounterVec(prometheus.CounterOpts{
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Namespace: plugin.Namespace,
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Subsystem: "cache",
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Name: "hits_total",
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Help: "The count of cache hits.",
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}, []string{"type"})
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cacheMisses = prometheus.NewCounter(prometheus.CounterOpts{
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Namespace: plugin.Namespace,
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Subsystem: "cache",
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Name: "misses_total",
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Help: "The count of cache misses.",
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})
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cachePrefetches = prometheus.NewCounter(prometheus.CounterOpts{
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Namespace: plugin.Namespace,
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Subsystem: "cache",
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Name: "prefetch_total",
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Help: "The number of time the cache has prefetched a cached item.",
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})
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)
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var once sync.Once
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