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Add a histogram for cached value sizes. #1569

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Merged
merged 2 commits into from
Aug 13, 2019
Merged

Add a histogram for cached value sizes. #1569

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15d7297
Add a histrogram for cached value sizes.
tomwilkie Aug 9, 2019
fd440c8
Set the name for the chunk cache metrics, so its not blank.
tomwilkie Aug 9, 2019
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36 changes: 30 additions & 6 deletions pkg/chunk/cache/instrumented.go
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Original file line number Diff line number Diff line change
Expand Up @@ -29,31 +29,51 @@ var (
Name: "cache_hits",
Help: "Total count of keys found in cache.",
}, []string{"name"})

valueSize = prometheus.NewHistogramVec(prometheus.HistogramOpts{
Namespace: "cortex",
Name: "cache_value_size_bytes",
Help: "Size of values in the cache.",
// Cached chunks are generally in the KBs, but cached index can
// get big. Histogram goes from 1KB to 4MB.
// 1024 * 4^(7-1) = 4MB
Buckets: prometheus.ExponentialBuckets(1024, 4, 7),
}, []string{"name", "method"})
)

func init() {
requestDuration.Register()
prometheus.MustRegister(fetchedKeys)
prometheus.MustRegister(hits)
prometheus.MustRegister(valueSize)
}

// Instrument returns an instrumented cache.
func Instrument(name string, cache Cache) Cache {
return &instrumentedCache{
name: name,
fetchedKeys: fetchedKeys.WithLabelValues(name),
hits: hits.WithLabelValues(name),
Cache: cache,
name: name,
Cache: cache,

fetchedKeys: fetchedKeys.WithLabelValues(name),
hits: hits.WithLabelValues(name),
storedValueSize: valueSize.WithLabelValues(name, "store"),
fetchedValueSize: valueSize.WithLabelValues(name, "fetch"),
}
}

type instrumentedCache struct {
name string
fetchedKeys, hits prometheus.Counter
name string
Cache

fetchedKeys, hits prometheus.Counter
storedValueSize, fetchedValueSize prometheus.Observer
}

func (i *instrumentedCache) Store(ctx context.Context, keys []string, bufs [][]byte) {
for j := range bufs {
i.storedValueSize.Observe(float64(len(bufs[j])))
}

method := i.name + ".store"
instr.CollectedRequest(ctx, method, requestDuration, instr.ErrorCode, func(ctx context.Context) error {
sp := ot.SpanFromContext(ctx)
Expand Down Expand Up @@ -82,6 +102,10 @@ func (i *instrumentedCache) Fetch(ctx context.Context, keys []string) ([]string,

i.fetchedKeys.Add(float64(len(keys)))
i.hits.Add(float64(len(found)))
for j := range bufs {
i.fetchedValueSize.Observe(float64(len(bufs[j])))
}

return found, bufs, missing
}

Expand Down
1 change: 1 addition & 0 deletions pkg/chunk/chunk_store_utils.go
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Original file line number Diff line number Diff line change
Expand Up @@ -108,6 +108,7 @@ type decodeResponse struct {

// NewChunkFetcher makes a new ChunkFetcher.
func NewChunkFetcher(cfg cache.Config, cacheStubs bool, storage ObjectClient) (*Fetcher, error) {
cfg.Prefix = "chunks"
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This has the effect that the name label in cortex_cache_hits changes from "memcache" to "chunksmemcache".
Which is a (minor) breaking change that should go in the changelog.

cache, err := cache.New(cfg)
if err != nil {
return nil, err
Expand Down